INDUSTRIAL AND ENGINEERING CHEMISTRY
1094
(4) Bayley, C. H . , and Hopkins, C . I’..Can. J . Research, 11, 50519 (1934). (5) Bridgeman, 0. C., and Querfeld, Dale, IND.Eso. CHEM.,25, 523-5 (1933). (6) Brown, G. G., paper presented before 3rd midyear meeting o Am. Petroleum Inst., Tulsa, Okla., May 18, 1933; Oil, P a i n t , Drug Reptr., 1933, July 24, p. 28D, and July 31, pp. 36-8.
(7) Brown, L. T., Iowa State Coll. Comm. on Use of Alcohol in Motor Fuel, Progress Rept. 2 (1932). (8) Brown, L. T . , and Christensen, L. M., IWD. ENG.CHEY.,28, 650-2 (1936). (9) Christensen, L. M., Hixon, R. M., and Fulmer, E. I., Iowa State C ~ l lJ. . Sei., 7, 461-6 (1933). :lo) Ibid., 8, 175-9 (1934). :11) Ibid., 8, 237-44 (1934). 32) Ibid., 8, 245-50 (1934). :13) Christensen, L. M., Hixon, R. M., and Fulmer, E. I., “Power Alcohol and Farm Relief,” New York, Chemical Foundation, 1934. (14) Fieldner, A. C., Straub, A. h.,and Jones, G. W., IWD.EXG. CHEM.,13, 51-8 (1921). (15) fiitzweiler and Dietrich, World Petroleum Congr., London, Proc. lQSS, 2, 784-7 (1934). (16) Gray, R. B., Agr. Engr., 15, 106-9 (1934). (17) Howes, D. A,, J . Inst. Petroleum Tech., 19, 301-6 (1933).
VOL. 28, NO. 9
(18) Hubendick, E., Petroleum Z . , 26, 3-9 (1930). (19) Hubendick, E., “Sulfite Alcohol as a Motor Fuel,” Svensk Motortiding, 1925. (20) Hubendick, E., Trans. Fuel Conference, World Power Conference, London, 1928, 3, 724-48 (1929). (21) Hubendick, E . , 2. Spiritusind., 53, 231-2 (1930). (22) Kuhring, M. S., Can. J . Research, 11, 489-504 (1934). (23) Miller, Harry, Agr. Engr., 14, 274-6 (1933). (24) Miller, Harry, Univ. Idaho Agr. Expt. Sta.. BUZZ.204 (1934). (25) Moyer, R. A., and Paustian, R. G., Iowa State Coll. Comm. on Use of Alcohol in Motor Fuel, Progress Rept. 7 (1933). (26) Naphtali, M., Chem.-Ztg., 54, 371 (1930). (27) Nash, A. W., and Howes, Donald, “Principles of Motor Fuel Preparation and Application,” Vol. 1, pp. 416-21, New York, 1935. (28) Ibid., Vol. 1, pp. 422-3. (29) Ricardo, H. R., “The High-speed Internal Combustion Engine,” Table X, London, 1931. (30) Ross, J. D., and Ormandy, W. R., J . SOC.Chem. I n d . , 45, 27380T (1926); Trans. I n s t . Chem. Engr., 4, 104-14 (1926). (31) Sauve, E. C., Mich. Quart. Bull. 15, 287-92 (1933). (32) Spausta, Franz, Er&Z u. Teer, 8 , 282-6 (1932). (33) Wawrziniok, Otto, Transportation Inst., Tech. Coll. of Saxony, Dresden, Monograph IV, Berlin, 1929. RECEIVED May 28, 1936
