THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES H-t^ayV- 2 Marine Engine ......... 295 160. Ki-upp Fovu'-Cycle Marine :\Iotor .... 297 LIST OF ILLUSTRATIONS xvii FIG. TITLE PAGE 161. Junkers 100 H.P. Marine Motor , , . .298 162. 150 H.P. Two-Cyele American Diesel Marine Engine . 299 163. 150 H.P. Kind Two-Cj'cle Marine Diesel Engine . 301 164. Details of Cylinder Cover of Hick, Hargreaves Motor . 304 165. Details of Piston of Hick, Hargreaves Diesel Motor . 307 166. Compression Curves in Two-Stage Compressor . . 326 167. Diagrammatic Representation of Two-Stage Compressor 328 168. Diesel Engine Indicator Diagram with Valve Scavenging 331 169. Diagram of Engine with Port Scavenging . . 3.32 170. Sulzer Diesel Locomotive built for the Prussian State Railways ••...... 338 171. Diagram ilkistrating Arrangement of Sulzer Diesel Locomotive . . . . . . . .339 172. Arrangement of Drive for Sulzcr-Diesel Locomotive facing 340 l.^ 2 3 4. 5- Relative to Diesel's Patent Specification, and are referred to "I in the Appendix. 7 8 9 10 INTRODUCTION By dr. RUDOLF DIESEL Very willingly do I accede to the Author's request to add an introduction to this book, because I am very glad that an attempt should thus be made to present the subject of the Diesel engine in a concise and well-ordered form, in view of the amount of scattered literature there is deahng Avith the question. Since its first appearance about fourteen years ago, many thousands of Diesel engines have been installed in all kinds of factories in all industrial countries, and also in the re- motest corners of the world ; proof has thus been obtained that the motor, when properly installed, is a reliable machine, whose operation is as satisfactory as the best of other types of engine, and, in general, simpler, owing to the absence of all auxiliary plant, and because the fuel can be employe:! directly in the cylinder of the motor in its original natural condition, without any previous transformatory process. In 1897, when after four years of difficult experimental work I completed the construction of the first commercially successful motor in the Augsburg Works, it was proclaimed by the numerous engineering and scientific committees and deputations from various countries, who tested the machine, that a higher heat efficiency was attained by it than with any other known heat engine. As a result of subsequent ex- perience in practice, and the gradual improvement in the manufacture, still better results have been obtained, and at the present time the thermal efficiency the motor attains is up to about 48 per cent, and the effective efficiency in some cases up to nearly 35 per cent. ' B 2 INTRODUCTION Technical knowledge and science are always progressing, and in later days these figures will be even further improved, but in the present state of our knowledge a higher efficiency cannot be reached by any process for changing heat into work ; a further advance seems only possible by a new process of conversion, with an essentially novel method of operation which we to-day cannot conceive. Therefore the Diesel motor is the engine which develops power from the fuel directly in the cyhnder without any previous transformatory process, and in as efficient a manner as, according to the present state of science, seems possible ; it is therefore the simplest and at the same time the most economical power machine. These two conditions explain its success, which hes in the novel principle of its method of operation and not in construction?. 1 improvements or alterations to earlier engine types. Naturally the questions of construction, and the careful design of the details, are of considerable moment in a Diesel motor as in every engine ; but they are not the cause of the great importance of this motor in the world's industry. A further reason for this importance Ues in the fact that the Diesel engine has destroyed the monopoly of coal, and has in the most general way solved the problem of the employment of hquid fuel for motive purposes. The Diesel motor has thus become in relation to hquid fuel, what the steam and gas engine are to coal, but in a simpler and more economical manner ; it has by this means doubled the lesources of man in the sphere of power development, and found employment for a product of nature which previously lay idle. In consequence thereof the Diesel motor has had a far-reaching effect in the liquid fuel industry, which is now progressing in a way that could not previously be anticipated. I cannot here enlarge on this point, but it may in general be said that owing to the interest which the petroleum producers have taken in this important matter, new weUs are being constantly opened out, and fresh develop- INTRODUCTION 3 ments inaugurated, and that from the latest geological researches it has been shown that there is probably as much, and perhaps more, liquid fuel than coal in the earth, and moreover in much more favourable and more widely distri- buted geographical positions. That the undertakings dependent on the petroleum industry have been equally strongly influenced is shown by the marked development which in quite recent times has occurred in the oil transport trade, especially the great development in the number of tank vessels which themselves use the Diesel motor for propulsion. But the influence of the Diesel engine on the world's industry does not end here. Already in the year 1899 I employed in my motor the by-products from the distillation of coal, and the manufacture of coke — tar or creosote oil — with the same success as with natural liquid fuel. The quality of these oils was however generally unsatisfactory for use in Diesel motors and subject to continual variations. Only recently the interested chemical industries have suc- ceeded in getting the necessary quality, and to-day this pro- duct enters definitely into the sphere of influence of the Diesel motor. It follows therefore that this engine has an important influence on the two further industries — ^gas and coke manu- facture — from which the by-products have now become so important that a great movement is beginning in connexion with this question. It is impossible further to discuss this matter here, but one fact arises distinctly from this movement, namely, that the coal which appeared to be threatened by the competition of Hquid fuels will, on the contrary, enter into a new and better era of utilization through the Diesel motor. Since tar oil can be employed three to five times more efficiently in the Diesel motor than coal in the steam engine, it follows that coal can be much more economically utiHzed when it is not burnt barbarously under boilers or grates, but converted into coke and tar by distillation. The coke is then employed in metallurgical work and for all heating purposes ; the valuable products 4 INTRODUCTION from the tar must be extracted and used in the chemical industries, while the tar oil, and its combustible derivatives, and under certain circumstances the atr itself, can be put to exceptionally favourable use in Diesel motors. It is, therefore, of the greatest interest to employ the largest possible amount of coal in this refined and more economical manner, and thus both coal mining and the related chemical industry come within the influence of the Diesel motor, which is not inimical but most helpful to the development of the coal industry. The proper evolution of the fuel question which has already begun and is now progressing rapidly is as follows : on the one side use liquid fuel in Diesel motors, on the other side, gas fuel, also in the form of coke, in gas motors : solid fuel should not be employed at all for power production, but only in the refined form of coke for all other uses of heat in metallurgy and heating. The liquid fuels already mentioned by no means exhaust the list of fuel which may be used for Diesel motors. It is well known that lignite, whose production is about 10 per cent, of that of coal, leaves tar on dry distillation which when worked for pure paraffin leaves as a by-product the so- called paraffin oil. Not all kinds of lignite are suitable for this purpose, nevertheless so much of this oil is produced that up to now it has supplied, for instance in Germany, a very large proportion of the demand for liquid fuel for Diesel motors. Further there are to be considered other products available in smaller but noteworthy quantities such as shale oil, etc. ; certain countries, as for instance France and Scotland, have large quantities of them and they are in use in many Diesel engine installations. But it is not yet generally known that it is possible to use animal and vegetable oils direct in Diesel motors. In 1900 a small Diesel engine was exhibited at the Paris exhibi- tion by the Otto Company which, on the suggestion of the French Government, was run on Arachide oil,^ and operated so well that very few people were aware of the fact. The motor was built for ordinary oils, and without any ^ Botanical name : Arachis hypogsea Jj, INTRODUCTION S modification was run on vegetable oil. I have recently re- peated these experiments on a large scale with full success and entire confirmation of the results formeily obtained. The French Government had in mind the utilization of the large quantities of arachide or ground nuts available in the African colonies and easy to cultivate, for, by this means, the colonies can be provided with power and industries, without the necessity of importing coal or liquid fuel. Similar experiments have also been made in St. Peters- burg with castor oil with equal success. Even animal oils, such as fish oil, have been tried with perfect success. If at present the applicability of vegetable and animal oils to Diesel motors seems insignificant, it may develop in the course of time to reach an importance equal to that of natural liquid fuels and tar oil. Twelve years ago we were no more advanced with the tar .oils than to-day is the case with the vegetable oils ; and how important have they now become ! We cannot predict at present the role which these oils will have to play in the colonies in days to come. However, they give the certainty that motive power can be produced by the agricultural transformation of the heat of the sun, even when our total natural store of solid and liquid fuel will be exhausted. Having now made a short survey of the importance of the Diesel motor to the world's industry in general, I would add a few words concerning its importance to England in particular. The following three facts must be kept in mind for consideration : — 1. England is an exclusively coal -producing country. 2. England is the greatest colonizing country in the world. 3. England is the greatest marine nation in the world. (1) England possesses (at any rate up to now) no natural liquid fuel, and is a purely coal-producing country ; owing to this fact the opinion has lately been frequently and strongly expressed that England has intrinsically no concern with the Diesel motor, and that it is against her most Aatal 6 INTRODUCTION interests to help in the more widespread adoption of this engine, since she would neglect her own wealth of coal and would render herself dependent on other countries by the employment of liquid fuel. Both these statements are wrong and the reverse is true. It is in England's greatest interest that the coal -devouring steam engine should be replaced by the economical Diesel motor, and particularly so as by such a change, economies can be effected in her most important wealth, the coal — and the life of the mines prolonged ; further, because it improves in a most rational way the use of coal and the results of the allied chemical industries, in utilizing the coal in the refined manner previously mentioned ; finally, because by this method of utilizing the coal (that is through the employ- ment of tar and tar oils in Diesel motors), England becomes free and independent of foreign countries for the supply of her liquid fuel. (2) The extent to which England may help her colonies through the Diesel motor can, as yet, hardly be conceived ; even when using natural mineral oils alone, the Diesel motor is a machine essentially adapted for work in the colonies, as only from one-fourth to one-sixth part of the weight of fuel has to be transported to the colony and into the interior, as compared with a steam engine ; because in the colonies the freight charges for the fuel are generally the decichng factor in the profitableness of power plants. Further, because the transport of this liquid fuel is in- comparably easier and more convenient than coal, and finally because the difficulties of running a boiler installation — particularly marked in the hinterland — put the steam plant out of question. It may be mentioned in this connexion that a pipe line for crude petroleum 400 kilometres long will be laid from Matadi to Leopoldville on the Congo, bj^ means of which this immense country will be provided with a constant source of liquid fuel, which will give its essential living element — the motive power — to agricultural and transport enterprises, and other industries about to be established. INTRODUCTION 7 This wonderful example should be followed in the English colonies ; it is unnecessary to follow the far-reaching effects of such a course on the prosperity of the colonies. When it is remembered that, as previously mentioned, the Diesel motor can also run on vegetable oils, it is not difficult to see that this fact opens out a new prospect for the pros- perity and industry of the colonies, a fact which is of great:r importance to England than to any other country owing to the large number of its possessions. On this point and as quickly as possible the problem should be tackled ; the Diesel motor can be driven by the colonies' own products, and thus in a great degree can aid in the development of the agriculture in the country in which it operates. This sounds to-day somewhat as a dream of the future, but I venture the prophecy with entire conviction that this method of the employment of the Diesel motor will in days to come attain great importance. (3) Finally, England is the greatest marine power in the world. When the first success of the Diesel motor as a marine engine became known in England last year ; when it was realized that already a large number of small merchant and naval vessels were equipped with Diesel engines, and that progress was gradually being made on a larger scale ; that already large American liners were to be propelled by Diesel motors, and at the same time a warship was in con- struction to be equipped with a very large Diesel engine ; then there was much stir and some excitement throughout the country which is still fresh in the mind. And rightly so ! The reports of satisfactory sea voyages with Diesel motors under very bad weather conditions are becoming more numerous. The ships' captains who have Diesel motors in their ships certify to their great reliability and convenience of running, and figures are published showing the economy effected ; it can no longer be doubted that in this direction the Diesel motor will create one of the greatest evolutions in modern industiy. That the greatest shipping nation in the world should derive 8 INTRODUCTION no advantage from such a change would be simply impossible. England is bound, in the face of competition with other countries, to take full advantage of this new departure. Finally, a few words on the manufacturing : — The Diesel motor must be constructed with extreme care, and the best materials employed in order that it may properly fulfil all its capabilities ; only the best and most completely equipped works can build it. Fourteen years ago there were very few factories which were able to undertake its construction, and it may be said that through the Diesel engine the manufacture of large machines has been raised to a higher level, in the same way as the manufacture of small machines has been brought on new lines by the automobile engine. The Diesel motor is therefore not a cheap engine, and I would add a warning that the attempt should never be made to try to build it cheaply, by unfinished workmanship, particularly for export. Tliese fundamental conditions regarding the construction of the Diesel engine are no disadvantage, as has been fre- quently proved ; on the contrary they are precisely the reason of its strong position and form a guarantee of its worth. Munich, DIESEL. December, 1911, CHAPTER J GENERAL THEORY OF HEAT ENGINES WITH SPECIAL REFERENCE TO DIESEL ENGINES EXPANSION OF GASES — ADIABATIC EXPANSION — ISOTHERMAL EXPANSION — WORKING CYCLES — • THERMO-DYNAMIC CYCLES— CONSTANT TEMPERATURE CYCLE — CONSTANT VOLUME CYCLE — CONSTANT PRESSURE CYCLE — DIESEL ENGINE CYCLE^REASONS FOR THE HIGH EFFICIENCY OF THE DIESEL ENGINE. Expansion of Gases.- — Though it is unnecessary to go fully into any detail regarding the theory of heat engines, a general study of the laws governing the expansion of gases, and the theoretically and practically attainable efficiencies of motors working on gaseous fuel, is desirable in order to understand the action of the Diesel engine, and the reason for its higher efficiency than that of any other heat engine. The basis of the various formulae quoted in the following pages will be found in any text -book on heat engines, and elucidation is only given in this volume where it bears directly on the theory of the Diesel engine. In a consideration of the expansion of gases with the consequeiit production of work there is always a definite relation, for the same weight of gas, between the volume, pressure, and temperature at any moment during the expansion, and this relation is given by the formula PV=>;T where P = absolute pressure in lb. per square foot. V = Volume in cubic feet. T= absolute temperature in degrees Fahrenheit. tf — constant. 10 DIESEL ENGINES FOR LAND AND MARINE WORK and of course the same formula applies for other units (e.g. metric units), with a different value for »/. The value of t] varies with different gases, and it is in fact the difference between the specific heats of the gas at constant pressure, and at constant volume and may be expressed as '/ = K^ — K, where K^ = Specific heat of gas at constant pressure. K„ = Specific heat of gas at constant volume. In the units given above, for air Kp = 184-7 K^ = 131-4 and >7 = 53-3. In the formulae which follow, it will be seen that the ratio of the two specific heats is of importance and this ratio, i.e. — ^ is usually denoted by the symbol y which for air is 1-405 and for other gases used in heat engines some- what less, 1-32 being for instance a fair figure for lighting gas. Since with all gases PV = >/T, it is evident that for the same quantity of gas either the pressure, volume, or tem- perature, is determinate if the two other values be known, P Vi PoVo i.e. = ^ — -" where Pi, Vi, and Ti, represent respec- T^ Ta tively the pressure, volume, and temperature of the gas in one state and P2, Vo and To the pressure, volume, and temperature of the same weight of gas in another state. For purposes of solving the problems of the behaviour of gases during expansion, there are two methods of expan- sion which are generally considered, neither of which how- ever is exactly attained in actual heat engines. These are : — 1. Expansion at constant pressure. 2. Expansion in which the pressure and volume vary according to the formula PV" = constant Under the heading (2) come the two special cases of expansion which are of the most importance in the theory of heat engines, namely (a) adiabatic expansion according to the formula PV^= constant, and (6) isothermal expan- sion, according to the formula PV = constant. Adiabatic Expansion. — When a gas expands adiaba- GENERAL THEORY OF HEAT ENGINES 11 tically no heat is lost or gained during the expansion, the whole of the heat being employed in doing external work, and it is evident at once that such can never be quite realized in practice. The relation between temperature and volume is important in considering the question of the efficiencies of the cycles on which the Diesel and other heat engines operate, and this relation may be arrived at as follows : — (1) (2) )r any gas P2V - hence P.T, = P2T, v^ ■■•■ also PiVi' ^=P2V; >7 hei V2 ice _ = .Pi^ 1 • • P2^ Substitutir ig (2) in (1) P.T, : = PoTi X^ P^^ T, or — = P2 1 Pi^ P2^ ■■.1. which is _P^ y — 1 y P." y (3) and in a similar manner it may be shown that ' (^) T2 ^ /v^Y Isothermal Expansion. — In isothermal expansion the temperature of the gas during the whole expansion remains unaltered, and hence the internal energy in the gas itself remains unaltered, and the heat given to the gas is equiva- lent to the external work done. In this expansion from the general formula PV = »/T, since T is constant the pres- sure must vary inversely as the volume, and since the equa- tion PV = constant is that of an equilateral hyperbola. 12 DIESEL ENGINES FOR LAND AND MARINE WORK isothermal expansion is sometimes known as hyperbolic expansion. The relation between isothermal and adiabatic expansion Adia.ba.cic Fig. 1. — isothermal and Adiabatic Ciu'ves. curves is readity seen on a pressure volume diagram, Fig. 1, in which the isothermal is above the adiabatic line, and Fig. 2. — Isothermal and Adiabatic Curves. Fig, 2 shows the same curves during compression in which the adiabatic is above the isothermal. During adiabatic GENERAL THEORY OF HEAT ENGINES 13 compression the temperature after compression must rise, since T /P \ ">'~ ^ — = ( — ) y and this must be greater than 1. It follows therefore that comparing adiabatic and iso- thermal compression a higher temperature may be reached with the former than with the latter (in which there is no rise of temperature), employing the same compression pressure, wliich is the reason of gas engines working with adiabatic compression rather than isothermal, since a high temperature is required with a minimum pressure. Working Cycles. — All heat engines work through a mechanical C3'cle of operations, which is continually repeated, that most commonly employed being the four- stroke cycle, in which the working fluid passes through a complete series of operations in four strokes of the piston, or in two revolutions of the crank shaft. It is obvious that if it be possible to complete the cycle for an engine in two strokes instead of four, nearly double the power might be obtained from the same size of cylinder, and this fact has led to the introduction and wide adoption of gas engines working on a two-stroke cycle. As will be seen later, the two-stroke cycle Diesel engine has already made much headway and must of necessity be adopted for large powers, and the ultimate general employment of this type for the propulsion of very large ships no longer seems in doubt. In the two-stroke cycle engine, one stroke in two is a working stroke, as against one in four with the four-stroke cycle, and a still further advantage may be gained by the employment of the former type, and using also the double acting principle so that every stroke of the piston is a working stroke. The possibilities of this system in so far as it affects Diesel engines will be discussed later and need not to be further entered into here, Thermo -Dynamic Cycles. — The principles upon wliich ."11 heat engines theoretically work, may be divided up into three main divisions, according to the cycle of changes of 14 DIESEL ENGINES FOR LAND AND MARINE WORK state, through which the working fluid continually passes, these cycles being thermo-dynamic cycles in contradistinc- tion to the mechanical cycles mentioned in the last para- graph. As a matter of fact no actual engine exactly follows along the lines of the theoretical machine, but these prin- ciples form a necessary and useful basis of comparison. They are : — L Constant temperature cycle. 2. Constant volume cycle. 3. Constant pressure cycle. In engines in which the working fluid passes through one of these cycles, there is a certain efiiciency which cannot be exceeded or indeed reached, and an examination of the maximum possible efficiency in each case v,ill lead us to the points of difference between the Diesel and other heat motors. Constant Temperature Cycle. — In this cycle all the heat is taken in from its source at a temperature which remains constant during the whole process, and the heat is rejected also at a constant temperature which is of course lower than the temperature at which the heat is received. All cycles can be illustrated diagrammatic ally by a closed series of curves drawn relative to two lines at right angles, the vertical line representing the pressure, and the hori- zontal line the volume of the gas at every stage of com- pression and expansion, and these curves are the indicator diagrams of perfect engines working on the various cycles. Fig. 3 represents the constant temperature cycle, the line OP denoting the pressures, and OF the volumes of the gas. be represents the compression line in which the gas is com- pressed adiabatically from the point b where the volume is V2, the pressure Po, and the temperature Ti, to the point c, where the pressure is P3 the volume V3, and the temi^erature T3. Heat is taken in from c to d, at constant temperature T3, the pressure and volume at d, being P4 and V4 respec- tively. From d to a is adiabatic expansion, the pressure, volume, and temperature at a, being Pi, Vi, and Ti, GENERAL THEORY OF HEAT ENGINES 15 respectively. From a to b heat is rejected at the constant temperature Ti, this completing the cycle. Tne efficiency of an engine working on this cycle may be V3 Fig. 3 •2 '4 r/ -Constant Temperature Cycle Diagram. yi V readily expressed in terms of the top and bottom limits of temperature during the process. If Q3 = the heat taken in by the gas and Qi = the heat rejected at the lowest temperature, then Q3 — Qi =the heat usefully employed in doing work, and the efficiency of the cycle is represented by the ex- pression Q3 - Qi n = Q= As generallj^ Q = tvkT, where w is the weight of gas and h its specific heat it follows that since neither iv nor k vary IG DIESEL ENGINES FOR LAND AND MARINE WORK during the cycle the quantity of heat is always directly proportional to the absolute temperature, or the efficiency of the cycle is This expression represents the efficiency of the constant temperature cycle, T3 being the top temperature and T^ the bottom temperature during the complete cj^cle. No actual engine can have an efficiency so high as the ideal constant temperature engine, and an ordinarily effi- cient steam engine, working between limits of say 150 lb. per sq. inch pressure and 28 inches vacuum, or say 819° F. and 563°F. absolute temperatures, would, if a perfect machine, have an efficiency = 31'3 per cent. As a matter ■^ 819 of fact steam engines are seldom more than half as economi- cal as the ideal constant temperature engine, and hence an ordinary steam engine would have an actual efficiency of something under 16 per cent., and this may be compared with the possible efficiencies of gas and Diesel engines, deduced later. Constant Volume Cycle. — An engine working on tlie constant volume cycle differs from one acting on the con- stant temperature cycle in that all the heat is taken in while the volume of the gas remains constant, and the heat is rejected under similar conditions. The cycle is shown in Fig. 4 in which as before OP represents pressures and OV volumes. Compression takes place adiabatically along the hne ah, the pressure, volume, and temperature changing from Pi, Vi, and Ti at a to Pa, V2, and T2 at h. Heat is then taken in at the constant volume V2, the pressure rising to P3, and the temperature to T3. Next there is adiabatic expansion along the line cd till the volume is once more Vi, the pressure and temperature then being P3 and T3 and finally heat is rejected while the volume remains unaltered until the original pressure P] and temperature Ti are attained. To obtain the thermal efficiency of the ideal constant GENERAL THEORY OF HEAT ENGINES 17 volume engine let Q2 = the heat taken in by the fluid, j\nd Q3 = the heat rejected by the fluid. ' -— <3 i^'iG. 4. — Constant Volume Cycle Diagram. The heat usefully employed is Q2 — Q3 and the efficiency IS ^2 — Mg Q2 or 1 Q3 Considering 1 lb. of gas to eliminate the question of weight — this remaining constant throughout the cycle — the quantity of heat taken in or rejected during a constant volume change is, generally, Q = A;„ (T„ — Tj) where T^ and T^ are the respective absolute temperatures before and after the change. Hence Q, = h, (T3 - T2) Q3 = K (T4 - TO from which it follows that the efficiency T4 -Ti w = 1 - T, 18 DIESEL ENGINES FOR LAND AND MARINE WORK From formula (4) page 11, with adiabatic expansion T4_ /Vsy-^ _T, since the vohime Vi is constant during the change of tem- perature from T4 to Ti and the volume V2 is constant during the change from T2 to T3 hence T\jzl} = !^ = ^i T3 - T, T3 T, T that is n = I * or from the above n = 1 ©'" Vi The ratio — is usually called the compression ratio and is designated by r, so that the general formula for the effi- ciency of the constant volume cycle is n= 1 - — 1 r " Practically all gas engines work on a cycle closely approxi- mating to the constant volume cycle. Constant Pressure Cycle. — In this cycle all the heat is taken in at constant pressure, and the heat is also rejected at constant pressure, expansion and compression of the gas being adiabatic as before. Fig. 5 represents the constant pressure cycle on the pressure-volume basis. Starting from b when the pressure, volume and tempera- ture are respectively Pi, V2, and T2, the gas is compressed adiabatically to c where P2 is the pressure, V3 the volume and T3 the temperature. Heat is taken in along the line cd at constant pressure P2, the volume at d being V4, and the temperature T4. Adiabatic expansion next occurs along the line da, to a, where the pressure, volume, and temperature become Pi, Vi and Ti respectively. Heat is then rejected at constant pressure Pi, along the line ab to the starting point b where the original conditions prevail. GENERAL THEORY OF HEAT ENGINES 19 As before let Q2 = heat taken in by the fluid, and Qi = heat rejected by the fluid. The efficiency of the cycle is then n = — ~-i- and, considering 1 lb of gas Qo = kp (T4 — T3) and Qi = k^ {T, - T,). The efficiency is therefore n = I T. - T, ^3 y. vz V, Fig. 5. — Constant Pressure Cycle Diagram. Expansion along da and compression along be are adiabatic 80 that, from formula (3) page 11. T, _ Tt -T, T. T= From this T4 -T, Pi\5^^* T /P \ The efl&ciency is thus n = I — -i = l — f— -M but with adiabatic expansion f — j r = f— "j 20 DIESEL ENGINES FOP. LAND AND MARINE WORK and the efficiency may be expressed » = i-(vj =1-7-' which is the same expression as was obtained for the efficiency of the constant vokime cycle, and in fact the efficiencies of the constant temperature, constant volume, and constant pressure cycles are identical. It is at once apparent from the above results that what- ever cycle of operations a heat engine works upon, the higher the compression ratio can be made, the less becomes the fraction — , by wliich the possible efficiency is reduced below unity, and hence the greater becomes the efficiency of the engine if mechanical and other losses are not increased in the same proportion. It is for this reason that in all gas engines it is desirable to work with a high compression ratio. In internal combustion engines of the ordinary design, that is to say gas engines working on the constant volume cycle, the compression ratio is limited by the fact that during the suction stroke a mixture of air and gas is drawn into the cylinder and the mixture is compressed in the compression stroke. The pressure to wliich this com- pression may be carried, may not reach beyond a relatively low figure, since it must not approach the temperature of combustion of the mixture, for were it to reach this point, ignition would occur before the commencement of the working stroke, i.e. there would be pre-ignition. In the Diesel engine pure air alone is dra\vii into the cylinder and compressed, and the fuel is admitted a\ter compression, so that very much higher compression pressures may be employed than with ordinary gas engines, there being of course absolutely no danger of pre-ignition. In actual working the compression ratio with Diesel engines is about 12, as against 6 or 7 with gas engines, which shows at once the possibilities of higher efficiencies with Diesel engines than with the usual tj^pe of internal combustion engines. This can be easily illustrated by working out the thermal efficiencies in the two cases GENERAL THEORY OF MEAT ENGINES 21 with r — Q and r = 12. In the first instance n = -51 while in the second n = -63, showing a gain of over 23 per cent. There are however other factors influencing the efficiency of the actual engines, and these can be better ihustrated by an examination of the cycle of the Diesel engine as constructed. Diesel Engine Cycle. — The complete cycle of operations of the Diesel engine will be fully discussed in the next : e Fig. G. — Diesel Cycle Diagram. chapter, but for present purposes it is sufficient to explain that in the ordinary four-stroke engine as at present con- structed, the cycle of operations is somewhat similar to constant pressure cycle, except that the rejection of heat to the exhaust is more nearly at constant volume than at constant pressure, and that the expansion and compression 22 DIESEL ENGINES FOR LAND AND MARINE WORK are not perfectly adiabatic which, of course, is impossible with any actual heat engine. Fig. 6 represents fairly accur- ately the Diesel cycle on the usual pressure volume basis. Compression takes place adiabatically along ah, then heat is taken in at constant volume to the point c, after which there is adiabatic expansion to d, and rejection of heat to exhaust at constant volume to a. The pressures and volumes at the various stages are indicated on the diagram, while the temperatures correspond. Let Q2 = heat taken in by the fluid, Qi = heat rejected to exhaust, then the efficiencv of the cycle is w = ^ ^", or 1 — —• Since the heat is taken in at constant pressure Q2=^^ (T3 -TO and since heat is rejected at constant volume Q. = K (T4 - TO. PV From the general formula — = constant we have c rp Mj=M?orT,=Tj'» hence T, T, V, similarly T4 = T, x — '. From the general formula for adiabatic expansion PV^ = constant it follows Pi = ^^-G/)^ '^"*^^ P4 ^ P2 (^\ and hence T, = T, {^^ = T, (J^J Substituting this value in the expression for Qi GENERAL THEORY OF HEAT ENGINES 23 The expression — ? is the ratio of the cut-off vohime to the V2 clearance volume and may be denoted by R. The efficiency of the Diesel cycle may then be expressed by substituting in the formula n = 1 — wliich then becomes k„ Ti (R^- 1) KT, (R - 1) Ti R^ - 1 = 1 - ;;^ X n = 1 - To 7(R - 1) Since the compression from a to b is adiabatic T, 1 To r^ — 1 as before, and the final expression for the efficiency of the Diesel engine is 1 Rv - 1 n = I — , X r^-i 7(R - 1) From this it would be seen that the cut-off ratio exercises an important influence on the thermal efficiency of a Diesel engine, this depending on the two variables, the compression ratio and the cut-off ratio. The effect of the alteration of the cut-off can be shown by giving actual values to R and r. Taking the clearance volume as yV of the volume swept through by the piston, and the cut-off as Vo which is common with Diesel engines and referring to Fig. 6 we have V3 — V2 = — and V2 = — and hence 10 15 Va Vs Vs ., Vs — — = — or V3 = - so that 15 10 R = ^^ = 2.5 Assuming that r = 12 and y = 1-405 (which is somewhat higher than in actual engines) the thermal efficiency of the 24 DIESEL ENGINES FOR LAND AND MARINE WORK Diesel cycle from the formula previously deduced, works out at -56, whereas with the same values of r and 7 but with R = 1-5 the efficiency becomes '61. In the above remarks it has been assumed that y re- mains constant, which is, of course, the case for any particu- lar mixture. In comparing the efficiencies of ordinary gas engines and Diesel engines it is to be noted however that the efficiency on any cycle becomes larger as y is increased, which occurs when the gaseous mixture has a larger propor- tion of air, or as it is generally termed, is a leaner mixture. In Diesel engines the mixture is very much leaner than in gas engines, and hence this accounts to a certain extent for the greater economy of this type of engine. Reasons for the High Efficiency of the Diesel Engine. — Summarizing the foregoing analysis it may briefly be said that the superior efficiency of the Diesel engine is due to several causes, the first being the successful employment of high compression pressures rendered possible by the fact that air alone is compressed in the cylinder and not a mixture of fuel and air in which the temperature of ignition always limits the compression pressure. In the second place, a leaner mixture may be employed than with gas engines, less weight of fuel is necessary, and the loss in the cooling water is correspondingly reduced. There are, moreover, fvu'ther reasons which probably exercise an important influence, namely, the perfect combustion of the fuel due to the high pressure during the whole combustion period and mechanical advantages such as the efficient method of its injection. It is obvious that oil with a high flash point is very suitable for the Diesel engine, thus permitting of the cheapest crude residue oils being employed. On the other hand, a separate compressor is necessary to inject fuel with compressed air at a higher pressure than the compressed air in the cylinder, and this causes a slight loss of efficiency, usually about 6 per cent., which is, however, of no great import. It must be distinctly remembered that the Diesel engine cycle itself does not account for the economy of the engine since, as a matter of fact, the constant pressure cycle is GENERAL THEORY OF HEAT ENGINES 25 rather less cificient than that at constant vohime, on which most gas engines work, provided the conditions are the same. In other words, for the same compression pres- sure the constant volume engine would be superior to the constant pressure engine, but for the reasons already given it is impossible that a gas engine should approach the con- ditions which are easily attained with the Diesel engine. The limits of pressure of the working fluid are fixed by the ultimate strengths of the materials of which the engine parts are constructed, and the Diesel cycle gives the maximum economy for these limits of pressure. Thougli very much higher compression pressures (but not maximum pressures) are employed in the Diesel engine than in gas engines, the temperature at the end of combustion in the first case is very considerably below^ that in the second, since the period during which the burning of the fuel occurs is so long compared with the explosion in the gas engine cylinder, thus allowing the heat to be taken up to a greater extent by the jacket water. The combustion in the Diesel engine is however by no means isothermal, and the tempera- ture rises a good deal after the injection of the fuel and also to a slight extent after the fuel valve is closed, but allowing for this the important fact remains that in Diesel engines, in spite of high pressures, the temperatures are less. The following table gives the actual consumption in British Thermal Units per B.H.P. hour for various types of engines, namely, non-condensing and condensing steam engines, tur- bines using superheated steam, suction gas engines, and Diesel engines. The figures quoted represent generally the limit- ing results obtained in practice, and the efficiencies are also given based on the heat equivalent of one H.P. hour which . 