LIBRARY UNIVERSITY OF CALIFORNIA. ^Accession Y.O.O..*"). -3 O Class &4r JiL^^r*. WORKING DETAILS OF A GAS ENGINE TEST INCLUDING A METHOD OF DETERMINING THE TEMPERATURES OF EXHAUST GASES BY ROBERT HEYWOOD FERNALD, M.E., MA. Sometime University Fellow in Applied Science at Columbia University Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy, in the Faculty of Applied Science, Columbia University NEW YORK CITY 1902 IJSTTKODUCTIOK THE work embodied in the following pages is but a small begin- ning toward the development of an investigation of some impor- tance to the engineering and commercial world the standardiza- tion of methods of comparison of gas engines. With the heterogeneous collection of gas and oil engines thrown upon the market to-day, some method of standardization is very essential, but the problem is one of too great magnitude to be com- pleted in the brief period of one college year, and it is the hope of the writer that some one may take up the work where it has been dropped. The general scheme, as roughly outlined, is 1. The history and development of the explosive engine. 2. The gas engine of to-day, and a comparison of existing en- gines, resulting in a classification into types and a study of these, including : (a) A complete bibliography of the subject, together with a list of patents granted, both in this country and abroad. 3. An investigation of the physical and mathematical problems involved, both quantitative and qualitative. 4:. A complete and detailed method of testing explosive engines, leading to (a) A criticism of points of design and construction and sug- gested improvements, based upon information obtained through 2 and 3. 5. General conclusions derived from the tests and observation, coupled with a comparison of the explosive engine with certain types of non-explosive engines. The historical section has been fairly well developed by previous investigators. It is seen at once that sections 2, 3 and 4 are to a certain extent interdependent and that a thorough investigation of one involves certain information obtained from the others. A brief inspection of the outline of procedure indicates that the main portion of section 4 is at the present time of greatest moment, and the complete and detailed method of testing explosive engines has, IV INTKODUCTION. therefore, received the entire attention of the writer for several months past. To avoid the possibilities of duplicating work already well under way, or completed, a special trip was made to three technical insti- tutions known to be especially interested in this subject, namely : the Massachusetts Institute of Technology, Boston, Mass. ; Wor- cester Polytechnic Institute, Worcester, Mass. ; and Cornell University, Ithaca, N. Y. Although more or less work upon the heat engine has been car- ried on, or is no win progress at the laboratories of these institutions, yet the lines followed are quite different from those undertaken by the writer, and the field for thorough research was found prac- tically clear, as the greater part of the work done is of the nature of ordinary commercial tests for the benefit of students taking the regular laboratory courses. Correspondence and inquiry led to the belief that nowhere had research been undertaken on the plan outlined above, and prep- arations were at once made for carrying on the investigations. The engines in the laboratory at Columbia University in New York City were put into commission and used for experimental pur- poses, the greater part of the data being obtained from an eight horse-power Otto engine and a five horse-power Nash engine. The results of the investigation have been prepared for presen- tation before the American Society of Mechanical Engineers at their meeting in Boston, in May 1902, which accounts for the form in which they are presented. The volumes of Transactions and numbers of papers to which references are made in the text and footnotes are those issued by the American Society of Mechanical Engineers. The writer desires to express his appreciation of courtesies ex- tended and valuable assistance rendered, to Prof. F. E. Hutton, Prof. R. S. Woodward, Prof. W. L. Cathcart, Prof. W. Hallock, Mr. F. A, Goetze, and Mr. C. E. Lucke. New York City, March 15, 1902. PAKT I. WORKING DETAILS OF A GAS ENGINE TEST. WORKING DETAILS OF A GAS ENGINE TEST. 1. .CONSIDERING the rapid advance of the gas 1 engine during the past few years, it is surprising to find how little has been done toward standardizing such engines, or at least toward adopting some form of test whereby a definite idea of the relative merits of different engines can be obtained. Of late years the market has been crowded with various types and modifications of heat engines, especially of the explosive type, many of which are mere freaks and of little or no value. 2. Although a very few types have received the careful attention of the expert, many engines thrown upon the market are the re- sults of a desire to invent, with the possible chance of " hitting the right thing," or the product of dull times in machine shops. Although in the case of the steam engine occasional forms are produced having entirely new features, yet the tendency is to con- form closely to a general standard which. usage and careful inves- tigation have shown to be desirable. * For further references on this subject see Transactions as follows: No. 0943, to be presented at this (Boston, 1902) meeting, "Final Report of Com- mittee Appointed to Standardize a System of Testing Steam Engines." Vol. xxii., p. 152 : "Efficiency of a Gas Engine as Modified by Point of Igni- tion." C. V. Kerr. Vol. xxii., p. 612; "Efficiency Tests of a One-hundred and Twenty-five Horse- power Gas Engine." C. H. Robertson. f The term " gas engine " is used throughout this paper to include engines commonly termed oil engines. 2 WORKING DETAILS OF A GAS ENGINE TEST. 3. Similar standards should be adopted for the gas engine as rapidly as possible. This does not prohibit or discourage inven- tion or modification, which are very essential in the present con- dition of these engines, but something should be done to classify and standardize those already on the market, thus determining what experience and study have thus far shown to be good form. The problem in its entirety is a large one, and will require many months or perhaps years of continued investigation and study. With this fact in mind, the writer has undertaken a few months' study of the subject, and although unable more than to begin the work, the results so far obtained may prove of interest to this Society. 4. Before the engines can be standardized some definite method of determining the relative merits of different engines must be settled upon, and this leads at once to the necessity of a standard method of testing gas engines, which will form the special part of the problem herein discussed. It is of interest, before taking up in detail the method of con- ducting the tests, to note some of the items that require careful investigation and study for a proper classification of the engines. Much of the data desired is simply for general information, and to obtain the views of the manufacturer on certain points and to determine what he considers good practice. Other information is needed because it enters into any test of the engine that may be made, while other questions lead toward a classification of such engines into general divisions. Although time has not permitted the testing of such data sheets practically, yet the following general form serves as a basis for beginning the investigation and experience alone can determine the necessary modifications and additions: GAS ENGINE DATA. No Test No Date 1. Name of Engine 2. Manufactured by 3. Is it two or four cycle ? 4. Kind of fuel used 5. Assumed heat of combustion of fuel B. T. U. per 6. Actual horse-power 7. Floor space occupied 8. Height, wheels to clear floor 9. Weight 10. Number of cylinders 11. How are cylinders arranged if more than one? 12. Diameter and weight of flywheel. Diam. = ins. Wgt. Ibs. WORKING DETAILS OF A GAS ENGINE TEST. 13. Diameter and width of brake pulley. Diam. = ins. Width = ins. 14. Diameter of piston = ins. Length of barrel = ins. No. rings 15. Piston displacement^ cu. ft. Clearance^ cu. ft. 16. Length of stroke^ ins. Length of connecting-rod = ins. 17. Revolutions per minute=: 18. Kind of governor 19. Method of governing 20. Special governor features 21. Kind of ignition : (A), hot tube ; (B), flame ; (<7), electric. Tf ( A \ J ( a ) location (b) dimensions (c) how heated Tf ( T*\ J ( a ) kind (b) size of flame port . > () special features If (C) -j | ( (1) current required ......... (2) voltage. . . (a) contact spark < (3) battery recommended ...(4) number... (5) specifications of coil ..... ............. (1) current required ........ (2) voltage. . . inrrm snark ^ kind of plu ............ (4) location J j. (5) battery recommended. . . .(6) number . . (_ (7) specifications of coil .................. 22. Kind of valves ........................................................ 23. Special features of valve mechanism ..................................... 24 Diameter of (a) gas valve ...... ins. ; (6) air valve ...... ins. ; (c) mixture valve ...... ins. ; (d) exhaust valve ...... ins. 25. Lift of (a) gas valve ........ ins. ; (6) air valve ........ ins. ; (c) mixture valve ...... ins.; (d) exhaust valve ...... ins. i(a) carburettor ................................................ (6) vaporizer ................................................. (c) mixer .................................................... 27. Means of maintaining constant proportions ............................... 28. Method of fuel 'feed .'.'.'. Y.'.Y.Y.Y.Y. . . . . !!.'.'.'!.'.'.'.'."."!!.".'.!.'"!'.'.'!!!!!"!! 29. Number of water inlets ........... ........ diameters .................. ins. 30. Number of water discharges ............... diameters .............. . . .ins. 31. Best rate of water feed ................................................ 32. Kind of muffler ........................................................ 33. Dimensions of muffler ................................................. 34. Does muffler use water? ........................ ........................ 35. Means for preventing noise at air inlet ................................... 36. Kind of gas bag ........................................................ 37. Dimensions of gas bag ................................................. 38. Means of clearing engine of exhaust gases ...................... ......... Devices for starting or aiding starting. 5. The investigations which have developed the details of con- ducting tests have been carried on at the mechanical laboratory of Columbia University during the present college year. The various experiments have been developed largely from work on a 6 x 12^ Otto engine, and a 6 x 9 Nash engine. Much time has been devoted to working out many details and to following inci- dental suggestions that offered themselves as the work progressed, and it is proposed to present rather fully many important points. This may seem unnecessary to those already familiar with such work, but it is believed that this part of the paper may prove of WORKING DETAILS OF A GAS ENGINE TEST. interest and value to those who propose undertaking such tests for the first time. For this reason some of the difficulties and errors that are likely to occur are especially emphasized. 6. It is hardly necessary to offer any explanation of the items called for in the " log " of the test, as information may be ob- tained regarding each of these points from the details of the corresponding items that appear in the final report. The form of " log " appended is found to be convenient for making the preliminary records : Date Log of Gas engine test Test No By Object Length of brake lever ft. Weight of brake lever Ibs. Cubic feet of vapor per pound of Weight of gallon of Ibs. 1. Number of run 2. Time 3. Speed and explosions, revolutions per minute, hand indicator 4. " " reading of speed counter 5. " " explosions per minute, special count 6. " " reading of explosion counter 7. Total load on scales Ibs. 8. Temperatures, degrees Fahr. QJ- Cent., gas 9. air 10. jacket water, entering 11. " " leaving 12. " " barrel 13. exhaust, observed 14. " at pressure of atmosphere. .. 