Engine Performance with Gasoline and Alcohol
L. C. LICHTY AND E. J. ZIURYS Yale University, New Haven, Conn.
HE object of these tests was to determine the performance characteristics of both gasoline and 190-proof ethyl alcohol as fuels for internal combustion engines. The gasoline used was the standard grade marketed by the Socony-Vacuum Corporation in Southern Connecticut in the fall of 1934. The A. S. T. M. distillation curve for this fuel is shown in Figure 1. The specific gravity of the gasoline was 0.745. Commercial ethyl alcohol (190 proof) was used in the alcohol tests; its specific gravity was 0.805. Three cc. of tetraethyllead were added to each gallon of gasoline for the tests a t compression ratios of 6 and 7 to 1; 5 cc. of tetraethyllead and 10 per cent of a gallon of Ani101 were added to 90 per cent of a gallon of gasoline for the tests a t a compression ratio of 8 to 1. These antiknock materials were added to the gasoline to prevent detonation a t the foregoing compression ratios. The first series of tests was run on a single-cylinder C. F. R. engine a t constant speed, varying the compression ratio, the mixture ratio, and the amount of heat supplied to the
air-fuel mixtures. A second series of tests was run on a six-cylinder 1935 Chevrolet standard engine, varying the speed, load, and mixture ratio.
Theoretical Aspects The power that can be developed in a given engine depends primarily upon the chemical energy of the charge that can be induced into the engine cylinder. However, a number of other factors influence appreciably the power obtained-namely, the air-fuel ratio, the amount of fuel vaporized a t the closing of the intake valve, the mixture temperature, the manner in which combustion takes place or the antiknock value of the fuel, and the nature of the products formed by the combustion process. The factor dealing with the burning characteristics may be eliminated by the use of a fuel which is high in antiknock characteristics and will permit optimum spark advance and wide-open throttle conditions. CHEMICALENERGY.The liberation of the chemical energy during the combustion process in the internal combustion engine produces the rise in temperature and pressure of the charge, which results in the work output of the engine. Assuming constant-volume combustion without heat loss . to the walls, the energy equation for the process is:
+
where
(1) c Em,, = EPll C = chemical energy of charge E,, = internal energy of mixture at end of compression,
at temperature tt
E,, -
k
Oo
lo
zo 30 4 0 50 60 EVAPORATED
FUEL
70
m
= internal energy of products at end of combustion, at temperature ta
loa
PEPCEnT
FIGURE1. A. S. T. M. DISTILLATION C U R v E FOR THE GABOLINE TESTED
From the constant-volume calorimeter for determination
of heating value of a fuel, the following energy equation results:
INDUSTRIAL AND ENGINEERING CHEMISTRY
SEPTEMBER, 1936
~
I
This paper deals with the power, fuel consumption, and other performance characteristics of internal combustion engines when using gasoline and ethyl alcohol as fuels. Theoretical analysis shows ideal possibilities ranging from 2.0 per cent increase in power with gasoline compared to pure alcohol, to 8.6 per cent increase with pure alcohol compared to gasoline, depending upon mixture conditions. The water in 190-proof ethyl alcohol has a negligible effect on power but increases the specific fuel consumption
+
where Q.
=
+
C Em,i= E,,, Qt heating value at constant volume
(2)
about 6.6 per cent, owing to lowered heating value per given quantity of fuel compared to pure alcohol. Tests on a variable-compression single-cylinder C. F. R . engine and on a 1935 Chevrolet engine under various conditions show a small average increase in power (not much more than experimental error involved) in favor of the 190-proof alcohol. However, the specific fuel consumption with 190-proof alcohol is about 60 per cent higher on a weight basis, and about 50 per cent higher on a volume basis than with gasoline.
11,930 B. t. u. per pound of fuel (6628 calories per gram) will be :
Combining Equations 1 and 2 . Qv
(E,
- Etl)Produets
CaHia
+ 12.5 02 + 47.25 Nz
2 CO, + 9 HzO + 47.25 N1
Thus, 60.75 moles of mixture contain the heating value of 1 mole of octane. On a corrected basis of 19,200 B , t . u . lower heating value* per pound of fuel (10,661 calories per gram), each mole of correct mixture will contain 19'200 60.75
= 36,030
B. t. u. (20,017 cal.)
The reaction equation for ethyl alcohol, CzHeO
+ 3 + 11.34 Nz 0 2
2 COz
+ 3 Hz0 + 11.34 Nz
indicates that the heating value contained in each mole of correct mixture, based on corrected lower heating value* of
* Corrected to the lower heating value at constant volume and including the internal latent heat of evaporation.