33000 X GO o;.<- T^rpi TT rru J- IS = 254o B.ih.U. Ihe correspondmg ranges 778 of pressure are also added. 26 DIESEL ENGINES FOR LAND AND MARINE WORK Type of Engine. Non-condensing steam en- gines Condensing steam engines and turbines using super- heated steam. Suction gas engines Diesel engines .... Range of Pressure lbs. per sq. inch. 160 to 220 300 to 370 500 to 600 B.Th.U. per B.H.P. Hour. 30,000 to 38,000 17,000 to 25,000 11,000 to 14,000 7,500 to 8,000 Efficiency per cent. 8-4 to 6-6 15 to 10 23 to 18 34 to 32 Two-cycle Diesel engines are about 2 per cent, less efficient than the four-cycle slow speed type, and all the efficiencies refer to the engines running under full load condition being of course lower with smaller outputs. These figures are all the effective efficiencies, but the thermal efficiencies are very much higher — ^the efficiency for Diesel engines being, for instance, from 42 to 48 per cent. Practical Diesel Engine Cards. — Needless to say, the actual indicator cards obtained from Diesel engines in prac- tice are by no means identical with the ideal diagram given on page 21. At the same time by very careful adjustment of the engine, it is possible to obtain a very good card show- ing quite a prolonged combustion at constant pressure, althovigh this is usually only possible at full load. The maximum pressure attained after the compression stroke is generally between 450 and 500 lb. per sq. inch, 470 lb. per sq. inch being an ordinary figure. In two-cycle motors it is frequently less than this, although in some cases it is exceeded, particularly for instance in a Junkers motor, for reasons which will be understood from the description of this engine later. Considerable improvement may some- times be effected in the card by an alteration of the lift of the fuel valve. In general this is between three and four GENERAL THEORY OF HEAT ENGINES 27 mm., although the actual lift clue to the knocker of the cam may be considerably in excess of this in order to allow a reasonable clearance between the knocker and the roller of the fuel valve lever. The amount of clearance to be allowed depends upon the accuracy with which the motor has been designed, and the experience gained in operation, and in some cases it is as much as 3 to 4 mm., and in others not much greater than | mm. The following table gives the actual setting of the valves of one of the cylinders in an engine of the four-cycle type running at 300 r.p.m. developing 300 B.H.P. and having four cylinders. The dimensions of the cylinders were 380 mm. bore and 420 mm. stroke. Fuel valve opens per cent, before upper dead centre . Lift fuel mm Fuel valve closes per cent, after upper dead centre . Starting valve opens per cent, after upper dead centre Stroke of starting valve mm Starting valve closes per cent, after upper dead centre Play between roller and cam (s.v. closed) mm. Air suction valve opens per cent, after upper dead centre Stroke of air suction valve mm Air suction valve closes per cent, after upper dead centre Play between roller and cam (air suction v. closed) mm. Exhaust valve opens per cent, before lower dead centre . Stroke of exhavist valve min Exhaust valve closes per cent, after upper dead centre Play between roller and cam (e.v. closed) mm. Fuel nozzle, bore of flame disc mm Diameter of holes in atomiser plates mm Distance apart of holes in atomiser plates Diameter of fuel test valve mm. Compression space in working cylinder mm Liner to be placed in connecting rod at top end 0-7 31 8 2 5 38 0-2 6 30 8 0-2 25 29-8 3 0-4 4-2 2 3 11 21-3 2-5 In a two-cycle marine engine of the Sulzer type Mith port scavenging having four cylinders 310 mm. bore and 28 DIESEL ENGINES FOR LAND AND MARINE WORK with 450 mm. stroke, running at 280 r.p.m., the following were the lifts of the fuel valve : — Lifts OF Fuel Value for Two-Cycle 380 H.P. Motor. Minimum Lift. ZMaximtii Lift. Angle of Lead. Angle open after dead centre. Per cent, stroke dura- tion. Lift of Valve. mm. Angle of Lead. Angle open after dead, centre. Per cent, stroke dura- tion. Lift of Valve. mm. Ahead . Astern , 3° 38' 4° 18' 23° 30' 24° 44' 4-94 5-46 1-5 1-75 10° 13' 10° 5' 43° 41' 43° 13' 16-24 15-94 5 5 In the descriptions of various Diesel engines given later, it is explained that in some types a fuel pump is provided for each cyhnder, whereas in other engines there is only one fuel pump for perhaps four or six cylinders. In stationary engine practice, it is still more common to use only one pump and supjjly the fuel to a distributing box from which pipes are taken to the various fuel valves of the cyhnders, but for marine work, especially for two-cycle engines, most builders prefer to employ one fuel pump for each cylinder. In cases, however, where one fuel pump has to supply a number of cylinders it is especially important to ascertain by means of indicator cards that all the cj^linders are doing approxi- mately the same amount of work, otherwise it is easy for one to become much overloaded, even though the whole engine itself is only developing the normal output. The set of cards given in Fig. 9 are taken simultaneously upon a six-cylinder four-cycle engine of 1,500 I. H.P. , and in this case one fuel pump supplies all the cylinders. It will be seen that even though the variation is not great it is quite well marked. 9J9i/ ^ I <0 ^^ Q \ s; "■^ ■^ \ 1 S 1 \ 4: ^ \ CJ \ *N, '3J3l/dfOU//y i/f 3jnsS3JJ 'i/3!/lfS0Wjyi/' 3Jn ^^OJJ 3>f3i^iOUJ^^ ui ajn^ssJJ 3J3t^d^0WJ^ UI 3JnsS3J^ ^ c ^ «J ,2k \ I ^ \ \ 1 ^ s? \\ CO ^ ^ p- ^ ^ \ <0 ^ ^ 1 .'^ f 1 , such as petrol motors, though useful for such engines as the Brons and Bolinder. Whilst the question of the price of fuel oil for Diesel engines is one of very great importance, it wdll never affect the prosperity of the Diesel engine industry in a vital degree, however high it may rise, since, as shown later, the fuel economy with this type of moto' is not its sole claim for consideration. A very large number of different oils are now employed for the operation of Diesel engines, among which may be mentioned the crude oil from Texas and Tarakan, and the residual oil from numerous other countries. Calif ornian oil, Roumanian oil and that from the Galician fields have been commonly utilized for a number of years, while recently, owing to the enormous supplies which are now available from Mexico, the Mexican oil has also been used. Trinidad oil is now iqDon the market, as is that from Persia, so that there is a wide choice. There is not much to say as regards their composition, since practically all of them are entirely suitable for the Diesel engine of every type. The only point to note is that those which have an asphalt base are liable to leave ACTION AND WORKING OF THE DIESEL ENGINE 53 a considerable amount of ash on the valves, and are there- fore not quite so good as the others which are not from an asphalt base. The Mexican oil is perhaps one of the worst in this direction. As regards the question of sulphur, which many people considered a serious and detrimental constituent in oil for Diesel engines, it has now been showii by a large number of experiments that its real effect (even when it is present in the oil to the extent of 4 or 5 per cent.) is practically negligible. This arises mainly from the fact that there is no moisture present in the Diesel engine cylinder, and that without moisture no liquid sulphuric acid is formed, which is the main cause of trouble due to the presence of sulphur. So clearly is this view now held, that the Admiralty specification for oil has been altered to suit the new ideas upon the subject. The specific gravity of most oils which are used in Diesel engines varies between 0-9 and 0-97; the flash-point is generally from 220^ to 250' Fahr. Further interesting details witli regard to the employ- ment of fuel oil for Diesel engines may be obtained from Dr. Sommer's book dealing with the subject, Petroleum as a Source of Power on Ships, from which the following table is extracted : — 1 S.P.G. Be. Gross Heating Value by Experiment. Per cent. Cals. B.T.U's. Roumanian gas oil 0-871 31-9 10,712 19,282 100 Admiralty fuel. 0-907 24-25 10,696 19,253 99-8 Roumanian fuel 0-927 20-95 10,557 19,003 98-5 Roumanian residuiun . 0-928 20-8 10,558 19,004 98-5 Trinidad crude oil 0-94.5 1805 10.200 18.360 95-2 Roumanian residuum 0-946 17-9 10,510 18,918 98- 1 Tarakan crude oil 0-948 17-6 10,487 18,877 97-8 Trinidad residuum 0-964 15-5 10,224 18,405 95-4 The British Admiralty issues a specification for fuel 54 DIESEL ENGINES FOR LAND AND MARINE WORK oil which has comparatively recently been modified, and now stands as follows : — " Quality : — The oil fuel supplied shall consist of liquid hydrocarbons, and may be either (a) shale oil or (6) petroleum as may be required, or (c) a distillate or a residual product of petroleum, and shall comply with the Admiralty requirements as regards flash-point, fluidity at low tempera- tures, percentage of sulphur, presence of water, acidity, and freedom from impurities. " The flash-point shall not be lower than 175° Fahr., close test (Abel or Pensky-Matens). (This compares with a flash- point of 200° Fahr. in 1910.) " The proportion of sulphur contained in the oil shall not exceed 300 per cent, (as against 0-75 in 1910). " The oil fuel supplied shall be as free as possible from acid, and in any case the quantity of acid must not exceed 0-05 per cent., calculated as oleic acid when tested by shaking up the oil with distilled water, and determining by titration with deci-normal alkali the amount of acid extracted by the water, methyl orange being used as indicator. (In 1910 it was required that the oil should be free from acidity. ) " The quantity of water delivered with the oil shall not exceed 0-5 per cent. " The viscosity of the oil supplied shall not exceed 2,000 sees, for an outflow of 50 cubic centimetres at a temperature of 32° Fahr., as determined by Sir Boverton Redwood's standard viscometer (Admiralty type for testing oil fuel). " The oil supplied shall be free from earthy, carbonace- ous, or fibrous matter, or other impurities which are likely to choke the burners. " The oil shall, if required by the inspecting officer, be strained by being pumped on discharge from the tanks, or tank steamer, through filters of wire gauze having 16 meshes to the inch. " The quality and kind of oil supplied shall be fully de- scribed. The original source from which the oil has been obtained shall be stated in detail, as well as the treatment to which it has been subjected and the place at which it has ACTION AND WORKING OF THE DIESEL ENGINE 55 been treated. The ratio which the oil supplied bears to the original crude oil should also be stated as a percentage." In view of the widespread employment of tar oil in Ger- many, and its probable utilization in this coimtry in the future on a much larger scale, the specification of this tar oil which is supplied by a large company in Germany is worthy of quotation. Specification of Tar Oil Suitable for Diesel Engines. (From the German Tar Production Syndicate of Essen- Ruhr.) — (1) Tar-oils should not contain more than a trace of constituents insoluble in xylol. The test on this is per- formed as follows: — 25 grammes (0-88 ounce av.) of oil are mixed with 25 grammes (1-525 cub. inch) of xylol shaken and filtered. The filter-paper before being used is dried and weighed, and after filtration has taken place it is thoroughly washed with hot xylol. After redrying the weight should not be increased by more than 0-1 gramme. (2) The water contents should not exceed 1 per cent. The testing of the water contents is made by the well- known xylol method. (3) The residue of the coke should not exceed 3 per cent. (4) When performing the boiling analysis, at least 60 per cent, by volume of the oil should be distilled on heating up to 300° C. The boiling and analj^sis should be carried out according to the rule laid down by the Syndicate. (5) The minimum calorific power must not be less than 8,800 cal. per kg. (15,800 B.T.U.'s per lb.). For oils of less calorific power, the purchaser has the right of deducting 2 per cent, off the net price of the delivered oil for each cal. below this minimum. (6) The flash-point, as determined in an open crucible by Von Holde's method for lubricating oils, must not be below 65° C. (7) The oil must be quite fluid at 15° C. The purchaser has not the right to reject oils on the ground that emulsions appear after five minutes' stirring when the oil is cooled to 8°. 56 DIESEL ENGINES FOR LAND AND MARINE WORK Purchasers should be urged to fit their oil-storing tanks and oil pipes with warming arrangements to redissolve emulsions caused by the temperature falling below 15° C. (8) If emulsion has been caused by the cooling of the oils in the tank during transport, the purchaser must re- dissolve them by means of this apparatus. Insoluble residues may be deducted from the weight of oil supplied. CHAPTER III CONSTRUCTION OF THE DIESEL ENGINE GENERAL REMARKS FOUR-CYCLE SINGLE ACTING ENGINE ; GENERAL ARRANGEMENT STARTING AND RUNNING DESCRIPTION OF FOUR-CYCLE ENGINE — VALVES AND CAMS REGULATION OF THE ENGINE TYPES OF FOUR- CYCLE ENGINES — HIGH SPEED ENGINE HORIZONTAL ENGINE TWO-CYCLE ENGINE AIR COMPRESSORS FOR DIESEL ENGINES SOLID INJECTION MOTORS. General Remarks. — In the manufacture of Diesel engines there is one point which must be most strongly kept in view, this being that greater care has to be taken in their construction than with ordinary steam engines. A properly designed and well-built Diesel engme has no superior, for reUability and simpUcitj^ of operation, but it i? essential that the materials employed should be well selected, the work should be of the best, and the greatest precision should be exercised in the fitting of the valves and gear, and other mechanism. It might be thought that these matters need no emphasis, but the difference in the running of an engine under working conditions, which has been built as a Diesel engine should be, and one which has been constructed with no more care than is given to a similar steam engine is so material that no excuse need be made for enlarging on tliis point. It is a well-knoA^-n axiom in the manufacture of internal combustion engines that in the attention to details of design and construction Ues the difference between success and failure ; and this is peculiarly applicable to the Diesel 58 DIESEL ENGINES FOR LAND AND MARINE WORK engine, whose satisfactory running depends so entirely on the high compression pressure in the cylinder. Practically aU manufacturers of Diesel engines now make them in standard sizes and types, which is rendered com- paratively easy by the fact that the larger machines have two, three, four, or more cylinders of the smaller standard type. By this means some of the chief manufacturers have as many as fifty standard stationary machines of the four-cycle type from 10 H.P. to 1,000 H.P. based on some fifteen stand- ard single-cyhnder engines ranging from 10 H.P. to 250 H.P. Some of the engines have the same power with a different number of cylinders, but it is possible with this range to have some thirty-five differently rated engines, though there are only fifteen actual standards. This point of standardization is of the utmost importance as regards reduction in cost of construction, interchangeability of parts between different engines, and reduction of spare gear in complete installations, particularly when engines of different powers are employed ; these advantages will be readily appreciated by all who have had experience with the operation of large plants. It is doubtful if in any other construction this matter has received such attention, and if, as should be the case, all the important portions of the engine are made most care- fully to gauge, any part of the mechanism may be taken from one engine and fitted on to another of the same class. Most manufacturers claim that this is possible with all their engines, and some of them make a point of interchanging the parts of several engines when on the test bed, to prove the point. Four -Cycle Single Acting Engine. — Figs. 14 and 15 show, diagrammatically, in plan and elevation, the general arrangement of a vertical single-cylinder Diesel engine of the ordinary type with all the necessary accessories. The cylinder K is cast with the engine frame of the A type, being secured to the bed-plate B by long bolts. The cyhnder cover K^ is of massive construction separate from the main cylinder and frame casting, and contains all the valves, of which there are four. A is the starting valve. CONSTRUCTION OF THE DIESEL ENGINE 59 connected by piping to the starting vessels Co and C^ ; D is the exhaust valve through which the exhaust gases pass from the cylinder into the exhaust pipe E and thence to the silencer F (often placed below ground level), to which is attached the long pipe for the escape of the gases to the atmosphere ; H is the air suction inlet valve by which air is drawn into the cylinder from the engine-room through the inlet pipe J of special construction ; X is the fuel inlet valve and pulveriser, the function of which is to admit fuel to the cylinder at the right moment and in the form of a fine spray. The oil reaches the fuel valve from the fuel pump L, whose action is controlled by the governor, the fuel pump chamber being a small reservoir into which the oil gravitates from the fuel filter M. The fuel pipe is also arranged that it may take its supply from another small cylindrical vessel N which usually contains paraffin, since it is an advantage to run the engine for a few minutes every day on paraffin, which is most helpful in cleaning the cylinder and valves. The fuel filter itself is connected by a pipe from a larger oil reservoir 0, fixed at a rather higher level, and it is convenient to have this reservoir of such size as will contain several days' supply. The main oil tanks containing perhaps several months' supply are commonly fixed miderground and the oil is pumped up into the reservoir as required by a small pump which may be driven in any convenient manner. The cool- ing water circulation is arranged so that the water enters the jacket through a pipe at the bottom and leaves at the top from the cylinder cover. This pipe is usually broken, the water flowing into an open funnel, this forming a ready means of ascertaining that there is no stoppage in the circu- lation. In some cases, however, water is expensive and a cooling tower is installed so that the suppty may be used continuously, and in this event the circuit is usually a closed one ; it is preferable wherever possible to employ open circuit piping, and in any case a thermometer should be fixed on each cyhnder to indicate the temperature of the cooling water. Referring to Figs, li^and 15 again, P 60 DIESEL ENGINES FOR LAND AND MARINE WORK represents the air compressor shown as being driven off the engine crank shaft (though there are various other methods), and de- livering air at the high pressure needed for fuel in- jection and start- ing the engine into the air reser- voir Ci containing the air for the in- jection of the fuel. AU the air vessels Ci, C2 and C3 are connected by air piping and valves so that the pres- sure in any one may be lowered by abstrac ting from either of the others ; of the two reservoirs O2 and Cz one may be considered as a spare to the other. During the run- ning of the engine, the only air used is, of course, that necessary for the fuel injection and hence the com- FiG. 15. — General Arrangement of Die- sel Plant — Elevation. FiQ. 14. — General Arranfrement Plan of Diesel Plant. CONSTRUCTION OF THE DIESEL ENGINE 61 pressor delivers its air directly into the reservoir Ci, the valves being regulated to suit the required pressure, but at the same time the starting vessels are replen- ished so that there is always an efficient supply for re-starting the engine. The vertical governor shaft R shown in the figures is driven through worm gearing off the crank shaft, and this through further gearing drives the horizontal cam shaft *S, supported between two bearings mounted on the C3dinder casting, and on which are all the cams for operating the various valves in the cylinder cover. The governor shaft also actuates the fuel pump L and the governor, the combined action of which regulates the speed of rotation of the engine. The cams and valve levers which they control are not shown in Figs- 1 4 and IG but the valves are in the relative positions most commonly adopted as being best suited for the arrangement of the four cams on the cam shaft. The exhaust and air suction inlet valves are on the outside (longitudinally), while the fuel and starting valves are close together, the object being to have their levers interconnected so that it is impossible for the two valves to be open at the same time. The fuel valve is, of course, in the centre of the cylinder cover, and thus allows the oil to enter centrally and give an equal dis tribution of pressure over the piston during combustion. A third outer bearing, separate from the engine bed-plate is always provided, with the flywheel T, mounted between this and the inner crank shaft bearing. Diesel engines are never constructed as two bearing machines with an over- iiung flywheel. Starting and Running. — The starting and running oi the engine is as follo\\s : The starting lever on the engine is put in the starting position, that is, so that the lever actuating the fuel valve is out of operation and the fuel valve remains closed, whilst the lever actuating the start- ing valve on the cylinder is in its working position, that is, it is moved by its cam on the cam shaft as it revolves and thus opens the starting valve. The engine is barred round till it is just over the dead centre, the fuel valve is pumped G2 DIESEL ENGINES FOR LAND AND MARINE WORK up by hand to ensure the oil piping is full of oil, and the air blast valve on the reservoir Oi is opened so that there is a supply of high pressure air on the fuel valve when it is ready to open. The valve on the starting reservoir which is to be used is then opened and the engine starts up as a compressed air engine. It is allowed to make two or three revolutions when the starting handle is moved so that the lever operating the starting valve on the engine is no longer moved by its cam, and the valve thus remains closed, while the same operation brings the fuel valve lever into working position, and thus opens the fuel valve as the cam operating it, comes round. The arrangement is such that when the starting handle is in the starting position the lever oj^erating the fuel valve is held well out of the range of its cam on the cam shaft, while \\ hen the starting lever is pushed back to the running position the lever operating the starting valve is similarly held away from its cam. Description of Four- Cycle Single Acting Engine. — Figs 16 and 17 show longitudinal and transverse sectional elevations of a single-cylinder Diesel engine of the ordinary slow speed four-cycle single acting type as constructed by the Maschinenfabrik Augsburg Niirnberg A.G. All the four valves are arranged in the cylinder head, the air inlet suction valve E and the exhaust valve A being simi- lar. These are of the mushroom type, opening down- wards directly into the cylinder, and they are kept on their seats by strong springs, the pressure on which may be regu- lated if required. The outlet from the exhaust valve is connected by piping to the silencer, while to the air suction inlet is coupled a pipe through which the air is drawn from the atmosphere. This consists virtually of a closed cylinder with a number of very narrow longitudinal slits arranged usually in two sections as shown, and by this means the access of dust is prevented, while the noise due to the rush of the incoming air is reduced to a minimum. The fuel valve and pulveriser, B — perhaps the most important detail of the engine — is fixed directly in the centre of the 10. — Longitudinal Section of M.A.N. Diesel Engine. [To face page 62. Fio. IS.— 1 000 H.P. Four-Cycle Augsburg Engin CONSTRUCTION OF THE DIESEL ENGINE 63 cylinder, and is likewise contained in the cylinder head, the needle being held in position by an adjustable spring. The starting valve V is fixed as close as is practicable to the fuel valve, and is of somewhat similar type in this design to the exhaust and suction valves, except that it is much smaller. The cam shaft H is supported between two bearings on brackets bolted to the cylinder casting, one of these brackets being seen in Fig 17. This shaft carries the four cams S in Fig. 17. The valve levers which are actuated by the several cams are pivoted on a spindle supported by two small standards fixed to the cylinder head, the starting valve cam lever D, and the fuel valve lever F being seen in Fig. 1 7. The vertical governor spindle C which operates the cam shaft, the fuel valve pump, the governor, and in some machines the small lubricating pumps, is driven off the main crank shaft by a worm drive, running in oil and provided with a coupling near the bed-plate to facilitate removal and inspection. The gear box contains the spur wheels through which rotation is given to the cam shaft at half the speed of the engine shaft. The governor M is of the ordinary type, and regu- lates the speed of the engine by controlling the amount of fuel admitted to the cylinder in a manner described later. The cyhnder liner is separate from the main casting, both of which are usually of cast iron, and ample space is left for the water jacket, the coohng water entering the bottom of the cyhnder and leaving at the top of the cyhnder cover, through the dehvery pife P. In some engines the exhaust pipe and the exhaust valve are also water jacketed, this adding shghtly to the efficiency of the machine. It is essential in any case that the cover should be well cooled, in order to prevent the valves becom- ing overheated, and it is made of massive construction, being secured to the cyhnder by eight studs of ample size. The piston is usually of the cast-iron trunk type, shghtly dished at the top, and is particularly long in order to provide a good bearing surface to reduce the pressure due to the obliquity of the piston rod. It is always fitted CONSTRUCTION OF THE DIE8EL ENGINE 65 with six to eight Ramsbottom rings to secure tightness, and lubrication is effected through a small pipe, which communicates with the cylinder liner near the centre, and delivers into an annular space in it, provided with a number of very small holes piercing the liner and giving access of the oil to the piston. The connecting rod brasses are made adjustable in the usual way to take up wear, and are well lubricated. The air compressor L in this machine is driven off the connecting rod by link levers, the compressor cylinder being bolted to the front of the engine cylinder, though this method is by no means generally adopted, the drive often being arranged directly off the crank shaft at the end of the machine remote from the flywheel, with the cyhnders fixed to the bed-plate. The compressor shown in Figs. 16 and 17 is of the two-stage type, as employed for small machines, and the cylinder is also water cooled, the same water being used as for the engine cylinder jacket, or by- passed from the main supply as may be desired. The com- pressed air from the compressor is delivered direct into the air injection blast reservoir through copper piping. An illustration of two M.A.N, four-cycle engines is shown in Figs. 18 and 19, the first being of 1,000 H.P. and the second of 880 H.P. Valves and Cams. — The action of the various cams may be examined at this point, this being a matter of importance, as the exact time of the opening of the valves, relative to the position of the piston, and the duration of this opening is controlled entirely by the cams which operate the valves through intermediary levers. The position of the cams relative to each other is thus an important point, and is best explained by a diagrammatic representation of them. In Fig. 20 the fuel valve cam is indicated by A, the exhaust valve cam by B, the air suction valve by C, and the starting valve cam by D. In a four-cycle engine each valve must be open once in two revolutions, and the cam shaft must necessarily rotate at half the speed of the crank shaft. In the diagrams, therefore, one revolution of the crank shaft is represented by a semicircle or 180°, while during one stroke of the F 66 DIESEL ENGINES FOR LAND AND MARINE WORK piston each cam makes a quarter of a revolution. The verti- cal and horizontal diameters in Fig. 20 therefore represent top and bottom dead centres of the crank, the vertical lines being taken as top dead centres and the horizontal ones as the bottom dead centres. The arrangement of the cam is now easily understood. The fuel cam opens the fuel valve just previous to the piston reaching the end of its up stroke, thus giving pre-admisson to the extent of perhaps 1 per cent, of the stroke or less, depending on the speed of the engine. The valve is then held open for the required period, Fuel Vslve Cam. A Exhaust Valve Cam. Admission Valve Cam. Starting Valve Cam. B CD Fig. 20. — Diagram showing Arrangement of Cams with Diesel Engine. the total amount of the opening being through an angle of 8 or 10 per cent. The exhaust valve cam similarly opens slightly before the end of the working stroke, remains open during the whole of the next or exhaust stroke, and closes just after the top dead centre is reached. Air admission commences through the air suction valve just before the end of the exhaust stroke, and the valve is kept open during the next stroke, and closes immediately after the crank passes the bottom dead centre. The starting valve cam is arranged to open the valve just before the top dead centre is reached, and to close it some considerable time before the end of the stroke. All the cams are arranged so that the CONSTRUCTION OF THE DIESEL ENGINE 67 valve opens very slightly during the first moment of contact of the cam with the lever, after which the valve opens Fig. 21. — Fuel Inlet Valve, Lever and Cam. rapidly to its full extent, and closes in the same manner, so that in the actual operation a very quick admission and 68 DIESEL ENGINES FOR LAND AND MARINE WORK cut off is obtained. The diagram does not show the cams in their actual relative positions, as if this were so all the levers would have to be arranged parallel with each other and the valves open in the same direction ; usually, in the actual engine, the exhaust, air suction, and starting valves all open inwards to the cylinder, whilst the fuel inlet valve opens outwards, and the lever actuating it has therefore to be set at a different angle from the other levers. The general arrangement of the fuel inlet valve with the cam and lever for its operation is shown in Fig. 21. When the nose of the cam comes in contact with the valve lever, this is forced outwards and the valve is opened against the pressure of a spring, which normally keeps the valve on its seat, the amount of the opening being extremely small. Fig. 21 also shows the starting handle which when in the horizontal position causes the starting valve lever to come in contact with the nose of its cam as the cam shaft rotates, while the fuel valve lever is held clear of its cam at the same time. When the starting handle is in the vertical position the starting valve lever is clear of its cam, and the fuel valve lever then comes into operation. It is a great convenience if the lever is so constructed that there is a joint between the spindle on which it is pivoted and the valve spindle, since this joint can then readily be broken and the valve easily removed. This arrangement, though not universal, is now adopted by a large number of makers, and the design employed by Messrs. vSulzer Bros. is shown in Fig. 25. Fig. 26 shows a detail drawing, partly diagrammatic, of the type of fuel inlet valve and pulveriser most commonly emploj^ed with Diesel engines, though there are slight differ- ences vaih. engines of various makes. The oil from the fuel pump enters through the pipe A, the amount being regu- lated by the action of the governor on the pump to suit the load on the engine. The oil flows dowai the small cylindrical hole B and enters the annular space C through D near the bottom of the needle valve E, ground to an angle of about [To face parje ()8. Fig. 1>1>.— Detnik of Furl Irih-t \^iivc (Carels Tj^it.-). [To face paije (iS. -^ CONSTRUCTION OF THE DIESEL ENGINE 71 30°, just above the pulverising or spraying arrangement. For this purpose there are four metal rings F, each containing a large number (twenty or more) of small holes usually one- tenth to one-sixteenth of an inch in diameter. The holes in the plates or rings are staggered as shown in the figure, so that the oil may not be blown directly through them, and between the plates are very small bands G. Below Fig. 25. — Jointed Valve Lever. the rings is a conically-shaped piece, in the periphery of which is about the same number of channels as there are holes in the rings, and these channels, which may be from one-sixteenth to one-twentieth of an inch deep, form a series of nozzles, through which the fuel has to pass, after getting through the holes in the rings. It then enters the cylinder by the expanding orifice, which is made of steel, the guides for the needle valve being of cast iron. The annular 72 DIESEL ENGINES FOR LAND AND MARINE WORK space C is always in direct connexion with the injection air reservoir as soon as the valve on the reservoir is opened, and the air enters the space near the top through another pipe and a cylindrical hole in the same casting as that for the Fig. 2(). — Fuel Inlet Valve and Pulveriser. fuel inlet. The space C is thus always subjected to the high pressure of the injection air, and immediately the needle valve lifts, the fuel is forced through the pulveriser by the air in the form of a very fine spray, and combustion at once CONSTRUCTION OF THE DIESEL ENGINE 73 takes place. A small cock 31 is provided having con- nexion with the inlet pipe and serves the purpose of a test Fig. 27.— Details of Fuel Inlet Valve of Deutz Engine. cock and an overflow. The oil may be pumped up by hand before starting the engine, and by opening the cock 31 it can be seen at once if the flow of oil is unmterruptcd. The 74 DIESEL ENGINES FOR LAND AND MARINE WORK / Fig. 28. — Fuel Inlet Valve oi Aktiebolaget Diesels Motorer T;y'pe. method of fixing the valve guides in position, and the ar- rangement of the stuffing box, will be understood from the CONSTRUCTION OF THE DIESEL ENGINE 75 figure. By removing the valve lever, the valve can readily be taken out and examined, and as is seen in Fig. 21, the compression of the spring can be altered as required. It might be expected that different pulverisers would be required when different fuels are employed, but as a matter of fact it is found that the same pulveriser will operate quite satisfactorily for grades of fuel of very different viscosity, and they are constructed to be suitable for the thickest oils. Fig. 29. — Moiitlipiece or Battum fart of i'uheriser. and no trouble is then experienced with less viscous fuels. The type of pulveriser and fuel inlet valve adopted by the A. B. Diesels Motorer of Stockholm dift'ers somewhat from the usual construction, and is said to give ver}^ efficient results. This is illustrated in Figs. 28 and 29, and the method of operation is shown in Fig. 30. The oil enters the annular space at the bottom from the fuel pumps in the usual way, position 1 {Fig. 30) showing the amount left immediately 76 DIESEL ENGINES FOR LAND AND MARINE WORK after the injection into the cylinder. In position 2 the oil has been pumped up from the fuel pump, while in position 3 the fuel valve has lifted, and the oil is being injected into the cylinder. The blast of air forces the oil through specially shaped passages, which are usually curved, or of Lregular form, and the mixture is given a spiral motion, the heavier particles of oil being throw n against the sides of the passage so that complete pulverisation takes place. The pulveriser is entirely cleared of oil with each injection, w'hich in rever- sible marine engines is a considerable advantage, and it (2) (3) Fig. 30. — Diagram sliowiiiK Action nf Pulveriser. necessitates that the exact amount of oil delivered by the pump is injected into the working cylinder. The general arrangement with the ordinary type of Diesel engine of the fuel valve, exhaust and air suction valves in the cylinder cover is shown in Fig. 31 , while Fig. 33 gives a section through the exhaust valve and cam shaft showdng the operation of the valve. It will be noticed from the illustrations that the removal of the valves can be carried out very expeditiously in all cases. In some engines, not- ably those constructed in America, the fuel inlet valve is arranged horizontally on the side of the cylinder head, w^hich projects well over the cylinder, and the exhaust valve and CONSTRUCTION OF THE DIESEL ENGINE 77 admission valve are also fitted into this projection, the exhaust valve in the top and the admission valve under- neath. Regulation of the Engine. — The same method of govern- ing the speed of Diesel engines of the land type with varying Fig. 31. — Air Inlet and Exhaust Valves (in section). load is adopted by practically all the chief manufacturers, there being naturally some differences in constructional detail. The control is effected entirely by regulation of the amount of oil admitted into the cylinder through the fuel inlet valve, and hence no alteration in the stroke or the dura- fe CONSTRUCTION OF THE DIESEL ENGINE 79 tion of the opening of this valve is required, which would be the necessary means of governing if the fuel supply were not varied ; the latter method is obviously more convenient from many points of view, particularly inasmuch as the Fig. 33. — Exhaiist Valve (section). valves may be set and never touched once the engine has been put to work. A small fuel pump is provided which pumps the oil to the fuel valve through a connecting delivery pipe. The oil is drawn into the pump cylinder on the up 80 DIESEL ENGINES FOR LAND AND MARINE WORK % b' 'I Fig. 34. — Arrangement of Governor and Fuel Valve of Mirrlees, Bickerton & Day Type. stroke of the pump plunger, through a small valve, and on the down stroke this valve remains open for a short period, after which all the oil is pumped into the cylinder. The CONSTRUCTION OF THE DIESEL ENGINE 81 period during which the suction valve remains open in the down stroke of the phniger of the pump, is controlled by the governor, so that if the speed rises too high the suction valve is held open for a longer time, and less oil is delivered to the engine cylinder, whereas if the speed is low the suction valve closes almost immediately at the beginning of the down stroke of the plunger, and most of the oil drawn in during the suction stroke is pumped into the cylinder dur- ing the delivery stroke. In multi-cylinder engines some makers prefer to have a separate fuel pump for each cylin- der, whilst others employ only one pump for supplying all the cylinders, though this is perhaps on the whole not quite so satisfactory, but is, of course, simpler. Fig. 34 shows diagrammatically the arrangement adopted by Messrs. Mirrlees, Bickcrton & Day, Ltd., for governing the supply of fuel to the cylinder. A is the plunger of the fuel pump, which obtains its motion from an eccentric on the cam shaft or vertical intermediate shaft of the engine. On the up stroke of the plunger, oil is drawn in through the suction valve C , which is opened by the motion of the rod D, attached to a link in the crosshead of the fuel pump. The action of the suction valve is more clearly seen in the illus- tration to the left of Fig. 34, the oil being drawn from the chamber E in the direction of the arrows. During the down stroke of the plunger the oil which has been dra^n in is forced up through the fuel delivery pipe to the fuel inlet valve so long as the suction valve remains closed, but while this latter is open no oil can be delivered, all being forced back into the chamber E. The action of the pump can now be explained in relation to the governor F, which is of the Hartnell type. When the speed of the engine rises, the governor balls or weights spring outwards to the positions as indicated by the centre lines, and by means of the link mechanism shown, the rod D, actuating the suction valve, is raised till the centre of the pin on which the lever G turns, reaches the level c/,and the stroke of D is then a b instead of a'b' when the governor balls are "in." The suction valve is thus held open for a longer period of the G 82 DIESEL ENGINES FOR LAND AND MARINE WORK down stroke of the plunger ^, and less oil is therefore de- livered to the engine cylinder, and the speed drops, when the governor balls move inwards and the lever 6-' returns to its normal stroke. In the type of fuel pump employed by the Maschinen- fabrik Augsbiirg-Niirnberg, the pump plunger is actuated Fig. 35.