15. Valve index reading, gas 16. " " " air 17. Areas of valve openings, gas or vapor , , sq. ins. 18. " " " oil " 19. " " " air " 20. " " mixture , 21. " " " exhaust 22. Weights and volumes, weight of jacket water Ibs. 23. " reading of gas meter, cu. ft or gals, of 24. " " reading of air meter 25. " " gas for igniter cu. ft. 26. Indicator springs used, power card 27. " " " compression card 28. Pressures,, gas, inches of 29. air, inches of 80. jacket water, Ibs. per sq. in 31. " exhaust, Ibs. per sq. in Remarks 7. Before entering upon a discussion of a complete test of a gas engine it is necessary to establish certain standard units. Without question the proper unit for the energy derived from the fuel used is the " British Thermal Unit," which has been adopted throughout this country and England, and is designated in this WORKING DETAILS OF A GAS ENGINE TEST. 5 paper by the usual symbols, B. T. U. In like manner the term horse-power is used to designate the rate of work, and I. H. P. and B. H. P. have their usual significance, meaning indicated horse-power and brake horse-power respectively. Further explanation of the units used will develop during the examination of the final report. It is hardly necessary to touch upon the proper methods of calibration of instruments to be used, with the exception of special instruments or instruments used under special conditions, as this subject has been so fully treated in many previous publications. These cases will be treated under their respective heads. PRELIMINARIES OF THE TEST. 8. Before beginning the test it is very essential to see that the engine is in good running order, thoroughly oiled, and properly adjusted. All valves should be carefully examined and adjusted. All connections to the engine, whether fuel, air, or water, should be tested for leakage. Special note should be made of any points out of the ordinary, and if they are of such a nature as to affect the results of the test, the difficulties should be set right as far as possible, and, when this cannot be done, careful estimates should be made of the changes in the results due to such conditions. It is of the greatest importance that each observer know exactly what is expected of him, and that he at least be made thoroughly familiar with the details of all apparatus and machinery bearing upon his portion of the work and he should be shown exactly what to do in case of emergency, in order to rectify difficulties as quickly as possible without interrupting or possibly destroying an entire test. 9. In the series of tests from which the results for this paper were obtained, more than one test was entirely lost after hours of work through the hasty action or lack of judgment of some one observer. Where possible, a picked and trained crew should be retained, and even then as far as practicable the director of the test should attempt nothing but the oversight of the observers, and should stand ready for all emergencies, allowing the individual observer to touch nothing but the instrument he is observing, and then only as directed. Unfortunate experience has shown this to be the only possible way of obtaining reliability in results. It is necessary that the engine be run a sufficient time before b WORKING DETAILS OF A GAS ENGINE TEST. the real start of the test, to enable all parts to become properly adjusted to the desired running conditions, or to get the engine " warmed up/ 7 and to determine accurately the proper working of all instruments and recording devices, and especially if the engine is to carry the maximum load which it can carry continu- ally. Much difficulty is often experienced in determining this maximum load, especially if the fuel used is city gas, for then the load carried yesterday may be far from the possible load of to-day. If a brake is used without cooling water, then the run previous to the start of the test must be of sufficient length thor- oughly to warm the brake pulley, to permit further expansion and a sudden increase in the load. A brief preliminary trial should in every case precede the regular run, to make certain that every observer understands his work, and it is found advantageous not to inform the observer of any distinction between the preliminary run and the true test. The reading of an ordinary meter used for measuring air supply is not a difficult matter, but it has been found that few men can obtain reliable readings without previous experience. OBJECT OF THE TEST. 10. It is absolutely necessary that the object of the test be def- initely determined, and this object should be kept constantly in mind during the run, whether the test be a general efficiency test, a test for proportions of air to gas, changes in conditions of igni- tion, temperature of jacket water, throttling of exhaust, or what not. FORM OF REPORT BLANK. 11. Careful study coupled with experience has developed the accompanying form for the final report of the test. At first sight it may appear to some as too comprehensive, consequently cumber- some, but the desire has been to secure a form that will serve for all purposes, whether for an efficiency test only or for a complete laboratory test in which much data is desired for further study that might of itself be of little value to the manufacturer directly, but of great value scientifically, especially along lines which will aid in further development of the heat-engine problem. It is deemed wise to take up each item of the report in detail, and, to assist in making the explanations clear, run number 6 has been selected from each of the two tests chosen, for this paper. WORKING DETAILS OF A GAS ENGINE TEST. 7 The engine from which the results recorded as test " A " were obtained was run under full load, while in nlaking test " B " the engine carried only half load. 12. It is not intended to draw any comparisons between the two runs, and they are both submitted simply to assist in further explanations of the method of working out a complete test if con- ducted on the plan outlined. WORKING DETAILS OP A GAS ENGINE TEST. o ^ W H M O S I I o- 8 I .3-.S8 fcss .^ 00 . t- 52 2S-2 h& t: &f H s,gl :J ^IIUKi 5 ! * : li |ilj ^.H 5 feX!^ S,S8 J^ fe* = *-.<5'25 !ili|o|,|^5|lSpi| 3 SISS . S > 2 O.-2 S'5S^o3J2X5S"Si^a5- ' C'S- b^= i^lgli^^lllllislli^i 1^3^ WORKING DETAILS OF A GAS ENGINE TEST. 15 SSSSSfe^gg'S^. so' ^ ei i-i TI* *' oo 'co *l3*i OD 5 Sis i^CO^CO 50 jje- oo E\f S g ig . 8 * ^r^^^fi^-tiv 1 ^'^ ''s^^^^'JU^ '^T- ,io^M;i-.coTf coos oro"o" l ~(N .fo" .r so" i- c*i-iTf<- O< TH rt * < i-H OO OO o co rt - " t- Girl' s s s s cfw THlO COr-H t- oo ri 1 10000: coot oo o ccioo - O S o o T-C : : .B s E s >> Sii 1 M s ! |ii ?! I rtR ill * !!<=1^ illl s lpil S| li'slsiiiiilslll im isllll^l^Hiliiilri 1 .^ aAJtio uoieaBdxa *>J'A'> EBBS < < B WORKING DETAILS OF A GAS ENGINE TEST. 11 The titles following paragraphs are numbered to correspond to the items as they appear in the report. Especial attention has been given to the arrangement of this report, the items appearing in the order in which they are most readily deduced; i.e., with one or two possible minor exceptions, no solution is called for for which the data have not already been supplied by the " log " or by a previous solution. 1. Number. 2. Time Intervals. 13. It is necessary to make frequent readings during the test, and item 1 corresponds to the numbers of these readings. What the interval between readings shall be is not material so long as the period is sufficiently long to eliminate errors that might creep in from too brief intervals. Ten-minute intervals are recom- mended in case the total run is not over two or three hours. When the nature of the test is such that several hours are necessary for the determination of average results, or quantities of fuel used, the time intervals may be lengthened as desired, although thirty minutes should probably be the maximum time between readings. When more convenient the time interval will be designated by " int." REVOLUTIONS AND EXPLOSIONS. 3. Total Revolutions. 14. Whenever possible a continuous speed counter should be used, and it is advantageous to obtain simultaneous records from two such counters. It is best to check the readings during each interval by a hand indicator, in order that some record may be had in case of acci- dent to the continuous recorders especially if one recorder only be used. The fluctuations in speed of a gas engine of the single cylinder type are so great and so varied that the readings of a hand speed counter taken for one minute are apt to be far from reliable, and dependence should be put upon them only in case of absolute necessity. 4. Revolutions per Minute (Mean). 15. The mean number of revolutions per minute is simply the total number of revolutions for the time interval divided by the number of minutes in that interval. The mean speed thus ob- 12 WORKING DETAILS OF A GAS ENGINE TEST. tained is far more reliable than that obtained by the hand speed counter. 5. Total Explosions. 16. The general remarks regarding 3 apply. A continuous counter should be used whenever possible for determining the number of explosions. This can usually be done by connections to some stem or arm of the inlet valve, so that the counter is operated by the movements of this valve. Care should be taken to see that the ignitions are reliable and that every ignition gives an explosion. Any method of simply counting the misses by sound or feeling, when they are frequent, is found to be absolutely unreliable. 6. Explosions per Minute (Mean}. 17. These figures are obtained by dividing the total number of explosions for the time interval (item 5) by the number of minutes in that interval (item 2). 7. Ratio of Revolutions to Explosions. 18. This item gives a clear idea of the regularity of the ex- plosions. In the single cylinder four-cycle engine making no misses, this ratio of the number of revolutions to the number of explosions would be 2.00. Any decrease in the. number of explo- sions per minute would cause this ratio to increase, and a hasty glance at this item indicates at once the regularity of the explo- sions. In a single cylinder two-cycle engine the corresponding ratio is 1,00, WORKING DETAILS OF A GAS ENGINE TEST. 13 o o I! S I !' 1 C< t- *! ' o* so 10 o o* so o 00 i- oo (?* oo o O CO ^i 07 *<* Qt 00 O 0* i-l T* SO CO Q 05 . eoi-i eo o 0;00'-'90>0< o I S8o : 15 53 1-1 O* -t> :g 4 I 5ff i-s^l ^ ii P i s si 3 snon xapui WORKING DETAILS OF A GAS ENGINE TEST. ! w o co co 5* to S ii 00 1-1 CO CO " i ' O O> CC* Tf ^* JC ^ ^5O Oi-iOCJ^iO C5 O5 05 OS rn C 00 10 ?D <_, I - O ' ^ rt ^ 10 so 9 'opoo^'ow 1-1 1-1 C5 S- 5 Sf il. ' -^ CO O -i-i < a o^ rrw; r- cs o o 35 71 O CT> f- < QO OTt< eoioe O O O35Ot^COi-H 22C5 CO i-i O O O O OS 5 00 g t- O Tf ' 10 1-1 1-1' 10 CO (N '~- rH o'o'* O =o' o W n 10 1-1 i-i O: O* QDOO SWtf-i& J3 O O : :p; :g :>> :S S ii g o : -2 :^J! -3 igs^s SJg ^fec^s^ WORKING DETAILS OF A GAS ENGINE TEST. 15 1 I so 0010 gills i e s Ci Tf g S QO 'Tf * cS S g E S 1 IS K s ss S|J8 S|'S v : :5 : :S moli iJTi J5 1 a '** \ fllS flal .^_ < rnS ' -s9TOU9TO^g; s p.a3aa3 - I ''' Mnoq lad s 8 I ; ill 3 2 S3 S3 53 03 03 oj QJ4J.O) B G OJ <5 < B 16 WORKING DETAILS OF A GAS ENGINE TEST. JACKET WATER. 8. Weight in Pounds. 9. Weight in Pounds per Hour. 19. The simplest method of weighing the jacket water is by means of two oil barrels, with proper outlet pipes, set upon plat- form scales. The piping from the engine should be so constructed that the water may be fed into either barrel at will. It is hardly necessary to take the weight of the jacket water for each of the time intervals, provided the water flow has been carefully regu- lated before the test actually starts and the temperature of the feed water is found to be constant. If the flow is maintained so nearly uniform that the fluctuations in temperature of the outlet water are not large say for ex- treme range not over 15 degrees Fahr. the total weight of water for the entire test may be recorded, and this result divided into equal proportions for the different runs. 20. Should the feed-water temperature show marked variations, which is likely to be the case if the water from the main passes through several buildings before reaching the engine, it should be weighed in small amounts and the weight and temperature entered on the " log." The weight per hour is calculated directly from the values in item 8. In case of long runs it is well to determine the weight for each hour and to assign to each time interval its proportionate part. 10. Temperature Range. 21. Keferring to items 10, 11, 12 of the " log," it is noticed that they are marked temperature of water entering, leaving, and barrel respectively. If the water used comes through a system of pipes running through warmed buildings, it is best, if possible, to allow the water to flow long enough to show fairly constant temperature before starting the test. This is especially necessary in winter when the water is taken from the city main a difference of 45 degrees Fahr. is often observed under these conditions. 22. In cases where the weighing barrels are near the engine the temperature of the discharged water may be taken as it enters the barrel, which is often more convenient than to obtain the tem- perature just as the water leaves the engine. It has been found advantageous to keep a record of both when the conditions admit. In the tests shown no special attention was paid to the best tern- WORKING DETAILS OF A GAS ENGINE TEST. 17 perature of the leaving jacket water. In general it seems to be the opinion that the hotter the water is allowed to get without injuring lubrication or giving premature ignition the better. Some authorities give 160 degrees Fahr. as the best temperature for the discharge. Experiments seem to indicate that pressure in the water jacket is of little moment. The range of temperature is the difference between the tem- perature of the leaving water and that of the entering. 