11J930 46 = 35,800 B. t. u. (19,889 cal.) 15.34
(3)
Thus the heating value of the charge a t constant volume i- equal to the internal energy change of the products for the constant-volume combustion process and may be used to determine the maximum temperature possible for a given air-fuel mixture and process. The bomb calorimeter determination of heating valuei: starts with the fuel in liquid form. The combustion process in the internal combustion engine starts near the end of compression with the fuel presumably in vapor form. Thu. the internal latent heats of the tn-o fuels should be added to the respective heating values as determined in the bomb calorimeter, depending on the amount of fuel vaporized. The effect of evaporation of a fuel during the compression process is to lower the compression curve and require lesb nork of compression. Howerer, this also lowers the temperature around the cycle, which tends to increase the efficiency and work of the cycle because of the effect of variable -pecific heats and chemical equilibrium. However, the actual effect of lowering the temperatures of the cycle from this cause is negligible. The heating value of fuels varies considerably but the air required for complete combwtion varies in much the qame manner as the heating value, making the heating value per unit volume of mixture, under given conditions, about the same for a given type of fuel. Using the octane reaction equation which represent. very nearly the relation for gasoline:
Original data from reference 4.
1095
Thus a given volume of the correct mixture of vaporized octane and air will have 0.6 per cent more heating value than the same volume of correct mixture of vaporized ethyl alcohol and air, both mixtures being a t the same pressure and temperature and both fuels being completely evaporated. The correct air-fuel ratios by weight are 15.11 for octane (being practically the same for gasoline), and 8.99 for ethyl alcohol. MIXTURETEMPERATURE. The amount of heat supplied the mixture in the manifold and the amount transferred to it in the cylinder from the clearance gases and the cylinder n-alls determines the amount of fuel evaporated and the final mixture temperature. The minimum mixture temperature required for 100 per cent evaporation of the gasoline used in these tests can be determined by using Bridgeman's method ( I ) for determining equilibrium air distillation temperatures from the -4.S. T. M. distillation curve. For complete evaporation of the fuel in a 16.11 air-fuel ratio the equilibrium air distillation temperature is 101" F. (38" (3,). The minimum heat required to raise the temperature of the mixture from an assumed air and fuel temperature of 70" F. (21" C.) will be:
+
Q = JfaCpa(Tz- 70) + -lf,C,,,,(T~ - 70)t P(L) where Ma, M, = pounds of air and fuel, respectively C,,, C,, = specific heats a t constant pressure for air and fuel, respectively P =: part of fuel evaporated L = latent heat of fuel Thus for the gasoline used, Q
= 15.11 X 0.24(101-70) = 274 B. t. u. per lb. of
+ 1 X 0.70(101-70) + 1.00 X 140
fuel (152 oal. per gram)
One mole of correct octane-air mixture has 114 + 60.75 = 1.877 pounds or grams of octane, whereas one mole of correct ethyl alcohol-air mixture has 46 f 15.34 = 2.999 pounds or grams of ethyl alcohol. Thus, equal volumes of the two gaseous mixtures at the same pressure and temperature will have 2.999 + 1.875 = 1.60 pounds or grams of alcohol in one mixture to 1.0 pound or gram of octane in the other. t Based on the assumption that liquid and vapor apecific heats are the same. Thilr item is small and the error introduced is negligible.
INDUSTRIAL AND ENGINEERISG CHEMISTRY
1096
If the alcohol-air mixture is at 101' F. (38" C.), the amount of heat required for the same volume of mixture will be Q
(101-70) 777 B. t. u. (432 cal.)