— Fuel Pump (Willans & Robinson Type). by an eccentric on the motion shaft as before, and the suc- tion vajve is opened by a finger piece attached to a vertical lever, which derives its up and down motion from another lever attached to the pump rod and pivoted eccentrically to the spindle driving it. The spindle has a small crank fixed to it, to which is attached a vertical rod, actuated by CONSTRUCTION OF THE DIESEL ENGINE 83 the governor mechanism, and when the speed of the engine falls so that the governor balls move inwards, this rod is depressed, and the small crank turned through an angle, thus causing the rod operating the suction valve to hold it open for a shorter period than the normal. More oil is then delivered to the fuel inlet valve and the engine speed rises. The level of the oil in the oil chamber is maintained con- stant by a float, and a pipe from this chamber is connected directly with the supply from the fuel filters. The fuel pump casing is usually fixed to the cylinder about the middle, and the plunger has a vertical motion from the eccentric on the horizontal cam shaft, while the governor lever is attached to the governor sleeve on the vertical governor shaft of the engine. Fig. 35 shows the design of fuel pump and governor adopted by Messrs. Willans & Robinson, Ltd., for their standard engines, this being of the horizontal type. The vertical governor shaft a, which also drives the cam shaft through bevel gearing, is driven off the crank shaft of the engine by worm gearing, and has fixed to it the governor casing. The governor consists of weights attached to a central sleeve, the effect being that any outward or inward motion of the weights due to variation of speed of the engine, causes an angular motion to the loose sleeve, carrying the eccentric h which operates the small rod c. The movement of this rod gives an angular motion to the crank piece d, which in turn raises the oil suction valve e off its seat and admits oil from the chamber / into the plunger cylinder g, the plunger itself being driven from an eccentric Jix on the governor shaft. The fuel inlet from the filters is seen at /. On the outward stroke of the plunger if the suction valve is closed, the oil is delivered past the valve h, which is opened against a spring, and the oil flows through the outlet pipe to the fuel inlet valve of the engine cylinder. The action of the governor, except for its mechanism, is similar to that already described. If the engine speed rises and the weights move outwards the sleeve carrying the suction valve rod eccentric is turned through a smaU angle. The stroke of the 84 DIESEL ENGINES FOR LAND AND MARINE WORK rod is then such as to keep the suction valve open during a greater portion of the outward stroke of the plunger, so that less oil is delivered through the outlet pipe, and hence the speed of the engine falls, and the eccentric regains its normal position. The spindle j) may be turned by hand, and this allows for three positions of the spindle. In the normal or running position both the suction and delivery valves are quite free ; in the second position the suction valve is closed, the fuel supply thus being cut off from the engine, which must then stop, while in the third position the suction valve still remains closed and the delivery valve is opened, so that any oil in the pipes between the pump and the fuel inlet valve runs back into the plunger cylinder. By this means the oil is prevented from being pumped in excess in the fuel chamber at starting, and if a separate fuel pump be provided with each cylinder, one cylinder may be readily cut out of operation. The pressure on the governor springs may be altered by means of the arrangement shown, and hence the running speed of the engine can be varied within reasonable limits. It is not usual, in the smaller sizes of Diesel engines, to employ any other form of governing other than by altering the amount of fuel injected into the cylinders, according to the load, by means of one of the methods previously described. In the larger engines, it is desirable for the amount of injection air to be independently controlled, and also the period of admission for the fuel and air, which is not generally arranged for in stationary motors. This is, however, accomplished in one of the designs of Messrs. Sulzer, as illustrated in Fig. 36, and it is useful for engines which have to be run in parallel with steam engines, gas engines or water turbines, and where there are sudden and substantial variations of load. Referring to the illustration, the governor r influences, according to its position, all the factors on which the desired output depends, i.e., the quantity of fuel injected, the volume and pressure of the air necessary for injecting and pulverizing the fuel, as well as the period of admission of the fuel valve, Flu. 37.— Front Elevation nf Mirrlecs Diesel Engir CONSTRUCTIOX DF THE BIE.SEL ENGINE 85 in accordance with the quantities of air and fuel. The quantity of the fuel and the volume and pressure of injec- tion air are adjusted from the governor by direct action, since the power for carrying out the movements is small. The quantity of injection air dejDends on the position of the piston valve d. which is inserted in the suction pipe of the first stage of the injection air pump. The control of the admission period of the fuel valve, however, requires some effort, owing to the re- sistance of the valves, which cannot conveniently be exer- cised by the governor direct. For this purpose, a small servo- motor S is employed, which is operated b}^ the variation of pressure effected in any stage of the injection air pump. Referring to the illustration, the pressure existing between the first stage / and the second stage k of the injection pump is used for the purpose, the servo-motor bemg connected by the pipe u. Types of Four-Cycle En- gine. — Figs. 37 and 38 show vertical front and side sectional elevations of the standard Diesel engine constructed by Messrs. Mirrlees, Bickerton & Day, Ltd. The usual long piston is employed, and the head is slightly dished and ribbed to add to its strength. The weight, however, of the piston is not excessive, as its thick- ness is considerably reduced below the gudgeon pin, which is hollow and is fixed to the piston by two studs screwed in from below. The big and small end bearings are lined with white metal, and the former is of the box type, and has dis- tance pieces in it so that the length of the connecting rod Fig. 36. — Arrangement for eon- trolling Fuel and Injection Air. 8G DIESEL ENGINES FOR LAND AND MARINE WORK may be varied, which besides taking up wear allows for variation of the clearance between the piston and cylinder, and hence is useful for varying the compression of the engine. A two stage vertical air compressor is used, driven direct off Section of 80 H.P. Engine. [To face paijc 87. ^ CONSTRUCTION OF THE DIESEL ENGINE 87 the end of the crank shaft, the high pressure cyhnder being directly above the low pressure, and an intercooler for reducing the temperature of the air between the two stages is provided. A longitudinal and transverse section of the standard slow speed type of single cylinder engine, manufactured by the Nederlandsche Fabriek of Amsterdam, are given in Fig.^^. 4,0 and ^\ respectively. The general arrangement does not differ in any marked degree from the designs already de- scribed, except that the air pump for the injection and start- ing air is mounted on the end of the engine on an extension of the bed-plate, and is driven by an overhung crank, the compressor being of the two stage type with intercooling between the stages. The piston is of the trunk type, made of high-grade cast iron, as is also the cylinder liner, a special mixture as usual being employed for the cylinder head, in view of the high pressures to which it is subjected. A small lubricating pump and oil reservoir are provided in the com- pressor end of the engine, seen in Fig. 40 and also in Fig. 42, which is a plan of the engine, and shows the general arrange- ment of the valves in the cylinder head, and the cam shaft, cams and valve levers operating them. The cam shaft is driven in the usual way at half the speed of the engine, by means of spur gearing through a vertical spindle, itself driven off the crank shaft by a worm drive. Fig. 43 shows the air inlet valve with its cam and valve lever, and also the by-pass through which the cooling water passes from the cylinder jacket to the cylinder head. In Fig. 44 a de- tailed section is given of the governor and fuel pump in their relation to the overhead cam-shaft. The prin- ciple of the action of the fuel pump and the regulation of the speed of the engine is the same as that generally adopted with Diesel engines — namely, the control of the period of opening of the suction valve of the fuel pump. If owing to increase of speed the governor balls spring outwards, the governor sleeve, to which the pivoted arms carrying the balls are attached, is lowered, carrying with it the horizontal lever seen in the illustrations. This lever is attached at one 88 DIESEL ENGINES FOR LAND AND MARLNE WORK i Fig. 42.— rian of 80 H.P. Ensine. 1 end to a piston moving in a dash pot to prevent too rapid motion, and at the other end is connected by a short Hnk to the rod controlling the opening of the suction inlet valve of the fuel pump. The plunger of the pump is driven by an eccentric off the vertical governor shaft, and this eccentric by means of a link attached to the eccentric rod, also gives CONSTRUCTION OF THE DIESEL ENGINE a regular oscillating motion to the suction valve operating rod previously mentioned and so opens and closes the valve. When the horizontal lever on the governor sleeve is depressed by the opening out of the governor balls due to the increased engine speed, the link connecting it to the suction valve operating rod becomes straightened out, and it is moved to the right so that the period of opening of the suction valve during the forward stroke of the plunger is increased ; less oil is consequently delivered through the outlet valve of the pump to the fuel inlet valve of the engine, a n d the speed of the motor falls until it reaches the normal, when the governor resumes its o r dinar y running posi- tion. In this en- gine a safety valve is fitted in the cylin- der head to prevent danger arising through any excess of pressure in the cylinder, and this valve may be operated b}- hand, by the lever seen in Fig. 43 and in the plan view Fig. 42. All the valves are provided with inserted cages for ease in remov- ing, while the jackets have large mud holes for purposes of cleaning, which is frecfuently of great advantage where engines are cooled with dirty water, as is occasionally necessary. With the ordinary type of Diesel engine, the piston has to be taken out from the top, which necessitates removing 43. — Arrangement of Air Inlet. 90 DIESEL ENGINES FOR LAND AND MARINE WORK Fig. 44. — Section of Fuel Pump. all the valve levers and lifting the cylinder top. In the more recent construction of the engines of the Nederlandsche ^^^^Xrrangement of Carels Four-Stroke Stationary Motor, 1 1 (irizontal Three-Stage Compressor. [To face page 90. Fig. 45.— General Arningernent of Carols Four-Stroke Stationary Motor, with Horizontal Throe-Stogo Compn CONSTRUCTION OF THE DIESEL ENGINE 91 Fig. 4G. — Method of removing Piston in Nederlandselie Fabriek Engine. Fabriek, an arrangement has been adopted by means of which the piston can be taken out from the bottom without interfering with the valves at all. This is illustrated in Fig. 46 and is applicable to the type of motor in which the trunk piston is adopted. The bottom half of the cylinder consists of an extended liner bolted on the upper half, and when the piston is lowered and the portion a of the liner removed, it can be swung forward in the manner sho^\•ll. Fig. 47 shows 92 DIESEL ENGINES FOR LAND AND MARINE WORK Fio. 4!). — 7011 H.P. Slow Speed Dieeel Engine, C'arels Typo. I7V/UCT imjc 03. CONSTRUCTION OF THE DIESEL ENGINE 93 the latest design of three cyHnder stationary engine adopted by this firm, in which a connecting rod and crosshead are employed, the same arrangement of removable extended liner being used. In this engine there is a two-stage vertical compressor mounted on the end of the bed-plate in line with the working cylinders, and driven direct of! the crank shaft. In Fig. 49 a dimensioned drawing is given of a four-cylin- der four-cycle slow speed engine of Messrs. Carels" construc- tion. The motor illustrated is one of 700 B.H.P., running at 150 r.p.m. , arranged for dynamo driving, with a generator in the centre and two cylinders on each side. Two air compressors of the Reavell type are provided — one at each end. The diameter of the cylinders is 570 mm. and the stroke 780 mm., and even for this relatively high power the trunk piston is retained. High Speed Engines.^ — As has been explained in C hapter II, there are certain advantages attaching to engines of the high speed type, and for special purposes they will probably be widely adopted in the future. The high speed machine is, of course, eminently adapted for direct driving of dyna- mos, and though it is hardly probable that it will come into general use for this purpose, its employment for many purposes is likely to be very extensive, since saving in weight and space is often of great importance, while the reduced cost of installation is always a point to be con- sidered. As a matter of fact, high speed Diesel engines direct coupled to dynamos have for some time past been installed on battleships. Some details of the size, power and speed of high speed engines are given in Chapter W , but in many cases these speeds are exceeded, and engines of 300 H.P. running at 400 revolutions per minute are common, while the type constructed by Messrs. Mirrlees, Bickerton & Day, Ltd., for British battleships consisting of a 120 H.P. engine coupled to the dynamo runs at 400 revolutions per minute. With larger powers the same speed of rotation is employed, being about double that of the ordinary land type. 94 DIESEL ENGINES FOR LAND AND MARINE WORK The high speed types of engine built by this firm is made in the following sizes, all at 400 revolutions per minute : — 3 Cylinder engine. 45 B.H.P 3 90 4 120 6 180 6 240 6 300 The chief feature of the construction of the high speed engine lies in the fact that practically all the moving parts are totally enclosed, and very efficient splash lubrication is effected, and a smooth operation of the machine is obtained. The bed-plate is usually of the flat-bottomed box pattern and has bolted on to it the crank casing, which is totally enclosed and provided with as many inspection covers on each side as there are cranks. All the outer cylinder walls are bolted on to the crank casing, instead of being cast in one A\ith the framing as is the case with low speed engines. In Figs. 51 to 56 inclusive are given drawings of high speed engines built by various firms, from which it will be seen that there is not any very marked difference between the several types. In each case they are totally enclosed and provided throughout with forced lubrication, which is of course an essential feature in motors running at rela- tively high speed. It should, however, be pointed out an engine rotating at say 350 revolutions per minute does not necessarily imply that the piston speed is correspondingly in excess of that in the slow running type, for the difference is in fact not usually very great. It follows from this that a larger number of cylinders is usually adopted for the same power in a high speed engine, whilst the ratio of stroke to bore is much diminished, being usually in the neighbour- hood of unity or slightly over. This does not give the maximum efficiency, but in cases where it is desirable to employ the high speed engine its advantages are usually Fig. 48.— End Section of (JOO B.H.P. Four-Cycle Engine. 95 96 DIESEL ENGINES FOR LAND AND MARINE WORK such as to counterbalance any slight increase in fuel con- sumption. The large high speed type of engine manufactured by the Nederlandsche Fabriek offers some important points of difference from that of the usual construction. Fig. 50 shows a front section of a 600 B.H.P. engine built by this firm, to run at 215 revolutions per minute. It is of the usual four-stroke type, with four cylinders, the two inner having the cranks set at 180° with the outer pair. A single air pump is employed, mounted on the end of the bed- plate, being of the vertical two stage type, and driven direct ofr the crank shaft. A trunk piston is not used, but there is a crosshead and a short connecting rod, and though the length of the piston is diminished, since it no longer has to be of the usual bearing surface, the engine is necessarily somewhat higher than the ordinary trunk piston type. The crosshead has two bearing surfaces, and the guides are bolted on to the engine framing, and a forked con- necting rod end is employed, as shown in the illustration. All the main bearings are water-cooled, as is also the piston, which is an unusual feature in a four-cycle engine, cooling with this type of engine usually being adopted for cylinders of more than 100 H.P. The arrangement for the piston cooling is clearly indicated in Fig. 50. The piston rod itself is hollow and is secured to the piston, which is also hollow, through a flange wrought on the piston rod, fixing studs being arranged in the piston body. Two small pipes are connected to the water spaces in the piston, and these slide up and down within two long tubes which are connected with the supply and delivery pipes for the cooling water. Both these tubes are of course provided with stuffing boxes, and although the water is under slight pressure no leak- age takes place. The water outlet for the cooling water for the crank shaft bearings delivers into a cup in front of the engine at the bottom, and as there is a separate cup for each bearing there is no occasion for trouble with any of the bearings, since the temperature can be readily ascertained and varied as required. Forced lubrication is {To face -page 90. Fig. 50.— Fruiit Section of COO B.H.P. High Speed Eiigii [To face pcKjc 90 Fig. 51.-21)0 H.P. Sulzer High-Speed FouT-CycIe Stationary Engine. [To Jacc pugc 90 [To face page 9G. Fig. 52. — General arrangement plans of Twa-Cylinder Hick. Hnrgrej Motor. 10 in. dinm.. 1!) in. ttroke. Speeil 250 r.|j.ni. [To fate paijr 90. CONSTRUCTION OF THE DIESEL ENGINE 97 adopted for all the main shaft bearings, as well as for the connecting rod bearings, and these latter are very accessible — more so, of course, than in engines in which a trunk piston is employed. The engine is constructed with a box frame, the cylinders which are cast together being supported directly on the frame, while further strength is given by means of long verti- cal bolts which attach the cylinders rigidly to the bed-plate. With a four-cylinder engine there are ten of these bolts — five at the front and five at the back. The crank chamber is entirely enclosed, a hinged door being provided in front of each connecting rod, and the piston rods pass through the stuffing boxes in the box frame, so that the connecting rod small end bearing is in a cool atmosphere away from the heat of the cylinder. One of the main variations in construction from the ordin- ary engine is the use of eccentrics for operating the valve levers instead of the cams, which are so commonly employed, the object being to diminish noise and increase the smooth- ness of running. The engine is constructed with a horizontal cam shaft driven in the usual way off the main crank shaft, but in place of cams, it has fixed on to it eccentrics. The eccentric rods are attached at the ends to horizontal levers pivoted eccentrically on a horizontal spindle, and these levers thus receive an up and down motion. At the oppo- site end to that at which they are connected to the eccentric rods, the valve rods operating the valves rest upon them, and hence the motion of the eccentric is transmitted to the valves, which open in the usual way. For the starting valve, which of course is only in operation for a few seconds, the ordinary cam and valve lever are employed. The governor is arranged on the vertical shaft driv- ing the horizontal eccentric spindle, and regulates the speed of the engine by controlling the duration of the opening of the suction valve of the fuel pump during the delivery stroke, and thus regulating the amount of oil admitted to the cyhnder. The construction of the pump and governor is similar to that described pre- H 98 DIESEL ENGINES FOR LAND AND MARINE WORK viously, and four fuel pumps are used with a single pump chamber. Engines of this type are hardly high speed in the ordinary sense, inasmuch as they run only about 30 per cent, faster than the usual stationary engine. They are standardized from about 200 B.H.P. up to 1,000 B.H.P. with speeds varying between 275 and 200 revolutions per minute. Under 300 H.P. the engines are made frequently of the three-cylinder type, but above that power, and sometimes below, four cyhnders are always used. The weight per B.H.P. is remarkably constant for all sizes, being some- where in the neighbourhood of 280 lb. per B.H.P. including all accessories. The approximate overall dimensions of the engine illustrated are 6 ft. 8 in. by 27 ft. 6 in. floor space and 12 ft. 6 in. in height. The high speed engine has of late been coming more into general use, particularly for driving electrical generators, centrifugal pumps, etc., and has led the chief manufacturers to take up its construction for powers up to about 1,000 H.P. As now developed, its cost may roughly be taken as 20 per cent, less than the corresponding slow speed engine, its weight some 25 per cent, less, whilst as regards the question of upkeep, the difference, so far as present experience goes, does not seem to be considerable. In Figs. 51, 55 and 56 the high speed four-cycle Sulzer engine is shown, the type being similar for all sizes from 150 to 1,000 B.H.P. The four-cylinder construction is usually adopted, with a vertical three-stage injection air pump mounted on the end of the engine, and driven off the crank shaft direct from an overhung crank. The engine, which runs at 300 r.p.m. for 200 H.P., and 220 r.p.m. for 800 H.P., is totally enclosed, and forced lubrication is adopted throughout . The oil is forced through the different bearings by a pump driven off the engine, and flows back into the crank chamber, being drawn from the bottom by means of another pump through a filter and an oil cooler. The consumption of lubricating oil is slightly higher than with a low speed engine, being in the neighbourhood of "015 to "02 lb. per B.H.P. ^^ ih. L« ^j-{.^|^ister & Wain High-Speed Diesel Engine. [To face page 98. Fio. 53.— Bnrmeister & \\'ain Higii-Spewl Diesel Engir [To face pnrje 98. ^Sl 1 J [To face pwje 98. Fio. 54.— C'arela' Higli S|)oc ^^^^^^^^^^^^^^^ fc direct off the crank shaft, are the high and intermediate pressure stages of the fuel injection pump. The crossheads CONSTRUCTION OF THE DIESEL ENGINE 111 Fig. C4. — Section througli Cylinder of Siilzer Two-Cycle Motor, showing auxiliary scavenge ports. 112 DIESEL ENGINES EOR LAND AND MARINE WORK of the scavenge pump are arranged as the two low pressure stages of the injection air compressor. CONSTRUCTION OF THE DIESEL ENGINE 113 The method of scavenging is identical with that employed in the marine engines and described later. (Scavenge valves in the cjdinder head are dispensed with, ports being provided at the bottom of the cylinder, uncovered by the piston, whilst auxiliary valve-controlled air-ports are also arranged just above the main ports. Only three of the cyhnders have starting valves, and in each case there are two valves in the cylinder head, whilst each cylinder has one fuel inlet valve. No other valves are required. An important feature of the engine and one which is much adopted in various marine designs, is that the cylinder is supported by steel columns and not by a cast-iron frame. The cylinder liner itself is quite free to move downward during expansion, which is a necessary safeguard in large cylinders. The weight of this engine complete is some 4r0 tons, and its length about 55 ft. A similar principle is followed in the design adopted by Messrs. Cards in their large two-cycle engines, which are built up to 2,500 H.P. in six cylinders. Fig. 68 shows a 1 ,000 B.H.P. stationary engine of four cylinders of the standard two-cycle type, running at 125 revolutions per minvite. Except that no reversing mechanism is provided, and the scavenge pump is driven direct off the crank shaft instead of by means of rocking levers off the erossheads, the motor is almost identical with the Carels marine engine which is described later. The motor is of the open type, somewhat resembling a steam engine in appearance, and the trunk piston has been dispensed with in favour of the crosshead and connecting rod ■ — a step which seems advisable for motors of large power. The cylinders are supported on " A " frames, and a Reavell three-stage air compressor (not seen in the illustration) is employed, driven direct off the crank shaft in the usual manner. There is much to be said in favour of arranging the scavenge pump on the end of the bed-plate, instead of by levers as in the marine type ; in the latter the method is objected to by I J " (New Type). [To face page 114. Sc3/e of Millimetres Isoo iOO lOd \poo \sooo k Fio. li(i. — Cards Two-Cycle Sttitionury Motor {N'l-w Typi [To face page 114. ^^^^^ ^^.^^.aa;--^^^,j»caas>- \'m. 07.— rUin .,( CorHs' Two-Cylc Sl.itinnnry Motor (Nnv T>-pi^: iro/m. ;»it (Jomim'.^or fur Curcln l.SDO H.l'. ')'w[i-(;yrli' Mnrino liiii!! [T,:l,we p'm 12 1- CONSTRUCTION OF THE DIESEL ENGINE 121 bearings and the crankpin is attached to the end of the shaft in just the same way. For small and very high pressure engines this vertical com- pressor is attached direct to the bearers which also carry the engine, brackets being cast on the sides of the compressor for this purpose. For larger engines a segmental facing is provided on the back of the compressor casing, attached directly to a similar facing on the engine bed. The advantage of this type of machine is that all valves below the centre line of the compressor are entirely done away with, and this not only simplifies the machine and improves its efficiency, but also makes periodical over- hauling quite an easy matter. It will be seen that the only valves requiring attention are rendered accessible by lifting the top water bonnet, which uncovers both low pressure and the high pressure cylinders, and in all these compressors the whole of the valves and caps are completely surrounded with water, which experience has shown will obviate the trouble arising from the gumming up of valves due to the heating of the air. For marine work a somewhat similar quadruplex com- pressor is emploj^ed, there being two modifications in the con- struction. A section of this marine type is shown on Fig. 78, and in comparing this with the sectional illustration of the land type of compressor, it will be noticed that the guide of the intermediate cylinder is removed and the valves are placed in pockets on the side of the cylinder instead of at the bottom. The omission of the guide is rendered pos- sible owing to the increased dimensions of these larger com- pressors for marine work, and the alteration in the position of the valves enables a fiat bottom to be provided for the compressor casing and makes it easy to place the casing directly on the tank tops in the ship or the engine seatings, in the same way as the bed of the Diesel engine itself. As the compressor must be capable of compressing its air satisfactorily, whether the engine is running ahead or astern, the gudgeon inlet for the first stage air, which is adopted in the land type of compressor already described, is here 122 DIESEL ENGINES FOR LAND AND IVLIRINE WORK replaced by ordinary suction valves, which obtain their air from a port leading into the crank chamber. In Fig. 77 are given details of a Carels compressor for a 1,500 H.P. motor, driven by means of levers from the crosshead of the engine. Solid Injection for Diesel Engines. — When the first experiments were first being made en Diesel engines by Dr. Diesel, it was attempted to carry out the cycle of opera- tions simply by forcing the fuel into the combustion cham- ber under pressure from a pump. This was found to be unsatisfactory and was entirely abandoned. It was not until recently that any actual progress was made in the direction of solid injection for Diesel engines, and at the present time motors working on this principle are built only by Messrs. Vickers for submarine engines . The advantages of the abolition of the air compressor for injecting air are obvious, particularly as it is found that in high-speed engines the air compressor represents one of the auxiharies most liable to cause trouble, and even with the ordinary slow-speed marine engine, air compressors often need special attention. It must be remembered, however, that compressed air is necessary for starting purposes on most engine % whilst it is also required for other purposes on board ship. In motors for submarines this does not invariably apply, as starting may be ac- complished by means of the electric motor which is installed for propelling the submarine when luider water. Reversing may be carried out in the same way, that is to say, the astern power being provided only by the electric motors. Naturally this is not in all respects satisfactory, but for the purpose is not altogether unsuitable for sub- marines as at present constructed, although when larger sizes become common, direct reversibility will be a necessity. (Solid injection is now being employed with a large num- ber of engines installed in British submarines, and has on the whole proved extremely satisfactor3\ In these vessels, however, a comparatively light oil is commonly employed, and although experiment seems to have demonstrated the [To face page 122 [To /ace pa.je li CONSTRUCTION OF THE DIESEL ENGINE 123 possibility of utilizing the heaviest oil, including the Texas oil and tar oil, no commercial application has yet been made. It is hardly probable that the combustion with solid injection can be so satisfactory as with the employment of compressed air for the purpose, but on the other hand, the power required to drive the compressor is eliminated, which is a matter of seven to ten percent, in many Diesel engines. As a heat engine, however, the motor with solid injection is not so efficient as the pure Diesel type with air injection, so that the advantage obtained Fig. 79. — Diagram of Vickers" Solid Injection System. by the abolition of the air compressor is to a certain extent counteracted. On the whole, the fuel consumption with this type is approximately the same as the ordinary engine using air injection. The principle of the arrangement for solid injection is shown in Figs. 79 and 80, these being, of course, diagram- matic in every respect. The main idea is that oil should be pumped into a tube with collapsible walls which expand under the high pressure, the oil entering the tube, and on the opening of the fuel valve the walls collapse, forcing 124 DIESEL ENGINES FOR LAND AND MARINE WORK the oil under high pressure through the fuel valve into the combustion chamber. In Fig. 19 C represents the pipe supplying oil from the oil pump, while A is the pressure tube referred to. B is the pipe leading to the injection valve which is shown in Fig. 80. — Sketch showing Sohd Injection Arrangement. the diagram at D. The pressure tube is usually made elliptical, and is forced into a cylindrical shape for the oil under pressure, which may be as much as 2,000 lb. to the sq. inch or perhaps more. There is a distance piece within this collapsible tube in order to prevent it collapsing to too great an extent. This arrangement has hitherto been applied on a com- mercial scale to four-cycle engines, though others of the two-cycle type are under construction. It is also likely to be adapted for mercantile work, that is to say for marine motors of the four-cycle type running at normal speeds of revolution of 100 to 150 r.p.m. CHAPTER IV INSTALLING AND RUNNING DIESEL ENGINES GENERAL REMAEKS — SPACE OCCUPIED AND GENERAL DIMEN- SIONS — ^STARTING UP THE ENGINE — MANAGEMENT OF DIESEL ENGINES — COST OF OPERATION OF DIESEL ENGINES. General Remarks. — The Diesel engine is perhaps the most scientifically designed motor in existence, and for that reason all its parts have to be constructed with great exactitude. From this point of view it may be considered as a delicate machine, and up to the time when the engine is actually put to work no emphasis is too strong as to the necessity of the utmost care to be taken, though after it is once in operation it becomes a machine of the greatest reUability, needing, on the whole, less care and attendance than a steam engine or gas engine. The installation of a Diesel engine therefore should be carried out with the same precision as its construction, and not be accompanied by the careless manipulation which is customary with steam plants. Above all, dust of any sort must be prevented from access to the essential working parts of the engine, particularly the fuel valve, which is very sensitive to any minute particles, owing to the restricted inlet passages for the air and fuel. The foundations required are relatively heavy, as is the case with all vertical engines, but 0"«ing to the evenness of combustion and the absence of shock from the explosion of mixed gases, there is less vibration than ^vith a gas engine of similar type. The depth to which it is necessary to 125 126 DIESEL ENGINES FOR LAND AND MARINE WORK carry the foundations depends of course to some extent on the nature of the subsoil, as it is essential to reach a firm basis. Holes are left in the concrete while the foundation is being built up, for the foundation bolts, either by means of boxes or pipes of ample size, which are withdrawn when the foundation is set. The bolts are thus put in when the engine is being installed, and in the usual arrangement an arched tunnel is left under the foundation so that a man may have access from the flywheel pit for tightening up aU the bolts when the bed-plate is fixed in its exact posi- tion ready for grouting up. It is desirable, particularly where engines are installed in existing buildings when the vibration of the engine might possibly be transmitted through the walls, to keep the engine foundations well clear of the foundations and footings of the walls. In cases where two, three or four engines are erected in a somewhat confined space, which frequently happens in installations in the basements of large buildings, a good plan is to make a through foundation upon which all the engines are placed, and this is a method that has frequently been adopted. The third outer bearing is always separate from the bed- plate, and this has to be carefully lined up with the other bearings, and the crank shaft is dropped in and all the bear- ings scraped till it is perfectly true, this being necessary even though the engine has already been running on the test bed, as there are bound to be variations when it is actually installed. The crank shaft is lifted out and re- placed after the bottom half of the flywheel is lowered in the pit, and the erection of the rest of the engine is a straight- forward matter, particularly so, as in the case of multi- cylinder engines, all parts of the different cj'lindcrs being interchangeable. The two starting vessels, and the air injection vessel, being commonly some six or seven feet high, are usually let into the floor three or four feet so that all the valves are at a convenient height for operation by the driver. Space Occupied and General Dimensions. — The space required for a Diesel engine installation \nth all INSTALLING AND RUNNING DIESEL ENGINES 127 accessories is much less than for a complete gas or stoam plant. The following table (Table I) gives the approxi- mate space necessary with Sulzer Diesel engines, of the stan- dard four-cycle slow speed type, the dimen- sions referring to the outline drawing Fig. 8 1, Many of t he mea- surements can be re- duced if it is essential, owing to limitations of the engine-room, and with engines of the high speed tjrpe all the dimensions be- come somewhat less. Table II gives measurements and weights of standard four - cycle engines built by the Maschi- nenfabrik Augsburg- Niirnburg, while Table III gives data relat- ing to engines of the high speed type. The engines given in the tables by no means exhaust the total number of stan- dard machines. Each firm has its own standards, but of these there are so many that it is almost alwaj's possible to choose a standard engine whatever be the power required. y////////////////////////// A ^ ^ Fig. 81.— Outline Drawing of Sulzer Four- Cycle Engines (to correspond with Table of Dimensions). 128 DIESEL ENGINES FOR LAND AND MARINE WORK '-Q .s "^ ■-H (M t> l-H t- o 1 O 1^ -H 1 o CO 4J 00 ■* 05 CO CO -+ Cj tn «- (M ^ '"' CI _C CO I> O »c CO 00 CO H o l-H Iz; o lO ^- CD -* I> ^ (M c-i C5 2; <« * 00 ^ CO (N Th oo CO CI CO o o "" l-H ■^ .£ '* lO O 1-H Tt< C-l Tj< •^ o o *^ Z^ (M CO 00 cc "^ L-l CO d CO l-H l-H CO o ^^ o H g »o O CO *j CO CO uo ,-H o 't t^ iz; **-• l-H l-H ^H W tf U .£ ® 05 05 o (M t^ CO Q o ?( o l-H (M ■># o C5 CO t^ 2 «tf ^H F— 1 ^H ^ O H ■S o (M CO »o o (M l-H ,^ i-H O lO g (M 4^* ^ (N CO t^ Ir- o Tt* M 1 Ph' • . • . • • : l-H , , , , , a 9 HH 1 M • M ^ -H >— 1 CO ^H (M .2 ^ o z _g t- .— 1 i> lO o l-H ptj o »o l-H l-H " - IC >— 1 (N T»* lO so t^ CO OS o 05 lO C-) o lO I--. lO in (M CO a> Tj< o (M o -H >— 1 •—1 l-H (M l-H c n m (M -* »o CO t^ (N ■^ o w o <£ l-H l-H -H IC z o OS oo 00 CO t^ CO CO i2 CO ^^ . 