11. Maximum Velocity, Feet per Second. 23. This has no direct bearing upon the test proper, but is in- serted for use in making comparative tests of different engines, and for the determination of points of design of water inlets and outlets for the most effective results. The data collected would undoubtedly show variations depending upon the method of deliv- ery, whether from natural circulation or forced. . 12. Heat Absorbed, E. T. U. 24. The heat absorbed by the jacket water is a very large per- centage of the entire heat supplied often about 50 per cent. Since the specific heat of water is taken as unity, the calculation consists only in multiplying the number of pounds of water used during the interval by the range of temperature, this range of tem- perature being equal to the number of heat units absorbed per pound of water. Data Given. s = specific beat of water 1. t r '= temperature range. W= weight water for time interval. To Find h w = B. T. U. for the time interval. Examples. "A" Run No. 6: s = \. t r = 72 degrees. W = 97 pounds. "B" Run No. 6: 8 =1. t r = 39 degrees. W = 93. 3 pounds. 2 Solution. h w = s x t r x W. h w = 1 x 72 x 97 = 6,984 B. T. U. Ji w - 1 x 39 x 93.3 = 3,640 B. T. U. 18 WORKING DETAILS OF A GAS ENGINE TEST. AIR. 25. It is very essential that the quantity of air used be accu- rately measured, and the simplest, and usually most accessible, method is by means of a gas meter of sufficient size. The accu- racy of this meter should be carefully determined. (For. methods of calibration, sec " Report of the Committee Appointed to Stan- dardize a System of Testing Steam Engines/ 7 paper No. 0943. 26. Even if the meter is carefully calibrated when working under suction, the readings will not be the same when the air enters under pressure, or vice versa. With the setting of the air valve as used in making test " B," the meter readings averaged for a given number of admissions 109.5 cubic feet when working under a pressure indicated by 2 inches of water, and 97.25 cubic feet when working under suction. The flow recorded by the meter was then 1.13 times as much when working under light pressure as when working under suction. The meter through which the gas is measured works at all times under slight pressure, and for accurate determination of the pro- portions of air to gas the meter used for air measurement for the experiments upon which this paper is based was put under equal conditions by supplying air under pressure by means of an Ingersoll air compressor. In the absence of a compressor a blower may easily be arranged to accomplish the same result. The method of piping used is best explained by reference to the cut, Fig. 1. 27. A is the main compressed air line leading from the com- pressor to the air meter B. C is a relief tank filled with water to a depth corresponding to the head shown by the manometer attached to the gas pipe, and causing the flow of air through the meter to remain fairly constant. From B the air passes through the pipe D, directly to the engine save for the interposition of air bags E and F and an old mufiler, used for the same purpose as the bags namely, to reduce the variation in pressure of the air. At H is shown a manometer for determining the air pressure, and by means of the inlet valve / this pressure can be maintained the same as that shown by the gas manometer. By this method an accuracy in determining the proportions of air to gas was as- sured that otherwise could not be guaranteed. WORKING DETAILS OF A GAS ENGINE TEST. 19 WORKING DETAILS OF A GAS ENGINE TEST. 13. Cubic Feet. 14. Cubic Feet per Hour. 28. In reading the ordinary meter it is not sufficiently accurate to catch the readings by noting the positions of the index hands at the beginning and close of the time interval, but it is necessary to keep an observer at the meter and require the readings to be taken from the hand which indicates the single cubic feet, and whose complete revolution records 10 cubic feet. The cubic feet per hour are readily calculated from the data for the given time interval. 15. Temperature, Fahr. 29. Under ordinary conditions it is sufficient to take the tem- perature of the air at the beginning and at the close of the test, but if the conditions are variable more frequent readings will be necessary, .^, 16. Weight per Cubic Foot. 30. This weight is that of a cubic foot of air at the temperature given in item 15, and is found as follows: Data Given. Wo weight cubic foot air at 32 de- grees Fahr. = .0807 pound. T = 32 + 459 = 491 (absolute). Ti absolute temperature of air. = item 15 + 459. To Find w\ = vvgt. per cu. ft. at given temp. Examples. "A " Run No. 6 : T, = 86 + 459 = 545 Run No. 6: m = 87 + 459 = 546. Solution. 491 0807 =j~ = .0727 pound. 0807 ^ = .0725 pound. 17. Maximum Velocity in Feet per Second. 31. Like item 11, this has no direct bearing upon the single test, but is for use in making comparative tests of different en- gines and for determination of points of design of air-inlet valves for the most effective results. WOBKING DETAILS OF A GAS ENGINE TEST. 21 18. Specific Heat, C v . 32. The specific heat of air at both constant pressure and con- stant volume may be found in any books on thermodynamics. The specific heat at constant volume, denoted by C VJ is the only value needed in this work C m .1691. FUEL. 33. The question of quantity of fuel used is the first to present itself, and the methods of determining this will depend entirely upon the kind of fuel. If coal is required the method of determining the amount is that usual in case of boiler tests, and is fully described in the Transactions of this Society, Vol. XXL, p. 34. The method used for ascertaining the amount of gas is by means of the standard gas meter. Methods of calibrating these meters are given in the "Report of the Committee appointed to Standardize a System of Testing Steam Engines," paper "No. .0943. If oil is used it can easily be measured by means of cali- brated tanks. For small engines using little oil, the tanks should be small in diameter, that the errors in measurement may be re- duced as much as possible. 19. Cubic Feet or Gallons. 20. Cubic Feet or Gallons per Hour. 34. The method of measuring the fuel has already been ex- plained. The quantities designated in item 19 refer to the amounts used for the given time interval, and if the fuel be gas, this would be the number of cubic feet as read directly from the meter. If the fuel be oil the number of gallons for the period should be recorded. 21. Temperature, Fahr. 35. As in the case of air, it is usually sufficient to take the temperature of the gas at the beginning and at the close of the test, but if the conditions be variable more frequent readings will be necessary. In case of engines that vaporize oil fuel before it enters the cylinder, this determination of temperatures is very difficult, if, indeed, possible. There are many forms of carburetors, and the temperatures of vaporization are found to vary greatly. 22 WORKING DETAILS OF A GAS ENGINE TEST. Further developments may determine the desired method of making reliable observations of the temperature of this type of fuel. 22. Weight per Cubic Foot or Gallon. 36. In case the fuel be gas, it is not always convenient to obtain the weight per cubic foot. If the temperatures of the air and gas be the same, this is hardly necessary, and even when these temperatures be different the necessity of knowing this weight is not sufficient to warrant great inconvenience or expense in obtain- ing it. 23. Maximum Velocity in Feet per Second. 37. As in items 11 and 17, this has no direct bearing upon the single test, but is for use in making comparative tests of differ- ent engines and for determination of points of design. 24. Specific Heat, O v . 38. Unless it is convenient to ascertain accurately the desired specific heat of the gas used, no serious error results from taking the specific heat at constant volume the same as for air; namely, O v = .1691. 25. Cubic Feet of Standard Gas per Hour (60 Degrees Fahr., 14.7 1 *o unds Pressure) . 39. The general standard recommended seems to indicate for " Standard Gas" the conditions given; namely, a temperature of 60 degrees Fahr. and a pressure corresponding to the usual atmos- pheric pressure. It is hardly necessary to make corrections for barometric readings, as the total possible variation is slight, and considering all other sources of error it is a question whether this supposed degree of refinement adds to the accuracy of the results. Atmospheric pressure will then be understood to mean as in- dicated, 14.7 pounds per square inch. 40. The pressure shown by the manometer attached to the gas pipe might also be neglected in making the computations, as its effect upon the result is hardly perceptible. It has, however, been considered in the illustrative problems, the value having been re- corded in the log of the test, thus adding no labor to the computa- tions. It may be of interest to note that the total effect of neglect- WORKING DETAILS OF A GAS ENGINE TEST. ing both the changes in barometric conditions and in the pressures shown by gas mains, when these changes are taken at a maximum, is less than one-half of One per cent, of the number of cubic feet per hour. Data Given. To g =. cu. ft. of gas per hour at t g F. T g = absolute temp, of gas = t, + 459. p g pressure under which gas is flow- ing. = 14.7 Ibs. + pressure shown by manometer. T. = 60 + 459 = 519 F., absolute temp, of standard gas. Po = atmospheric pressure. = 14.7 Ibs. per sq. in. To Find v, = cu. ft. standard gas per hour. Examples. "A" Run No. 6: v g = 157.5 cu. ft. T g = 86 + 459 = 545. p g = 14 7 + .1 = 14.8 Ibs. per sq. in. "B" Run No. 6: v, = 91.5 cu. ft. T g = 87 + 459 = 546. p g 14.7 + .1 = 14.8 Ibs. per sq. in. Solution. > P, r, .. ft. VALVE INDEX HEADING. 26. Gas. 27. Air. 41. This refers to the setting of the graduated inlet valves, and has no direct bearing on the single test, but is of value in making comparative tests. 28. Value of n in PV n I\ V for Expansion Curve. 42. At this point in the analysis, more or less difficulty is likely to be encountered. The necessity of carefully working out this value of n for each card may not at first seem apparent, but slight investigation shows it to be of great importance. It is not unnatural to assume that the expansion curve and the compression curve, as given by the indicator card, follow very closely the* adiabatic law. 24 WORKING DETAILS OF A GAS ENGINE TEST. Working upon this supposition leads in many cases to a network of difficulties, from which it is not easy to free one's self. For example, a case that came to the attention of the writer was as follows : In making a preliminary test, owing to the fact that it was inconvenient to determine the exact clearance volume of the engine, instructions were given to work out the clearance from the indicator card. The method is quickly shown by the following deductions and reference to the card shown in Fig. 2: FIG. 2 43. ^Let Vi = clearance volume of cylinder. v z = total volume of cylinder. po atmospheric pressure = 14.7poundsper square in. p b = pressure at compression, from card. I = length of stroke in feet or inches, as desired. x = length of clearance in feet or inches, as desired. It appeared a simple matter to solve for x in the following for- mulas : J_5 ( _ 2 i>i or = - 2 which readilv reduces to 14.7 2 V - x + I on the assumption that n for the compression curve was 1.41 or = 71 n This gave an excessively large clearance volume, and the values of n worked out for the expansion curve varied greatly, but the best value seemed to be about 1.7, although the necessity of care- fully determining the value of this exponent for each card was at once apparent. WORKING DETAILS OF A GAS ENGINE TEST. 25 Maximum temperatures computed on the basis of the value of n above proved to be in the neighborhood of 4,00.0 degrees Fahr. This surprisingly large value of n, together with the excessively high temperatures, led at once to a careful study of the problem, for it was apparent that no assumptions regarding the laws of ex- pansion could safely be made. The clearance volume was at once determined by the usual method of filling the space with water. It may be well here to emphasize the necessity of great care in releasing all air from this clearance space as the water- is poured in. 44. The values of n now deduced from the expansion curve for FIG. 3 the diagrams taken from this particular engine showed for portions of the curve values as surprisingly low as those first determined were high. It was found that this, exponent varied greatly in dif- ferent parts of the curve for the diagrams taken from this engine, but no satisfactory law of variation could be determined. With the high pressure spring used in the indicator it was very difficult to obtain accurate values from the cards secured. 