= l.6[8.99 X 0.24 X
+ 1 X 0.7(101-70) + 3971 =
Assuming that the alcohol mixture receives the same amount of heat as the gasoline mixture, the following relation remlts: 274 = 1.6 iS.99 X 0.24(Tz - 70)
+ 1 X 0.70(T2 - 70) + P(397)]
The assumption of various values for T z , the mixture temperature, results in corresponding values of P , the part evaporated. The actual air-fuel ratio is fixed a t 8.99 for the correct mixture, but the air-vapor ratio will be air-fuel ratio Air-vapor ratio = part evaporated
VOL. 28, NO. 9
The same quantity of air is induced in both cases with no evaporation of the fuel, since it i q a-eumed that the fuel does not evaporate before the intake valve closes or e1.e that the fuel is injected into the cylinder after intake valve closure. d given quantity of air will require 59.75 14.34, or 4.17 moles of alcohol compared to 1 mole of ga2oline. This indicates about 2.2 per cent more heating value for the alcohol charge, based upon heating values for liquid fuels. EFFECTOF SPECIFICHEATSOF PRODUCTS. The specific heat of the products and the heating value per mole of mixture fix the temperature rise of the products of combustion, neglecting chemical equilibrium effects. The mean specific heats a t constant volume for the range of 1000" to 4000" F. (556' to 2222" C.), for the products per mole of air-fuel mixture, as computed from data given by Marks is), are 7.26 and 7.42 for the gasoline and alcohol mixtures, re5pectively. This indicates about a 2.2 per cent higher temperature and pressure rise, which means approximately this much more work from the gasoline-air mixture for this effect. EXPASSIOS OF MOLES DURISG COMBUSTIOS.The increase in moles of products compared to moles of mixture has the same effect on pressure as a corresponding increase in absolute temperature. Octane has a 5.76 and ethyl alcohol a 6.52 per cent increase in products compared to niixture moles. This indicates about 0.8 per cent more increase for the alcohol mixture than for the gasoline mixture. EFFECTOF RATER IX ALCOHOL. The effect of water in the 190-proof alcohol, which is 93.8 per cent ethyl alcohol by weight, is to introduce about 0.17 mole of water into the mixture of 1 mole of ethyl alcohol and 14.34 moles of air. If the water is completely evaporated, it displaces 0.17 -+ (15.34 0.17), or 1.1per cent of the mixture volume and reduces the combustible charge by this amount. Outside of this possibility of reducing the mixture induced, the water has no appreciable effect on the performance with alcohol. It does, however, reduce the heating value per gallon by 6.2 per cent which increases the specific fuel consumption over pure ethyl alcohol by a corresponding amount. Computation of maximum pressures of combustion with quantities of water up to 1 pound per pound of octane in an
Thus the relation between the mixture temperature and the air-vapor ratio for the given heat transfer was determined and iq plotted in Figure 2 as "computed from heat input." The a i r - v a p o r ratio that can exist at any temperature is determined by the saturated 2 20 c temperature-pressure relation 5 for alcohol and by Dalton's P( ' 5 partial p r e s s u r e r e l a t i o n , 8 This w a s d e t e r m i n e d b y S t r e e t e r and Lichty (e) at & 10 9 various temperatures and is a 50 60 10 eo plotted in Figure 2 as "maxiM'XT"Rf T€"PfR*WRf m u m p 0 s s i b 1e a i r - \, a p 0 r FIGURE2. REL~TIOS BEratios." The intersection of TWEENMIXTURETEMPERAthe t w o c u r v e s a t an airTCRE AND AIR-VAPORRATIO vapor ratio of 16.5 indicates that 274 B. t. u. (152 calorie;) supplied the mixture results in 8.99 16.5 = 54 per cent of the aloohol being evaporated with a resultant minimum mixture temperature of 55' F. (13" C.). Thus, the alcohol mixture temperature will be about 46' F. (26' C.) lower than the gasoline mixture temperature with 100 per cent evaporation for the gasoline and the same heat supply for both mixtures. This indicates a greater relative charge density for the alcohol mixture of 8.9 per cent. However, 46 per cent of the alcohol is in the liquid state and occupies a negligible volume. This permits an increase in charge of about 0.46 f (15.34 - 0.46), or 3.1 per cent, making the same volume contain about 108.9 X 103.1 = 112.3, or about 12.3 per cent more charge. If both mixtures were a t the same temperature and volume, the gasoline mixture would have 2.0 per cent more heating value than the alcohol mixture, c o r r e c t i n g for the partial evaporation of the alcohol. Thus, while temperature and partial evaporation increase the alcohol charge to 112.3 per cent for the same volume, the gasoline mixture has 102.0 per cent heating value compared to the 100 per cent charge for the alcohol mixture. From Figure 2 it is obvious that, a t atmospheric pressure, 71" F. (22" C.) is the minimum temperature a t which an 8.99-1 alcoholair mixture can exist with 100 per cent evaporation of the fuel. Comparison of the two correct mixtures a t their minimum temperatures for complete evaporation of the fuel indicates a greater relative charge density of 5.6 FIGURE 3. SECTIOXAL VIEW OF C. F. R. ENQINECYLINDERHEADFOR MOTORMETHOD per cent for the alcohol-air mixture.