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The cooUng water circu- lation has to be tried, to ascertain there is no obstruc- tion to the flow, and the engme may then be prepared for starting. It should be run if possible for an hour or two on no load in order that all the bearing parts of the machine may settle down into their bearmgs, after which a load equivalent to one-quarter or one-half of the full output should be put on. Indicator cards can be taken during this time, so that, if necessary, adjustments may be made should the combustion be not satisfactory. After shut- ting down, all the bearings should be well examined before the engine is put on full load, which may be done imme- diately on starting up again, and the machine may be put into service at once. The only adjustment with regard to the fuel supply which is at all Hkely to be necessary is in the event of one cylinder in a multi-cylinder engine taking more or less than its proper share of the load. Tliis can be readily put right b}' adjusting a small screw with a conically pointed end, which when screwed into the fuel inlet pipe between the fuel pump and the pulveriser of any one of the cylinders reduces the supply of oil to the pulver- iser, and vice versa. Tliis arrangement is only adopted where a single fuel pump suppHes all the cyhnders, the oil being pumped into a so-called " distributor." Where a separate pump is provided for each cylinder the distribu- tion is effected by means of a hand screw on each pump which controls the small suction valve of the pump. The Management of Diesel Engines. — With a well- designed and properly installed Diesel engine no special difficulties are to be encountered in the operation of the machme, which may be safely left in the hands of an un- skilled workman, apart from the overhauls, repairs and periodic cleaning of the fuel pump valves ; it is a fallacy to consider that the cost of attendance is higher than with steam engines — the contrary being actually the case. As 132 DIESEL ENGINES FOR LAND AND IMARINE WORK with all internal combustion engines the water supply is one of the first considerations, and needs to be carefully watched. Thermometers are usually provided giving the temperatures of the jacket water in each of the cylinders, and the supply of water can be separately regulated by means of cocks for each cylinder. The thermometers however are more necessary with a closed pipe circulation than with the ordinary arrangement where the flow of water can be seen, and this latter method is to be preferred where circumstances permit. As the supply of water is separate in each cyHnder jacket, being arranged by branch pipes off the main supply pipe, and delivering into a com- mon outlet pipe for all the cylinders, it is quite possible if there be an obstruction in one pipe for the water to be entirely cut off one cylinder without interrupting the main flow. The only indication in this event with the closed circuit system is a rise in the temperature of the jacket of the cyhnder so obstructed, but with the open flow arrange- ment the stoppage is at once noted by the driver. The temperature of the cooling water as it leaves the jacket is best kept in the neighbourhood of 120° Fahr. in temperate climates, though it is perfectly safe to allow it to rise to as much as 180° Fahr. for a prolonged period. In Diesel engines of the ordinary design, the heat carried away by the jacket water is usually between 20 and 25 per cent, of the calorific value of the fuel, or some 60 per cent, of the heat actually converted into useful work reckoned as indicated horse power developed by the engine. One H.P. 1 • • 1 ^ ^ 33000 X 60 o ^,, T,mi TT hour IS equivalent to = 2,544 B.Th.Us. per hour, so that the heat abstracted by the jacket water may be taken as 2,544 X '6 or about 1,500 B.Th.Us. per hour. Allowing a temperature rise in the water of 60° F. the quantity required per hour per I. H.P. developed by the engine should be about 25 lb. or 2| gallons per I. H.P. hour, and the allowance usually made is 4 gallons per B.H.P, hour, which from the above figures is an ample supply and INSTALLING AND RUN^^ING DIESEL ENGINES 133 is indeed never exceeded. Generally the quantity is con- siderably less and is frequently under 3 gallons per B.H.P. hour at full load. The perfect combustion of the fuel oil in the cyUnder prevents the valves from becoming very dirty, but if the machine is run for a considerable period without cleaning the combustion is not so good, the exhaust becomes smoky and the exhaust valve gets foul more quickl}\ In any case it is preferable to clean this valve regularly and as frequently as possible, though where careful attention is paid to the operation of the engine and no smoking of the exhaust allowed, it is c^uite feasible and satisfactory to clean it only two or three times a year. In most cases it is con- venient to take out the exhaust valves about once a fort- night, and as the whole valve and seating may be cj[uickly removed and as quickly replaced by a spare valve and seat- ing the time lost during the operation is very small. The valve can then be cleaned at leisure and put back when the spare one is taken out at the end of the next fortnight. Such frequent cleaning is by no means absolutely essential for the satisfactory operation of the engine, but as in most installations it does not cause the least inconvenience, it is to be recommended. It is, however, of more importance that the fuel valve should be cleaned regularly, and cer- tainly once every fortnight if possible, while the valves of the fuel pumps should also be overhauled at the same time and cleaned with oil and, if necessary, ground on their seats. Such attention, which takes very Uttle time, materi- ally reduces the running costs, and frequently minimizes the cost for repairs. Owing to the high pressure of compression it is essential that all valves and joints subjected to the pressure should be perfectly tight and free from leakage. Leakage may occur through any of the valves, through the joint between the cylinder head and cylinder, or past the piston, and of course would also be apparent in the event of a crack devel- oping in the cyUnder. The effect of such leakage, which is also a trouble with most other internal combustion engines, 134 DIESEL ENGINES FOR LAND AND MARINE WORK is to prevent the necessary high temperature corresponding to the top compression pressure being readied, and hence combustion of the fuel is in such cases incomplete. It is evident that this state of affairs will render it difficult for the engine to maintain its full power, since leakage is a pure loss of power, but vdth. a liberally designed com- pressor it is always possible to overcome the difficulty by raising the pressure of the air used to inject the fuel into the cylinder, though this necessarily lowers the effi- ciency of the engine, and must only be looked upon as a temporary measure. The exhaust valve is generally the most liable to leak as it is subjected to the severest con- ditions, but with frequent cleaning not much trouble is likely to be experienced. In any case a very short time spent in grinding the valve upon its seat will soon render it tight. Leakage past the fuel inlet valve occasionally takes place, resulting in too early ignition, with a corre- sponding drop of efficiency, as may be readily seen on an indicator diagram, besides causing a knock on the engine ; and it is a good plan, in order to avoid this, to test the valve at the same time as it is cleaned, that is about once a fort- night. In the event of leakage the valve should be ground in, but occasionally it is a result of a loose valve spindle, as very little play is allowable. Great care should be taken at all times when handling the fuel valve, as any neglect of this valve may result in considerable diminution of the efficiency of the motor, even though it does not have a more serious effect. The needle {E, Fig. 26) should work easily in the glands and also in its guide above the lever where it enters into the spring casing, and it should be gently handled when taken out, as if bent in a slight degree it is liable to work badly. The adjustment of the needle is usuali}^ arranged by means of a lock nut at the top where it screws into or is otherwise connected to the spring spindle above. The lock nut should be marked so that it is alwaj'S set back at the same position as previously, when the needle is taken apart, and when required the length of the needle can easily INSTALLING AND RUNNING DIESEL ENGINES 135 be varied by setting the lock nut at a different angle, so that very minute alterations may be made. If the bottom of the needle becomes damaged by any means and a cut or mark of any sort is caused, the surface should be carefully rubbed with sandpaper, to make it smooth, though usually it is sufficient to clean with oil. If the face of the needle has been altered at any time, the opening of the valve must be adjusted before running the engine, this being done first by admitting some compressed air to the injection pipe from the air reservoir, whose valve however is immediately closed. The engine is then barred round very slowly, and the exhaust valve held open by hand. At the moment when the fuel inlet valve is lifted off its seating by the cam and valve lever, the air can be heard issuing from the exhaust valve, and the timing of the opening can be properly adjusted by altering the lock nut previously mentioned, so that the lifting of the valve occurs at the exact moment required, namely, just before the crank reaches its top dead centre in its direction of rotation, or in other words just before the piston reaches the top of its stroke. All the parts of the pulveriser should be cleaned with paraffin and a small brush, so that all the holes and chan- nels should be quite free. It will not be found necessary to renew the packing for the needle at very frequent inter- vals, provided it is well packed in the first instance, tallow string packing being preferable to any special composition. Occasionally it happens that the needle shows a tendency to stick to the seat, which may be caused by bad combustion and consequent smokiness, due to an overload, or possibly to the cylinder cover becoming hot, o\Adng to poor or insuffi- cient circulation of cooling water, and in this latter case the cooling space in the cyhnder cover should at once be cleaned out. The same effect may also be produced by the injection air carrying with it small particles of matter, caused hy too liberal lubrication of the compressor, some of the oil being forced into the reservoir and thence to the fuel valve. 136 DIESEL ENGINES FOR LAND AND MARINE WORK It is not often that any trouble occurs with leakage past the piston, as particular care is taken in the construction of the rings, but it may happen that one or more of them becomes cracked or broken, when, of course, replacement is necessary, this being the most troublesome repair that is likely to have to be made on a Diesel engine in the ordin- ary course of running. The two top rings are subjected to the greatest heat and are the most liable to stick, and hence great care is taken in fitting them. Very little clear- ance is allowed between the piston and cy Under cover — only about one-third of that usually permitted with most other internal combustion engines on account of the high compression pressure — and should this be diminished to an appreciable extent by wear, the piston rod must be lengthened by the insertion of a liner of the requisite thick- ness on the top side of the crank pin bearing. This is not a common trouble, and is perhaps the least likely reason of imperfect combustion, and a knock on the engine is more likely to arise from a wTong setting of the cam operat- ing the fuel inlet valve and causing it to open too early, while another possibility is end play in the top or bottom end connecting rod bearing. The latter defect is generally due to the bearing being wrongly fitted in the first instance, and does not often develop after the engine has been put to work. In any engine, springs may always be expected to be some source of trouble, and it is necessary to have at least one and preferably more spare sets for every spring on the machine. As a matter of fact, a broken spring seldom has any serious effect, and engines often run a considerable time without the breakage being noticed, and in any case a broken spring can be replaced in a very short time. With the long pistons which are always employed with Diesel engines the obliquity of the connecting rod seems to have little tendency to wear the cylinder liner oval to any extent, and an 80 H.P. engine which the author gauged after running some eight years showed that the cyHndcr was true within two thousandths of an inch. With tho INSTALLING AND RUNNING DIESEL ENGINES \:i1 excellence of the design and manufacture of the air com- pressors employed for Diesel engines, in spite of the heavy duty they are called upon to perform, no special precautions need be taken in their operation. The possible troubles are those common to all machinery of this class, namely breaking of piston rings, and the springs, but such occur- rences are rare. The lubrication of the parts of a Diesel engine needs no more than ordinary attention, but as the quantity of fuel oil used is so small, the amount of lubricating oil employed appears to be relatively large, and it is indeed an item in the cost of running quite comparable with the fuel cost, hence the supply should be well regulated. The small fuel pumps which are provided are arranged so that the quan- tity dehvered from the oil reservoir may be varied within a wide range, and the difference in the consumption with careful attention is well worth consideration. With large engines the oil which collects in the crank chamber is gener- ally freed from water by being passed through a filter and used over again. As an outside figure it may be taken that the consumption of good lubricating oil with a 250 B.H.P. engine is about 1 gallon for four hours' running ; being lower for slow speed than high speed engines, but of course if the oil is filtered the total cost should not be debited against the engine. It is very desirable, especially in the case of multi-cylinder engines, to take indicator cards at not too widely spaced intervals to ascertain that each cylinder is doing its proper amount of work, since it is quite possible to throw a considerable overload on one or more of the cylinders which could be avoided in a few minutes were the fact known, by altering the test cocks. More- over, in installations in which the engine is emploj^ed for a drive where the power is intermittent (as for instance a mill, or shafting of any sort), by the addition of machines, the driving engine may become overloaded without the fact being apparent, and though a Diesel engine will readily take a 10 or 15 per cent, overload for two or three hours, it is inadvisable to allow this continually, and it is a 138 DIESEL ENGINES FOR LAND AND MARINE WORK point of real economy in such cases to provide additional power. Cost of Operation of Diesel Engines. — It is, of course, always difficult and sometimes misleading to institute direct comparisons between different types of engines without a particular knowledge of all the conditions pre- vailing, but it is at the same time possible to take a general view of the advantages to be derived in certain common cases, more especially as there is at the present time a large amount of data relating to actual results which cannot be refuted. At sea, as is shown later, there may be many reasons for the employment of Diesel or other oil engines apart from the question of economy, but on land that is not the case, and, speaking generally, the success of the Diesel engine for this work must depend entirely on the reduction in total running costs it can show in comparison with steam and gas engines. The question is obviously not merely one of fuel economy, since there are a host of other considerations which come into play, and were it solely a matter of the cost of the oil consumed, in compari- son with the cost of the coal used with gas and steam engine plant, the adoption of the Diesel engine would of necessity become almost universal. Capital cost, however, must always be an important consideration, and this also exer- cises a considerable effect upon the annual running costs owing to the necessary allowance which has to be made for interest and depreciation on the plant, and as at the present time a Diesel engine is dearer than either a steam engine with boiler and accessories, or a suction gas plant, this point puts the former at a certain disadvantage, though the difference is relatively small. In all new installations, and also frequently in additions to existing ones, the question of space occupied by the plant becomes of importance inas- much as suitable buildings have to be constructed for the accommodation, and where the land is of high value, which is often the case, the expense involved in acquiring this makes the question an even more urgent one. In this matter the Diesel engine has the advantage, since it is much INSTALLING AND RUNNING DIESEL ENGINES 139 cjmaller for the same power tlian a steam or gas plant, and in many instances where additional power is required, and extension of premises is impossible, the question of the type of engine to be employed solves itself automatically in favour of the Diesel motor. Though on land, reliability of operation is not usually of the same vital importance as at sea owing to spare power commonly being available, it frequently happens that perfect freedom from any possibility of breakdown is the deciding factor, and that a stoppage of but a few hours' duration may nullify the whole advantage of very much decreased running costs. It is for this reason that new types of machinery are so long in finding general adoption in spite of the undoubted economies the}^ are capable of effecting until they have passed through long periods of satisfactory operation. After the wide experience of the last sixteen years with Diesel engines this point can no longer be said to weigh against them, and it is now ad- mitted that in reliability they are quite equal to the best class of steam engine, and rather superior to gas engines. There is further the important point to be remembered that a Diesel engine is practically self-contained, whereas with the gas and steam engines there are the producer and boiler respectively to be considered as possible sources of failure, besides some auxiliaries which are unnecessary with Diesel engines. The next point which has to be con- sidered is the cost of attendance and repairs, and it is well known that this item may easily reach a figure comparable with the fuel bill. This question is really dependent on the last, and the fact that the Diesel engine is a reliable and simple machine naturally reacts on the amount which has to be expended annually on wages, renewals, etc., which is relatively small, and may with safety be put at not more than three-quarters of that allowed for steam and gas engines. In fact this figure is very conservative, as may be under- stood when it is remembered that stokers for the boilers or producers may be dispensed with entirely, and it has generally been found that two-thirds is a more relative 140 DIESEL ENGINES FOR LAND AND MARINE WORK estimate. The amount to be apportioned in any esti mate for renewals and repairs is always difficult to deter- mine, as there are such wide variations, but there are many actual instances where this cost is but a few pounds per annum for large Diesel engines. There are certain advan- tages which should not be lost sight of in any comparison between engine types, but which cannot readilj^ be expressed in money value, though their importance is great. There is the question of standby losses which always enters into consideration, and may cause a large addition to fuel costs, more particularly in the case of steam engines, and to a lesser extent with gas engines, that is to say, losses pro- duced in the generating portion of the plant (the boiler or gas producer) when the engine itself is not running. In a Diesel engine these are, of course, absolutely non-existent, since the machine may be started up at a moment's notice immediately it is required. Another point of importance is the fact that in the large majority of installations, engines, during the greater portion of their operation, run at a com- paratively low load factor, that is to say, generate a power much below their normal (and consequently most effi- cient) output. In a steam engine the efficiency falls very considerably ^^ith a decrease of the load, and in a gas engine the variation is very marked though not so serious. In a Diesel engine, on the other hand, the difference per B.H.P. hour at full load and at half or even quarter is relatively small, as may be seen from the following figures of consumption which most manufacturers guarantee with cyhnders of 80 H.P. and upwards. •42 lb. per B.H.P. hour at full load. •45 ,, ,, ,, „ three-quarters load. •50 ,, ,, ,, ,, half load. •31 ,, ,, ,, ,, quarter load. The following figures which are given regarding the run- ning costs of Diesel engines must not be taken too definitely as applj'ing to every case, but they give a fair idea of what may be expected in ordinary installations. The size of the INSTALLING AND RUNNING DIESEL ENGJNES Ml plant naturally makes some considerable dilTcrence, though not so much as with other engines for reasons given above, while the nearer the annual load factor approaches unity the lower becomes the cost of running per B.H.P. hour. Considering an engine of 200 B.H.P. running for 300 days in the year an average of 15 hours per day at a load factor throughout of 60 per cent., the number of B.H.P. hours per annum w^ould be 300 X 15 x 200 x -6 = 540,000, The fuel consumption may be taken at 0-5 lb. per B.H.P. hour, which from the guarantee figures given above is a high estimate, and with the price of crude petroleum at 455. per ton the cost of fuel would be £ '■ x 2i ^ 2,240 ^ = £270 per annum. The wages for the attendants would be about £200, while general maintenance and repairs may be estimated at £50, and waste, water, stores and sundries at another £20. Good lubricating oil for Diesel engines can be purchased at Is. 3d. per gallon, and the quantity consumed by such an engine, assuming that it is not filtered and used over again, w^ould be in the neighbourhood of 2 to 3 gallons per day, according to the care exercised by the attendant, and the annual cost may be put at £50. The cost of a Diesel engine, including erection, foundations and setting to work, varies at the present time from £8 to £11 per B.H.P., being dependent on the size, type (high or low speed, two or four cycle), the cost of foundations, acces- sibility of site, and other considerations, but for the pur- poses of estimate may be taken as £10 per B.H.P., or £2,000 for the engine in question. Making the usual allowance of 10 per cent, for interest and depreciation on the plant, an amount of £200 per annum has to be added to the 3'early running costs, which may then bo summarized as follows ; — 142 DIESEL ENGINES FOR LAND AND MARINE WORK Estimate of Annual Working Costs of 200 B.H.P. Diesel Engine Running 4,500 Hours Fuel oil at 45^. per ton Wages for attendants . Maintenance and repairs . Waste, water, stores, etc . Lubricating oil . Interest and depreciation on plant Total £ 270 Per B.H.P. hr. }3once. 012 200 0089 50 0022 20 0009 50 0022 200 0089 Total .... £790 . . 0-351(i. Omitting interest and depreciation, the working costs aggregate to £590 per annum or 0'26fZ. per B.H.P. liour, and this figure may be relied upon as Hkely to cover by far the larger number of cases met with in ordinary practice, while in big installations an overall cost of 0'25d. per B.H.P. hour, including interest and depreciation charges, maybe assumed as correct. In four installations with which the author is familiar, in none of which does the annual load factor rise above 30 per cent., the yearly working costs, excluding interest and depreciation, amount respectively to 0-26fZ., O'Sld., 0-2 kZ. and 0'23d. per B.H.P. hour, or an average of 0'2ofZ. for the four plants, the period over which the costs were reckoned being in no case less than six months. Although in the matter of economy the Diesel engme shews more particularly to advantage in the smaller sizes, that is to say, up to about 1,500 B.H.P., now that the manufacture of very large engmes has become a practical proposition, it is interestmg to note how motors up to 4,000 B.H.P. can be shewn to compare favourably with the most efficient modern steam turbmes. The following data are based upon an actual case and refer to an mstallation of 2,500 K.W. miits, considering Diesel enguies in the one case and steam turbines in the other. The Diesel motor is of the two-cycle smgle-actmg type, running at a normal speed for this size of about 130 revolutions per minute. The estimates are based on a INSTALLING AND RUNNING DIESEL ENGINES 143 year's working assuming an actual running period of G,000 hours per annum, and an average load on the generator of 2,000 K.W. The eost of fuel oil is taken at BOs. per ton, and of coal at 155. per ton. Considering first the capital costs, and omittmg switch- board and cables, etc., although the Diesel set is more expensive, there is a substantial saving in the cost of build- ings, and the figures work out as follows — £ 2,500 K.W. Diesel generating set with all necessary acces- sories 25,000 Engine room, foundations, etc., including cost of site . 5,000 Total cost of Diesel plant ...... 30,000 2,500 K.W. Turbo-generator with condensing i:)lant, boilers £ and accessories ....... 13,000 Engine and boiler house, foundations, chimney, etc., includ- ing cost of site ....... 13,000 Total cost of steam plant ...... 26,000 The approximate annual running costs in the two cases are as under : — Diesel Set. — ^The consumption of oil with a Diesel motor of this size is about 0-45 lb. per B.H.P. hour, or with an alternator of ordinary efficiency about 0-66 lb. per K.W. hour. The lubricating oil, which is admittedly an expensive factor with Diesel engines, may be taken at 01 lb. per K.W. hour, although the builders would probably guarantee a lower figure if necessary. The cost of suitable oil is about Is. 6d. per gallon. With regard to cooling water a good deal depends on the circumstances, but in the case in question, sea water was available at a total cost of kl. per 1,000 gallons. The amount required is about 6 gallons per K.W. hour, but for piston cooling, fresh water is necessary, about H gallons per K.W. hour being the quantity. This would of course be recooled in a cooling tower, and only the usual 10 per cent, make up losses need be reckoned upon. 144 DIESEL ENGINES FOR LAND AND MARINE WORK Calculating on this basis, the total cost becomes : — £ . 8,850 Cost of fuel 2,000 X 6,000 X -66 x 2'5 2,240 Cost of attendance ; four men and one foreman at an average of £2 per week .... Water for jackets and pistons Lubricating oil, etc. .... Repairs and maintenance at 1 per cent. Interest and depreciation at 10 j^er cent. 520 200 1,000 250 2,500 £13,320 Steam Plant. — A steam turbo-generating set of 2,500 K.W. has a consumption of 15 lb. of steam (superheated) per K.W. hour, or allowing 30 per cent, stand-by losses, and an evaporation of 7 lb. of steam per pound of coal, the quantity of coal per K.W. hour at an average load of 2,000 K.W., is 2-8, which is 5,600 lb. per hour, or 15,000 tons per annum. The amount of condensing water necessary is some 1 50,000 gallons per hour, or 900 million gallons per annum, for which the total cost of pumping may be taken at Jc?. per 1,000 gallons as before. The following gives the overall estimate : — Cost of coal = 15,000 tons at 155. Cost of attendance ; 6 men and 1 foreman at an average of £2 per week. .... Condensing and feed water . Lubricating oil, etc. .... Repairs and INIaintenance at 1 per cent. Interest and depreciation at 10 per cent. £ 11,250 730 2,000 250 135 1,350 £15,715 The saving with the Diesel set thus amounts to about £2,400 or more than 15 per cent., and it will be noticed INSTALLING AND RUNNING DIESEL ENGINES 145 that no allowance has been made for depreciation of build- ings, which item would greatly favour the Diesel equipment. The respective costs per K.W. hour are 0-314 0 M 1 1 ■* CO lO 1 1 e<5 ■* 00 >^ o M C5 11 -* t~- o o CO o o « CO CO cc M l^l ' 05 ei o t- uj 00 00 •* T)< r- N (^^ lo f? -^ -i< I I 00 CO lO '^ o o ' ' jr C5 CI -* r- h- O CD CO c r^ do ? -J cr. 03 ^ CO lo C 05 © 05 CO CI 00 Mcoioqj gcpiooo^r^t^ oiom I |r--^o o I Ot^co-^cjcciccocoiof2 'ICOCSOJO ' -TrtrtTtCO lOCD r-i" r-< ii C) (M -H rH d C-1 Oc^-HcbiociocD^C]t--t-- Z Cl (M rt -^ ^ *' 00 CO CO IC C-1 (M Tl( 1 1 CO oo o r- t- o r^ 4< 03 ^ — I fh 00 •O lO O CO I— 1 3 t< !D ;-! C r: O o >..-s e .2 'S bb ^ T3 o 2 03 O ^- i S S r tc t- C f -. • • o o • • cS ft >.£ S • • -^Tr o ■"S fl '-' fP «4H >.<« O ou P^ ' ■ • ii^ w . • aw 1— 1 -PQ Ph' 2 w^ • ? o s « c ,^ -^§S53 cQ, i-SCf Ph'pm" ■ P^Ph B^ S S OH O u/ • D fc. G >* : o s o o 3 3 ® o w ci go 2 T;i—^^—"o^',< OS ■* lO -^ - -00 "^ ^ CO -H CI 03 OJ o o o o ffl lO t- <33 Tji CO O CO "^ -,<-co--r: O t^ CI ^ o o o o O -H <35 -H U3 CI CI CS ■"tCo'-Hjo o o o o lO O lO CO ■<* O lO CO ■>* cf-5JO o o o o t^ 00 o: •>*< lO O CI CI I IS p.§ 1* s a T3 ^ OS'S w w TESTING DIESEL ENGINES 153 lO OS o to to o c4 O —I 1 •:-^ to 1 1 ■f "7 1 fill 1 6 CO o 1 to o IN -^ 4< OS ! 1 ^•^ CO 1 INI 1 oo' ^-1< n (M ^5 CO o © • "? "? Op op 9 Op ep f •f , 1 ^ "T OS in ■^ o 6 o 'J" 05 t^ O C5 — OJ to 00 1 1 (M OS ci) to oo_ in in OS <£> eo U5 m o o o -f F-l ep o to e^ ep "? o 1 1 •?'■? t^ in O CO OJ r^ o l^ t~ 1 1 t-. .* SSI OS_ o^ 00 •^ ^ a> to to in o' .* 0\ -H i-H to 00 t-- ..H 05 o t^ 00 in o T T* C3 .^ o in e-i "? "? . 1 9 V o lO ei o o o .* .* o m o oco in 00 .* T)< Cl CO rt 00 N •»*< fO O n CO o o Op ■* M CS in N n T ■?* "f "? op ■* O r- o CO 6 CI O OS o t^ to 1^ in ci) "* do CO ■^ 00 o OS OS OS OS t^ in in OS CO in I> 't M —1 (M r~ w 't' 00 M e-i o o T' f op lO op ep "?* "f in ■^ T ^ 1 to .— 1 IN rt to CD to O to OS r^ in OS r- do 1 to to o OS lO OS en t^ in in OS CS in t-^ eo d -H e-1 6 do OS M to in CO e-1 to do t^ in >o -f 1^: 00 OS 00 to in OS — 1 in t-^ e^j (M -H to s • 3 o . er — power pressor H.P. . K.W. o/ /o acq ^5 to M C C ler I.H.P. pressor) lb. er B.H.P. , . . lb. er B.H.P. cq >> o p. .2 fe o P S , . . °F. arature °F. dioxide % 0/ /O er pound B.Th.U. per I.H.P. m h o Ph . 3 C ■ s -»^ (- ■X © -p p. "o c „ o J h ir-ie pow led by air com] )f dynamo y of dynamo . srse power de' II u C .2 '3 ® .2 M p a, a • o a, e . 3 '& . nsumption p with oil 18,00( und) . 3 a 3 o ■p M 1 3 o S gases. Temp ,, Carbon ,, Oxygen value of oil pi 73 © s • 3 a ' o 1 • i • o 2 o H tt-t o o c ■- .2 3 II 3 1) Indicate! absorb Output c Effieienc 2 ® "S 03 .a o 3 1- O 3 •32 3 " o % 3 " 2 3 u O o 05 'JD oc oo •7" o? -^ O O iX 4> ■? o ■* M rt M (M 1 H t3 o o o o c o "* c -f >* r- (M CO H lO '-D C5 -; '^ 1 ■"1 W t-^ U-3 — r -^ T)^ 00 ^^ 00 ^ -t- 00 -H TO o° CO -^ ■?i -^ -t o ■* ■* CO ^ fo C) + "« H 13 lo o >o o o in c ^ lO c >o -^ 1- ■* CO H C3 I-- iri 1^ «o + ■"1 CQ r-^ in ffi in •* CC cr ci -r) 00 o lo Q° lO o'l CO — CO ^ ri- CO — > CO CI 1 CO 1 "en H U> O O O O O _ c; si H O Tji CO tc -f p CO CO CO -t t- CO J."- ■"1 cc in c-i in -* 'i 00 C3 ^ CO C5 ^^ in C3 r^ o? -* c'l -^ CO iri A Ti< CO ^ CO C) 7 ci 1 H ta o o o c o o ^ in tc C5 -o -* cj CO H o o = O^ C -H '~l. CO in ^i'i CO ■*' 1 00 CQ ^ '9 '* T '^ T ^ ^ CO CO 6 4< -i< ^ 1— i •* CO rt CO CI 1 H U> o o o o m in c '^'J "^ cs '^S o .S § .a o-;:— to • -«^^.| cS 6 ^ o "" "t;? g H '^^ ' K-i O c •- -^ t> c tj > .St; '^ ■3 fc OT) cr =^'57 3 u «3 W KKW TESTING DIESEL ENGINES 155 B.H.P. four-cylinder foiir-cj'Cle engine, wiiich at its normal output was designed for a speed of 400 revolutions per minute. The engine is totally enclosed and the cranks are set at 180° ; a vertical two stage air compressor mounted on the end of the bed-plate and driven direct off the crank shaft serves for the air supply to all the cjdinders. The four fuel pumps are arranged together in the front of the engine and are all driven off the horizontal cam shaft. Forced lubrica- tion is of course adopted, and two small lubricating pumps are driven direct off the end of the crank shaft, the oil being cooled after passing through the bearings, etc., and used over again. Two other small pumps are also driven off the crank shaft for the circulation of the cooling water both for the cylinders and for the exhaust pipe, which was jacketed in this engine. Being intended for ship propulsion the machine is not provided with a governor, but has a safety regulator to prevent the engine running away. The weight of the engine, including the starting vessels and all pumps, was only about 10 tons, while a similar slow speed engine would weigh something over 50 tons. This is equivalent to 30 H.P. per ton weight, which is extremely high. In the tests the engine was coupled direct to a continuous current generator, which was loaded as required on a resist- ance, and the power measured by a tested ammeter and voltmeter in the usual way. The engine was run at various speeds between about 250 and 500 revolutions per minute, the variation being obtained by controlhng the amount of fuel entering the cylinders by means of a lever. The tests carried out were as follows : — (1) With normal admission of fuel and speeds of 250, 300, and 500 revolutions per minute. (Tests 1 to 6 in Table Y.) (2) With half normal admission and speeds of 250, 300, 400 and 500 revolutions per minute. (Tests 7 to 10 in Table V.) (3) With maximum admission and speeds of 400 and 500 revolutions per minute. (Tests 11 and 12 in Table V.) The efficiency of the dynamo was carefully determined for each speed and output by running it at the various speeds at loG DIESEL ENGINES FOR LAND AND MARINE WORK no load, whence all the losses were calculated and the efficiencies obtained. These are included in the table, but the figures from which they are deduced are omitted. The oil consumption was obtained by taking the supply direct from a vessel "with a gauge glass, and at the beginning and end of each test the level of the oil in the vessel was arranged to be at the same point as indicated on the gauge glass, the consumption being made up by adding an accurately weighed 100 200 300 Brake Horse Power Fig. 83. — Curve showing Fuel Consumption, 400B.H.P. amount of oil as required, and by this means intermediate check readings could be taken. The cooling water was passed through measuring tanks and its quantity determined, and the temperatures at the inlet and outlet as well as that of the exhaust gases were registered by mercury thermometers. In Fig. 83 the fuel consumptions are represented graphically under all the con- ditions of the tests, and show remarkably constant results. At about 250 revolutions perminute the consumption was 189 TESTING DIESEL ENGINES 157 grams., at 300 revolutions per minute 192 grams., and at 400 revolutions per minute 196'5 grams, per B.H.P. hour. Be- tween the working limits for which the engine was designed, namely 250 to 400 revolutions per minute, with normal fuel admission the difference w-as only 189-5 to 196'5, or about 4 per cent., this being readily accounted for by the greater power for the compressor. Even for speeds up to 500 revolutions per minute the variation was less than 7 per cent., excluding the trial at this speed wdth partial admission. In test No. 6, where a consumption of 211 grams, per B.H.P. hour is sho^vn, there was an obstruction in one of the fuel pipes, and hence the cylinder it fed worked uneconomically, and vitiated the result which should therefore be neglected. From the results in Tests Nos. 1 to 5, vrith the engine on its normal load, it is seen that the heat employed in doing useful work varies between 31 to 33 per cent. — the heat carried away by the cooling water is 33 to 34 per cent., w^hile 23 to 25 per cent, is rejected in the exhaust gases. The last figure is rather low, while that for the cooling water is high, which is accounted for by the fact that a large amount of water was used, varying from 5 to over 6 gallons per B.H.P. hour, whereas the quantity usually allowed is little more than 3 gallons per B.H.P. hour ; probably also the exhaust pipe was w^ater cooled. Herr Eberle makes the following comments on the tests : — (1) The engme works from 250 to 500 revolutions per minute, with varying admissions, and develops from 100 to 400 H.P. with perfect combustion, and without any trouble in operation. (2) The change from one speed to another is easily and rapidly effected by the movement of a single lever. (3) The average fuel consumption for all powers and speeds is little if any different from that of slow speed engines. (4) The mechanical efficiency is equal to that of slow speed engines. (5) The lubrication is good, and during a twelve hours' run no heating was observed in any part of the machine. 158 DIESEL ENGINES FOR LAND AND MARINE WORK Tests on 500 B.H.P. Engine. — The following is a slightly abbreviated account of a complete test carried out by JNIr. IMichael Longridge, on a three-cylinder slow speed four-stroke engine manufactured by Messrs. Carels, Freres, of Ghent ^ : — The engine was a three-crank inverted vertical, with three single acting cylinders numbered 54, 55, and 56, No. 54 being above the idle end of the crank shaft. Each cyhnder was 22-05 in. (560 mm.) diameter, with a piston stroke of 29'53 in. (750 mm.). The normal speed was 150 revolutions per minute. The valves were placed in the cylinder covers as usual, and were actuated by levers driven by cams on a horizontal shaft, which in turn was driven by a vertical shaft and bevel gear from the idle end of the crank shaft. The cylinders, cylinder covers, and exhaust valves were water cooled, but the pistons were not. The engine drove a d3'namo carried upon a prolongation of the crank shaft. The air for pulverr^ing the oil and spraying it into the cj'linders was compressed in an independent pair of three stage vertical air compressors worked by a two-throw crank shaft, belt driven by a motor receiving current from the dynamo upon the engme crank shaft. The air compressors, therefore, though essential to the working of the engine, were not in this case parts of the engine, and in calculating the mechanical efficiency of the engine from the dynamo output and the indicator diagrams this fact should not be lost sight of. Had the compressors been driven direct 1}^ by the engine the difference between the work put into the dynamo, which is the brake horse-power, and the indicated horse-power would have been increased by the power required to compress the air. The areas of the compressor pistons were : — 102-40 sq. in. (660-5 sq. cm.). 32-30 sq. in. (208-1 sq. cm.). 8-79 sq. in. (5675 sq. cm.). ^ Annual Report of British Engine, Boiler, and Electrical In- surance Co., Ltd. TESTING DIESEL ENGINES 159 and the stroke 7087 in. (180 mm.), the speed, when com- pressing to about 64 atmospheres, being about 160 revolu- tions per minute. The dynamo was twelve-pole, continuous current, shunt wound, by Lahmeyer & Co., rated to give 450 kilowatts at 550 volts when running at 150 revolutions per minute. The eflSciencies given by the makers are : — At 112 kw. 225 kw. 337 kw. 450 kw. 562 kw. Efficiency about . -88 -925 -935 -91 -935 and these figures have been adopted in calculating the brake horse power of the engine corresponding to the measured output of the d^'namo. The power was absorbed by iron wire resistance coils, and the load regulated by appropriate switches. The motor for driving the air compressors was six-pole, shunt wound, continuous current, by the same makers, rated to give 75 B.H.P. at 630 revolutions per minute. The calculated efficiencies given by the makers are : — At . . Full load. Three-quarter load. Half-load. Quarter -load. Efficiency 90-5 .. 89 .. 86 . . 