45. With a 240-lb. spring, which was the one used, each .01 of an inch in vertical measurement corresponds to 2. 41bs. pressure, and errors resulting from irregularities in the curve, variations in the width of line, and mistakes in observation render it almost impossible to work with the degree of accuracy desired. In Fig. 3 is show r n one of the cards taken in making test " A." The upper dotted curve represents isothermal expansion and the lower dotted curve adiabatic expansion. It is seen at a glance that early in the expansion the full line follows very closely the adiabatic curve and then approaches nearer and nearer the isothermal as the expansion continues. The value of n that has been chosen for recording in item 28 is the value 26 WORKING DETAILS OF A GAS ENGINE TEST. found for the latter parof the expansion, as this value is the one most needed in computations that follow. Owing to the fluctu- ations in many curves near the beginning of expansion, it has been Fernald FIG. 4. found extremely difficult to obtain values that could be regarded as reliable for the pressures desired. 46. The card shown in Fig. 4 was taken during test " B," and although the expansion curve seems to follow the adiabatic more closely than in Fig. 3, yet there is considerable variation even in this case. Repeated calculations showed the best value of n for the expan- Fernald FIG. 5 sion curve for the cards of test " A " to be 1.14 and for test " B " 1.21 or 1.20. The mathematical work involved in obtaining n is explained below : WORKING DETAILS OF A GAS ENGINE TEST. 27 Data Given. Any corresponding values of pressure and volume obtained from the indicator card. Great care should be exercised in theselection of these points if the equation of the expansion curve is found to vary for different portions of the curve. All measurements must, of course, be made from the zero of volumes and zero of pressures. Vi = some assumed volume. P! = pressure corresponding to V t . F 2 = another assumed volume. Pa = pressure corresponding to F 2 . Examples. "A" Run No. 6 (For this problem the values of P and V are selected as shown in Fig. 5) : Fa = 62 Pi = 141 F 2 = 12.2 P 2 = 65 B " Run No. 6 : F, = 5 Pi = 1(8 V,=8 P 2 = 61 Solution . P! 71 = log. P. - log. P, - log. F 2 - log. F, log. Px = 2.14922 log. P 2 = 1.81291 .33631 log. F a = log. Fi = 0.79239 .29397 _ .smi_ _ ~ .29397 ~ Solving by the first formula, shortens the work if a slide rule is used ^i = ^= 1.77, log. =0.24797 Z? ^ ? = 1.6, log. = 0.20412 K j 5 .24797 .20412 = 1.21 47. The following values of n were worked out with great care from a series of volumes and corresponding pressures, and show the fluctuations to which this calculation is subject. The values are arranged as derived in regular order from left to right, but do not include values for very small volumes, as the variations in pressure were too great to enable any reliable readings. As de- rived from the card selected n = 1.21,1.12,1.14, 1.16, 1.13, 1.135, 1.12, 1.10, 1.10 1.12, 1.15, 1.15, 1.15 1.14, 1.16, 1.13. A variation of a single pound in the pressure, or, in some cases, of one-half pound, determines the accuracy of the deduction, but with such high pressure springs this degree of refinement is im- possible. It was noted in several cases that the value of n for the 28 WORKING DETAILS OF A GAS ENGINE TEST. compression curve was slightly higher than for the expansion curve. A simple method of ascertaining whether this exponent is the same for corresponding compression and expansion curves is as follows : 48. Locate a series of different volumes upon the card in ques- tion and determine the corresponding pressures for both the com- pression and expansion curves. If the ratio of the corresponding pressures of the two curves remains constant, the exponents for the equations of the two curves will be found to be identical. Let Fj and V. 2 = two volumes chosen, as in Fig. 5. For the ex- pansion curve the two pressures = P l and P 2 and for the com- pression curve the pressures corresponding to the same volumes = P s and P 4 . Let x be the exponent in the equation of the expan- sion curve, viz : P l Vf P 2 V 2 X and let y be the corresponding- exponent for the compression curve, or P 9 V? = P V/ By division y Y^ P * M If now the exponents for the two * 8 '1 *4 * 2 curves be the same, i. e., ify = x then ^_^L = ^_p* or ^ = P \ *8 M ^4 '2 * 8 -*4 MIXTURE. 29. Temperature, Degrees Falir. 49. One of the longest deductions, as well as one of the most difficult, but at the same time of great importance, is that of ob- taining the temperature of the mixture in the cylinder, composed of air, gas, and exhaust gases, or neutrals, as the last are some- times called. The problem involves the larger portion of all the readings made during the test, as well as the careful determination of the temperature of the exhaust gases. The mixture passes through a wide range of temperatures, and the only one that can be determined is that of the exhaust. This has proved to be of such great importance and so little seems to be known regarding the determination of this factor, that much of the time devoted to the subject of gas engine testing was given to the solution of this problem. Very few methods for measuring this temperature seem to exist, and these are either too inaccurate to be of any value, or in cases where the results seem to indicate accuracy, the method is too WOKKING DETAILS OF A GAS ENGINE TEST. 29 complicated or the apparatus too expensive for use under ordinary circumstances. 50. Even the committee appointed by the Society to "Standard- ize a System of Testing Steam Engines " avoids the question en- tirely. This committee speaks of the " observed temperature of the exhaust gases/' but in no way is any intimation given of a method of observation. A simple device for determining these temperatures seems so necessary that it is deemed wise to give a complete description of the apparatus used by the writer, in a separate paper entitled, "A Method of Determining the Temperatures of Exhaust Gases/ 7 and to be presented as paper ISTo. 0932 at this meeting. To avoid confusion, the computations for determining the tem- perature of the mixture will be divided into two parts. PART I. 51. To determine the combined volumes of air and gas per stroke and the temperature of the same : Case 1. When the temperatures of the incoming air and gas are equal: Data Given. Mins. = No. minutes in time interval. item 19 = gas per min. = item 13 = air per min. = -^7^- Ti = absolute temp. gas. = T\ absolute temp. air. = item. 21 or 15 4- 459. Ex. P. M. = explosions p. min. item 6. R. P. M. = re volutions p. min. = item 4. Ms. P. M. = explosions missed per min. = | R. P. M. - Ex. P. M. for single cylinder four-cycle engine. To Find D' = cu. ft. gas per explosion at Ti. v" = cu. ft. air per explosion at 1\. T^ = absolute temperature in F. re- sulting from combining air and gas = Z\ = 2>. v aff combined vol. in cu. ft. of air and gas per explosion at T^. Solution. Ex. P. M. \R. P. M.] Since T ag = 30 WORKING DETAILS OF A GAS ENGINE TEST. A " Run No. 6: 26.25 9 = 10 194 10 = 2.625cu. ft. = 19.4cu. ft. Ti = T* = 86 + 4o9 = 545 C Ex. P. M. = 133.9. R. P. M. =267.9. Ms. P. M. = 0. B" Run No. 6: 15.25 9 = a = 10 125.0 10 = 1.586 en. ft. = 12.5 QU. ft. 2\ = 2\ = 87 + 459 = 546 C Ex. P. M. = 93.4. R. P. M. =301.2. Ms. P. M. =57.2. v "'WH = - 196cu - ft - 19.4 - .0196 x And since Vaa V 133.9 T ag = i\ = r,, = . 145cu.ft. v" = 1646 cu. ft. = =.. .18. 5-. 0163 x 57 2 150.6 = .<>769 cu. ft. And since T ag = 7\ = 7' a = 546, 4 . To Find cu. ft. air per explosion at 1\. cu. ft. neutrals per explosion at I \. /Solution. v^ = T L ,,T*_ v " Ti Ti Taking v ' as the basis, i.e. calling v' unity, then WOKKING DETAILS OF A GAS ENGINE TEST. Examples. A" Run No. 6: r, = 86 + 459 = 545. T 2 = 86 + 459 = 545 T. = 180 + 459 = 639. i)' = .0196 cu. ft. v" = .1450 cu. ft. V e = .0550 CU. ft. B " Run No. 6 : Ti = 87 + 459 = 546. T-2 = 87 + 459 = 546. T e = 188 + 459 =647. v' = .0163cu. ft. v" = .0769 cu. ft. v e = .0370cu. ft. xi x = .145^p = -145 cu. ft. FJ4K v z = .055g^= .0469cu. ft. v x :' :v g = 7.4 : 1 : 2.4. v x = .0769 f^ = .0769 cu. ft. 545 KAK v z = .037 ~= .0312cu. ft. 41. /Stroke to Expansion. TO. This ratio shows the regularity of the opening of the ex- haust valve, i.e., the position in the stroke of the point of release, and is equal to the ratio of the full stroke to the horizontal projec- tion of the expansion curve taken to the release point. In this diagram shown in Fig. 17, it is the ratio of FA to FJ. FIG. 17 For " A " run No. 6, this ratio was 1.14, and for " B " run No. 6, 1.10. The point of release does not seem always to correspond to the point of opening of the exhaust valve. The piston is moving rapidly and the drop in pressure is not always shown at once, especially if the exhaust valve motion is not rigid, or if the exhaust valve is of insufficient area. 42. Volumes v 2 to v^. 71. In the diagram (Fig. 18), ^ is proportional to the length OZ, and represents the clearance volume of the cylinder. v 2 is WOKKING DETAILS OF A GAS ENGINE TEST. 45 proportional to the length OR and represents the full cylinder volume the clearance plus the stroke. The ratio is therefore Vi equal to 7 r^. For "A" run No. 6 this ratio was 4.68 and for "B" run No. 6, it was 5.00. 43. Maximum Pressure to Mean Effective Pressure. This ratio shows the relation between the pressure produced by explosion and the true working pressure, and gives an especially good idea of the possibilities of different engines in comparative tests, as well as determining the possible degree of constancy in this relation for any single engine. It is stated by some writers FIG. 18 that in practice it is found advantageous to proportion the amount of metal in the moving parts to this ratio. For " A " run No. 6, the maximum pressure was 298 Ibs., and the mean effective pressure as given in item 36 was 66.3 Ibs., thus giving a ratio of 4.50. For " B " run No. 6, the maximum pressure was 238 Ibs., and the mean effective pressure 56.5 Ibs., giving the ratio of 4.21. 44. Maximum Pressure to Compression Pressure. 72. Not only will variations in this relation tend to show changes in the quality of the mixture, due either to fluctuations in the quality of gas used, or to differences in the proportions of air to gas; but it also gives insight into possible changes in the form 46 WOBKING DETAILS OF A GAS ENGINE TEST. of the combustion chamber for securing the best possible flame propagation after explosion, thus insuring the most complete com- bustion of the mixture, or maximum measure of heat that becomes effective. It has been jclaimed that conditions have been attained under which this ratio has reached a figure as high as ten, but in general it is found to be about three or three and one-half, and occasionally as high as five. Cases have been reported of six and seven, but investigation revealed the fact that the pressures were measured from the atmospheric line. " A " run No. f = 3.28. " B " run No. 6 = 2.62. 45. Value of R. 73. In order to compute the temperatures corresponding to dif- ferent points in the indicated diagram, it is necessary that the temperature of some one point be known, and it is for this reason that the temperature of the exhaust gases proves of so much interest. In engines of the ordinary size it is hardly possible to perceive by means of the indicator diagram when a high-pressure spring is used any considerable reduction in the pressure of the mixture just after entering the cylinder. In most cases the reduction in pressure is slight and has very little effect upon the temperatures, and it is sufficiently accurate to regard the pressure of the mixture at full cylinder volume as that of the atmosphere, or 14.7 pounds per square inch. If the temperature of a perfect gas varies during expansion, the product of the pressure and volume is in proportion to the absolute temperature. " R " is the constant which enters into the mathematical state- ment of the above law, viz.; PV ET. Data Given. = atmospheric pressure per sq. ft. = 2,117 Ibs. per sq. ft. p ^ _ a = total vol. of cylinder in cu. ft. T m = absolute temperature of mixture filling cylinder before compres- sion begins. = item 29 + 459. To Find R a constant. Solution. By the above law : WOBKING DETAILS OF A GAS ENGINE TEST. 47 Examples. A" Run No. 6: Po = 2,117 Ibs. per sq. ft. t>a = -260 CU. ft. T m = 106 + 459 = 565. B " Run No. 6 : Po = 2, 117 Ibs. persq. ft. 0a = .1844cu. ft. ^, = 113 +459 = 572. 5<2 46. Temperature^ Degrees Fahr., at Compression. 