76-5 m. Four trials were made, the results ef which are sho^^•n on the accompanj'ing Tables. The first, a preliminary trial, intended to be at full load but actually a little low, the second at full load, the third at half load, and the fourth with no external load, the engine driving the air compressors only, and, of course, the dynamo and motor which transmitted the power to them. With respect to the figures in the Table, the following explanations should be read : — Line 4. — The diameter of the cylinder of No. 56 engine was gauged. The diameters of the other two were taken from the drawing. Line 6. — The revolutions were recorded by an engine counter, and the speed indicated by a tachometer. Line 7. — The water for the jackets was supplied from the to^vn's main, and measured through a water meter which was said to have been recent Iv calibrated. 160 DIESEL ENGINES FOR LAND AND BL^RINE WORK Line 9. — The discharge pipes from the jackets were con- ducted to a common pipe discharging into a drain. The same thermometer was used for measuring the temperature of inlet and discharge. Line 11. — The temperature of the exhaust was measured close to the engine by a mercury thermometer passing through a gland in the exhaust pipe, with compressed nitrogen above the mercury to prevent the latter boiling. All these observations were taken at intervals of ten minutes. Line 12. — The gas samples were collected and analysed by Professor Van de Velde, of Ghent. Line 13. — The oil used was from Galicia. There is con- siderable doubt about the calorific value of the oil. A sample taken at the lime of the trial, and analysed by Professor Van de Velde, gave : — Carbon 84 81 per cent. Hydrogen 14-78 Sulphur 17 99-76 per cent. and therefore had a calorific value by calculation of : — •8481 X 14,540 + -1478 x 52,000 + -0017 X 4,000 = 20,049 B.T.U. As the Professor made no calorimeter test, a sample was sent over to England in March, and tested by Mr. C. I Wilson, who gave the calorific value as 10,120 calories, or 18,220 B.T.U. Owing to the great discrepancy between the two results, and to the improbably high efficiency of the engine resulting from the adoption of the latter value, another sample was sent to England in May and analysed and tested by Dr. Boverton Redwood, who gave the follow- ing figures : — Carbon 83-17 per cent. Hydrogen 11-56 ,, Sulphur 0-36 Oxygen, nitrogen, etc., by difference . . 4-91 „ 100-00 TESTING mESEL ENGINES 161 l-H O n 1 O CO 1 C5 O o CSl ^ T' II 1 eo I;- l-H o 00 ei C^J 6 o ci c'l 00 »o ' ' 1 ^ lb lO i-O o o 1 1 o IM LO ■* Tti CO ■>* t-- Tt< Tt< CO 00 CO o - (Tl -t< Ci iri c^ 6 t^ O -i< CO O CO rl( o ^ CI o O O lO 1 1 (M C-4 o lO •^ O -* O V CO t^ -tJ l-H IC (N CSl C^l Ci o t— CO CO CO l-H l-H 00 t^ o >0 LO o l-H i (71 lO o Tj< ) o o '^ C-J -^ CO -* o o 05 o p-H -^ Cl > CO lO l-H CO r-l UO >0 lO < ~^ _d -1-a fe p^; Ci; D^ O '^ o o o o ?< ■■< ^ o ^ < to , • .5 S3 "o 1—1 ' o :£, -tj cS . ■-3 CS -tJ > a .^H • >. ^ t) -ti tc •/ (0 u a § -^ '^ :' i s © o -4-^ •— » T-i ii cS (D r/: ^ ^ -^ g ^ 1 s^^ i 3 o S^ o o-^ o © r/3 O h ."2 tn L4 © O t- (D O O Ph O t| ti -2 s a S .2 ■? -S S c S hH Pl^ H H -to o H5 ■^ -3 cc — — 03 O O pq 03 k!H 1— 1 IM M Tj^ »« o l> 00 O O ^ ■ >• " 05 C3 S'?!^. Ph' S ^i- o s G © © 5: £. a. 5 ~ 6 -l;i "^ ^ = "* 00 . 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In all instances the relative fuel consumption of oil and coal for motor and steam ships respectively which were given pre- viously are well borne out, and it is probable that in most cases a corresponding steamship would consume about 4 to 4| times the weight of fuel as compared with a motor vessel, the one burning coal and the other using oil. Engine -Room Staff for Motor Ships. — The staff required in the engine-room for motor vessels is consider- ably below that necessary for corresponding steamships, being usually in the neighbourhood of two-thirds. As, however, it is mainly the cheaper men such as the greasers who are dispensed with, it does not mean there is a reduc- tion of one-third in the pay bill, one-quarter probably being a nearer figure. As instances of the staff required in various cases may be cited four motor vessels in which two engines each of 850 H.P. are installed, the deadweight capacity being 5,000 tons, and the length overall just over 370 feet. In these vessels the staff consists of 4 engineers, 3 assistant engineers, 3 greasers, 1 donkey man and 1 pump man. In another motor vessel -iOO feet in length, having two Diesel engines capable of developing about 2,400 B.H. P., the staff consists of 4 engineers, 4 assistant engineers and 4 greasers, whereas a similar steam vessel or one to carry the same cargo, which in this case is about 7,500 tons, would require 4 engineers, 1 apprentice, 1 pump man, 1 donkey man, 3 greasers and 16 firemen and trimmers. Weights of Marine Diesel Engines. — Though it is usually accepted that the weights of Diesel engines for marine work are below corresponding steam equipment, a few figures may be given showing the \\eights of actual installations. As a generalization it may be taken that for powers up to 1,000 H.P., the weight inclusive of piping, starting air bottles, manoeuvring air reservoirs, with the direct driven scavenge pump and air compressor, and also the accessory circulating water and lubricating pumps, is in the neighbourhood of one ton to every 10 B.H. P. for DIESEL ENGINES FOR MARINE WORK 203 two-cycle single-acting motors, whilst a four-cycle engine would in general be 15 to 20 per cent, heavier. The auxi- liary compressor, which is practically the only auxiliary in addition to those which are necessary for a steam-driven ship, would add some 8 to 10 per cent, to the weight. For higher powers the weight per horse power decreases unless there is a considerable reduction in speed, but not to a very large extent, and a 4,000 H.P. two-cycle single- acting marine motor, with accessories as before, weighs about 350 tons. The figures are naturally only approximate, and for moderate speed such as best suit conditions and propeller efficiency, say from about 160 revolutions per minute in the smaller engines to 120 in the larger. With double-acting motors the weights are decreased, though to what extent it is difficult at present to estimate. A 12,000 B.H.P. six-cylinder double-acting engine should, however, not weigh more than 600 to 700 tons complete. To take a few instances, a Sulzer-Diesel marine engine of 850 B.H.P. at 160 revolutions per minute weighed 77 tons, or about 200 lb. per B.H.P., whilst another two-cycle single-acting motor of 2,000 B.H.P. weighed 170 tons or about 180 lb. per B.H.P., though at a lower speed of 130 revolutions per minute. A Krupp-Diesel motor of 1,250 B.H.P. at 140 revolutions per minute, also two-cycle single- acting, weighed 115 tons or about 210 lb. per B.H.P., whilst similar slow-speed engines of the M.A.N, type work out as follows, where it will be noticed that the 2,000 B.H.P. motor is relatively heavier than the 1,2C0 B.H.P. : — 13.H.P. Revs, per Miii. Weight in Tons. Lbs. par B.H.r. 1,200 1,600 2,000 150 120 120 91 145 178 170 200 200 The Design of Large Engines, with Particular Reference to the Motor Battleships. — In view of the 204 DIESEL ENGINES FOR LAND AND MARINE WORK probable imminence of the advent of the motor battleship, the design of very large engines, and the general arrangement of the plant which is to be anticipated, may be discussed. There is little doubt that a triple screw arrangement offers most advantages, particularly from the point of view that one or two of the engines may be shut down as desired. For the moment it may be taken that each engine should be capable of developing 20,000 H.P. in six cylinders, which is in excess of the power required on any existing battleship, excluding battle cruisers. It is doubtful if engines of this power will be built both of the single acting and double acting type (necessarily two-cycle), and present indications point to the utihzation of double-acting motors. Such large motors will probably be quite separate, and also the air compressors. With regard to the scavenge pumps, there would seem to be advantages in driving these direct off the crank shaft of the engine, although separate operation by means of Diesel engines may also be adopted. With the latter arrangement, easy regulation of the quantity of air would be possible. By a direct drive off the crank shaft, it should not be understood that the scavenge pumps are coupled imme- diately to the engine shaft, as it w^ould be preferable to ar- range them some distance aft of the main engines, in separate chambers. Not only does this allow a better disposition in the engine room, but it permits of a variation in the supply of scavenge air by increasing or decreasing the pressure in the scavenge pump room. Each engine should be provided with its own air com- pressor, and as these can be of such size that two are sufficient for the requirements of three engines, there is no need for an auxiUary set. There would be ample room to arrange these parallel to the main engines or at right angles, as probably the centre engine would be some distance aft of the two outer motors. Double-acting engines require two fuel inlet valves at the bottom in any case, because of the piston rod, and no doubt there will always be two for the top, although in Fio. 90.-2.0011 H.P. Sinsjle Cylinder Two-Cycle D.iuble-Actmg Die,sp| Ensim DIESEL ENCJINES FOR MARINE WORK 205 single-acting engines it is quite likely that only a single valve will be employed up to 2,000 H.P. Indeed, some manufacturers take the view that immediately two valves become necessary, the limit in single-acting engines has been reached. So far as the disposition of the machinery goes with such a design, there seems no reason to anticipate any serious difficulties either in battleships or large liners. There would be no interference with the gunnery arrangements, and the length of engine room would probably be little more than one-half of the total length of boiler and engine room combined, in the case of steam plant, whilst the weight should be 30 per cent. less. There are apparently no unknown factors in the problem of the adoption of very large Diesel engines for battleships and the biggest merchant vessels, and there remains solely the question of application. This, however, will not rest long in abeyance, as can readily be gathered by the wonder- fully rapid progress which has been made, and the now generally accepted opinion that the Diesel engine is the motor of the future for marine propulsion. In Fig. 90 an illustration is given of an experimental two-cycle double-acting Diesel engine built by Messrs. Krupp, designed for 2,000 B.H.P., which gave considerably more power than this. Although this actual motor must not be taken as the prototype of the large Diesel engine, it will be found that 12,000 B.H.P. motors will embody many features of the design, one of which is the operation of the valves by means of oil under pressure. CHAPTER VII CONSTRUCTION OF THE DIESEL MARINE ENGINE TWO-CYCLE ENGINE : SWISS TYPE BELGIUM TYPES SWEDISH TYPE- -GERMAN TYPES BRITISH TYPES FOUR-CYCLE ENGINE : DUTCH TYPE^ — GERMAN TYPES DANISH TYPE RUSSIAN TYPES SMALL DIESEL ENGINES Two -Cycle Engine : Swiss Type. — At the present time the engine which is perhaps finding most general appKca- tion for marine work is the two-cycle single acting type. With the marine engine there are more differences of con- struction than with the stationary motor, owing to the intro- duction in the two-cycle marine engine of a suitable reversing and regulating arrangement. The small engine of Messrs. Sulzer's construction is of the two-cycle single acting type, and it is built with four or six working cylinders — a small flywheel being provided. The cylinders are supported by pillars instead of the usual A frame, and easily removable covers enclose the crank chamber. The valves (scavenge, fuel and starting) are arranged in the cylinder head, but in each cylinder two scavenge valves are fitted, one on each side of the fuel valve, as shown in Fig. 91, which illustrates a typical engine of this design. By this means relatively small valves are permissible to allow the entrance of the large amount of scavenging air, and the valve bodies are lighter and morp easily operated, but in the latest designs scavenge valves are omitted altogether, and ports are employed at the bottom of the cylinder. In the engine illustrated in Fig. 91 there is one double acting scavenge pump in line with the working cylinders, 206 CONSTRUCTION OF DIESEL MARINE ENGINE 207 with a piston diameter of nearly double that of the latter. The scavenge air is delivered into the long cyhndrical receiver seen at the back of the engine, and thence to the various cylinders through the valves. The burnt gaseous 208 DIESEL ENGINES FOR LAND AND MARINE WORK g '5b 10^^ "^P^s^ CONSTRUCTION OF DIESEL MARINE ENGINE 209 mixture is e x- hausted through longitudinal ports at the bottom of the cyhnder ar- ranged round the whole of the cir- cumference, into a common exhaust pipe running the length of the en- gine and thence to the silencer. A two stage air compressor is pro- vided arranged as shown for the supply of injec- tion air and for filling the com- pressed air ve sels with air required for starting and manoeuvring, al- though this method is not always adopted, the pumps being placed in front of and behind the scavenge cylinder in some engines, being then driven by links off the scavenge p u m p piston rod. The pumps are \\'ater cooled, inter- 210 DIESEL ENGINES FOR LAND AND MARINE WORK mediate cooling between the stages being also arranged for. A long trunk piston is employed, serving at the same time as a crosshead, and in the larger engines this piston is water or oil cooled. Forced lubrication is adopted for all the main bearings, the oil pumps being driven off the crank shaft at the end of the engine, and also the cooling water pump, while a thrust block is arranged on the engine itself, though for large powers it may be fixed separately on the propeller shaft as near the engine as convenient. The operation of starting and reversing the engine is carried out by means of compressed air. The cam shaft is first put into the position in which the cams are set to operate the valve levers for ahead or astern, by turning a vertical spindle which drives this cam shaft, this operation being performed by turning the hand wheel controlling the engine. By a further rotation of the hand wheel the spindle, on which are pivoted the levers working the valves, first brings the starting valve lever into operation, thus running up the engine on compressed air, and then the fuel and scavenge valve levers, cutting out the starting valve at the same time. This is accomplished by having all the levers mounted eccentrically on the pivot spindle as sho\^ii in Fig. 91. The engine has an automatic arrange- ment for regulating the fuel and air during the reversing period, so as to assure the correct positions of the fuel inlet mechanism, and a governor is also provided to prevent the motor running beyond a determined maximum speed which, however, is only likely to occur in the event of a propeller shaft breaking or the engine racing. The actual speed is con- trolled by a small hand lever which regulates the amount of fuel delivered from the fuel pumps to the fuel inlet valves. This type of motor is now seldom constructed owing to the new designs that have been brought forward, and is chiefly of interest as showing the tendencies in construction in the earlier machines of relatively small power. It was of much value, however, in affording experience in the operation of small marine motors. 212 DIESEL ENGINES FOR LAND AND MARINE WORK Fig. 92 shows the general arrangement of a single engine and accessories of this type in which the references are as follows : — A Engine coupled direct to propeller shaft. BiB^BsBi Working cylinders. C Scavenge pump. Di Suction pipe for scavenge air. D-i Exhaust pipe. El Starting and manoeuvring air reservoirs. E2 Reserve starting air reservoirs. E3 Ignition air reservoir. F1F2 Air pumps. O1G2G3 Fuel tanks, G4G5 Fuel reservoirs. H C^ooling water pump. This is a typical arrangement which has been adopted for small engines, the auxiliary air compressor being in- stalled in any convenient position, not necessarily in the engine-room, but if desired at some portion of the vessel above the water line. Fig. 93 shows the general arrange- ment of a comparatively small Diesel engine plant, installed as an auxihary on a sailing vessel, in which the compact- ness of the engine and its accessories is well seen. The various portions will be understood from the above descrip- tion without further details. The type of engine adopted by Messrs. Sulzer for sub- marines and torpedo boats is a six-cylinder machine with two scavenge pumps in line with the working cylinders and an air compressor for the injection and starting air in front of each scavenge cylinder. Figs. 94 and 95 show respec- tively the arrangement of the engines for a torpedo boat and a submarine — the engines being staggered owing to the restricted width of the engine-room. In their most recent design of marine engine particu- larly adapted for large cargo vessels, Messrs. Sulzer Bros, have made several important modifications in design, and 214 CONSTRUCTION OF DIESEL MARINE ENGINE 215 Figs. 97, 98, 102 illustrate the present construction for slow speed engines of high power. The two-cycle prin- ciple is retained, and the main point of difference lies in 216 DIESEL ENGINES FOR LAND AND MARINE WORK the abolition of all scavenge valves in the cylinder cover, the actual method of scavenging being described later. For sizes up to 800—1,000 H.P. a four-cylinder design is employed, engines of SCO B.H.P. for a vessel of the Hamburg South American Line having a cylinder diameter of 16J inches and a stroke of 27 inches, the speed of revolution being 150 at maximum output. The engine is of the cross- head type, and although the crank chamber is enclosed, it is provided with covers at the back which are readily removable. The arrangement of the scavenge pump differs from that adopted by Messrs. Krupp and Messrs. Carels for similar slow speed two-cycle marine engines. Only one pump is provided for each engine, and this is driven direct off the crank shaft, being mounted on the same bed-plate at the after end. The low pressure stage of the injection air pump forms the crosshead for the scavenge pump piston, and there is a certain advantage in this arrangement in mini- mizing the vibration which otherwise occurs due to the heavy scavenge pump piston. The high and intermediate pressure stages of the air pump are mounted in front of the scavenge pump, and are actuated by means of a rocking lever from the connecting rod of the low pressure pump. The method is illustrated in Fig. 99, in which both the high and intermediate stages of the three-stage compres- sor set are mounted in front of the scavenge cylinder. The drive is arranged from a crank fixed to the main crank shaft, and as is seen from the illustration, the piston of the L.P. pump forms the crosshead of the scavenge pump. The general arrangement is evident from the diagram and need not be further explained. The scavenge pump is controlled by a piston valve as seen in Fig. 98, and the gear on the extreme left shows the Stephenson link motion for reversing the delivery of the scavenge air when the engine is reversed. Fig. 100 shows diagrammatically the method adopted for the supply of scavenge air to the engine cj^hnders. Ports are provided at the bottom for the discharge of the exhaust gases, as in all two-cycle engines, these extending only haK-way round the periphery and being represented Fig. 99. — Arrangement of Scavengo Pump and Air Compressor with Sulzer Marine Engine. 217 Fig. 100. — Scavenging Arrangements by means of Ports in Siilzer Engine. 218 COXSTRUf'TTOX OF DIESEL :\rARlXE EXGIXE 219 in the illustration by A, the discharge into the exhaust pipe taking place through B. The scavenge air is delivered into the pipe C from the scavenge pump, and the main supply enters the cylinder through the ports D, Avhich are spaced half-way round the periphery and are inclined so as to deflect the air upwards. In the actual scavenge pipe itself is arranged a piston valve actuated directly from the cam shaft by means of the eccentric E. The air which passes through this valve enters the cylinder through the ports F, which extend round one-half of the circumference and are immediately above the main scavenge ports. The opening of the piston valve is so arranged that air is introduced through the slots F after the ports D have been closed by the main piston start- ing on its upward stroke. By this arrangement the scaveng- ing appears to be very effective, and it is of interest to note that so many different methods of overcoming the undoubted difficulties of thoroughly efficient scavenging have been adopted in varying designs. There is, of course, the advan- tage that the air remaining in the cylinder after scavenging is at a pressure of about 3 lbs. per square inch instead of at atmospheric pressure. As no valves are employed in the cylinder head for exhaust or scavenge air, there remain but the fuel inlet valve and the starting air valve. Reversing is thus simpli- fied and is accomplished merely b}^ turning the cam shaft through an angle relative to the crank shaft and so setting the cams operating the fuel inlet valve in a position for reverse running. This operation is carried out by raising the vertical intermediate shaft which drives the cam shaft from the crank shaft. This intermediate shaft is broken, and a sleeve coupling interposed, which permits of its being raised or lowered, and thus turning the cam shaft relative to the crank shaft. As previously mentioned, the scavenge air supply is changed on reversal by means of a Stephenson link motion. From the illustrations of the engine, and in particular from Fig. 97, it can be seen that there are two hand wheels 220 DIESEL ENGINES FOR LAND AND MARINE WORK A and B in the centre, which serve for reversing and manceu- vring the engine by hand, in the event of the breakdown in the auxihary air motors, by means of which the operations are visually carried out. The levers C and D below the wheels A and B respectively control these servo motors, the first (operated by D) being for the purpose of reversing the link motion of the ports for the scavenge pump, and also rotating the cam shaft, whilst the second (operated by C) controls the starting and fuel valve levers for starting and running. The reversmg may be followed out in stages. In the first place the scavenge pump valve has to be reversed, and the link motion previously mentioned is changed over by means of the horizontal shaft E (Fig. 102). A partial rotation of this shaft causes the link to reverse, and the rotation is given it by the compressed air auxiliary motor controlled by lever D on the hand wheel B. The same operation of this motor causes the cam shaft to be turned through a small angle relative to the crank shaft. As regards the valves, there is but one cam, F, for the fuel valve, both for ahead and astern, and as in reverse running, all that is required is a change of lead from one side of the dead point to the other, it is evident that the rotation of the cam shaft is sufficient to provide this with one cam. The fuel valve cam is thus set for reverse running by the partial rotation of the cam shaft. This, however, would not set the air starting valves correctly for astern running, as the leads are different, and hence two cams are provided for each of these valves. These are fixed side by side on the cam shaft {G and H), and as there is no longi- tudinal motion of this shaft in reversing, as in most other engines, arrangements have to be made for bringing the starting air valve levers over the astern or ahead cam as required. This is carried out by having a vertical rod J attached to the air valve cam, at the bottom of which is the roller which is lifted by the cam. The joint of the vertical rod and the valve lever is a double one, and allows the former to move longitudinally so as to bring the roller 222 DIESEL ENGINES FOR LAND AND MARINE WORK above one or other cam. The longitudinal motion is given to the shaft K from the auxiliary air motor controlled by lever C at the starting platform, the roller being coupled to this shaft K by means of a small connecting rod. When starting up, the air valve levers (or rather the verti- cal rods attached to them) are brought down on the cams by a rotation of the spindle L, on which the levers are pivoted, this operation also being controlled by the auxiliary air motor from the starting platform by the lever C. The engine runs up on air, the fuel valve levers being out of action for the time being. When the engine has run up to speed after a few revolutions, the air valve levers are Hfted up and the fuel valves come into operation, and the arrangement is such that the engine can run (1) with only two cylinders on air, (2) with four cylinders on air, (3) with two cylinders on air and two on fuel, and finally, (4) with four cylinders on fuel. The dial seen in the centre of the engine in Fig. 102 indicates how the cylinders are working in this respect. In order that this arrangement may be carried out, the spindle L on which the valve levers are pivoted is divided in two portions in the centre, so that two of the air valve levers may be down on their cams on two cylinders and two of the fuel valve levers on the remaining two cyUnders. The quantity of fuel admitted to the cylinder is controlled by means of the lever M seen in Fig. 100 in the centre of the engine, whilst the air injection pressure is also regulated from the starting platform, being about 60 atmospheres for full speed and 4.0 atmospheres for slow running. Four fuel pumps are provided at N, one for each cylinder, and the supply to each cyhnder may be regulated by hand. The lever seen in front of the fuel pump chamber is for pumping up the fuel before starting. The governor O is also connected to the fuel chamber by the vertical rod P, so that when the speed exceeds the normal, the supply is reduced. An interesting feature of the design of the engine is the control of the timing of the fuel valve at varying speeds. = p.; i; [To /ace page 222 r^\ [To fare page 222. Fin. IIK),— Siilzor T%v..-C'.vcl,' Suhninrinc Motor of IJOU JVH.l'. [To lure fine 222 CONSTRUCTION OF DIESEL MARINE ENGINE 223 This is accomplished by means of the hand wheel P, which turns the shaft R and moves the vertical rod 8 connected to the fuel valve cam out of the vertical, so that the timing of its contact with the fuel valve cam is altered as required. The various pumps seen in front of the engine are for auxiliary purposes. Forced lubrication is adopted and the oil is used continuously, being cooled in circulation. For the cylinder lubrication eight small pumps are provided, two for each cylinder, alloA\ing four points in which the lubricat- ing oil may enter each cylinder. The pistons are water cooled, a tube being attached to the hollow body of the piston, which dips into a water reservoir, forcmg the water up into the piston. The exhaust pipe is also water cooled, and the cylinder jacket cooling is carried out in the usual way. The fuel consumption of the engine, with all the auxiliary pumps as shown, is 0*46 lbs. per B.H.P. hour, and the weight of the engine without any auxiharies is 55 tons. Including all pipes, air reservoirs, silencers, etc., the weight is 77 tons, and the fly-wheel weighs 9i tons. Belgian Types. — In Belgium the Diesel engine has been mainly developed by Messrs. Carels of Ghent, and the original marine motor of this firm did not differ greatly from that of the earlier types of Messrs. Sulzer's, as described previously. Fig. 104 shows one of the first large marine engines (of 1,000 B.H.P.) of four working cylinders and one scavenge pump, this motor now being utilized for experi- mental work and for dynamo driving. Although con- taining many features which are not now considered the best practice, the engine was a remarkable achievement in that it was by far the largest directly reversible two- stroke machine built at the time. The marine engine which has now been developed at Ghent for general ship propulsion, and which is constructed by a number of firms, is of a different type, based on the experience gained with the earlier motors. The general type is illustrated in Fig. 108, whilst i^ig'. Ill shows an 1,800 H.P. engine for a large oil tank vessel. Crossheads are employed and the design is of the open type with a view CONSTRUCTION OF DIESEL MARINE ENGINE 225 to conforming to the ideas of marine engineers, and to render the parts accessible. There are four or six cylinders according to the size, and generally speaking the engine is a four-cylinder one up to about 1,000 or 1,200 H.P., and six cylinders if above. Two scavenge pumps are always em- ployed, which is a point of difference from the Sulzer motor. These scavenge pumps are arranged at the back of the engine and driven off the crossheads of two of the cylinders by means of connecting rods, in much the same way as the air pumps on some reciprocating steam engines. A Reavell compressor is arranged at the end of the engine in the same manner as in many types of stationary Diesel engines. The scavenge pumps, which are double acting, are provided with piston valves — a method which seems well adapted for the purpose. Usually the bed-plate is divided into two or three portions, and the frame is built up by hollow box columns, on the top of which the cylinders are supported, there being two columns for each cylinder. Several of these columns (usu- ally four) are employed for the purpose of conveying the scavenge air to the main scavenge pipe, thus reducing the complication of piping on the engine. The crank shaft is also divided, and this is of advantage in that a smaller spare length may be carried in the vessel. In large two-cycle marine engines the question of scaveng- ing is one of some difficulty. A big volume of air at low pressure has to be admitted, and it is impossible to accom- plish this by means of one valve only, when valves are employed. In the Carels engine for large powers, four scavenge valves are fitted to each cylinder, arranged in the cover and operated by two levers and two cams. The method is somewhat expensive, and to a certain extent complicated, and largely minimizes the advantage of sim- plicity which the two-cycle engine might otherwise claim over the four-cycle, but it ensures very efficient scavenging. In spite of the many valves necessitated by this arrange- ment, reversing is very rapidly carried out, the time taken from full speed ahead to full speed astern being about Q 226 DIESEL ENGINES FOR LAND AND MARINE WORK 10 seconds. The general principle of the method of revers- ing is to provide a separate ahead and astern cam side by side, both for the fuel valve and the starting valve, and only one cam for each pair of scavenge valves. It is evident that as far as] the actuation of] these valves is concerned, this arrangement is sufficient if the cam shaft is turned CONSTRUCTION OF DIESEL MARINE ENGINE 227 through a certain angle relative to the crank shaft. When the engine runs in the astern direction, the scavenge valves will be opened at the correct moment for reverse running. ria ^z -A» 0^! -I I" s The turning of the cam shaft is accomplished by means of the vertical intermediate shaft seen in the centre of Fig. 108, by which the cam shaft is driven from the crank shaft as in stationary engines. This vertical shaft is raised 228 DIESEL ENGINES FOR LAND AND MARINE WORK either by means of the large hand wheel in the left of Fig. 108, or by means of a small compressed air motor. It is in two parts coupled by a sleeve, and only the upper portion is raised, thus carrying the cam shaft round through the required angle. The operation just described sets the scavenge valve cams in their correct positions. For the fuel and starting valve cams, since the cam shaft is not capable of moving longi- tudinally, a secondary or manoeuvring shaft is provided in front of the cam shaft. When it is desired to reverse the engine, this manoeuvring shaft is moved lengthwise a distance equal to the width of one of the cams, and by this means the rollers of the levers actuating the valves are caused to come over the astern cams instead of the ahead. Before this can be done, however, the levers have all to be lifted off the cams so that the movement may be given to the manoeuvring shaft. The whole of the actions for reversing or starting up the engine, except turning the cam shaft, as described previously, are accomphshed by means of the handwheel seen in the centre of Fig. 108, which causes the manoeuvring shaft to rotate. After the cams are set, the engine is started upon air, then some of the cylinders run on air and some on fuel ; in the third stage all starting air is cut off, and finally all the cylinders are in operation running on fuel. The various levers and handles are interlocked, so that it is impossible for the engine to start up until the cams are in their correct positions, and no fuel can be supplied to the engine until it has run up on compressed air. The sloping handwheel seen on the right in Fig. 108 is for controlling the governor, which is of the centrifugal type and acts on the fuel pumps to regulate the speed of the engine. The pistons are of cast iron and are water cooled, whilst the cylinder covers are of cast steel. The exhaust ports are at the bottom of the cyhnders, and a stuffing box is fitted at the bottom to prevent leakage of exhaust gases into the engine-room. Figs. 113 and 114 show an engine of this type of 800 Fig. 1 Fic. I(n._l.r,l)ll B.HI'. CureU Tviio .Murine Mi Eml View, sliowing Scavenge Pump. [Tojacc pagei 1 F7 n—i ' \® 'f I [To face page 228. Fig. 108.— Marine Diesd Engine, Carels Type. m le Engine. Scavenginj Puerp Steer ng Compressor Bilge Pump Fui. ]0n.— Plan of 1,500 H.P. Carels Marine Engi [To face page 228. 'ype)- Fio. 110.— Sectional Elevation of 1,500 H.P. Carels MarineJM.itor (New 'S^y). [To lace page 228. [Tu Jure iMUJi -l-l^. Fio. 112.- l.tllll H.l'. faiPb-Ti-cklenbi.rg M»iim. E.igii CONSTRUCTION OF DIESEL MAIUNE ENGINE 220 B.H.P. built by Messrs. Richardson, Westgarth &Co., Ltd., whilst Fig.]] 2 represents a similar motor of 1,500 B.H.P. built by the Tecklenborg Co. of Bremerhaven for tlie motor ship Rolandsecl- . Cockerill Engine. — In conjunction with Dr. Diesel, 230 DIESEL ENGINES EOR LAND AND MARINE WORK Messrs. CockeriU, of Seraing, have produced a design of en- gine which is built in relatively large sizes, and is indeed not specially suited for smaller motors. It is of the two-cycle eingle-acting type, but up to the present the engines which have been constructed have been non-reversible, although directly reversible motors are now being built. The reason for the adoption of a non-reversible type was solely on account of the ship in which the engines were installed being destined for West Africa, and the consequent desirability of the absence of as many new features as possible. In the arrangement of the motor of 650 B.H.P. at 280 revolutions per minute, there are four working cylinders with a scavenge pump at each end. Outside each of these are the high and intermediate pressure stages of the air pumps for injection and starting air, the low pressure stages being above the scavenge pumps — a method by which it is believed a smoother running may be obtained. The object is for the air pump to act as a sort of damper to the scavenge pumps, and this arrangement, or one of similar principle, has also been adopted in other designs. The engine is of a type in which scavenging is accom- plished by means of ports in the cyhnder. In order to avoid the necessity either of cutting away the piston to deflect the scavenge air towards the top of the cylinder, as in the case of the Polar Diesel engine, or utiUzing an auxihary scavenging valve, as is done by Messrs. Sulzer, the scavenge ports are themselves shaped vdth the idea of causing the air to clear the whole of the cylinder effectively. These ports occupy rather more than half of the circum- feren:e of the cylinder, leaving therefore less than one-half for the exhaust ports. There are two sets, one pair being arranged tangentially, so that the air entering them sweeps round the walls and rises to the top of the cyhnder, whilst the other pair cause the air to rise right to the centre. By this method there is probably an economy in the quantity of air necessary to give complete scavenging. In the cover of each cylinder there are two valves — the fuel inlet valve and the starting air valve. The motor CONSTRUCTION OF DIESEL MARINE ENGINE 231 Fig. 114. — End View of 800 H.P. Carels' Tj-pe Two-Cycle Marine Motor. is of the enclosed chamber type with forced hibrication, and a trunk piston is employed, which is quite suitable for powers of the motors such as have up to the present been constructed. 