74. Having determined "R" as in 45, the temperatures cor- responding to any point in the diagram are readily determined by the general formula used in obtaining "R" after solving for T. Data Given. In general. P = pressure in Ibs. per sq. ft. V= corresponding vol. in cu. ft. R = constant determined in 45. To Find T = absolute temperature corresponding to the point of the diagram se- lected. For the temperatures of compression. Examples. "A" Run No. 6: P pressure at compression per sq. ft. = 91 x 144 = item 35 x 144. V Vb = clearance vol. .Ooo cu. ft. R = .973 from 45. "B" Run No. 6. P pressure at compression per sq. ft. = 91 x 144 item 35 x 144. V = v b = clearance vol. = .037. R = .681 from 45. rp Solution. PV R T - 459 = F T = 91 x 144 x .055 __ 7410 _ 4590 _ 2 Tb = > LJ < _- - 7110 711 -459 =252F. 47. Maximum Temperature, Degrees Falir. 75. Since the maximum temperature does not necessarily cor- respond to the maximum pressure, but depends upon the maxi- mum value of the product of pressure -and volume, it would in general be determined by the formula used in 46. In cases where the ignition line rises vertically from the point 48 WOBKING DETAILS OF A GAS ENGINE TEST. of maximum compression and where the expansion curve drops at once from the maximum pressure, it is apparent that the maxi- mum temperature corresponds to the maximum pressure. Under these conditions, the volumes being equal, the absolute tempera- Fernald FIG. 19 tures will be proportional to the pressures. The diagrams from the two engines considered present the different conditions very clearly in the runs selected. Consider first the diagram for run No. 6, test " A." Data Given. p c maximum pressure, Ibs. per sq. in. = item 36. p b = compression pressure, Ibs. per sq. in. = item 8%.*X T b = absolute temp, at compression = item 46 + 459. To Find T c = absolute maximum temperature. Example. p c = 298 Ibs. per sq. in. p b =. 91 Ibs. per sq. in. T b = 282 + 459 = 741. If the same computation be made by the formula of 46, the clearance volume v b , is necessary. c 6 = .055 cu. ft. Solution. T c = 741 ~ = 2.429 2,429 - 459 = 1,970 F. By the method of 46 g , = 898xmx.05 = .y t o 2,429 - 459 = 1,970 F. Consider the diagram, Fig. 20, for run No. 6 of test " B." '76. In this case it is not apparent without some calculation at P V which point the maximum temperature will occur. Since T = ^ it is only necessary to determine the point for which the product WOKKING DETAILS OF A GAS ENGINE TEST. 49 of the pressure and volume is a maximum. The most direct and simplest method seems to be by direct trial by measurement, as follows : Fernald Female! FIG. 20. For the points 0, 1, 2, 3, 4, the volumes in cubic feet are re- spectively .0395 . .0417 .0438 .0453 .0460 and the pressures in pounds per square inches are 238 233 228 225 221 The products of the corresponding pressures and volumes are 9.42 9.74 10.00 10.20 10.15 showing the point marked 3 to have the highest temperature. Using the value of R deduced in 45, the temperature for the point 3 is found to be 225 x 144 x .0453 = 1,700 F. ENERGIES. 48. Brake Work, in Foot Pounds. 77. The usual method of measuring the output of an engine is by means of some form of friction brake. At times special dyna- mometers are used, but usually some form of the simple prony brake. For moderate powers the form of brake shown in Fig. 21 has been found very satisfactory. It consists of two or more cotton or hemp ropes one-half or five- eighths inch in diameter encircling the wheel and. held in place by five or six blocks of wood fitting loosely over the rim of the wheel, and to which the ropes are fastened. The bottom tie-bar 4 50 WORKING DETAILS OF A GAS ENGINE TEST. of the standards is fitted with a knife edge which rests on ordinary platform scales. The upper ends of the ropes are attached to a movable block, which can be adjusted by means of the hand- wheels to produce any desired friction upon the wheel. FIG. 21. 78. The downward pull of the ropes produced by this friction is transmitted through the frame of the brake to the scales. If the wheel face be fairly wide and the diameter of the wheel large, the surface exposed to the air will allow sufficient radiation to keep the temperature of the wheel low enough to avoid the neces- sity of the use of water. This form of brake has been found very steady, requiring little regulation. While the writer was at the Case School of Applied Science, such a brake was used upon the ten-foot fly-wheel of a Corliss en- gine from which seventy-five horse-power was readily taken, and no water was found necessary for a continuous run of three hours. Six ropes one-half inch in diameter were used, the wheel rim being fifteen inches in width. The same ropes were used for several seasons, and showed no signs of wear or burning. In many cases other forms of brake would undoubtedly prove more con- venient or desirable. WORKING DETAILS OF A GAS ENGINE TEST. 51 The determination of the brake work in foot pounds is as fol- lows : Data Given. P net pressure on scales, in Ibs. I = effective lever arm, in ft. JV = No. revs, per time interval. To Find Foot pounds per time interval. Examples. "A" Run No. 6 : P = 70 Ibs. 21 = D = 3.75 ft. N = 2,679 revs, for 10 mins, Tt = 3.14. "B" Run No. 6: P = 30 Ibs. 21 = D = 3.25 ft. N = 3,012 revs, for 10 mins. it =3.14. Solution. Ft Ibs. per min. = P 2nl (R. P. M.) In case of the special rope brake, I z radius of wheel, or 21 = 1), then ft. Ibs. per int. = PnDN. Ft. Ibs. per int. = 70 x 3.14 x 3.75 x 2,679 = 2,210.000 ft. Ibs. Ft. Ibs. per int. = 30 x 3.14 x 3.25 x 3,012 = 921,000 ft. Ibs. 49. Brake Work, Foot Pounds per Hour. 79. This is readily deduced from the last deduction: For " A " Run No. 6 = 2,210,000 x 6 = 13,260,000 ft. Ibs. For " B " Run No. 6 = 921,000 x 6 = 5,526,000 ft. Ibs. 50. Brake Horse-power, B. H. P. 80. Horse-power being ft. Ibs. per min. -D TT p __ ft. Ibs. per int. from 48 33,000 ' 33,000 x int. For A Run No. 6 : B. H. P. = ?^ = 6.7. oo,OUO x 10 For B " Run No. 6 : B. H. P. = -^J4' - = 2.79. 51. British Thermal Units Equivalent to B. H. P. 81. The heat unit being taken as the consumption standard, it is necessary, in order to determine thermal efficiencies, to express 52 WORKING DETAILS OF A GAS ENGINE TEST. the horse-powers, or ratio of doing work, in terms of this unit. Since one thermal unit is equivalent to 778 foot pounds, to convert horse-power to thermal units proceed as follows : Data Given. 1 H. P. = 33,000. ft. Ibs. per rain. , B - T - 1 B. T. U. = 778 ft. Ibs. B. H. P. = brake horse-power of 50. int. = time interval of item 2. To Find B. T. U. per int. equivalent to B. H. P. Examples. "A " Run No. 6 : B. H. P. =6.70 int. = 10 mins. "B" Run No. 6: B. II. P. = 2.79. int. 10 mins. Solution. min. for B. T. U. per int. = 42.4 x B. H. P x int. B. T. U. per int. = 42,4 x 6.70 x 10 = 2,840. B. T. U. per int. =42.4 x 2.79 x 10 = 1,180. 52. Indicated Horse-power, I. II. P. 82. The indicated horse-power is determined by means of the mean effective pressure obtained from the indicator diagram. When the load is variable these diagrams should be taken at fre- quent intervals, and it is often advisable to allow the pencil to trace three or four diagrams on the same card and use the aver- age mean effective pressure obtained from these. Under uniform conditions these successive tracings will show little variation. When the test is continued for many hours, so that the time inter- vals Are long, it is well to take cards at stated periods during the regular interval. These periods should seldom exceed fifteen minutes. When the regular time interval for all readings is ten or fifteen minutes one card for each interval is sufficient, provided slight variations only are found in the different cards as taken (see remarks under Pressures for Indicator Cards, following para- graph 31 of this paper, and for the calibration of indicator springs, see section xiv. of paper No. 0943, the " Report of the Committee of this Society for Standardizing a System of Testing Steam Engines." WORKING DETAILS OF A GAS ENGINE TEST. 53 TO DETERMINE THE INDICATED HORSE-POWEK. P = M. E. P. from diagram = item 36. L = length of strokes in ft. A =. area piston in sq. ins. -N = No. explosions per min. Examples. "A" Run No. 6: P = 66.3 Ibs. L = 1.04 ft. A = 28.3 sq. ins. N= 133.9. "B" Run No. 6: P - 56. 5 Ibs. L = .75ft. A =28.3 sq. ins. .# = 93.4. ~ 33,000 66.3 x 1.04 x 283 33,000 33,000 133.9 = 7.93 53. British Thermal Units Equivalent to /. 77. P. 83. The determination is the same as that of 51, with the ex- ception that indicated horse-power is substitued for brake horse- power. A" Run No. 6 : I. H. P. _= 7.93 B" Run No. 6 : I. H. P. = 3.40 B. T. U. = 42.4 x 7.93 x 10 = 3,360 B. T. U. = 42.4 x 3.4 x 10 - 1,440 54. Gas Horse-power. 55. B. T. U. Equivalent to Gas II. P. H^. 84. In order to determine the theoretically possible power, it is necessary to know the heat equivalent of the fuel used. This heat of combustion may be determined by chemical analysis or by means of a calorimeter. The calorimeter generally recommended seems to be the Mahler, for solid fuels and oils, and Junker for gas. (See " Report of Committee on Standardizing a System of Testing Steain Engines/ 7 paper ~No. 0943, and " Efficiency Test of a One Hundred and Twenty-five Horse-power Gas Engine/' by C. H. Robertson, paper No. 907, American Society of Mechanical Engineers.) Since the mixtures considered are explosive mixtures and are used under such conditions, a calorimeter designed and calibrated for such conditions should be used for accurate determinations. Such a calorimeter is now in operation at Columbia. When it is inconven- ient to secure either a chemical or calorimeter test, it is usually possible to learn through the company supplying the fuel its ap- proximate heat equivalent. 54: WORKING DETAILS OF A GAS ENGINE TEST. The number of heat units is equal to the heat equivalent of one pound of coal or oil, or one cubic foot of gas, multiplied by the quantity of fuel in corresponding units. Data Given. H f = heat of combustion of fuel deter- mined by analysis or calorimeter. .F=lbs. of coal or oil, or cu. ft. of standard gas per interval. To Find- Hi = heat equivalent to G. H. P. //, x 778 Gas H. P. = 33,000 x int. Examples. " A " Run No. 6 : H f 650 B. T. U. per cu. ft. gas at standard temp. 60 F. F ' = 25.2 cu. ft. gas for 10 mins. = item 25 -T- 6. int. . 10 mins. = item 2. "B" Run No. 6 : /// = 650 B. T. U. per cu. ft. gas at standard temp. 60 F. F 14.6 cu. ft. gas for 10 mins. = item 25 -f- 10. int. = 10 mins. item 2. Solution. = H f x F //, = 050 x 25.2 = 16,400 B. T. U. 16.400 x 778 <**'= 33.000x10 =88 - 6 - 77, = 6oO x 14.6 = 9,500 B. T. U. GasH P - 9 ' 500 x 778 - 2* 4 MM '-r- -33,000 x 10 ~ 56. Heat Supplied, B. T. U.,from Indicator Card = ///. 85. There is always a wide discrepancy between the supply of heat shown by the indicator by the pressure rise line BC of the diagrams and that shown by the calorimeter or chemical test of the fuel. The great difference in the values of these two quantities is readily seen by a glance at items 66 and 67, which show the efficiencies based on these different values. The computation for the heat supplied, as shown by the indica- tor diagram, involves not only the temperature of compression and the corresponding temperature from the expansion curve, but strictly the specific heat of the gases before and after explosion, and during the process of explosion a value which is indeter- minate and the total weight of these gases. This tends to seriously complicate the problem, but the specific heat will be as- sumed the same before and after explosion and can in both cases be regarded, without serious error, as the value given for air. WORKING DETAILS OF A GAS ENGINE TEST. 55 Gicen. Solution, T m = absolute temperature of mixture \ in cylinder before compression = item 29 + 459. T ag = absolute temp, of entering air and gas as computed in para- graph 29. Vag = vol. of entering air and gas per explosion at T ag as computed in Part I. of 29. r b clearance vol. of cylinder. w$ = wgt. per cu. ft. of mixture at T m as computed in 30. T m C v = specific heat at constant vol .1691. v t = T, = absolute temp, of point C of ! w m diagram. TI, = absolute temp, of compression = item 46 4- 459. Kxps = total explosions per time in- terval. To Find v t = vol. entering air and gas at T m . \ v t = total vol. per explosion of mix- j ture before compressing. w m = total wgt. of mixture in cylinder. , H\ = heat supplied in B. T. U. peri time interval. Examples. "A" Run No. 6 : T m = 106 + 459 = 565. T ag = 545. Vag= -1646 CU. ft. f> 6 = .055 cu. ft. w, = .0701 Ib. C,= .1691. T = 1,970 + 459 = 2,429. T b = 282 + 459 = 741. Exps. = 1,339 for 10 mins. 86. The determination of the temperature (T c ), corresponding to the point C of the diagrams is not always as readily made as in the case just cited, as may be observed by inspecting Figs. 10 and 20. In Fig. 19, which corresponds to run No. 6, of test " A," the line BC of the diagram coincides with the line drawn through B parallel to the line of zero volumes, thus making T c and the maximum temperature, deduced in 47, identical. When these fortunate conditions do not exist, as in Fig. 20, or run ]STo. e= .1646?^= .I7l0cu. ft. 545 v. = .171 + .055= .226cu. ft. w m = . 226 x .0701 = .158 Ib. Hi = .1691 (2,429 - 741) .158 x 1,839 = 6,040 B. T. L T . 56 WORKING DETAILS OF A GAS ENGINE TEST. 6 of test "B," it is necessary to continue the expansion curve to the point C, as in the computation for II' \ it is specified that the tem- peratures must be taken for constant volume points. When any question exists regarding the true value of n for the equation of the expansion curve near the point (7, the curve may be continued from points below by the eye and the value thus ob- tained for C checked with that found by the equation. In the present instance the pressure at C was found to be about 282 pounds. Having determined the pressure at C as just indicated, the PV temperature maybe readily computed by the formula T- p- or more easily by direct proportion, since the temperature at B is already known. By the latter method T r =T b l or T c = 711 \ f = 2,203 or 1,744 F. 7 ? 6 This result is quickly checked by the other method, or 288 x 144 x .037 Continuing with the original problem, B" Run No. 6 : T m = 113 H- 450 = 572 v b = .037 cu. ft. v s = .0976 + .037 = .1346 cu. ft, tO> = .0692 Ib. : w m = .1346 x .0692 = .009:3 lb. C,. = .1691 /// = .1691 (2,203 - 711) .0093 x 934 T c = 2,203 =2,190 B. T. U, T b = 711 .Ztapa. =-- 934 per 10 min. 87. In the solution of Heat Extracted, B. T. U. from indicator cards, = HJ, item 58, the same values of C v , w m , and Exps. enter the calculations. It is, therefore, well in working the above to take the product C v , w m , Exps. for each run and tabulate the results under a heading " K ?? for further use. Thus for "A" No. 6, K= .1691 x .158 x .1339 - 3.58, and for "B" No. 6, K= .1691 x .0093 x 934 = 1.47. WOBKING DETAILS OF A GAS ENGINE TEST. 57 57. Heat Extracted, B. T. U., ~by Observation = 7/ 2 . 88. This value is determined by an analysis of the exhaust gases from which the heat equivalent of a cubic foot of these gases is determined. Data Given. T e = absolute temp, exhaust at at- mospheric pressure. = item 14 of log + 459. T m absolute temp, of entering mix- ture = item 29 + 459. Op = specific heat at constant pressure. Tag = absolute temp, of combined air and gas as found in 29. v ag = combined vol. of air and gas per explosion at T ng . T k = absolute temp, of exhaust as analyzed. h = B. T. U. per cu. ft. exhaust gases at Tk as found by analysis. Exps. = explosions per time interval. w^ ~- weight per cu. ft. by analysis. To Find v k = vol. in cu. ft. at Tk per explosion. w/c total weight per explosion. H z = total heat exhausted, B. T. U., per time interval. Solution. T k ag T -L aa 2 = C p (T e - w k x Exps. + h 58. Heat Extracted, B. T. U., from Indicator Card = H 2 '. 89. This is the heat thrown off in the exhaust as derived from the pressures shown by the indicator card. Data Given. Th = absolute temp, of exhaust = item 37 + 459. T m = absolute temp, of mixture at at- mospheric pressure = item 29 + 459. K = C v x w m x Exps. as found in 57. To Find- Hv =heat rejected, B.T.U., per time interval. Solution. h - T m } 58 WOBKING DETAILS OF A GAS ENGINE TEST. Examples. "A" Run No. 6 : T h = 1,387 + 459 = 1,846. T m = 106 + 459 = 565. K = 3.58 from 57. " B " Run No. 6 : T h = 1,120 + 459 = 1,579. T m = 113 + 459 = 572. K=IA1 from 57. = 3.58 (1,846-565) = 4,580 B. T. U. = 1.47 (1,579-572) = 3,480 B. T. U. Both in this solution, and in that of 57, since the difference of temperatures is involved, the common factor may be omitted if desired, and the temperatures taken directly from the report blank in Fahrenheit degrees. Thus for " A " run No. 6. t h = 1,120' t m = 113. 1.47 (1,120-113) = 1,480 B.T.U. 59. Indicated Horse-power Minus Brake Horse-power. 90. The difference between these powers is frequently called the friction horse-power. It is not alone the power required of the engine to drive its own mechanism, but includes the error due to inability to take indicator cards every explosion. This is es- pecially important with two cycle engines with throttling gover- nors. The calculation consists simply in subtracting the value of item 50 from item 52. For " A " run No. 6 this is 7.93 - 6.70 = 1.23, and for "B" run No. 6, 3.40 - 2.79 = 0.61. 60. Throttling of the Entering Mixture, Cu. Ft. per Explosion. 91. It is found, as might be expected, that the final volume of the mixture in the cylinder before compression is not equal to the full cylinder volume if the mixture is taken at atmospheric pres- sure. This is caused in part by the brief time allowed for entering, and in part by valve friction. In large engines this throttling may become serious, and all valves should be positively moved and not moved by suction. Owing to many conditions that affect this result, the calculation of the amount is approximate only, but gives an idea of results of this throttling action. WuBKING DETAILS OF A GAS ENGINE TEST. 59 In computing 56 the value v g obtained is equal to the total vol- ume for explosion of mixture at atmospheric pressure before com- pression, expressed in cubic feet. The total volume of the cylinder minus this value gives the effect of throttling. " A " Run No. 6. Total cylinder vol. = .260 cu. ft. From 57, v 8 = .226 cu. ft. Throttling .034 cu. ft. " B " Eun No. 6. Total cylinder vol. = .1844 cu. ft. From 57, v 8 ,1346 cu. ft. Throttling = .0498 cu. ft. 61. Percentage of Throttling. This is the ratio of the cubic feet throttled to the total cylinder volume in cubic feet. " A " Run No. 6 : " B " Run No. 6 : 034 ~ = 13.1 per cent. = 27.0 per cent. 62. Work that would he Added if Expansion were Complete. 92. A point of considerable interest was presented in attempting to make the computations involved in this column. The math- ematical work required is given below : FIG. 22. To find the area under the expansion curve proceed as follows The general expression for the area is ffla A-\ pdv, M 60 WORKING DETAILS OF A GAS ENGINE TEST. Substituting the value of p found above f 2 A pi Vi n v~ n dv which reduces to A _ .z-L _ . n 1 A glance at this formula reveals the fact that the value of A, which corresponds to the work done, depends upon the value of n, and in carrying out the solution any variation in n makes such serious variation in the value of A that no dependence can be placed upon the values obtained unless the values of n can be guaranteed correct. The time at command does not allow further investiga- tion at present, but the trial solutions revealed a possible method of making more accurate determinations of the value of n than can possibly be made by the method employed in paragraph 28. The difficulty arising from slight variations in n prevented any at- tempt to supply the results called for in this column of the report. EFFICIENCIES. 93. The efficiency may be expressed in many different .forms, as indicated, and in general it is very essential, when referring to the efficiency of a gas engine, to designate clearly to which effi- ciency reference is made, in order to avoid serious misunder- standing. The mathematical deductions are so fully indicated in the head- ings of the various columns that further explanation about the details seems unnecessary, and only general remarks will be made under each paragraph. o T/ -L -7 item 50 63. Mechamcal - -- ^tem 52 94. This efficiency is the ratio of the power which can be taken from the engine to the power shown by the indicator card. It therefore depends much upon the smooth, easy running of the en- gine itself. WORKING DETAILS OF A GAS ENGINE TEST. 61 " A " Run No. 6 = ^ = .846 i .UO 9, 7Q " B " Eun No. 6 = |^ = .822 64 and 66. Thermal for B. II. P. and /. //. P. 95. In these cases the efficiency is based upon the total heat put into the engine as shown by the calorimeter or chemical analysis of the fuel. Item 64 shows what percentage of the total heat in the fuel is converted into useful work and item 66 shows the percentage of the total heat converted for both useful and use- less work. "A" Run No. 6: B" Run No. 6: 65 and 67. If the basis for computing the efficiency be that of the heat actually shown to be supplied by the indicator, then the thermal efficiency is much higher. This basis has been used in computing items 65 and 67. "A" Run No. 6: B" Run No. 6: F "-H.P.=S 68, 69 and 70. 96. In these columns are given other methods of estimating the efficiency, based as before on both the heat supplied and extracted 62 WOKKING DETAILS OF A GAS ENGINE TEST. as determined directly from the gases, and as determined from the indicator diagram. TT l _ TT I For item 69, l i , the efficiencies were H l 6,040 - 4,580 "A"RunNo.6: -^- = .242 "B" Run No. 6: 8 ' 1W ~J!'g = .824 iC, lyu The necessity of clearly designating the efficiency selected is made very apparent by a comparison of the values given in the pre- ceding paragraph. STANDARD GAS PER HOUR. 97. In order for comparison to be made it is very essential that some standard be adopted for estimating the quantity of gas used. The basis of reckoning item 25, which has previously been recommended by a few writers, seems to be the proper one, and therefore standard gas is interpreted to mean gas under atmos- pheric pressure and at a temperature of 60 degrees Fahr. 71. Fuel for Indicated Horse-power per Hour. 98. This is readily obtained by dividing the values in column 25 by the corresponding values in column 52. " A " Run No. 6 : ^^ = 19 cu ft - P er hr - < . "o " B " Run No. 6 : ^^ = 25.7 cu. ft. per hr. 72. Fuel and Igniter for Indicated Horse-power. In case of flame or hot tube ignition the gas used should be passed through a separate meter and for the data in this column the quantity of standard gas used for fuel combined with that used for the igniter will give the total standard gas per hour. This quantity, divided by the indicated horse-power, will give the de- sired value. 73 and 74. Fuel, and Fuel and Igniter, per Brake Horse-power. 99. The method of procedure is the same as in 71 and 72, save that the brake horse-power is now used instead of the indicated horse-power. WORKING DETAILS OF A GAS ENGINE TEST. 63 FUEL PETC B. H. P. il A" Run No. 6 : ^~ = 22.5 cu. ft. " B " Run No. 6 : |-^ =31.4 cu. ft. 75. Cost per Indicated Horse-power per Hour, Cents. 100. The value $1.00 per thousand cubic feet of standard gas is taken as a basis for determining the comparative cost of different engines. A similar deduction would be made for other fuels, based on an average cost of that fuel. In case the gas used for the igniter is reckoned in this cost, then when electric ignition is used the cost of maintaining the battery should also be considered, in order to make a proper comparison. For relative cost it is as well to disregard the igniter and base the computation alone on the quantity of fuel alone. Since the fuel used in run No. 6 was 19 cubic feet for " A " and 25.7 cubic feet for " B," it is readily seen that the cost per indi- cated horse-power per hour was 1.9 cents and 2.57 cents re- spectively. TOTALS AND AVERAGES. 101. In order to get a general series of values for the engine in question it is often well to average the results obtained under the same conditions. For this purpose space has been reserved on the report blank for the necessary totals and averages. HEAT BALANCE. 102. By means of the heat balance a general idea is formed of the distribution and uses of the heat. As is apparent, the first result is .the average of the results in item 53; the second of those in item 12; the third of those in item 58. To the last result is charged all the heat otherwise unaccounted for. The average of the British thermal units obtained from the gas as determined from item 55 is used as the basis in determining the percentages. PART II. A METHOD OF DETERMINING THE TEMPERATURES OF EXHAUST GASES. A METHOD OF DETERMINING THE TEMPERATURE OF EXHAUST GASES. 1. IN preparing detailed specifications and instructions for con- ducting tests of gas engines (paper No. 0933 presented before this Society at this meeting) the attention of the writer was di- rected to the necessity of an accurate and inexpensive method of determining the temperatures of exhaust gases. This problem had apparently received little attention, at least not sufficient to develop any simple means of making accurate determinations. In cases in which the results seemed to be reasonable, the apparatus used was far too expensive or too delicate for ordinary conditions, and efforts were at once centred upon the desired solution. 