232 DIESEL ENGINES FOR LAND AND MARINE WORK Swedish Type. — tSome manufacturers of the two-stroke engine make use of the scavenge air cyhnders for starting and reversing, with the object of doing away with the neces- sity of the starting valves on the cylinders. An engine of this construction, if it is provided with ports at the bot- tom of the cylinders for both the exhaust and the scavenge air, is thus simplified to the extent of having only one valve to be operated in the cylinder cover — namely the fuel inlet valve, and a very convenient reversing gear can be designed. The Aktiebolaget Diesels Motorer of Stockholm have developed an engine on these lines for power up to 1,000 I.H.P. It is usually constructed with four working cyhn- ders and two scavenge air cylinders mounted on the same bed-plate, in a line with the engines. During the ordinary running of the engine the air from the two scavenge pumps is delivered into the receiver, and as the pumps are double acting and have their cranks set at 90° a very regular supply is obtained. The air, which is drawn into the cylin- ders from the atmosphere before compression, is delivered from the receiver into the various working cylinders as the scavenge ports are uncovered by the pistons, the pres- sure of the scavenge air being approximately the same as that with most other two-stroke engines, namely about 3 lb. per sq. inch above atmosphere. The scavenge or manoeuvring cylinders, as they may also be called, run as compiessec^ir engines during the periods of starting and reversing these engines, but as air is only employed for this purpose for two or three revolutions there is not a heavy call on the air receivers in which compressed air is stored for carrying out these operations. The starting and manoeu- vring receivers (of which there is usually one main and one auxiliary) are replenished by means of a special pump which may be situated on the top of one of the scavenge cylinders, or in any other convenient manner. The valves are arranged so that whenever the air in the receivers falls below a certain predetermined limit, the pump immediately begins to charge them until the requisite pressure is reached. The compressed air for injecting the fuel into the ^- F =Silniar. J =Tool Cheat. K =Air Inlet Pipe. L = Exhaust Pipe. H ^Cooling ll'oKr Pump. Ni=Bilge Pump. N,=OU Pump. A,=Hand Air Pump. Flo. 115 — General Arrangement of Engi CONSTRUCTION OF DIESEL IMARTNE ENGINE 233 working cylinders is provided from another compressor, and the usual type of vertical cylindrical air reservoir is employed to store this air. A separate fuel pump is fitted for each cylinder, and the type of fuel inlet valve and pulver- iser described and illustrated in an earlier chapter is em- ployed, being the same as for the stationary engine. These pumps work generally on the principle commonly adopted for Diesel engines, but as there is no governor the opening of the suction valves is not automatically controlled. The pumps are operated by links which receive their motion from the main cam shaft, and are pivoted eccentrically on a spindle which can be turned by hand, thus altering the positions of the links relative to the cam and so varying the opening of the suction valves. This in turn controls the amount of fuel admitted to the cylinder and hence the speed of the engine. For reversing, a second or reverse set of cams is provided on the cam shaft, which is moved hori- zontally until these cams come beneath the levers operating the fuel inlet valves, which thus open at the required point for reversing. The valves of the scavenge pumps which are worked by eccentric rods are also reversed, and their eccentrics, together with the eccentrics for driving the fuel pumps, are mounted on a separate horizontal spindle, wiiich in reversing does not move in a longitudinal direction. When the reversing handle is put in the " astern " position the fuel pump is unable to deliver any more oil to the cylin- der, and the fuel valve levers take up thepositionsforreverse running after the last charge of oil has been injected into the cylinders. This is arranged by the fuel valves being provided with wider cams than the regulating arrangement for the pump, so that the fuel valve opens for one revo- lution after the pump has been out of operation. The scavenge cylinders absorb the energy of the flywheel by running as pumps, and when the engine comes to a standstill the scavenge valves are in such positions as to allow com- pressed air to enter from the receiver, and the pumps then run as motors. The fuel pumps, immediately upon the engine starting, force oil up to the fuel valves, which open 234 DIESEL ENGINES FOR LAND AND MARINE WORK at the required moments, so that the engine when starting up, receives two impulses — one from the scavenge pumps operating as motors and then later from the fuel injection, which is of great value in accelerating the speed at the begin- ning. The scavenge pumps after one or two revolutions as air motors take up their ordinary work. One of the first British ocean-going motor vessels was the Toiler, a boat of 2,000 tons, built by Messrs. Swan, Hunter & Wigham Richardsort, equipped with two engines of this construction, each of 180 H.P. She made a successful voyage across the Atlantic in 1911. In the Toller the steering gear, windlass, and auxihary pumps are all driven by compressed air, and a separate small Diesel engine driven compressor is provided for this work ; but as at sea only the steering gear is usually required, the compressed air is then taken direct from the main engine and the auxiliary plant is shut down. Independent tests have recently been carried out on several of these engines, with a view to ascertain- ing the fuel consumption at full load, the results of which are most interesting in comparison with the consump- tion of the ordinary four-cycle engine, and from the figures obtained it appears that the difference is extremely small. Tests were made by different authorities on four separate two-cycle marine engines of standard type, after being erected in the works and before installing in the vessels for which they were built, the power being absorbed in each case by a brake of the Heenan & Froude type. In the four engines tested it was found that the fuel consumption per B.H.P. hour was respectively 211 grams., 210 grams., 201*6 grams, and 196 grams., or an aver- age of 204"5 grams, or say "45 lb. per B.H.P. hour, which is very much the same as for the usual four-cycle motor. All the engines were of the standard four-cylinder type, with two manoeuvring cylinders in line. An illustration of a 260 H.P. engine is shown in Fig. 122. For larger marine Diesel motors, that is to say any- thing over about 500 B.H.P., a different type of engine is built by the same firm, although many of the essential 236 DIESEL ENGINES FOR LAND AND MARINE WORK details are embodied in the larger engine. A somewhat similar design, which has, however, modifications of their own, is built by Messrs. Swan, Hunter & Wigham Richardson in this country. As before, the motor is of the two-cycle single-acting type, but the manoeuvring cylinders arranged in line with the working cylinders are abolished, and replaced by combined scavenging pumps and mancBuvring cylinders below the actual working cylinders. There is thus one scavenge pump for each cylinder, but the arrangement is not exactly that adopted in many other cases and known as the stepped piston design, since the pistons of the w^orking cylinders and the air pump are quite separate and the air is compressed by the scavenge piston on its downward and not on its upward stroke. The engine is, in many ways, an extremely simple one. Unlike practically every other type, the cylinder and liner are cast in one piece, the cylinder for the scavenge pump being quite separate. Port scaveng- ing is employed as in the smaller motors, and as there is no auxiliary valve for the admission of scavenging air, the piston is shaped in order to deflect the air upwards and downwards so that good scavenging may be obtained. The advantage of port scavenging is shown in the construction of the cylinder cover, which contains only one valve, this being the ordinary fuel inlet valve in the centre of the cover. This valve is of the same type as that described for the smaller Polar engines. The motor is practically of the open type, and naturally owing to the arrangement of scavenge pumps, there is an external crosshead and connecting rod. The cylinders are supported at the back by means of a cast-iron framing carrying also the guides for the crossheads, and at the front by cast-steel columns, as with some other motors, notably the Sulzer type and also the Werkspoor engine. The important feature of using the scavenging cylinders for starting purposes is retained in this motor with the result that not only is the simplest possible design of cover obtained, but also the undesirable admission of cool air CONSTRUCTION OF DIESEL MARINE ENGINE 237 into the heated combustion chamber during manoeuvring is avoided. The method involves a certain complication in connexion with the valves for the scavenge cylinder, Fig. 1 17.— Xear View of Cam Sliaft of 800 H.P. Polar Diesel :\Iarine Engine. but otherwise has much to commend it. The arrangement, however, can be reduced to comparative simplicity in operation, since when starting up there is a two-way valve 238 DIESEL ENGINES FOR LAND AND MARINE WORK which shuts ojff the admission of atmospheric air into the scavenge pump, and allows compressed air at a pressure of about 75 lb. per sq. inch to enter the scavenging cylinder beneath the piston, and start up the engine. The admission and discharge valves on the scavenge pumps are mechanic- ally operated by means of eccentric rods from a horizontal spindle driven off the crank shaft. Although the pressure of the starting air in the scavenge pump only needs to be 75 lb. per sq. inch it is supplied from res&rvoirs at 150 lb. per sq. inch to a reducing valve to bring it down to the desired figure. For the operation of the fuel valve in the cylinder cover there is one lever for each cylinder and two cams are arranged on the cam shaft, one for ahead and one for astern running. An interesting and useful feature, however, lies in the fact that the two cams are tapered away, so that the roller of the fuel valve lever need not be lifted when reversing as is usually the case, when ordinary flat cams are adopted. There is also a half-speed cam for slow running. With this engine the whole cam shaft is not moved longitudinally, as is common, but only a sleeve carrying the two cams for each cylinder, this movement being effected by means of a lever from the starting platform. Following a practice which is now becoming more and more usual for marine engines one fuel pump is provided for each cylinder, but instead of bunching all the pumps together, as is frequently done, each one is arranged in front of its cylinder and is driven off the cam shaft by means of an eccentric, the pump itself being only slightly below the level of the shaft. For the control of the speed of the engine the usual method of operating upon the suction valve of the fuel pump is adopted, and in order to carry this out there is a long spindle in front of the engine, attached to levers which, when the spindle is rotated, alter the stroke of the suction valve of the pump, and thus vary the speed of the engine. The movement is carried out by means of a control lever on the starting platform. With the motors of this type which have hitherto been tc c >. o 239 240 DIESEL ENGINES FOR LAND AND MARINE WORK built, two separate two-stage compressors have been adopted, driven by means of levers from the crossheads of the two central cylinders. Probably in larger motors compressors of the three-stage type will be employed, and this has in fact been done in the Neptune engine of Messrs. Swan, Hunter & Wigham Richardson. In reversing, apart from altering the timing of the fuel inlet valve it is necessary to operate the scavenge pump inlet and discharge valves at 180° after the ordinary timing for ahead running. This is accomplished in a com- paratively simple manner by converting the inlet valves into delivery valves, and vice-versa. The cylinders are worked in pairs and it is arranged that the two inlet valves for two adjacent cylinders are one above the other, whilst there is also a delivery valve above another delivery valve for the two cylinders. Above the casing which contains the two inlet and two delivery valves is what may be termed a distribution box in which is a valve that can be moved to the right or left. On moving it to the extreme right the deliver}' valves become the inlet valves for the scavenge pump and the inlet valves are changed to the delivery valves, which corresponds to the operation necessary for the valves when running in the opposite direction. For the general control and working of the engine there is one main hand- wheel which carries out all the operations necessary for reversing, and a lever which serves the purpose of admitting starting air to the scavenging cylinders for starting up. The hand-wheel moves the cam blocks longi- tudinally so as to bring the ahead or astern cam under the valve lever roller as required, whilst there is also an inter- mediate position which corresponds to the stop position on the hand- wheel. A half -speed cam is moreover provided which is brought underneath the lever roller when it is required to run at slow speed for some time. In turning this hand-wheel the distributing valves for the admission of air to the scavenging pump are also operated at the same time, but the engine only starts up when the main starting lever on the control platform is actuated so FiCi. 12(1.— 050 B.H.P. Neptuno Polar Marine Engine, built by Messrs. CONSTRUCTION OF DIESEL MARINE ENGINE 241 as to admit compressed air at 75 lb. per sq. inch, first to two manceiivring cylinders, then to four, and finally to six. It may incidentally be mentioned that if the engine is warm it is not usually necessary to carry the operation beyond two cylinders. For controlling the speed of the engine in the ordinary course of running there is a ratchet wheel operated from the starting platform which controls the suction valves of B CONSTRUCTION OF DIESEL MARINE ENGINE 243 the various fuel pumps, the action being very much the same as is utiHzed in the land engines. A governor is fitted which also varies the stroke of all the suction valves of the fuel pumps at the same time, but this motion is not con- nected at all with the throttle control on the starting platform. 244 DIESEL ENGINES FOR LAND AND MARINE WORK All the cylinders are provided with horizontal relief valves which may be operated from the starting platform by means of a lever if necessary. It is not usually essential for these relief valves to be opened, but if it is found that the motor is difficult to start, which may be accounted for by com- pressed air acting upon the bottom of the scavenge pump pistons when the engine is endeavouring to fire, then the relief valve may be opened, and at the same time compressed air is automatically cut off from the injection valves. Fresh water is employed for the piston cooling, but for all other piu'poses sea water is used. The delivery into and discharge from the piston head is arranged by means of concentric pipes within the piston rod itself, the water being taken to these piston rods through the levers which operate the air injection pumps on the front of the engine. For employment on submarines a new type of engine working on the four-cycle principle is built by the Polar firm ; this is capable of running at a speed as high as 500 r.p.m. and has been adopted owing to the difficulties of scavenging and other troubles with high-speed two-cycle engines. German Types. — A large number of two-cj^cle single acting engines of the Diesel type have been constructed by Messrs. Krupp of Kiel, of which several were for the German and Italian Navies, but recently four engines each of 1 ,250 B.H.P. running at 14.0 revolutions per minute have been built for the Deutsch-Amerikanische Petroleumgesellschaft for tank vessels. All engines of over 300 H.P. are made on the two-cj^cle principle, Mhile those below this power are four cycle, in each case being directly reversible except for the very smallest sizes. Fig. 123 shows a high speed two-cycle reversible marine engine of Messrs. Krupp 's construction, of 1,000 B.H.P. , recently supplied to the German Admir- alty, and this is typical of the general design of the two- cycle engine. There are six working cylinders divided into two sections of three each, with the air compressor in the centre and a scavenging air pump at each end, the peculiar construction of the suction chambers being well I I I I I ' I I I I r-'--L, 246 DIESEL ENGINES FOR LAND AND MARINE WORK seen in the illustration. Each scavenging pump supplies three of the cylinders, which thus form a completely inde- pendent set, so that for low powers only one-half of working cylinders need be in operation and a greater reduction in power may thus be obtained, with corresponding increase in manoeuvring facilities. For the engine exhaust, ports at the bottom of the cyhnder are employed as usual with two-cycle motors, and the scavenge air is admitted through valves in the cylinder head. The crank chambers are totally enclosed, with inspection doors in front of each cylinder for examining the cranks and bearings. The method of reversing in this engine consists in the employment of ahead r 1 r - and reverse cams on the same cam shaft, which is moved axially during reversing so as to bring the ahead or astern cams under- neath the valve levers .._ operating the valves as required . The valves which require an alteration in the Fig. 124.-Diagram shovving action of ^-j^^g ^f opening dur- Cams for Krupp s Engine. . ^ ® ing reversal are the fuel inlet valve, the starting valve and the scavenge valve, unless ports in the cylinder be employed instead of the latter, which is sometimes the case. The cams for the fuel and scavenge valves are arranged somewhat as shown diagrammatically in Fig. 124, there being a flat space be- tween the ahead and astern cam pieces, this being the position of rest for the roller of the valve lever when the engine is stopped. For the starting valve two separate cams are provided, one for ahead and one for astern, and either of these may be put into operation according to the direc- tion of rotation required. The action of reversing may be explained as follows. Assume the engine is running ahead, -f CONSTRUCTION OF BTESEL MARINE ENGINE 247 in which case the rollers for the scavenge air and fuel inlet valves will be in position as at A in Fig. 124, while both the rollers of the starting valve levers will be raised well above the cams which operate them. To bring the engine to rest the whole of the cam shaft is moved to the left, a dis- tance equal to half the longitudinal distance between the centres of the ahead and reverse cams. The rollers operat- ing the valve levers then rest on the flat portion of the cam sleeve as at B, Fig. 124, and the valves are not opened as the cam shaft rotates. This movement of the cam shaft is carried out by means of the hand- wheel seen in the centre of the engine in Fig. 123, which causes the motion through screw gearing. The scavenge air and fuel inlet valve levers being in the stop position the engine comes to rest, after which the starting valve lever for reverse running is brought down on its cam by means of one of the two levers seen in the centre of the engine, which give an angular motion to a shaft underneath the cam shaft and connected to it by small coupling rods. The starting valves are opened, the engine runs up as an air motor, and after two or three revolutions the starting valve levers are raised off their cam by putting the main controlling handle back to mid position, and the cam shaft is moved further to the left a distance equal to the first until the rollers of the valve levers are in the position C, Fig. 124, which is the astern running position. The main starting lever controlling the starting valves and the wheel controlling the position of the cam shaft are properly interlocked so that there may be no possibility of the fuel inlet valve being opened during the starting period. For their standard engine of the slow speed type, suitable for large cargo and similar vessels, Messrs. Krupp have adopted a different design, and several of this new type have already been constructed. The two-cycle single acting principle is retained, and in some respects the engine is similar to that developed by Messrs. Carels, as previously described, being of the open crosshead type. In all sizes of motor which have at present been constructed (ranging 248 DIESEL ENGINES FOR LAND AND MARINE WORK Fig. 125. — Section through Cylinder and Scavenge Pump of 1,250 B.H.P. Krupp Engine. from 1,000 B.H.P. to 2,500 B.H.P.) six cylinders have been employed, with two scavenge cylinders arranged at the CONSTRUCTION OF DIKSEL MARINE ENGINE 249 back of the engine, driven from tlie crossheads of the two centre working cyHndcrs through rocldng levers. The air compressors for the supply of starting and injec- tion air and for manoeuvring are separately driven, so that the engine itself consists only of the working cylinders and the scavenge pumps. Scavenging is effected by means of valves in the cylinder cover, there being two per cylinder, but it may be mentioned that this is not likely to be the 250 DIESEL ENGINES FOR LAND AND MARINE WORK ultimate design. As v^iU be noticed from Figs. 125 and 126, the scavenge pumps are supported from the engine frame and raised above the engine-room floor level, thus differing from the arrangement adopted by Messrs. Carels. A stuffing 'So c box is provided at the bottom of the cylinder, to prevent the escape of exhaust gas into the engme-room. The cylinders are supported on an "A" shaped frame formed by box columns fixed to the bed-plate, and the CONSTRUCTION OF DIESEL MARINE ENGINE 2ra crosshead guide surfaces are formed on the inside of the cohimiis and are \\ater cooled. The arrangement and construction of the piston are seen from the illustration, which also indicates that the stroke is relatively long com- pared with the bore of the cylinders. It may be mentioned that the speeds of this type of engines vary from 1 00 to 1 60 r.p.m., accoi^ding to the size and also the speed of the vessel in which they are installed. The arrangements adopted for reversing follow much on the lines of those already described for the high-speed two- cycle engine of this firm. A single cam shaft is employed, on which both ahead and astern cams are mounted, and this is moved longitudinally to bring the astern or ahead cams underneath the valve levers, according to the direction of rotation required. The movement is effected either by hand or by means of a small compressed air motor, and a manoeuvring hand-wheel is provided, which allows the engine to run up on compressed air, and finally brings fuel on to all the cylinders for full speed. Before moving the cam shaft longitudinally, all the valve levers are raised off the cams, in the usual manner adopted with two-cycle engines when this method of reversing is employed. The weight of this type of engine is about 250 lb. per B.H.P., and the fuel consumption is about 0*44 lb. per B.H.P., which includes the operation of the scavenge pumps but not the air compressors. Reversing from full speed ahead to full speed astern is accomplished in about 12 seconds. An illustration of the reversing mechanism is given in Fig. 128. Diesel engines for marine work are built at the Niirnberg Works of the Maschinenfabrik Augsburg-Niirnberg, of the two-stroke cycle type, but are divided into two classes — the light and the heavy weight type, the former being chiefly designed for submarines, gunboats and torpedo boats, while the latter are more suitable for tug boats and cargo vessels. The weight of the light type is from about 30-35 lb. per B.H.P. hour for large engines up to 40 lb. per B.H.P. hour for small engines, this being an inclusive weight. The engines are commonly built of six cylinders 252 DIESEL ENGINES FOR LAND AND MARINE WORK without a flywheel, or four cylinders with a flywheel, but sometimes eight cylinders are employed. The types stan- dardized for the light weight engine are as under : — 150 H.P. at 550 revs, per min. 200 „ „ 550 300-500 ,, ,,500 600 „ „ 450 900 ,, „ 420 1,200 „ ,, 400 The approximate dimensions of some of these engines are as under : — Horse power 150 200 300 400 500 GOO ft. in. ft. in. ft. in. ft. in. ft. in. ft. in. Overall lengtli . 9 101 11 5| 12 9| 14 51 14 9i 15 9 Overall width . 2 2^ 2 7| 2 Hi 3 41 3 7 3 Hi Height required for dismantling . 4 41 4 111 5 7 6 3 G 6| 6 10| Depth required below centre of crank shaft 1 li 1 21 1 5 1 53- 1 7 1 n The usual speeds of the heavy weight engines are as follows : — 150-200 B.H.P. at 300-400 revs, per min. 300-330 ,, ,, 300-330 450-550 „ 225-275 600-750 ,, 225-275 900 ,, 260 1,200 „ 215 The heavy engines are cheaper as the framework and bed-plate are of cast iron, whilst with the lighter type manganese bronze is usually employed. The speed is also less and the fuel consumption is lower with the heavy type than with the light weight motor. [To face page 252. Fla. 1 28.— Rovereiiig Meclionism of Krupp Engi ITo/acr pant 252. ^^^^^^^^^^SSS^v^SZ 7T» *i w f:!^?;^ - - 'i^i^Ir-^- iJfelfib^Ki' .^'— ■; - ISiM^ San ■ 'ci^^lJ^B ;^^-i^ « ■ % Mr k^""-s!_ i^^ 1 IJj ^^ "^ '-rp' ^^Idi K]i:. IJ'.l— l.jr.u llHl'. Krupp IVu Cy.l.- Mil CONSTRUCTION OF DIESEL MARINE ENGINE 253 \X Large engines are provided with two two-stage com- pressors for the injection and starting air, while smaller motors have but one compressor, the usual arrangement being to have it at one end of the engine. The scavenge pumps are below the working cylinders, one for each cylinder, the pistons being stepped and enlarged at the bottom to form the piston of the scavenge pump, while it also acts as the crosshead for the piston rod. The admis- sion of the scavenge air takes place through <^-^p^ valves in the cylinder head. The arrangement of the working cylinder and the scavenge cylin- der is shown in trans- vere section in Fig. 130, the effective sectional area of the scavenge cylinder being the dif- ference between that of the working cylinder and the scavenge cylin- der itself. A s t h e volume of scavenge air required is usually taken as 1'2 to I'S times the volume swept through by the piston of the working cylinder, the diameter of the ^^^- 130.— Diagrainniatic Representation of Niirnberg Two-Cycle Marine Engine, scavenge piston is from showing Scavenge 'Arrangements. 254 DIESEL ENGINES FOR LAND AND MARINE WORK r4 to r6 times the diameter of the working piston, the latter figure being for high speed engines . In Fig. 130, which is purely diagrammatic, A represents the working cylinder, B the scavenge cylinder, G the fuel admission valve, D the starting valve, and E the scavenge air admission valve. F is the outlet valve in the scavenge cylinder, through which the scavenge air passes, after being compressed to a few pounds above atmosphere, into the receiver G, whence it enters the working cylinder through E, when this latter valve opens. H is the admission valve of the scavenge cylinder through which air is drawn into the scavenge cylinder, during the suction or downward stroke of the piston. In the position shown in the figure, the working piston is just finishing the compression or upward stroke in which the air is compressed to the pres- sure required for combustion of the fuel. When the crank has nearly reached the top dead centre J, the fuel admission valve opens and combustion takes place, and the piston starts on its downward or working stroke, while // is also opened and air is drawn into the scavenge cylinder. Just before the crank reaches the bottom dead centre K, the YStlveE opens, scavenge air enters from the receiver G, and expels the exhaust gases in the worldng cylinder through the ports L which are then uncovered by the piston, F being closed and H open during the whole of this stroke. After the crank passes the dead centre, F opens, and H closes, while the valve remains open till just after the exhaust ports L are closed by the piston, when it closes, and during the remainder of the upward stroke F is kept open and the receiver G is charged with scavenge air from the scavenge cylinder, while the air in the working cylinder is compressed. When starting up the engine by the admis- sion of air through the starting valve D in the usual way, this air is effectively discharged through the exhaust ports in the cylinder by admitting scavenge air through the scavenge valve E so long as these ports remain uncovered by the piston. The working pistons are cooled with oil and the cylinder CONSTRUCTION OF DIESEL MARINE ENGINE 255 jackets have removable covers which are useful for clean- ing the jackets, rendered necessary by the employment of salt water for cooUng purposes. Forced lubrication is adopted and the oil passes through a cooler and is enabled to be used over again. Fig. 131. — Diagram illustrating Metliod of Reversing Niirnbcrg Engine. As is necessary in all two-cycle engines in which scavenge valves and not ports are employed, in reversing, the times of opening of three valves have to be altered-^namely, the starting valve, the fuel valve, and the air inlet and scavenge valve. This is accomplished in the case of the two latter by turning the cam sliaft itself through a certain angle 256 DIESEL ENGINES FOR LAND AND MARINE WORK (about 30° in the case of the Niirnberg engine) so that but one cam is needed for each scavenge valve and each fuel valve, both for ahead and reverse running. In order that the scavenge and fuel valves may be set in the reverse position together, by the same movement of the cam shaft, it is necessary that the angles of opening and preadmission of these valves should be in a certain definite ratio. This can be better explained by a reference to Fig. 131, which represents a crank diagram for the engine, A being the top dead centre and E the bottom. The question to be solved is, to so adjust the angle of opening (referred to the rotation of the crank shaft) of the scavenge and fuel inlet valves, that the cams operating their valve levers will have an axis of symmetry, with the result that by the same alteration of angle of the cam shaft, both the fuel valve and the sca- venge valve are set for reverse running. In Fig. 131 B is, the point of admission of the fuel, the angle of preadmis- sion being d. The valve closes at D so that the total angle of opening is a. K represents the point of uncovering of the exhaust ports and L of their closing, but these do not enter into the ques- tion since, of course, no alteration is necessary in reversing. At i^ the scavenge valve opens, the closing point being H , and the full angle of opening h. The angle of preadmission for the scavenge air is e. The respective total angles of opening of the fuel valve {a) and the scavenge valve (h) are so adjusted that a = c + 2fZ and 6 = c + 2e or in other words the angle of opening in both cases is twice the angle of preadmission, plus a constant angle c. In the diagram if the lines 0^ and O2 be drawn bisecting the angles a and h it is easy to show that the angle gr is 180° and therefore the line Oj O2 is the axis of symmetry for the fuel valve and scavenge valve cams. To explain the action of reversing consider the engine to be running in the ahead direction as indicated by the arrow CONSTRUCTION OF DIESEL MARINE ENGINE 257 S, A and B are the top and bottom dead centres of the crank, and the angles BOA or d and F O E or e are the respective angles of preadmission for the fuel and the scavenge valves. When the engine is started up in the reverse direction, which is accomplished by means of compressed air, as is explained later, the crank is running in the direction indi- cated by the arrow R, and all that is necessary to set the cams in the correct position is to move the cam shaft through an angle equal to c so that in the diagram C and G become the respective top and bottom dead points. The angles of preadmission are then D C or d and G H or e for the fuel and scavenge valves respectively, which are exactly the same as when running in the ahead direction. The cams are therefore in the correct position for reverse running and the operation is exactly the same as for the ahead rotation. For the starting valve, if its cam were turned through an angle of only 30°, the opening of the valve would be a small period, since it would also have to be 30° plus twice the angle of preadmission, which is small. Hence an insufficient starting torque would be produced and other means have to be adopted. The arrangement used is to have two cams for each starting valve (of which there is of course one for each cylinder), one cam for ahead and the other for reverse running. These cams actuate a small valve which regulates the admission of compressed air to the starting valve, and according to which cam comes into operation the direction of rotation of the engine at starting is controlled. A single lever controls the whole operation of reversing. In the stop position it is in the middle, while for ahead run- ning it is moved to the right, and for astern to the left, its movement allowing the injection air to pass to the ahead or astern air valve previously mentioned. When the engine starts up in the required direction it automatically sets the cams for the fuel and scavenge valves in their right position, namely, in reverse running it turns the cam shaft through an angle of 30°. This is carried out by driving the vertical intermediate shaft operating the horizontal cam shaft by s 258 DIESEL ENGINES FOR LAND AND MARINE WORK means of a claw coupling, the teeth or claws of which have a clearance angle of 30° instead of the faces bearing against each other as is usual with these couplings. When the engine is running in the ahead direction the front faces of the claws of the half of the coupling keyed to the crank shaft bear hard against the hack faces of the half of the coupling attached to the vertical shaft. On reversing the engine, by movement of the controlling handle and starting up on compressed air, the part of the coupling on the crank shaft runs free for an angle of 30° when the hack faces of its teeth come against the front faces of claws of the half of the coup- ling on the vertical shaft. The coupling then drives this shaft, and hence the cam shaft in this position, the result being that the cam shaft is automatically turned through an angle of 30° relative to the crank shaft, and the cams are thus in the required position for astern running. In order that there may be no play in the coupling when the engine is running, strong springs keep the two halves of the coupling together. The engines are of six or eight cylinders, the cranks being set at 120° or 90° in the two cases respectively. The general arrangement of this type of motor can be seen from Fig. 132, which represents a longitudinal section of the engine. The air pumps are fitted on the forward end of the engine, these consisting of two two-stage compressors, and the design may be compared with the submarine motors of the Krupp and similar designs. The cranks for these two pumps are set at 180°, which aids con- siderably in the smooth running of the machine. The cylin- ders may be of cast steel or cast iron, and the pistons are oil cooled — a point of more than ordinary interest. The speed can be reduced to 20 per cent, of the normal full speed of the engine. The circulating pumps for the cooling water are driven off the engine, and the water passed through the air-pump cylinder jackets, the bearings, the oil cooler, cylinders, exhaust valves, the exhaust pipe, and thence overboard. Forced lubrication is adopted throughout, the oil pressure Fio. 132. — Sectional Illustrations of Xiirnborg Marine En. [To face ]>aji 258. Fig. 133. — End View of Niirnberg Marine Engine. 259 260 DIESEL ENGINES FOR LAND AND MARINE WORK being from 30 to 50 lb. per sq. in. It passes through the hollow crank shaft and the gudgeon pins, and is then utilized for piston cooling. The consumption in these motors is relatively low, being in the neighbourhood of 0"44 lb. per B.H.P. hour, which may be taken as a very fair figure for this type of engine. An illustration of one of the heavy weight type engines (which it must be remembered is purely a relative term) is given in Figs. 133 and 135. A motor of this type of 900 H.P., running at 250 revolutions per minute, has six cylinders, each of diameter 360 mm., the stroke being 600 mm. The two-stage compressors are direct driven from the crank shaft and have cylinder diameters of 200 and 100 mm. respec- tively, with a stroke of 450 mm. The pistons are cooled with lubricating oil, and the cylinders, in the ordinary manner, with water. The oil pumps and cooling water pumps are fitted to the front of the main engine. The weight of this engine, calculated on its rated power of 900 B.H.P. , is about 120 lb. per B.H.P,, and as an indication of the overloads which Diesel engines will take, it may be mentioned that the engine can be speeded up to 300 revolutions per minute and deliver 1,100 B.H.P. continuously. The minimum speed at which the motor runs is 50 revolutions per minute, i.e. 20 per cent, of full speed, which is quite sufficient for all purposes of manoeuvring, and this is accom- plished by cutting out three cylinders entirely. The fuel consumption is about 0*47 lb. per B.H.P. hour, and in this respect is slightly inferior to the best open type slow- speed marine Diesel engines, which usually have a consump- tion of 0-42 to 0-44 lb. per B.H.P. hour. For larger powers an intermediate type of motor is con- structed by the M.A.N., resembUng in many ways those of the Krupp and Carels designs. It is an open type engine for powers of 1,000 to 2,000 H.P., and is naturally much heavier than the relatively light motors already described, its weight being between 180 and 220 lb. per B.H.P., accord- ing to the size and circumstances, whilst the speed varies between 100 and 150 revolutions per minute. CONSTIirCTrON OF r)TESP:L MAPxTNE ENGINE 261 The scavenge pumps are situated at the side of the main engine and driven by rocking levers off the crossheads, the stepped piston arrangement on this type naturally being 262 DIESEL ENGINES FOR LAND AND MARINE WORK abandoned. The compressors are driven direct off the crank shaft at the forward end of the engine m the usual manner. Engines of the two-cycle double acting type are now being built by the Maschinenfabrik Augsburg-Niirnberg, and apart from the principle of action there are various points in the construction differing from the single acting type. The engines have three working cylinders, and the scavenge cylinders are separate, though there still remains one for each working cylinder. These scavenge pumps may either be mounted in line with the main cylinders and driven direct off the crank shaft, or arranged in front of the engine, and driven by levers from the crossheads. Fuel and starting valves are provided at both ends of the cylinders, and are worked from separate cam shafts in front of the engines, the means employed for reversing being similar to that already described for the single acting engine, but the reversing gear operates both cam shafts. As previously mentioned in dis- cussing this type of engine, two fuel valves are fitted in the bottom of each cylinder on account of the stuffing box, which is of the same type as used for double acting gas engines. For running at low speeds the fuel valves at the bottom may be put out of operation, when the engine works single acting. The scavenge air is usually arranged to enter at both sides, and there are exhaust pipes both at the back and the front of the engine. The following are the standard sizes to be adopted ; engines of 1,000 H.P. are already running, while two of 1,500 H.P. each have also been built: — Output B.H.P. Pvovs. por minuto. 750-1,100 100-140 1,100-1,900 100-140 1,700-2,700 100-140 2,400-3,800 100-140 3,100-4,900 100-140 4,100-5,200 100-120 [To face page, 262. M aikors Marine Diesel Engine. [To face page 262. Fig. 130.— S5(1 B.H.P. Wps.-i--.Juiikci« jMoi in.' Dipscl Engiiii?. [To face page 262. M Fn;. l:!7.-siO B.H.r. W,«.i--Juiik.ra Marine Enjjiuo. [To /uic j/fijc 2li2. CONSTRrCTTON OF BTESEL MARINE ENGINE 2G3 One of the most distinct departures from standard practice in the design of Diesel engines is that of Professor Junkers, although in his arrangement he has brought some well- known applications from gas-engine construction into force. Two pistons are employed in each cylinder, moving out- ward from, and inward to, the centre of the cylinder at the same time. The bottom piston drives the crank shaft in the usual manner through a connecting rod, whilst the upper one is attached by means of a beam lever to two long side rods outside the cylinder coupled to connecting rods driving cranks on the crank shaft. Both top and bottom of the cyHnder are open and the only valves required are one or two fuel inlet valves in the centre of the cylinder, these being of course horizontal, and injecting oil between the two pistons as they reach the centre of the cylinder. With the Junkers engine scavenging can be very effectively carried out, the arrangement of ports being that those for scavenging are disposed right at the bottom of the cyUnder whilst the exhaust ports are at the top, and these can be of more liberal dimensions than usual owing to the greater available area. As the pistons reach the outer end of their stroke, air enters the scavenge ports and sweeps right through the cylinder upwards, passing out through the exhaust ports at the top. There is little doubt that this method is a very satisfactory one, and particularly so from the fact that the scavenging air is quite cold, which is not the case with most other types of scavenging gear. Usually two double-acting scavenge pumps are mounted on the end of the engine driven direct off the crank shaft, and these are provided with automatic valves. These pumps can, if de- sired, owing to exigencies of space, be arranged at right angles to the engine driven off the crossheads, as in the case of the Carels and other motors. In the usual design a fuel pump is provided for each cylin- der, and the governor controls the admission of fuel by means of the suction valve of the pump. The method of reversing is relatively simple, owing to the small number of valves, and consists in altering the angular position of the cam 264 DIESEL ENGINES FOR LAND AND MARINE WORK shaft in respect to the crank shaft. Starting is effected by compressed air, and the compressor is usually separately driven. These motors have been built in as small sizes as 100 B.H.P. and up to 1,200 B.H.P. British Types. — There are two interesting designs of marine Diesel engines which have been developed in this country, and which, although they are not likely to be pro- duced commercially on an extensive scale, offer some points of interest, especially as they show the trend of thought in Diesel engine design of those who take up the question independently. The Tanner-Diesel motor, illustrated in Fig. 138, is the one which perhaps shows most marked deviation from ordinary practice, and an experimental engine of this type was built by Messrs. Workman, Clark & Co. It is of the two-cycle, single-acting design, and in view of the desire to render it particularly suitable for large powers, certain peculiar points have been incorporated which render it of special interest. As far as possible, valves are dispensed with, and at the present stage of Diesel engine development, there seems no doubt that this will find general favour. The scavenge ports at the bottom of the cylinder do not call for any special comment, no auxiliary valve being employed, as in the Sulzer type. The ports occupy one-half of the circum- ference, the other half being utilized for the exhaust ports. Instead of having a scavenge pump driven separately or directly off the crank shaft, a turbo-blower is employed, the advantage of which is its comparatively high efficiency and the ease mth which the supply of air may be regulated. It would seem that this arrangement possesses some advan- tages in the case of large units, although for small powers it is somewhat of a detriment to add to the number of auxiliaries to which attention has to be given. The pressure of the scavenging air is about 2 J lb. per sq. in., which is rather lower than the ordinary. In this design, the aim has apparently been to render it suitable for a double-acting engine with as little alteration i [To face page 2G4. Fici. 13S.— TaimcrDicsol Moriiie Engine — Two-Cjclp SinglcAcling Typo. tro face ,,aqc £r,4. CONSTRUCTION OF DIESEL MARINE ENGINE 265 as possible, and the cover has been kept completely free of valves, except for a non-return safety valve to prevent excessive compression. Both the fuel inlet valve and the starting valve are arranged horizontally, which is quite a novel construction. The motor is of the enclosed type and has a trunk piston — a design which will, however, not prove final, especially for the larger sizes, although even in a so-called enclosed type the parts can be made readily accessible by removing the light covers in front of the crank chamber. The cylin- ders are supported by steel columns in a somewhat similar manner to the Sulzer marine engine. The pistons of the motor, contrary to usual practice, are not provided with special cooling, and in order to prevent the metal becoming overheated, shield plates are fitted, which protect the body from the greatest temperature ; but this arrangement may have to be modified. Reversing is simplified by the absence of valves, and for each fuel valve three cams are provided, one for ahead, one for astern, and the third for half injection, this latter being a novel feature. The actual operation of reversing is carried out by means of a large hand- wheel, which can be seen in Fig. 138, representing a Tanner-Diesel motor. This wheel controls a distributing valve, which passes over three ports in a three-cylinder engine, and thus admits starting air to the cylinders one after the other. The direction of rotation of the engine on starting up depends on ^^'hether the large hand- wheel is turned to the left or right, the movement causing one of two valves to open and admit air to the distributing valve as desired. In the normal position of the hand- wheel, the air supply is cut off. In order to set the fuel cams in the correct position, the cam shaft is auto- matically turned through an angle of 36°, in a similar manner to that adopted in the M.A.N, engines already described. The first experimental cylinder built to Tanner's designs was of 19 in. diameter by 30 in. stroke, and at 150 revolutions per minute developed 250-300 I.H.P. Fig. 139. — Experimental Doxfoid Diesel Engine. 266 OONSTRIT'TTOX O? DTKl^EL MARINE EXGlNE 2G7 In order to make the engine of the double-acting type, another cyUnder would be arranged above the first, with a piston rod connecting the two pistons. The Doxford Diesel engine, as built by Messrs. Doxford & Sons, resembles in some respects motors of Continental design. It is of the two-cycle single-acting type, provided with scavenge valve and an overhead cam shaft. The single-cylinder engine illustrated in Fig. 139 is of 19J in. diameter and 37 in. stroke, and develops about 250 B.H.P. at 130 revolutions per minute. Reversing is accomplished by turning the cam shaft through an angle of 38° relative to the crank shaft, and as is usual in this class of engine in which four scavenge valves are used per c^^Knder, these are operated in pairs from two cams on the cam shaft. As reversing is carried out by turning the cam shaft, two separate cams and rollers are provided side by side for operating the starting air valve, since the angle turned through to set the fuel valve cams is insufficient for the air valves. The construction of this type of motor has no\\' been abandoned. Four-Cycle Single Acting Engine : Dutch Type.— ^ As has been explained, the four-cycle engine is milikely to be the ultimate solution of the problem of the Diesel engine for marine work, but it has been adopted by some makers as being the easiest step from stationary to marine work. The marine engine constructed by the Xederlandsche Fabriek of Amsterdam is of this type, and a six-cyUnder Werkspoor motor of 500 B.H.P. was installed by this firm in the Vul- canus, which was the first large ocean-going Diesel engine propelled vessel, being 196 feet in length and having a displacement of 1,960 tons. This engine is illustrated in Fig. 140, M'liile i^igr. 141 shows a cross-section of the engine- room of the vessel. There are, as is almost universal with four-cycle marine engines, four valves for each cylinder operated in the usual way by levers actuated by cams on the horizontal cam shaft. The arrangement for reversing in this case consists of having two perfectly independent cam shafts A, B {Figs. 140 a7id 141) of which one (A) has on it 268 DIESEL ENGINES FOR LAND AND MARINE WORK the cams set in the positions for operating the various valves when going ahead, and the other (B) carries the reverse cams. These two shafts are supported in forked end pieces to which the spindle C in front of the engine is fixed. This spindle may be turned by the hand-wheel D, which by the link motion seen in Fig. 141 rotates the forked arms around the spindle C and so brings either the ahead or astern cam shaft in the position to operate the valve levers. The rotation of the cam shaft is obtained from the shaft E, which carries a small spur wheel, which gears into a spur wheel on each of the cam shafts, and thus drives both of them continual^ when the engine is running. This might be considered somewhat of a disadvantage, but the power required to drive the cam shaft which is running idle is practically negligible and entails no trouble. The shaft E is itseK driven direct off the crank shaft of the engine from eccentrics by means of the two long connecting rods which operate the shaft E by means of two small cranks, as is seen in Fig. 140. For the supply of fuel to the fuel valves two small horizontal oil pumps F are used driven off a connecting rod, but only one of them is in operation in the ordinary way. This design is contrary to the means usually adopted, since the most common method is to have a separate pump for each cylinder. The pressure of the oil pumped into the valve is regulated automatically by the arrangement G, which operates on the suction valve of the oil pump, much in the same way as the governor lever in the stationary engine, no governor being fitted to this engine. The air compressor for the injection and starting air is of the three- stage type, and is driven off the crossheads, the first stage forming a separate pump, but the second and third stage are combined. The pumps are arranged at the back of the engine, the high pressure cyHnder being seen in Fig. 141 ; water cooling is adopted between all the stages. Crossheads and connecting rods are adopted for this engine ; hence the piston rod is short, but the engine is relatively higher than ordinary motors of the four-stroke type. An auxiliary compressor is installed driven by a stationary type two- [To face page 268. Fio. 140.— .-,0n n.P. Engine tor llie Villi |7'o face page 268. CONSTRUCTION OF DIESEL MARINE ENGINE 269 cylinder Diesel engine of 50 H.P. for the supply of starting and manoeuvring air, and also the air which is used for auxiliary purposes. Two auxiliary pumps are driven direct bC a oft" the engine, these being the jacket cooling water and the bilge pumps, while a second centrifugal oil pump for unload- ing the oil in the tanks is driven off the auxiliary engine 270 DIESEL ENGINES FOR LAND AND MARINE WORK since this is only required when in port. The oil pump for pumping the oil up to the tanks is also driven off the main engine crank shaft by means of an eccentric. A small 10 H.P. oil engine coupled direct to a dynamo provides the electric power required for lighting and other purposes. Forced lubrication is adopted for the main engines, and the crank chamber is enclosed but is fitted with readily remov- able cases at front and back, these being seen in Fig. 140. It vnW be noticed that in general design this engine differs but little from the stationary type of engine manufactured by the Nederlandsche Fabriek previously described, except in the reversing arrangement, and it was the object of the designers to render the departures from marine engine prac- tice as regards steam engines as few and unimportant as possible. In their later types the Nederlandsche Fabriek have slightly modified their design in view of the experience gained with the first large engine. The six-cylinder type is adopted for all engines of 500 H.P. or above, and at present the largest power for a single engine is 1,100 B.H.P. and the limit expected is about 2,000 H.P. for a six-cylinder motor. The following table of sizes and speeds of various engines mil be useful, one only being a high speed motor of 300 r.p.m. for a small gunboat. All the engines have six cylinders. B.H.P. of Engine. Rev. per rain. Diam. of Cylindsr. Stroke of Piston. 1,100 850 600 125 125 300 Mm. 560 520 390 :\im. 1,000 920 500 As with the engine previously described, the larger motors are of the open crosshead type, and the cylinders are sup- ported solely by vertical steel cylindrical columns some two inches in diameter, the inclined cast-iron columns being CONSTRUCTION OF DIESEL MARINE ENGINE 271 mainly for the purpose of taking the thrust due to the con- necting rod. The advantage of this design Hes in the fact that the strength of the columns is known exactly, whereas cast-iron framing is always to a certain extent an unknown quantity. Moreover, the bed-plate can be made lighter since the supporting columns are closer together, and the 142.-250 H.P. Werkspuor Engine. bending moment is less. The front of the engine is then quite open, only light and easily removable covers being fitted, and the arrangement is well seen in Fig. 142, which is an illustration of the three-cvlinder 250 H.P. encrine of the same type fitted in the SemhUan, and in Figs. 143 and 144, which show a 1,100 B.H.P. motor. The arrangement of valves is as usual in a four-cycle 272 DIESEL ENGINES FOR LAND AND MARINE WORK engine, there being four in the cover of each cyHnder. The fuel inlet valve which is in the centre is of a novel construc- tion. Instead of the spring holding it on its seat being immediately above the valve, the valve lever is continued M'^ Fio. 14:!.— \\Vrlis[..».r l.lcill B.H.I'. Diesel Mot. Oudet cooh/uj water Fig. 145. — Arrangement of Piston Cooling in Werkspoor 1,100 B.H.P. Marine Motor. 273 'p Fig. 140.— Section of Werkspoor 1,100 B.H.P. Four-Cycle Marine Motor. 274 CONSTRUCTION OF DIESEL MARINE ENGINE 275 beyond the valve, so that the valve serves as a sort of ful- crum, the spring exerting its pressure at one end and acting against the force of the cam, causing the lever to be de- pressed at the other end. The object of this design is to render the removal or examination of the fuel valve more easy. In principle, the reversing arrangements are the same as those of the engine already described, but the detailed method of operation is quite different. All the gear is arranged in the centre of the engine, but the same method of driving the ahead cam shaft is employed, three long connecting rods coupled to eccentrics fitted on the crank shaft being used. There are two separate cam shafts, one carrying the ahead cams and one the astern ; these are at the same level and are a fixed distance apart, but are connected together with gear wheels, so that, although the ahead cam shaft is alone driven direct from the crank shaft, the astern cam shaft is always rotating. The bear- ings for the two cam shafts are supported on flat guide bases and can move bodily towards or away from the engine, carrying the cam shafts with them. The various pairs of bearings are cast together, so that they must move at the same time, and the relative positions of the cam shafts never vary. The bearings in the centre of the engine are fixed to an auxiliary horizontal spindle behind and just below the cam shafts, and if this spindle rotates, the bearings and cam shafts are thus moved backwards or forwards, according to the direction of rotation. This rotation is effected from the starting platform in front of the engine by means of a screw and link motion, either operated by a small air-engine or by hand, as required. It was originally intended to use a small steam engine, but this was found to be inadvisable. The reversing is carried out quite simply by means of this arrangement in about twelve seconds from full speed ahead to full speed astern. The levers are lifted clear of the cams, the cam shafts move back or forward as the case may be, the levers dropped down again, and the engine is then ready for running in the opposite direction. o ^ CONSTRUCTION OF DIESEL MARINE ENGINE 277 In other details the engine does not present many points of difference from the Vulcanus motor. The lo^^•er part of the cyhnder is bolted on to the main casting so as to be readily removable in order to examine and dismantle the pistons, and this means is certainly an advantage for marine work. The pistons are water cooled, and the exhaust pipe consists of a channel of large rectangular section, which enables a silencer to be dispensed with. It was desired to use exhaust gases for heating a donkey boiler, which provides steam for various auxiliaries, but this evidently requires some modification in the boiler. The Gusto Motor. — This is an engine of the two-cycle single-acting type hitherto built in relatively small sizes, that is to say, in powers of 350 H.P. and below. It is mainly of interest in that it is one of the few Diesel engines of the two-cycle type in which scavenging by means of ports is employed instead of the utilization of valves. In the type which is designed for powers of 200 H.P. or below, the construction is of the stepped piston type, with the scavenge pump arranged below each working cylinder as in the M. A.X. engine, but in the larger motors, the method illustrated in Fig. 149 is adopted. In this, although the scavenge pump is below each working cylinder, they are separated b}" means of a distance framing, which has the advantage that the working piston can be drawn out from below the heat cylinder with comparative ease. As no scavenge valves are recjuired, there is only the starting valve and fuel valve in each cylinder, and in this motor a special construction of cylinder is adopted in which the jacket and liner are cast in one piece, and no actual cyhnder cover is fitted. This method, although suitable for the engine under discussion, of relativeh' small type, would probably be undesirable in larger motors. Referring to the illustration, 1 represents the working cylinder in which the specially shaped top can be noticed corresponding to the shaping of the piston. This is necessary in order that the scavenge air which enters through the port 10, from the reservoir 7, formed in the framing, 278 DIESEL ENGINES FOR LAND AND MARINE WORK Fig. 148. — Custu Twu-Cycle Marine Mutor. may be deflected upwards, so as to scavenge out the whole of the contents of the cyhnder, which are exhausted through port 11. 3 represents the cyhnder of the scavenge pump, and 4 its piston, whilst 8 is a piston valve controlling the 280 DIESEL ENGINES FOR LAND AND ]VL4PvINE WORK admission of scavenge air into the reservoir 7, and thence into the cylinder. The air from the atmosphere is drawn in through tliis piston valve to the scavenge cylinder, after which it is compressed and the port then allows it to enter the reservoir 7. This piston valve 8 is driven by means of a small crank 9, operated from an auxiliary horizontal shaft which also drives the cam shaft 13, through the auxi- liary shaft 16. In order to reverse (for the motor is directly reversible) the camshaft is moved eccentrically in its bearing, bringing the cam in the correct position for astern running. The hand- wheel 15 has the function of setting the piston valve of the scavenge pump in the correct position according to the direction of rotation of the engine, whilst 23 represents the fuel pump which may be controlled by means of the lever seen close to it, thus varying the speed of the engine and shutting off fuel altogether when required. A two- stage compressor is employed driven direct from the end of the crank shaft, and the connecting rod 5 and the crank 6 are of the usual steam-engine design. The motor is of the enclosed type, as forced lubrication is adopted, but there are wide doors which are readily removable by hand. The engine has been adopted for a number of relatively small commercial vessels such as tug boats and motor coast- ing vessels, and it runs at a relatively high speed, usually between 220 and 300 r.p.m. Naturally its fuel consump- tion is not so satisfactory as that of small four-cycle motors and the construction is not suitable for high powers, but for its purpose it appears to be well adapted. German Types. — Several firms manufacture a four- cycle engine for marine work for lower powers, and almost invariably employ a high speed engine, which differs slightly from the stationary type of high speed motor which has already been described. Four or six cylinders are employed, and if six, the engines will start up on the working cylinders in any position of the crank shaft, while if there be only four cyUnders, the air pump must be arranged to be used as a fifth cylinder for starting purposes when required. CONSTRUCTION OF DIESEL MARINE ENGINE 281 At the Augsburg works of the Maschinenfabrik Augsburg- Niirnberg, four-cycle engines are constructed up to 1,000 B.H.P. usually of four cylinders with two compressors on the end of the bed-plate, driven direct off the crank shaft. An engine of 1,000 H.P., running at 465 revolutions per minute, has a weight of only about 45 lb. per B.H.P. and a fuel consumption of about "42 lb. per B.H.P. hour. With the high speed engines, it is customary to fit a safety governor to come into operation in case of emergency, as, for instance, in the event of the propeller shaft breaking, and so prevent the engine running awaj% the arrangement adopted being that the governor acts on the suction valve of the fuel pump much in the same way as with a stationary engine. In the Augsburg engine the method of reversing which has been employed differs somewhat materially from tlie means generally used. There is a single cam shaft provided with separate cams for the forward and reverse running, for each of the four valves on all the cylinders, but these cams do not actuate the valve levers direct, as is customary. Instead of this, the nose of the cam lifts a small roller, of which there is one for each cam, and the valve lever thus receives its up and down motion indirectly from the cam through the roller. Considering any single valve, there is a forward and reverse roller, both of which are attached to a drum concentric with the cam shaft and capable of being turned by means of a hand lever, and of width equal to the combined widths of the two cams. In the position of the forward running the " forward " roller is down on its cam and the " reverse " roller raised out of range of its cam and the valve lever, which thus receives its motion from the forward cam. To reverse the engine the hand lever previously mentioned is moved to the right or to the left, thus turning the drum carrying the rollers through a certain angle, -with the result that the '' forward "' roller is lifted away from its cam, whilst the " reverse " roller falls on to the reverse cam and actuates the valve lever, so as to give the valve its proper timing for reverse running. Fig. 150 shows a four- cycle engine of the Augsburg type of 850 H.P. at 400 r. p.m., 282 DIESEL ENGINES FOR LAND AND MARINE WORK ^, ^A ■ ■• H^^^B Wl 1 1 J^Bm ^^^Hjl^^^^Hpii m ■|HS|^&\\ : ^niilKi jw'^H ^^^^^^^^8Va^^BL\ < p JH iBl ■SeZcmf/w, which is a vessel of 10,000 tons. There are eight cylinders, each having a diameter of 20 1 inches and a stroke of 28| inches, the normal speed of revolution being 130-140 revo- lutions per minute. The engine is of the crosshead type and is totally enclosed with crank chamber doors, \^ hich can be readily removed for inspection. The general design does not otherwise present many marked peculiar- ities, beyond that the cylinders are divided into two sets of four, which is found to be a convenient design, and allows the reversing gear to be arranged in the centre, so as to be readily operated. A further difference from the ordinary construction is in the position of the cam shaft, which is on a level with the bottom of the cylinders instead of the top, which is usually the case. This prevents the four valves in the cover being operated directly from the cams by means of 284 CONSTRUCTION OF DIESEL MARINE ENGINE 285 short levers, and necessitates the employment of the long vertical (or nearly vertical) hollow connecting rods seen in the bD c illustration. It may be mentioned that this method has been adopted by some other manufacturers in their four-cycle engines, and notably Messrs. Krupp, who do not, however, 286 DIESEL ENGINES FOR LAND AND MARINE WORK build large engines of this type. When this design is em- ployed, it is of the utmost importance that the connecting rods should be rigid, as their motion is so slight for opening the valves that any small amount of play is most undesir- able and will lead to some trouble. Lack of attention to this point has already been the cause of much difficulty in some engines. From the illustrations it can be seen how the short horizontal valve levers are arranged for operating the valves, and it will be noticed that all the valves open downward, this being exceptional for the fuel inlet valve, which usually opens upwards. The former method somewhat simplifies the construction and apparently gives good results as regards efficiency. In the earlier pages, the general means of reversing Diesel engines were described, and the arrangement employed by Messrs. Burmeister & Wain is one which was mentioned as being common — namely, by providing side by side a separ- ate ahead and astern cam for each valve on the cam shaft, which is moved in a longitudinal direction when reversing the engine, so as to bring the rollers at the bottom of the long connecting rods above the astern cams. The distance which the cam shaft has to be moved is, therefore, equal to the width of the cams, and the motion is carried out in a novel way. As seen in the front elevation in Fig. 151, slightly to the left of the centre of the engine, there is a wide disc mounted on an auxiliary shaft, in which a slot is cut about one- third of the width of the disc. This slot slopes from the top from right to left, and another disc, nearly equal in width to that of the slot and fixed on to the cam shaft, fits into the slot. The auxiliary shaft can be turned either by hand or by means of a compressed air motor, and in turning it causes the disc on the cam shaft to move to the right or left, according to the direction of rotation, and hence the cam shaft itself is likemse moved until the reverse cams are in the required position. Before this operation is carried out, the rollers which the cams lift are raised above the cams, and are Fig. 1 9 IruAm \o~ Fia. 154.— Starting, Inlpt, niul Fiul \'n !.000 I.H.P. Burmclst^r A- Wain Jlarino Diesel Engir [To lace pngc 2Sli. CONSTRUCTION OF DIESEL MARINE ENGINE 287 brouglit down again when the cam shaft has been moved. The lifting of the rollers is accomplished through the medium of the same auxiliary shaft, which, in the first period of its rotation, actuates eccentrics fixed to it. These are connected by short connecting rois and levers to the bottom of thelong, vertical rods, which transmit the motion of the rollers to the horizontal valve rods. Only the high pressure stage of the compressor for the provision of injection air is mounted on the engine, this compressing the air from about 300 lb. per square inch up to 800—900 lb. The low pressure compressor is direct driven from an auxiliary stationary type Diesel engine, which has also coupled to it a dynamo for the provision of electric power for lighting and auxiliaries. This low pres- sure compressor supplies air at about 300 lb. per square inch to the high pressure stage on the engine, and also provides the air for manoeuvring purposes. In a twin-screw vessel, as the Selandia, two auxiliary sets are provided, one for each engine, and there is also usually a further 'steam-driven compressor working up to 800-900 lb. per square inch. The exhaust from all the cylinders of the engine delivers into a common D shaped pipe and thence to a silencer, whilst the atmospheric air is drawn into the cylinders through horizontal inlet slotted pipes, as seen in the illustra- tion, this being a slight modification from usual practice where vertical inlet pipes are employed. This is the general design adopted for motors up to about 1,500 I.H.P., but in some recent engines of 2,000 I.H.P. many modifications have been carried out. Engines of this power are made with six cylinders, having a bore of 740 mm. (29 inches) and a stroke of 1,100 mm. (43-4 inches), and run at a normal speed of 100 r.p.m. The main point of difference lies in the method of supporting the cyUnders, for in the larger engines instead of having a continuous framing, made of four pieces and bolted together, there is an A frame of very heavy construction over each bearing, and the cylinder jackets of the six cylinders are cast in pairs of three each with feet which are bolted direct Sale of Metns Fig. 155. — Section of Six-Cylinder Burmeistar & Wain 2,000 I.H.P. Marine Engine. 288 CONSTRUCTION OF DIESEL AIARINE ENGINE 289 to the top of the A framing. In the front of the engine, Hght doors are fitted between the standards ^^•hich are oil- tight (since forced lubrication is adopted as with the other motors), but are readily removable so that the engine, when they are taken away, is practically of the open type. Between the upper portions of the standards, however, stiffening pieces are bolted to which the crossheads guides are fixed, and, moreover, there are steel columns running right through from the bottom of the bed-plate to the cylinder covers through the cyUnder jackets, which serve to support the cylinder head. On theto23 of the A standard a light cover is fitted to the cylinder through which the piston rod passes by means of a suitable gland. There is a tray fixed in this cover so that any lubricating oil dropping from the piston does not mix with the oil circulating in the crank-chamber, but can be carried away and filtered and used over again. With this design of cylinder and framing a more accessible construction of cylinder is obtained. Instead of having only the high pressure stage of the air compressor driven direct from the engine as in the motors previously described, in the larger type all three stages are directly driven. An auxiliary compressor is of course provided in a ship if equipped with this arrangement. Starting is accomplished, however, in the same way at a lower pressure than that ordinarily adopted, 360 lb. per sq. inch being the usual pressure employed. Instead of having a single fuel pump for all the cylinders there is a separate one for each cylinder in the larger motor, and this is natur- ally an improvement in design, especially from the point of view of safeguarding against breakdo^viis, or a consider- able loss of power. A new type of bed-plate is also employed very similar to the bed-plate of a marine steam engine, and is open at the bottom instead of enclosed as with the smaller engines. To it, however, throughout the whole of its length is bolted a tray in order to collect the oil. In the smaller engines oil is used for cooling the piston, this being recooled itself by a circulation of sea water around the oil cooler ; but in u 290 DIESEL ENGINES FOR LAND AND MARINE WORK the larger motors, owing to excessive amount of oil which is required and the difficulty of cooling such a large quantity, sea water alone is employed, being pumped directly into the piston which it reaches by means of a telescopic pipe. The methods of operating the valves and the reversing Fig. 156. — 2,000 I.H.P. Burmeister & Wain Marine Diesel Engine, show- ing intermediate shaft and push rods for operating the Valves. system are practically unaltered, the cam shaft as before being low down so that long tappet rods are necessary. There are also two sets of cams for every valve, one for ahead and one for astern, and the cam shaft is moved length- ways to the engine so as to bring the correct cams under- neath the tappet rods. The cam shaft, however, is not CONSTRUCTION OF DIESEL MARINE ENGINE 291 driven by connecting rods, but by means of two spur wheels which seems to be a more accurate and reHable method. This motor is of special interest owing to its dimensions, which are very large for a four-cycle engine, and also for the lo.v speed, namely 100 r.p.m., which is naturally very desirable in order to obtain an efficient propeller. No difficulties appear to have been encountered in the operation of these engines, and it is possible that even larger sizes may be built, although probably the limit in economy of construction has almost been reached with motors of this power. Russian Types. — Owing to the abundance of oil in Russia some considerable progress has been made in the employment of Diesel engines for all purposes. For several years boats have been running in Russian waters equipped with Diesel engines. However, in most cases, ordinary stationary motors have been supplied and some type of reversing mechanism employed, either mechanical or elec- trical. Two firms are now engaged in the construction of the engine, Messrs. Nobel Bros, and the Kolomna Co. In both cases the greatest attention has been paid to the four-cycle engine, although the two-cycle motor is now being developed. Up to the present, the engines built by Nobels have mostly been of the high speed tj^pe, varying from 400 B.H.P. and 250 revolutions per minute to 120 B.H.P. and 450 revolutions per minute, although there is a type of 400 or 500 B.H.P. and 310 revolutions per minute. The motor is of the enclosed type, the chambers being mounted on a crank chamber, and, unlike some other designs of four-cycle engines, the cam shaft is overhead. Engines up to 1,000 H.P. are built of the four-cycle tjrpe. The method of reversing adopted for this engine is some- what different from that employed in all other 4-cycle motors. There are two cams for each valve as usual, but instead of sliding the cam shaft along in order to bring the cams under the valve lever roller, this lever is provided with two rollers. When the hand- wheel is turned to bring about the reversing 294 DIESEL ENGINES FOR LAND AND MARINE WORK of the motor, the roller of the valve lever immediately above the astern cam is brought down on to this cam, whilst the ahead cam is kept well out of range. In some motors, however, built by Nobels, the ordinary methods of reversing is adopted by moving the cam shaft longitudinally. This method is mostly employed for the smaller engines, as in the larger sizes the shifting of the cam shaft by hand becomes too difficult a matter. The engines built by the Kolomna Company are also of the four-cycle type, and have been constructed up to 1,000 H.P., the engines illustrated in Figs. 157 and 158 being respectively of 250 and 600 B.H.P. These engines are of relatively high speed, and in some ways resemble the Nobel con- struction. The method of reversing is a novel one. Above the cam shaft are two separate spindles on which are pivoted the vari- ous levers for operating the valves. When it is desired to reverse the motor, the levers seen in the illustration at the front of the engine are turned to an angle of 45°, which operation rises the fuel- valve lever of the cam and puts the fuel pumps out of operation, so that no fuel can be admitted to the cylinders. The same action admits air into two small air cylinders seen above each of the working cylinders, these being fitted just over the air inlet and exhaust valves in each cylinder. These cylinders act as air motors, in which the piston, being forced do^A^lwards by the admission of air, causes the valve levers of the exhaust valve and fuel inlet valve to be raised off their cams. This having been done, the cam shaft is then able to move longitudinally, and the reverse cams are brought underneath the various valve rod levers. The rollers of the levers are then once more brought down on to their cam and the engine is in a position for reverse running. The motor is started up by compressed air, before the fuel valve lever is dropped down on to its cam and fuel admitted into the cylinders. In the larger engines all these operations are carried out by compressed air in the usual way, but in the smaller type it is thought better to effect the various movements by hand. CONSTRUrTTON OF DIESEL MARINE ENGINE 295 Small Diesel Marine Engines. — At the present time it may be said that the minimum limit for Diesel engines from a commercial point of view for land work is about 50 B.H.P., below which power it is generally found advisable to employ a motor of lower first cost even though the fuel consumption is higher. There are one or two exceptions to this such as small horizontal motors which are made 29G DIESEL ENGINES FOR LAND AND MARINE WORK in such large numbers as to reduce the cost of construction and put the engines on a par from the point of view of cost with other types such as the hot bulb engine. For marine work it has generally been thought that the Diesel engine is hardly particularly applicable below powers of about 200 H.P., mainly again owing to the first cost, and also because of the greater simplicity of other types. There are, however, many engines of 100 H.P. and upwards designed to be specially suitable for installation in craft requiring about this power for their propulsion. These need not be discussed at length as they have none of them received wide application and have in fact only been adopted in special instances where they have particular advantages. It must, however, be remembered that this type of motor will probably make much more headway in the future, particularly if it be designed as simply as possible so that it may be operated by unskilled men, and may be con- sidered equally reliable with other engines which are com- monly installed in moderate size motor craft. These small Diesel motors have been built both of the four and two-cycle type, and in spite of the higher fuel consumption it is probable that the latter design will find most favour owing to the greater simplicity which is per- haps the essential point in the construction of an engine working on this principle. One of the four-cycle engines which has been manufac- tured on a fairly large scale is the Daimler type, which is constructed largely of bronze in order to reduce the weight, for heaviness is usually one of the disadvantages of the small Diesel engine. The four-cylinder set shown in Fig. 159 has a cylinder diameter of 200 mm., a stroke 230 mm., and when running at 530 r.p.m. develops about 100 B.H.P. It is made directly reversible, and weighs only about 45 cwt. complete, which appears to be about the limit in lightness for a Diesel motor of the four-cycle type of this power. There is nothing peculiar in the design apart from the fact that the cylinder covers are cast in pairs, and that there is an extra valve to each cover for reversing, 298 DIESEL ENGINES FOR LAND AND MARINE WORK which of course is carried out by means of compressed air. Reversing is accomplished by shding the cam shaft longitudi- nally in the usual manner, this shaft being provided with two cams for each valve, one of which operates the valve lever when going ahead and the other w^hen running astern. In Fig. 160 is illustrated another four-cycle motor also of 100 B.H.P. in six cylinders, this being of the Krupp design. It has a speed of revolution of SCO r.p.m., but is not quite so light a construction as the motor previously described. 