2. In the books at hand on engine tests, no mention is made of any method, and even in the very recent report of the com- mittee appointed by this Society " To Codify and Standardize the Methods of Making Engine Tests," the committee says (paragraph XX.) : "The computation of temperatures corresponding to various points in the indicator diagram is, at best, approximate. It is pos- sible only when the temperature of one point is known or as- sumed, or when the amount of air entering the cylinder along with the charge of gas or oil, and the temperature of the exhaust gases are determined.^ In the fine-print detailed instructions under the same paragraph the report states, " T' may be taken as the temperature of the exhaust gases leaving the engine, pro- vided the engine is not of the i scavenging ' type." Again, in referring to the value represented by T in formula 68 DETERMINING THE TEMPERATURE OF EXHAUST GASES. B of the same paragraph is found the expression, "If T be the observed temperature of the exhaust gases." 3. While references thus made indicate the necessity of obtain- ing these temperatures, yet nowhere in the report is there any suggestion of a method of making these determinations. Even if pyrometers and thermometers are regarded as sufficiently ac- curate, yet no measurements made at or near the muffler can give the true temperature of the exhaust gases unless proper correc- tions be made for the fluctuations in pressure. This at first ap- pears to present little difficulty, but more careful thought shows the fallacy of the first impression. Consider for a moment the action taking place at the opening FIG. 1. of the exhaust. Although the gases in the cylinder have under- gone rapid expansion after explosion, yet the expansion is far from complete, and at the point of release the pressure is still relatively high, as shown by a glance at Fig. 1. 4. At the instant the exhaust opens there is an outrush of gases at this high pressure and correspondingly high temperature. Then follows, upon the forward stroke of the engine, a flow of a large mass of gases through the exhaust port, at a pressure little above that of the atmosphere and at a temperature necessarily less than that of the first discharge. In order to make the succession of events more apparent an indicator was attached directly to the exhaust pipe, and the cards obtained, as shown in Figs. 2 and 3, verified the statements just made in regard to the action taking place within the pipe. The diagrams represent the same condi- tions, the spring used for Fig. 2 being only one-half as heavy as that used in Fig. 3. DETERMINING THE TEMPERATURE OF EXHAUST GASES. 69 5. There is, as it were, a mixture of pressures in the exhaust pipe and muffler, and also a corresponding mixture of tempera- FIG. 2. tures, which must rapidly adjust themselves to an equilibrium of pressures and of temperatures. Temperatures determined at the muffler are, therefore, not the temperatures corresponding to the pressure at exhaust, but those corresponding to a much lower pressure, which is not determined. This accounts, no doubt, for the very low values of exhaust tem- peratures which have been reported even by recognized authorities upon gas-engine problems. The problem, therefore, resolves itself into the determination of the temperatures of the exhaust at some known pressure. 6. As a matter of simplicity atmospheric pressure was the natu- PIG. 3. ral selection, and a method was at once sought for reducing the exhaust gases to atmospheric pressure without losing any of the heat to which they are entitled. It was at once decided that a receiver, of a form to be deter- mined, should be placed close to the exhaust outlet of the engine, and some means devised for admitting the exhaust gases and al- 70 DETERMINING THE TEMPERATURE OF EXHAUST GASES. lowing their pressure to fall to that of the atmosphere. The de- sired temperature could then be ascertained. 7. What the form of the receiver should be was not at first apparent, and, as practically no information could be found bear- ing upon the subject, the problem was reduced to one of experi- ment. The first steps in the development were necessarily very crude and the results were of value only as furnishing a basis upon which to judge future determinations, and as such were of great value. The first experiments were conducted as follows : Two cylinders of sheet iron were made, one ten inches in diameter and the other fourteen. They were sixteen inches high. The ten-inch cylinder, after being generously perforated near the bottom, was placed inside the fourteen-inch cylinder, the latter having several deep notches cut out at the top. A cover of the same material, and fifteen inches in diameter was made, with a central hole about two and one-half inches in diameter, through which the exhaust pipe from the engine could be passed. A T was placed as close to the exhaust outlet of the engine as possible, and from it one line of pipe was run directly to the exhaust muffler, as usual, and the other line brought out horizontally and at right angles to the first, and then directed downward to the receiver just described, the end of the pipe projecting about two inches through the cover, into the inside cylinder. Fig. 4 gives a rough idea of the arrangement. 8. Valves were inserted in both pipes, so that the passage of the gases to the receiver or to the muffler or to both at once could be regulated at will. In the receiver the gases were passed downward through the inside cylinder, out through the perforations and upward between the two cylinders, finally passing out through the notches in the top of the outside cylinder. The object of this arrangement was to prevent any direct draught or chimney action, which would cause an inrush of cold air at the bottom as soon as the inlet valve was closed. Two holes, large enough to receive the thermom- eters, were punched in the cover, one midway between the centre and the inner wall and the other about one-half inch from the inner wall. There was no expectation that temperatures even approaching correctness could be obtained by this arrangement, but such a preliminary step was essential in order to have values with which future results could be compared. DETERMINING THE TEMPERATURE OF EXHAUST GASES. 71 9. The exhaust was directed to the receiver, and after being allowed to flow until the cold air in the receiver was entirely expelled, was shut off and the thermometers quickly inserted. The gases were now held in the receiver at atmospheric pressure. The pressure before closing the inlet was much greater, but dropped almost instantly to that of the atmosphere when the FIG. 4. valve was closed. The difference in the readings of the two ther- mometers, one near the wall of the cylinder and the other about tAvo inches from the wall, was not sufficiently marked to be of importance. The temperatures observed were : 370 degrees Fahr. 395 394 degrees Fahr. 372 370 398 degrees Fahr. 400 10. Various problems were now to be considered. Radiation and conduction from the cylinders to the outside air might be so 72 DETERMINING THE TEMPERATURE OF EXHAUST GASES. rapid as to vitiate the results. The thermometers might be af- fected by radiation from the inside walls. Radiation from the iron exhaust pipe, which projected into the cylinder, might make the readings too high. Longer runs might tend to cause the cylin- ders to store up heat. Many such difficulties had to be considered, and, no data being found bearing- directly upon the subject, the experiments were continued. An asbestos lining was now placed in the outside cylinder, and the temperatures obtained were : 474 degrees Fahr. 511 degrees Fahr. 52$ degrees Fahr. 540 " 552 " 517 Evidently the gases were retained at a much higher tempera- ture than before, but were these higher temperatures due to ex- cessive storing up of heat, or simply to the prevention of excessive radiation ? A similar lining was also placed in the inside cylinder and the temperatures immediately shot up to over 600 degrees Fahr., which were unquestionably far too high. In all of the above experiments radiation through the cover was prevented by an asbestos lining. 11. After considering cylinders of various materials, a clay fire flue 10 inches in diameter was secured and used in place of the inner iron cylinder, the outside iron cylinder with its asbestos lining being retained. The temperatures now recorded were : 360 degrees Fahr. 484 degrees Fahr. 585 degrees Fahr. 498 " " 560 512 " " 564 541 " 554 552 " " 569 554 " " 576 405 442 465 469 567 These figures seemed to indicate a gradual storing of heat from the first to about 560 degrees Fahr., when the readings became more constant, but not sufficiently so to warrant the conclusion that the apparatus was nearly correct. The conclusions at once reached were that the volume for the gases was too small and the thermometers too near the walls. The absorbing of heat by the receiver must also be prevented. In DETERMINING THE TEMPERATURE OF EXHAUST GASES. 73 studying this problem it was seen to be undesirable to allow the gases to enter the receiver at such high pressures and tempera- tures, and that it would be of great advantage to admit the gases at a pressure and temperature little above those desired at the time of reading the thermometers. This would do away to a large extent with the tendency of the receiver walls to store up heat, as at no time would they be excessively heated. 12. The proper throttling was secured by the device shown in Fig. 5. It consists of a 2-inch T with a plug in the top, through which passes a |-inch bolt, and a nipple and cap in the bottom; the bolt FIG. 5. is supported by a helical spring, and in turn supports at the bottom a flat iron disk which rests against the 2-inch cap the bottom of the cap being freely perforated. By screwing down the nut at the top, against the spring, any desired resistance to the passage of the gases can be obtained, and at the same time any tendency to wire-drawing is obviated, as would not be the case if the throttling were done by means of the valve in the pipe alone. Before experimenting to any extent with this device for reduc- ing the pressure, a new clay fire flue, 18 inches in internal diame- ter, with cover of the same material, was obtained. In order as far as possible to prevent any radiation to the thermometer from 74 DETERMINING THE TEMPERATURE OF EXHAUST GASES. the iron pipe delivering the gases to the receiver, the lower end of the device was allowed to pass barely through the cover, ex- tending not over an inch below the inner face. 13. The bottom of the receiver was notched in several places to allow free passage of the gases from within. The gases were thus received at the top, passing downward and out at the bottom. FIG. 6. A rubber band 3 inches wide was bound about the bottom of the receiver, thus acting as a flap valve, the pressure of the gases entering the pot forcing the band outward, but the falling of the band preventing any inrush of cold air when the admission of the exhaust to the receiver was stopped. In Fig. 6 is shown the completed receiver as attached to the engine. Many series of experiments have been carried on by means of this device, with most satisfactory results. With the feed so ad- justed that the exhaust entered the receiver at a pressure but little DETERMINING THE TEMPERATURE OF EXHAUST GASES. 75 above that of the atmosphere, the storing of heat in the walls was practically prevented. 14. In case the exhaust was delivered to the receiver for an hour or more without ceasing there was a slight rise in tem- perature, but as in practice the exhaust is cut off about every 10 minutes no difficulty is experienced from this cause. The pressure under which the exhaust enters the receiver does not have to be closely regulated, as a slight difference does not affect the resulting temperatures, when taken at atmospheric pressure. Especially satisfactory results have been obtained when the pressure was so regulated that the temperature of the gases in FIG. 7. the receiver, while under pressure, was between 50 degrees and 100 degrees above the temperature at atmospheric pressure. 15. One or two preliminary tests will quickly determine what this temperature should be. The temperatures recorded from the new receiver did not range from 400 degrees Fahr. to over 600 degrees Fahr. but were : 200 degrees Fahr. 195 195 202 degrees Fahr. 201 203 203 degrees Fahr. 200 200 The radiation from the receiver was not large. The walls were 1 inch thick and the hand could at all times be held on the outside. Any change in the conditions tending to change the tempera- tures of the exhaust is quickly noticed by a corresponding change within the receiver. For example, if the point of ignition be changed, a corresponding change in temperatures is immediately 76 DETERMINING THE TEMPERATURE OF EXHAUST GASES. observed. With the point of ignition as shown by the diagram, Fig. 7, the following temperatures were recorded : 199 degrees Fahr. 198 198 197 degrees Fabr. 196 196 ] 97 degrees Fahr. 198 198 FIG. 8. 