300 DIESEL ENGINES FOR LAND AND MARINE WORK It is not, however, directly reversible, and its only peculiar feature lies in the method of operating the valves, the cam shaft being low down and the valve rockers actuated through the intermediary of long vertical push rods. Among the small two-cycle engines constructed is one of the Junkers design illustrated in Fig. 161. This is a two- cylinder motor of 100 B.H.P. running at about 300 r.p.m_., the third vertical cylinder being the scavenge pump. The principle of operation of. this motor is the same as that described earlier in connexion with the Junkers large engine, there being two opposed pistons in each cylinder with the fuel inlet valve horizontal in the middle of the cylinder. This engine is said to give the particularly low fuel consumption of about 0-41 lb. per B.H.P. hour. Fig. 162 shows a four-cylinder two-cycle motor which has recently been developed in America by the Gas Engine & Power Co. In this case the motor is of somewhat slightly larger size than those previously described ; the dimensions of the cylinders are 9 inches bore by 12 inches stroke, the speed of rotation being 2£0 to 300 r.p.m., whilst the power is about 150 to 175 B.H.P. The motor is directly reversible, and reversing is provided for by having two cams for each valve, one for ahead and one for astern as in the previous cases. It will be noticed also with this engine that long push rods are employed with a low cam shaft. In each cylinder cover are two scavenge valves besides the usual starting valve, fuel valve and relief valve. There is a single scavenge pump driven direct off the end of the crank shaft, and the two-stage air compressor is driven by means of a lever from the crosshead of this scavenge pump. Another two-cycle reversible motor which has been employed to a certain extent in fishing vessels and small commercial craft is the Kind engine, a six-cylinder design being shown in Fig. 163. This motor is one of 150 B.H.P. running at about 300 to 350 r.p.m. It is arranged with the scavenge pumps directly below the working piston, the usual stepped piston being adopted as with other high- CONSTRUCTION OF DIESEL MARINE ENGINE 301 speed engines such as the M.A.N, and the F.I.A.T. submarine motors. There is a single scavenging valve in the cyhnder cover besides the fuel valve and starting valve, no relief valves being provided with this engine. CHAPTER VIII THE DESIGN OF DIESEL ENGINES CYLINDERS AND CYLINDER COVERS PISTONS ^CYLINDER DIMENSIONS — CRANK SHAFTS AIR COMPRESSORS SCAVENGING PUMPS It is quite impossible to develop the design of Diesel engines along such lines as would apply generall}^, owing to the fact that the many different types vary considerably in important matters of construction, and not only in detail. In the first place, of course, four-cycle and two-cycle engines must be treated separately, and in each essential type we have differing methods of driving the air compressors, different arrangements for the scavenge pump, and other variations, so that the efficiencies in the several types are by no means the same. These facts must be borne in mind when using the formulae and rules given later for calculation, and allowance made for the peculiarities presented by any special type of engine. Cylinders and Cylinder Covers. — The cylinder covers and liners of a Diesel engine form perhaps the most vulner- able portions of the motor. They are now practically invariably constructed of close grained cast iron, although in several marine engines of the two-cycle type cast steel was employed for the covers, but this in practice was found to be unsuitable and to give rise to cracks. It has therefore been almost entirely discarded, and will probably not be employed in the future, although there is a possibility that it may be utilized for very large motors in which a totally different design from the ordinary is adopted. In motors for submarines, steel has also been brought into use. It might be thought that the first essential reason for cylinders designed for great strength in Diesel engines would THE DESIGN OF DIESEL ENGINES 303 be owing to the high pressure of compression and combus- tion in the cyhnder itself. Probably, however, the most important point is the rapid fluctuation of heat through the cylinder liner, and the consequent stresses which are set up in it. These stresses naturally increase as the dia- meter of the cylinder increases, and it is easy to see that owing to the great heat on the inside of the Hner, expansion takes place, whilst the outside is cooled by the cooling water, so that excessive stress may result. When it is considered that in a two-cycle engine with a cylinder of say 30 inches in diameter, the thickness of the liner has to be about 3 to 3| inches, it is not difficult to understand that trouble may result, and this is indeed one of the points which increase the difficulty of the design of very large Diesel engines. Apart, however, from the ques- tion of the regularly alternating stresses, owing to the high temperature to which the material of the cylinders is con- tinuously exposed, there is a possibility of what is commonly called " growth " of the cast iron which is of course a well- known factor in other directions, particularly in regard to steam turbine. In a two-cycle engine, the fluctuation of heat is twice as rapid as in a four-cycle motor, and indeed in the latter type comparatively little trouble has been experienced in the matter of cracked cyhnder liners or cracked covers, which, however, is not the case with two-cycle engines. The following remarks therefore apply more particularly to the two-stroke type of Diesel engine. No matter what the design may be, it is impossible to avoid very severe stresses in covers and liners of two-cycle motors, and the designer has therefore only to aim at dimin- ishing these stresses so far as possible, by a careful examina- tion of the causes which give rise to them. Even from the very earliest experiments which Dr. Diesel made on his first engines it was apparent that the shape of the combustion chamber had an important effect upon the reliability of the Diesel motor. Later experience has more clearly shown that it is essential for the combustion chamber, so far as THE DESIGN OF DIESEL ENGINES 305 possible, to be enclosed by plane surfaces and that all pockets and projections should be avoided. Moreover, the ratio between the cooling surface enclosing the combustion chamber to the total volume of the chamber should be as large as possible in order to maintain good cooling effect. This point has been overlooked in some designs which other- wise showed great possibilities. The stresses caused in the cylinder cover are greatest nearest the point where combustion is at its maximum, and therefore it is desirable to arrange the necessary valves in the cover as remote from this point of maximum combus- tion as is possible and practicable ; for the points where the casting is weakest are naturally those where it has been pierced in order to accommodate the various valves. It is obviously desirable, therefore, to space these valves as far apart as possible, and above all to limit their number to the absolute minimum. This naturally points to the great superiority of an engine in which a number of the usual valves are dispensed with, and in this category may be placed the tw^o-cycle motor in which scavenge ports are employed instead of scavenge valves. Experience has already shown that W'here such a design is adopted the danger of the cracking of the cylinder cover and cylinder liner is not so marked as with the valve scavenging engine. This question is further discussed later. Apart from the stresses which are produced both by the pressure in the working cylinder, and also the stresses due to the heating, there are those arising in the ordinary way during the casting, but by modern methods these can be kept within a reasonable margin. It is not possible to calculate theoretically the thickness of a cylinder liner which is necessary in a Diesel engine owing to the fact that the chief stress (which as men- tioned above is that due to heat and not to pressure) cannot be precisely determined. If the liner is made too thick the stresses due to heat which increase with the thickness of the liner beyond a certain point, may be so augmented as actually to counter-balance the diminution of stress X 306 DIESEL ENGINES FOR LAND AND MARINE WORK due to pressure, so that the resultant stress is greater by an increase of thickness. This does not apply to rela- tively small engines, but it is not difficult to see that it might be the case in regard to very large motors. In fact it would seem that when we come to engines which have to develop say 1,500 H.P. per cylinder or more it might be desirable to adopt a totally different design of cylinder liner, and to have an inner liner which is relatively thin (say one inch in thickness) so as to allow the rapid transference of the heat from the interior to the exterior of these walls. Outside of the first liner another barrel with web could be shrunk on, and take the stresses due to the pressure. An arrangement of this sort was proposed to the author by Mr. Thunholm and seems to offer great possibilities, although there are various methods by which the same principle could be carried out. Pistons .^ — Owing to the high compression in a Diesel engine cylinder and the obvious necessity for the absolute prevention of any leakage with the consequent loss of com- pression, the piston rings have to be made with special care. There are usually five to seven of these, generally of cast iron, and perhaps the best construction is that com- monly adopted for all rings which have to preserve tightness against a heavy pressure. With the old method of ham- mering it is difficult to prevent some eccentricity in the ring, which naturally may cause unequal wear on the cylinder walls. In the design referred to, the ring after being cut (having then no spring) is fixed in a die which is slowly rotated, and is struck on the inner side by a light chisel- pointed hammer. The strength of the blow is varied auto- matically, being maximum at the side of the ring remote from the cut and minimum near the cut. The width of the face of the hammer is slightly less than the depth of the ring. After the process, the ring is found to have sufficient elasticity for the purpose, is perfectly round and certainly gives excellent results in operation. The piston is a detail of the Diesel engine which requires special attention in its design and construction mainly THE DESIGN OF DIESEL ENGINES 307 omng to the high temperatures in the cyhnder and also because of the excessive pressures involved. It is usually 308 DIESEL ENGINES FOR LAND AND MARINE WORK made to taper slightly from the top, and is of course always of cast iron. A good clearance is allowed around the portion where the gudgeon pin enters, and where there is necessarily an extra thickness of metal, in order that the greater expansion may not cause it to bend on the cylinder walls. The gudgeon pin is made a tight fit, is keyed and often locked by means of a set screw, the pin having a hole through the centre to allow the passage of lubricating oil from the cylinder walls. It is desirable that the gudgeon pin be placed as low as possible so as to be away from the zone of greatest heat. The lubrication of the piston is carried out by admitting oil from sight feed lubricators or other means through two or more connexions passing right through the cylinder jacket. For small cylinders (up to about 15 inches in diameter) two are satisfactory, but above this size there should be four and for large cylinders six or even eight. For marine engines it is very desirable that each pair should be supplied by separate plunger pumps so that any failure should not cut off all the lubricating oil to a cylinder. As a general rule it may be taken that the thickness of the liner for a Diesel engine of the four-cycle type varies between 0-085 and O-IO of the cylinder diameter, whilst in a two-stroke engine it is between 0-10 and 0-125 of the diameter. The exact ratio depends to a large extent upon the experience which each particular firm has had in the construction of such parts and the maximum intensity of stress which in consequence they feel justified in allowing. Up to the present in the very large two-cycle engines which have been employed for sea-going work, the cylinder liners have been generally rather thicker than necessary, and the highest figure given, namely 0-125, has been frequently adopted. In four-cycle engines the thickness increases as a rule with the diameter (that is to say the ratio of liner thickness to the cylinder diameter), but the variation is not very marked, largely owing to the experience which has been gained with four-cycle motors in the past. It has been found that in order to diminish the stresses THE DESIGN OF DIESEL ENGINES 309 resulting from the transference of lieat, an extremely desirable feature in an engine is that this heat shall be rapidly conducted to other remote parts of the machine. From this point of view the cylinder cover as ordinarily designed is of course very badly placed, and one of the advantages of a design adopted by Messrs. Krupp for large two-cycle marine engines and the Werkspoor firm for four-cycle engines in which the cover is in one piece with a liner, lies in this fact. It has obvious corresponding dis- advantages, since the whole cover and liner must be replaced if one part is cracked, and the question of the relative value of the methods is no doubt largely one of personal preference. Needless to say the penetration of the liner in order to accommodate valves is quite as detrimental as carrpng out the same purpose by utiUzing valves in the cyhnder cover, and this is one of the unsatisfactory features of engines which, like the Junkers type, have fuel and other valves entering into the liner. It is also an argument against the horizontal fuel injection valve which has been adopted in one or two designs. Cylinder Dimensions. — A good deal of latitude is allowed the designer in calculating the cyhnder dimensions for a Diesel engine. Taking the ordinary four-cycle Diesel engine, the following formula applies for the calculation of the indicated horse-power : — — T>- X X'^ X p X 71 4 12 1 H.P. ^- — 33000 in which D = diameter of cylinder in inches L = length of stroke in inches N = r.p.m. p = mean effective pressure (lbs. per sq. inch). n = no. of cylinders. For two-cycle single acting engines. TT L — ^x— xNx:»xw 1 H.P. =i 12 X 2 33000 310 DIESEL ENGINES FOR LAND AND MARINE WORK The variables upon which the output of the motor depends are therefore the diameter of the cyhnder, the length of the stroke, the speed of revolution, the mean effective pres- sure and the number of cylinders. Of these, the number of cylinders and the speed of revolution are usually determined beforehand from the various considerations, and the mean effective pressure which it is desirable to employ in a Diesel engine is now a fairly definite quantity for the various types of motor. The following table gives the values commonly adopted : — Table showixg Mean Effective Pressure in Diesel Engines. Type of Engine. Lb. per sq. inch. Four-cycle slow speed high „ Two-cjxle slow ,, liigh „ 95-105 90-100 85-100 70-85 In marine engines some firms have a smaller figure for continuous oj)eration. For instance, in four-cycle motors of the Burmeister and Wain type the mean effective pressure allowed is about 90 lb. for marine work and 103-105 for land motors. The maximum allowable for this type of engine is about 120 lb. per sq. inch. In the Werkspoor four-cycle engine the usual mean effective pressure is 95 lb. per sq. inch. It is probable, as more experience is gained with the two- cycle motor, that a slightly higher mean effective pressure will be allowed for in the design, possibly by increasing the pressure of the scavenging air and augmenting the C[uantity of fuel injected. Naturally an increase in mean effective pressure brings with it an increase in the heat generated and so adds to the difficulties in connexion with the stresses in the cylinder covers and cylinder hners. Even in recent designs, pressures as high as 120 lb. per scj^. inch have been obtained with two-cycle engines, but it camiot be said that THE DESIGN OF DIESEL ENGINES 311 the result is satisfactory on the whole, particularly for marine work. Having fixed upon the speed of revolution of the engine, the length of stroke is naturally dependent upon the piston speed which it is permissible to employ in the engine. Although engines are sometimes constructed in which the piston speeds are not within the limits given in the table below, it may be taken as generally representative of the best practice, and any variations would only be made if necessitated by special conditions. It will be noticed that while in the ordinary four-cycle land engine the speed usually adopted is 750 to 800 feet per minute, it may rise to as much as 1 ,000 feet per minute in the high-speed engine, the highest figure being that adopted in the very high-speed motors employed for submarine propulsion. Table of Piston Speeds in Diesel Engines. Piston Speed, Type of Engine. Land or Marine. Ft. per Min. Metres per Sec. Foiir-cj'cle slow si^eed . Land . high ,, . „ . . . „ slow ,, . Marine . Wgh „ . „ . . Two-cycle slow ,, . Land or Marine liigh „ . 750 to 800 800 to 900 650 to 800 850 to 1,000 700 to 800 850 to 1,000 3-75 to 4 4 to 4-5 3-25 to 4 4-25 to 5 3-5 to 4 4-25 to 5 It is probable that in larger four-cj'cle engines than have hitherto been built, say 350 B.H.P. per cyhnder and upwards, higher piston speeds would be permissible, but 900-950 ft. per minute may be taken as an absolute maximum limit according to present ideas. For any desired indicated horse-power all the variables can thus be determined from the tables, except the diameter, which can then be calculated. The length of the stroke is, 312 DIESEL ENGINES FOR LAND AND MARINE WORK of course, calculated from the piston speed from the equa- tion — T _ 6 S ^~ N in which S equals the piston speed in feet per minute. Usually, however, it is a definite brake horse-power which is aimed for and not indicated horse-power, which involves the question of the mechanical efficiency of the motor. In other words, B.H.P. = e X I.H.P. in which e equals the mechanical efficiency of the engine. The following table gives the efficiency usually obtained with Diesel engines of ordinary construction of the various types named : — Mechanical Efficiencies of Diesel Engines. Type of Engine. Efficiency = e. Four-cycle slow speed high Two-cycle slow ,, high 75-79 69-72 69-73 65-70 The question of efficiency, however, is apt to be very delusive, and whilst with a given type of motor constructed on usual lines the mechanical efficiency may not vary as much as | per cent., in some cases differences of as high as 10 per cent, may be noticed in different four-cycle slow-speed engines. This is due mainly to the manner in which the accessories are driven. The figures given apply to what may be termed the ordinary design of Diesel engine in which the air com- pressor for injecting air and, in the case of the two-cycle engine, the scavenge pump are driven directly off the engine. If, however, the air compressor is separately driven, as, for instance, in the case of some Krupp marine motors THE DESIGN OF DIESEL ENGINES 313 of the two-cycle type, the efficiency may rise to about 0-78 as against the usual 0-70. Again, in the smaller of the Burmeister and Wain four-cj'cle marine engine only the high-pressure stage is driven directly off the motor, the low and intermediate pressure stages being operated from another engine and the efficiency of the motor is as much as 0-84 to 0-85. Various other questions may compUcate the issue, such, for instance, as the method of dri^^ng auxiliary pumps for cooling and lubricating oil, as well (in the case of marine engines) as the operation of accessory pumps such as bilge pumps, etc. When there are any marked variations in efficiency, therefore, these matters should be kept well to the front, otherwise a totally erroneous idea of the actual efficiency of a certain motor may be gained. Taking all the factors into consideration, and assuming an average mean pressure and a mechanical efficiency as given above, the output of a Diesel motor of the two-cj^le single-acting slow-speed tj'pe may be expressed approxi- mately as B.H.P. = 000014 D- L N n As a matter of fact, this may be taken as a very fair figure for the engines as at present constructed of speeds say between SO and 150 r.p.m., and for powers of cOO H.P. upwards. The actual figure may vary between such Umits as B.H.P. = 0000125 D- L N ?i and B.H.P. = 0000155 D2 L N n In four-cycle motors the horse-power is, generally speaking, represented by B.H.P. = 00008 D- L N n though, here again, a substantial deviation is possible. In order to see that the design conforms to ordinary practice various checks may be made upon the dimensions 314 DIESEL ENGINES FOR LAND AND MARINE WORK obtained in the manner given above. The ratio of stroke to bore in various types of Diesel engines is fairly definite, although there are marked deviations among different firms according to their peculiarities in design. In fact, the actual ratio varies from unity to just over 2, as will be seen from the tabulated list of dimensions of various engines given later. The last-mentioned figure is, however, an exception, whilst the ratio of unity is that which is adopted on very high-speed engines, such as those of the submarine type, for obvious reasons, since it is necessary to keep down the piston speed to a reasonable amount. For four-cycle slow-speed engines of the ordinary sta- tionary type, where practice has become much more stan- dardized than with other motors, the usual ratio of stroke to bore which is adopted is 1-4 to 1-5, whilst in the case of very high-speed motors, say those running at 350 r.p.m. and above, the ratio hardly varies from between unity to 1-1, according to the speed and power of the motor. For two-cycle slow-speed engines, particularly those of the marine type, 1-4 to 1-5 is quite a common figure, although many engines have the ratio 1-8 to 1-9 and even above. Although there is no absolute line of demarcation Diesel engines are generally divided into two classes, known as the high-speed and slow-speed type. The average figures are given in the following table : — Speeds of Rotation of Diesel Engines. Type of Engine. Land or Marine. Revs, per Minute. Four-cycle slow sjieed . Land 140-190 high ,, ... 200-400 , , slow Marine . 100-160 high 11 ... 300-500 Two-cycle slow Land or Marine 90-150 liigb " 300-450 THE DESIGN OF DIESEL ENGINES 315 The volume swept throiigli by the piston of a Diesel engine per B.H.P. per minute is a fairly constant quantity for a particular type of engine, and this fact may be used as a check upon the values which are obtained for the stroke and bore of a motor, by the rules and formulae given previously. The table below gives a fair idea of the various volumes for the different type of engines, al- though the figures are naturally dependent upon several varying factors, and above all upon the mean effective pressure which is employed in the motor. It may be taken that the ordinary engine will come within the limits given in the table unless there are some exceptional conditions imposed. Piston Volume swept through per B.H.P. in Various Engines. Type of Engine. Piston Volume swept through per B.H.P. Cubic Metres per Min. Cubic ft. per Min. Foiir-cycle slow speed high ,. . . Two-cycle slow ,, . . high „ . . 0-34 to 0-38 0-30 to 0-38 0-17 to 0-20 0-18 to 0-22 120 to 134 106 to 134 60 to 70 03 to 77 As was stated earlier in the volume (see page 23) the clearance space in an ordinary Diesel motor of the four- cycle slow-speed type is so designed that the volume is approximately one-fifteenth of the volume swept through by the piston. This may of course be varied, depending on the maximum pressure of compression which takes place within the cylinder, and moreover the fact must be remem- bered that in general the piston is dished, so that there is less than one-fifteenth of the length of the stroke between the top of the piston and the bottom of the cylinder cover at the sides. The clearance volume may be calculated by following out the law of the compression of the air durmg 316 DIESEL ENGINES FOR LAND AND MARINE WORK the compression of the stroke. From the ordinary formulae, the following equation as usual holds good : — Referring to Fig. 6, page 21, it will be seen that Va = clearance volume Vi = clearance volume + V^ where V^ = volume swept through by piston Pi = Pressure before compression Pa = Pressure after compression In another form P3 y- =p, (V. + V,) « /Va + Va« p. or log ^' =71 log (1 + „'^) Pi ^ V V In general n = 1-25 to 1-3 say 1-25 P /500\ Taking the ratio — ^ = 31 as an example ( y^J we have 1-25 log M + ^j = log 31 or log (1 + — ^j - yj 1-25 = M933 = log 16 V Or -lii = 15 THE DESIGN OF DIESEL ENGINES 317 10 00-too oooooooc-.r35ao" "•• "^ icm-mo'-o >o«« -t<-tcO'^-iio-ra 10 'o O! c -f c ic "f: ic "C ■>) C5 c 03 s 00 >o — 10 — >c — — ' eo 05 ;r t^ CI 00 — 00 r^ — 01 c-i -c -^ 00 — 1 00 -x 'M w "M T)< — 1 00 — — ' -t 1- >~ 00 M J3CC C eiioin -f >ot^„in >^ t^ioio 0010 io>n Stroke. OCCOOOC-IOOCOCOOCOOOOCCCCOCOCOOOO cc tc t^ -f -* m -+ (^ 00 — © 35 CO fc cc -+ q_ — _^ c: -^ 00 -M^^ 'O 00 -f "O cc -M CO c<5 --o Boro mm. ' 3lliiiSliiiiiiiilsii?liiSISiSii5 f4 - PM oooooiooooocooooo^coccoooooooooooo ^^^^ -f r^ r^ -Tim' « a. IV 1 . . .1 . . J . . . .1 . . .1 . . : : . . . .1 : = . . 1 : : :;.St — rj r :; 1 :.£."= :: :; r^ :. ^ ^ :. i i : :;-^'^' r : — c '^ s. ^ — •- ■§sg J 1 ^1 2 a . . . n li '^5 . - g-:?; . s . - ^ - s-*^ -^ j- ■'^ » r S- ^ * ^ i ^ .5 S-^ 318 DIESEL ENGINES FOR LAND AND MARINE WORK Crank Shafts. — Making allowances for the special char- acteristics of the engine, the diameter of the crank shaft for a Diesel motor can be calculated ab initio from the known rules which are applied in steam engine practice. The calculations are based on the equivalent twisting moment, deduced from the combination of the twisting and bending moment of the crank shaft, considering the shaft as a beam supported from two fixed points, namely the centres of two adjacent bearings. As, however, the maximum pressure exerted on the pistons in Diesel engines is fairly constant, and as the dis- tance between the bearings generally has a definite relation to the diameter and stroke of the cylinder, it is possible to obtain a simple and accurate formula for a crank shaft diameter in terms of the diameter and stroke of the cylinder. In the formula given below the assumption has been made that the distance between the centre of two adjacent bear- ings is approximately 1-3 times the stroke of the engine, and about twice the diameter of the cylinder. Even, how- ever, when this is not correct the formula holds true within a very close margin. If D = diameter of cylinder in inches L = stroke of piston ,, ,, d = diameter of crank shaft ,, then d = K^B^i, where K = a constant. The value of K is given in the following table for various types of engines. Table of Constants for Determination of Crank Shaft Diameter. Number of Cylinders. Four-cycle Engine. 6 or under Two-cycle Single Acting. 3 4 () 8 Two-cycle Double Acting. Constant K. •525 •53 •539 •555 THE DESIGN OF DIESEL ENGINES 319 The diameter of the crank shaft in a Diesel engine varies from 0-55 to 0-65 of the cylinder diameter, the former figure being common in ordinary four-cycle land engines of the slow-speed type, increasing to about 0-58 for high-speed four-cycle engines, to 0-6 for four-cycle marine engines and 0-62 up to 0-65 for two-cycle marine engines in which, how- ever, the margin of safety appears to be somewhat large. For marine engines, although no regulations have yet been issued by Lloyd's, the Germanischer Lloyd have published the following rules for the calculation of crank shafts. The result, however, gives practically the same figure in every case as that when applying the formulae given above. The rule is that the diameter of the shaft shall be cal- culated from the following formula : — d = n/D^IT in which d = the diameter of the crank shaft in centimetres. D = cylinder diameter in centimetres. A = a constant determined from the following table. H = stroke of piston in centimetres. L = distance between the centres of two adjacent bear- ings in centimetres. No. of Cvliiiders. A. 1, 2, and 3 0-09H + 0-035L 4 0-lOH + 0-035L 5 0-llH + 0-035L 6 013H + 0035L The above table applies only to two-cycle single-acting engines. For four-cycle engines the number of cylinders in the engine should be divided by two when arriving at the constants given above. For two-cycle double-acting engines the number of cylin- ders in the engine should be multiplied by two in order to arrive at the constants. 320 DIESEL ENGINES FOR LAND AND MARINE WORK In determining the diameter of the crank shaft by the above-mentioned rules the maximum stress which is allowed is about 7,500 lb. per sq. inch. The crank pin is almost invariably made of the same diameter as that of the crank shaft. The length of the crank pin is kept as low as possible, being generally about 1 -3 times the diameter of the crank pin and often below this figure. The length of the journal is also kept within reason- able limits, and the bearing pressure on the crosshead pin and the crank pin bearing is not allowed to exceed 2,000 lb. per sq. inch, although this figure is quite a common one in modern Diesel engine practice. In those engines in which the compression pressure in the cylinder is kept down to a figure below that ordinarily adopted, for instance in the case of Werkspoor motor, a correspondingly diminishing pressure on the crank pin is allowed for, and its diameter is made about 5 per cent, less than that actually calculated from the formula given above. The practice, however, is hardly one to be gener- ally recommended in view of the uncertainty as to the exact pressures which come on the crank shaft. The rules given above for the calculation of the diameter of the crank shafts are those for ordinary Diesel engines in which the air compressor for injection and starting air is driven diiectly off the engine. If this compressor, how- ever, is separately driven, as is sometimes the case with large marine installations, a very slight allowance, say about 5 percent., of the diameter may be deducted from the figures obtained from same by the rules given. Having obtained the diameter of the crank shaft, the cranks may be designed from the ordinary known rule which applies equally in the case of a steam engine. With marine engines in calculating the diameter of the tunnel shaft the same relations between this and the diameter of the crank shaft holds as is applied in steam engines, namely that the diameter of the tunnel shaft is about 5 per cent, less than that of the crank shaft. In most Diesel engines of the ordinary four-cycle land THE DESIGN OF DIESEL ENGINES 321 type, with trunk pistons the length of the connecting rod is approximately 2| times that of the stroke of the pis- tons, but as a rule this is diminished when crossheads are employed. In many four-cycle marine engines of large size the length of the connecting rod is twice that of the stroke, whilst in two-cycle and marine engines the figure is about 21 times. For large engines, particularly for marine work, it is desirable to have built up crank shafts, and this is one of the reasons for the employment of a fairly long stroke in engines of this type. SizK OF Craxk Shafts. (All dimensions are in millimetres.) 'J'vi)e of Engine. Fovu- or Two Cycle. B.H.P. No. of Cylin- ders. Dia. Stroke R.P.M. Crank Shaft dia. (Jrank Pin dia. Ratio of Crank Sliaft to cylinder dia. ]\rup]) . 4-cycle land 300 4 380 450 300 220 220 •58 Werks- 4-cycle GOO 4 500 640 215 270 280 •54 poor Carels . land 4-cycle land 700 4 570 780 150 320 325 •56 Werks- 4-cycle 1,100 6 560 1,000 125 340 340 •60 poor Schnei- marine 2 -cycle 900 4 450 560 230 260 260 •58 der marine Tecklen- 2-cycle 1,500 6 510 920 120 330 330 •64 borg marine Reiher- 2-cycle 1,800 G 600 1,100 90-100 390 400 •65 stieg marine Air Compressors. — In view of what has already been said in regard to the diflliculties that exist in comiexion with the exact determination of the cylinder dimensions of a Diesel engine, it will readily be understood that the calculations relating to air compressors are even more Y 322 DIESEL ENGINES FOR LAND AND MARINE WORK subject to variation. The exact quantity of air required for injection has not been accurately determined ; more- over, since it varies with different fuels, and the compressor has also to provide air for starting purposes, most builders prefer to allow an ample margin in the design. In four-cycle slow-speed stationary practice the many years' experience in operation which has been gained enables this margin to be reduced nearly to the minimum limit, but even in this case, in any design which is a departure from the standard, a reasonable excess should be allowed. With high-speed four-cycle engines, however, the same knowledge has not yet been obtained and the variations in different designs are more marked, whilst as regards two- cycle motors there is little doubt that in most cases the capacity of the compressor has been considerably in excess of actual requirements. At sea it is of course especially important that there should be no lack of compressed air, since not only is it used for other purposes besides injection and starting, such as the operation of servo motors for reversing, etc., and for certain auxiharies, but tlie demands for manoeuvring are at times excessive. This is to a certain extent counteracted by the fact that an auxiliary compressor driven by an inde- pendent engine is practically invariably installed, which is put into operation if the pressure in the receivers falls, and when much manoeuvring is required, as, for instance, when in a river or harbour. It is undoubtedly preferable that an air compressor should be over designed than that it should scarcely be capable of its normal work, but the desire for safety has certainly been carried too far in some cases. For instance, it is probably sufficient to design the compressor for a two-cycle marine engine with an output of 6 litres (-21 cub. foot) per B.H.P. per min. of the main engine, whereas in some cases as much as 10 or 12 litres per B.H.P. per min. has been allowed. In one of the most usual type of compressor constructed which is of the vertical design, driven off one end of the engine directly from the crank shaft, it is not difficult to THE DESIGN OF DIESEL ENGINES 323 increase the deKvery volume of air should tests show that it is insufficient. This can be carried out merely by the replacement of the connecting rod by a shorter one so as to increase the length of the stroke of the compressor and thus increase the volume of air compressed. Naturally this " trial and error " method is not to be recommended and in any case would only have to be adopted on an abso- lutely new design. The following table gives some data regarding the usual capacities of compressors for various types of engine, the volumes being based on the air entering the low-pressure stage of the machine. It is usual to express the amount of air in terms of the ratio of volume swept througli by the piston of the low-pressure stage of the compressor to that by the pistons of the working cylinders — that is to say by as man}' pistons as there are cylinders. Table of Capacities of Air Compressors. Type of Engine. Capacity of Compressor. Litres per Cub. ft. per B.H.P. per B.H.P. per Min. Mint. Volume Ratio of Compressor to AVorking Cylinders per cent. Four-cycle slow sjieed 6 to 9 •21 to -31 5-5 to 7 high „ . . 8 to 10 •28 to •So 9 to 8 Two-cj'cle slow ,, . . 6 to 9 •21 to •SI 6 to 12 high „ . . 9 to 12 •31 to^42 10 to 14 In reversible compressors of the marine type some de- signers allow an extra capacity of 10 or 12 per cent, above that for the non-reversible motors, but this is by no means general. In many respects it is not advantageous to design a com- pressor in excess of requirements since in this case air has to be discharged from the delivery of the first stage or else the suction has to be throttled. This means that the ratio of compression in the H.P. stage is too high (it should 324 DIESEL ENGINES FOR LAND AND MARINE WORK not exceed 9 to 1 ) and too much work is pnt upon the H.P. stage. On the whole it may be said that the lower limits of the figures given in the above table represent the best practice. Design of Air Compressors. — Air compressors for Diesel engines are designed to deliver air from the high- pressure stage at from CO to 70 atmospheres, or from COO to 1 ,000 lb. per sq. inch. It is obviously impossible to employ single-stage compressors for this work owing to the fact that the temperature of the air after compression would be excessive. Machines of the two-stage type are gener- ally utilized for the smaller sizes of engine, and as the diminu- tion in the number of stages reduces the complication, two-stage compression has much to recommend it. For engines up to 500 B.H.P. it appears quite suitable, but above this power it is common to adopt three-stage com- pression. With some types of compressors, however, such as the Reavell quadruplex machine, it is convenient to employ more than two stages in any case, so that even with the smiall engine when this type of compressor is employed three-stage compression is adopted. Inter-cooling and after-cooling are, of course, necessary with all types of com- pressors in order to keep the temperature of the air down to a moderate figure. The pressure for the stages are obtained in the following manner, in a two-stage compressor — If P = Final compression pressure (absolute) in lb. per sq. inch, Pi = Pressure (absolute) at end of first stage in lb. per sq. inch, then Pi = V P X 14-7 taking atmospheric pressure as 14-7 lb. per sq. inch. If the pressure be expressed in the Continental system in atmospheres then Px=Vp THE DESTGX OF DIESEL ENGINES .325 In a three-stage compressor if P^, = pressure in 11). per sq. inch at end of second stage, ^ 14-7 ^V 3/14-7 P or if the pressure again be expressed in atmospheres, Pi =

i= ,, ,, H.P. ,, S = stroke of piston of compressor P, P„,Pi=the pressures (absolute) at the beginning of the L.P. stage, the eni of the L.P. stage, and the end of the H.P. stage respectively. 326 DIESEL ENGINES FOR LAND AND MARINE WORK V„, Yi = Volumes of air at the end of first stage and second stage compression respectively, V„^ = Volume of air after intercooling between first and second stage. 7]- = Di-iS omitting clearance and losses. . . .(1) From reference to Fig. 166 it will be seen that the action Pa RVJ, PaVaTa Pa ]mk Atmospheric Line .PV.T Volume "^ Fig. IGG. — Compression Curves in Two-Stage Compressor. of the compressor is to comjtress according to the equation P V = constant from conditions P, V, T, to conditions Pa, V„, T,, ; next to cool the gas till conditions P„, V^S T„i, are reached, and then compress to conditions Pi, Vi, Ti. The value of n is as follows : — For adiabatic expansion n =1-41 ,, isothermal ,, n = 1-00 In general practice n =1-25 THE DESIGN OF DIESEL ENGINES 327 To determine V„^ which is first necessary, proceed as foUows : — PV« =P„ V/ (2) V is known, P = l-i-T lb. per sq. inch, and P„ can be determined from formulae given above, whilst n may be taken as 1-25, hence P V" V/=-y (3) from which V„ can be determined. After cooling the compressed gas (P„, V„, T„) in the intercooler, its temperature becomes T/ and the volume is reduced to V„^. From page 11 equation (2) T /P \*t=l T?=(i?)" W since in this case y is replaced by n / P \^^ / P \''^ °'^"=(i4:7) ^^ = (i4^) ^'^ ^'^ T may be taken as 520° F. or 288' C. absolute, hence T„ is then known. We may now obtain V,/ since the pressure P„ is constant during the cooling. y 1 ^ 1 1^=±± (6) V T The temperature T^^ to which the air is cooled will be about CO" F.. or say 32° C. Temperature must of course be absolute, the.cfore T„i = 460 + 90 = 550 V T 1 hence ^ . Svo, 2 50 Aitken, W. Manual of the Telephone Svo, *8 ( o d'Albe, E. E. P., Contemporary Chemistry i2mo, *i 25 Alexander, J. H. Elementary Electrical Engineering 12 mo, 2 dO Allan, V/. Strength of Beams Under Transverse Loads. ( Science Series No. 19.) i6mo, o 50 — — Theory of Arches. (Science Series No. 11.) i6mo, Allen, H. Modern Power Gas Producer Practice and Applications. i2mo, *2 50 Gas and Oil Engines Svo, *4 50 Anderson, F. A. Boiler Feed Water Svo, *2 5a Anderson, Capt. G. L. Handbook for the Use of Electricians Svo, 3 00 Anderson, J. W. Prospector's Handbook 12 mo, i 50 And^s, L. Vegetable Fats and Oils Svo, *4 00 Animal Fats and Oils. Trans, by C. Salter Svo, *4 00 Drying Oils, Boiled Oil, and Solid and Liquid Driers Svo, *5 co Iron Corrosion, Anti-fouling and Anti-corrosive Paints. Trans, by C. Salter Svo, *4 00 Andds, L. Oil Colors, and Printers' Ink. Trans, by A. Morris and H. 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