16. With the ignition retarded as shown by Fig. 8, the tem- peratures were : 210 degrees Fahr. 216 214 210 degrees Fahr. 212 211 210 207 degrees Fabr. 212 209 While making this particular series of experiments on points of ignition, the engine became stalled when set for a certain point of ignition and refused to run. The igniter was removed and FIG. 9. found to be badly burned. It was adjusted for sharper contact and a new series of readings taken. An immediate drop of about 50 degrees in the temperature re- DETERMINING THE TEMPERATURE OF EXHAUST GASES. 77 suited, showing at once the quick response of the receiver to changed conditions. The spark was now sharp and short, while previously the condition of the sparker was such that it was " hold- ing fire." The new series on the variation of the point of ignition resulted FIG. 10. as follows, the temperatures in each column corresponding to the point of ignition shown in the diagram having the same num- ber as the column of temperatures : For Fig. 9. 151 degrees Fahr. 149 151 152 152 For Fig. 10. 166 degrees Fahr. 168 168 167 167 For Fig. 11. 172 degrees Fahr. 176 " 178 175 178 17. Owing to the size of the receiver and to the necessity of having other connections made to the engine, the exhaust pipe FIG. 11. leading to the receiver was longer than desired, having a drop of about 1 foot and a horizontal length of 27 inches. The question of the necessity of covering the pipe, to prevent excessive radiation in conducting the hot gases to the receiver, was quickly settled by the following temperatures obtained : 78 DETERMINING THE TEMPERATURE OF EXHAUST GASES. Covered. 155 degrees Fahr. 155 154 156 158 158 158 160 Not Covered. 160 degrees Fahr. 158 158 155 156 157 156 157 Having become satisfied that the apparatus as outlined was work- ing with a reasonable degree of accuracy, the next step was to devise a receiver which can be erected quickly and cheaply, as it FIG. 12. is not always convenient to procure a fire flue of the right size. Accordingly, a receiver was built of ordinary brick laid together loosely, as shown in the cut, Fig. 12. 18. This receiver was made of two layers of brick, the inside layer being laid on the face and breaking joints, the outside layer being laid on edge, thus breaking joints both vertically and horizon- tally with the inner layer. While the cracks furnished sufficient passages to prevent any overcharging of the receiver, yet the break- DETERMINING THE TEMPERATURE OF EXHAUST GASES. 79 ing of the joints prevented direct draughts, or inrush of cold air. As first constructed, the volume of the new receiver was made equal to that of the 18-inch fire flue previously used, and the fire flue cover was fitted to the new receiver. The results were highly satisfactory, the temperatures being the same as before. The-interior was then partially filled with brick until the volume was reduced from 16 x 16 x 23 to 16 x 16 x 13, and again tested, with the same results. In all of these tests with the two larger receivers the thermom- eter bulbs were kept about 4 to 7 inches away from the walls and from the entering pipe. In the last receiver, when partially filled with brick, the thermometer bulbs were placed about the same distance from the cover and bottom. 19. It seems unnecessary, therefore, to have excessive volume, but there must be sufficient space so that the thermometer bulbs shall not be too near the retaining walls. Experiment indicates that the figures suggested for these distances are about right. During the test the valve leading to the mum er in the . main exhaust is kept wide open, unless the exhaust pipe is larger than is needed for the quantity of exhaust, and the valve in the pipe leading to the receiver is opened as desired. It is necessary to expel fully the cold air in the receiver before any readings can be taken. With the larger receiver and an 8 horse-power engine this required about 20 minutes. The time can be much reduced when desired, by careful manipulation of the valves after one becomes familiar with the apparatus. 20. It is of great value to keep suspended within the receiver at all times a thermometer of sufficient range not to be broken by accidental increase of temperature. In the initial warming of the receiver this thermometer will readily show when the tem- perature has become constant. It also serves as a very efficient guide in adjusting the pressure as controlled by the inlet. For most of the readings taken the pressure was so regulated that this permanent thermometer recorded, while the gases were still under pressure, temperatures from 50 degrees to 70 degrees Fahr. higher than the final temperatures at atmospheric pressure. The clay cover not being obtainable in all cases, gave way to one made of 2-inch plank, chinked with cotton waste, and this has proved entirely satisfactory. 21. Previous methods of measuring the temperatures of the 80 DETERMINING THE TEMPERATURE OF EXHAUST GASES. exhaust have in most cases furnished results which were surpris- ingly low, and not until Professor Robertson's paper on " An Effi- ciency Test of a One-hundred-and-twenty-five Horse-power Gas Engine " (Vol. XXI. Transactions A. S. M. E., p. 396), has the writer seen a series of temperatures for the exhaust, which seemed reasonably accurate. Professor Robertson secured by means of a copper-ball calorimeter values above 1,000 degrees Fahr., and in one instance records 1,209 degrees Fahr., occasioning this remark by Professor Thurston : " The possibilities of still further thermo- dynamic gain are indicated by the temperature of the exhaust gases, above 1,000 degrees Fahr., and far above that of the prime steam of our steam engines. 77 In Professor Robertson's second paper upon the same subject (Transactions, Vol. XXII., p. 612) he reports temperatures of the exhaust, as found by a La Chatelier pyrometer, ranging from 1,410 degrees Fahr. to 1,805 degrees Fahr., and states: "These temperatures appear to be rather high so high in fact that the author has examined other data at hand to see if any confirmation of the above figures could be found." It is the opinion of the writer that the last figures quoted by Professor Robertson are not far from correct for the engine tested, but the pyrometer used is far too expensive and requires too much special apparatus, as well as special calibration, to make its use possible in most tests. 22. It takes but a moment's consideration of the problem to show that very little if any thermodynamic gain is possible by any attempted reduction of the temperatures of exhaust, in the average gas engine of good modern design, unless accompanied by a reduction of the terminal pressure as shown by the expan- sion curve. 23. With terminal pressures ranging near 50 pounds it is quickly shown that the exhaust temperatures must of necessity be much higher than generally recorded. Suppose, for example, that the expansion line of the card shown in Fig 9 be continued to full cylinder volume, as shown by the point H. The pressure at H is found to be 50 pounds absolute. Suppose the temperature of the mixture in the cylinder, composed of air and gas, taken in during the suction stroke and mixed with the neutral gases filling the clearance space, to be only as high as that of the room, say TO degrees Fahr., or 529 degrees absolute at the point A, Fig. 9. DETERMINING THE TEMPERATURE OF EXHAUST GASES. 81 Since the volume at H is the same as that at A, the absolute temperatures will be proportioned to the absolute pressures, or if T a = absolute temperature at A = 529 degrees. P a = absolute pressure at A = 14.7 pounds. P h = absolute pressure at // = 50 pounds, then jT A , the absolute temperature corresponding to the pressure 2> at H will be derived from T h = T a TT/ T h = 529fS = i; 800 de ~ -* a grees absolute or 1,341 degrees Fahr. with the temperature of the mixture taken at TO degrees Fahr. only. Actually the tempera- ture of the mixture is much higher than this, and by means of the new apparatus described in this paper this temperature is readily deduced. The temperature secured at atmospheric pres- sure by means of the exhaust receiver is the temperature of the neutral gases that fill the clearance space of the cylinder. The method for determining the temperature of the mixture after having obtained the temperature of the exhaust gases is described in detail in paragraph 29 of paper No. 0933, to be presented at this meeting. 6 INDEX. PAGE Introduction iii PART I. Air 18 Cubic feet and cubic feet per hour 20 Maximum velocity of 20 Specific heat of - 21 Temperature of 20 Weight of 20 Averages 63 Brake work in foot pounds 49 Brake work in foot pounds per hour 51 Brake horse-power 51 British thermal units equivalent to 51 Efficiencies for : GO, 61 Brit'sh thermal units, equivalent to brake horse-power 51 " equivalent to indicated horse-power 53 " " " equivalent to gas horse-power 53 " " ' extracted, by observation 57 " extracted, from indicator card 57 " " " supplied, from indicator card. 54 Cost per indicated horse-power per hour 63 Data sheet 2 Efficiencies 60 Thermal 61 Thermal for brake horse-power 61 Thermal for indicated horse-power 61 Energies 49 Exhaust 40 Maximum velocity of 43 Specific heat of 43 Temperature of 40 Explosions 12 Explosions per minute 12 Fuel.... 21 Cubic feet, or gallons 21 Maximum velocity of 22 Per brake horse-power 62 Per indicated horse-power 62 Specific heat of 22 Temperature of 21 Weight of S2 84 INDEX. Gas 22, 62 Standard, per hour 22, 62 Standard, j er brake horse-power 62 Standard, per indicated horse-power 62 Gas engine tests , 6, 8, 13 Data sheet of : 2 Log of 4 Report of 6, 8, 13 Gas horse-power 53 British thermal units, equivalent to 53 Heat: Absorbed by jacket water 17 Extracted, British thermal units, by observation 57 " " " " from indicator card 57 Specific of air 21 Specific of exhaust 43 Specific of fuel 22 Supplied, British thermal units, from indicator card 54 Heat balance 63 Horse-power : brake 51 British thermal units, equivalent to brake 51 " " " equivalent to gas 53 " " " equivalent to indicated 53 Cost per indicated 63 Fuel per brake 62 Fuel per indicated ... 62 Gas 53 Indicated 52 Indicated minus brake 58 Introductory remarks v, vi Indicated horse-power 52 British thermal units, equivalent to 53 Cost per hour per 63 Fuel per hour per 62 Indicated horse-power brake horse-power 58 Indicator card 33 Heat extracted, British thermal units, from ... 57 Heat supplied, British thermal units, from ... 54 Pressures from 33 Ig Her 2 Fuel for 62 Jacket water 16 Heat absorbed by 17 Maximum velocity of 17 Temperature range of 16 Weight of 16 Log of gas engine test 4 Mechanical efficiency 60 Mixture 28 Maximum velocity of 33 INDEX. 85 Mixture : Per cent, of throttling of entering 59 Temperature of 28 Throttling of entering 58 Weight of 32 "n" 23 Value of, in P V n = P, F, 23 Object of test 6 Preliminaries of test 5 Pressures from indicator cards 33 At end of compression 38 At end of expansion 39 If expansion carried to end of stroke 39 Maximum 38 Mean effective , 40 " R," value of 46 Revolutions 11 Revolutions per minute 11 Ratios 43 Air to gas to neutrals 43 Maximum pressure to mean effective pressure 45 Maximum pressure to compression pressure. 45 Revolutions to explosions 12 Stroke to expansion 44 Volumes 2 to Vi 44 Remarks iii Introductory iii Report of test 6, 8, 13 Specific heat 21 Air 21 Exhaust 43 Fuel 22 Standard gas 22, 62 Per brake horse-power 62 Per indicated horse-power ... 62 Per hour 22, 62 Time intervals 11 Test : Log of 4 Object of 6 Preliminaries of 5 Report of 6, 8, 13 Temperature : Air 20 At compression 47 Exhaust 40 Fuel 21 Jacket water 16 Maximum 47 Mixture 28 Thermal efficiencies. . . 61 86 INDEX. Throttling of entering mixture 58 Per cent, of 59 Totals , 63 Velocity 20 Maximum for air 20 ' ' for exhaust , 43 " for fuel 22 " for mixture 33 Valve index reading 23 Air 23 Gas 28 Water, jacket 16 Heat absorbed by 17 Maximum velocity of 17 Temperature range of 16 Weight of 16 Weight : Of air 20 "exhaust 23 1 ' fuel 22 " mixture 32 Work: Brake in foot pounds 49 Brake in foot pounds per hour 51 That would be added if expansion were complete 59 PAKT II. Covering pipes 77 Effect on exhaust temperatures 78 General Remarks and Method of Procedure 67 Receiver 70, 72 Forms of 72, 78 Size of ' 73, 79 Temperatures, recorded 75, 76, 77, 78 With varied points of ignition 76 Discussion of high exhaust 80 Thermometers 70, 79 Positions of 70, 79 Throttling device . 73 INSTITUTIONS WITH WHICH THE WRITER HAS BEEN CONNECTED MAINE STATE COLLEGE UNDERGRADUATE STUDENT - - 1888-1892 MASSACHUSETTS INSTITUTE OF TECHNOLOGY GRADUATE STUDENT - 1892-1893 CASE SCHOOL or APPLIED SCIENCE INSTRUCTOR 1893-1896 CASE SCHOOL OF APPLIED SCIENCE ASSISTANT PROFESSOR - - 1896-1900 COLUMBIA UNIVERSITY GRADUATE STUDENT 19CO-1902 DEGREES AND HONORS CONFERRED B.M.E. MAINE STATE COLLEGE - - 1892 M.E. CASE SCHOOL OF APPLIED SCIENCE - 1898 FELLOW COLUMBIA UNIVERSITY - ... 1900 M.A. COLUMBIA UNIVERSITY - - - - 1901 SOCIETY MEMBERSHIP AMERICAN SOCIETY OF MECHANICAL ENGINEERS SOCIETY FOR THE PROMOTION or ENGINEERING EDUCATION YC 127