+
IYDUSTRIAL AND ENGINEERING CHEMISTRY
SEPTEMBER, 1936
0 W A T S HEATINPUT
4
8
12
AIR-FUEL I'IGURE
4
16
8
20 4
R A TI0
12
16
20
A/R-FU€L RA7/0
DIFFEREXCES BETWEEN M 4NIFOLD (C F R
l\.IIXTURES AND ETr,IsE)
ROOMAIR
TEMPERATURES
1097
line-air mixture should show t h e o r e t i c a l l y 2.0 per cent more power. W i t h t h e same amount of heat input, the correct alcohol-air mixture should show theoretically 8.6 p e r c e n t m o r e power. With no evaporation the power should be about 0.8 per cent higher for the correct alcohol-air mixture. With complete evaporation and minimum mixture t e m p e r a t u r e in both cases, the power should be 3.5 per cent higher with the correct alcohol-air mixture. These results are obtained from equilibrium air-tfistillatioii cornputations which can neyer exist in the short time allon-ed betw een the time
o c t a n e - a i r mixture, 58 52 made by Goodenougli 56 50 a n d F e l b e c k (3), 54 48 showed no appreciable 52 46 change in maximum pressure. The Brinker50 44 I, hoff tests ( 2 ) on truck 42 engines showed no $ effect o n p o w e r and 2 A / P - f U € L RATIO efficiency with w a t e r quantities up to six56 54 tenths of the weight of 54 52 gasoline. 52 50 The water should 50 48 evaporate during the c oiripr e s s i o n stroke 4 5 6 7 8 and reduce slightly the AIR-FULL RA TI0 A/R-fU€L RATfO CONPR€SS/ON P A T/O work of compression, (C.F. R. ENGINE) BASEDON AIR AND VAPORVOLUMES but bhould S ~ O Wdcwn FIGURE 5. VOLUMETRICEFF~CIENCIES the rate of combusthe fuel leaves the carburetor jet and tile clohinx of the intion, the two effects tending to offset each other. take valve. Consequently, the results that might be exSummary of Theoretical Aspects pected in practice woukl probsblv lie somewhere between 0 and 2.0 per cent in bhe first case- and between 0 and 8.6 per of the foregoing analysis, omitting the effect The cent in the second case, etc. of water in alcohol which would decrease the values for the FUELC o N s u m T I o N . The mixbure Tyhich results in the alcohol mixture, are summarized in Table I for the following larger power output per unit volume of correct mixture four different sets of conditions: induced, in the gaseous state, would have the lower specific 1. Both fuels completely evaporated and a t the same temconsumption On a gaseous mixture basis. perature, which requires mu& more heat input for the alcohol-air ever, alcohol is a t a distinct disadvantage since, in equal mixture. 2. The gasoline completely evaporated and the alcohol 54 -____ _ _ _ ~ ~ _ _ _ - .~ -~~_ _ _ _ per cent evaporated, which requires the same heat inputs. TABLE I. RESULTS OF A 4 s a ~ r s ~ ~ 3. Both fuels c o m p l e t e l y --Condition 1--Condition 2---Condition 8-Gasoline Alcohol Gasoline Alcohol Gabo1ir.e .Alwhol evaporated, but at the mini---Conditi,in 4--at at at at at mum mixture temperature in 101' F. 101' F. 101' F. 55' F. 101' F. 71ttF. G l s J i i n e Aicohul each case. 102 2 Heating r a l u e a 100.6 100.0 102.0 100.0 100.6 100.0 100 0 4. No evaporation or heati t e l a t i r e charge deneity ... ... .,. 12.3 ... 0.6 ing of either fuel-air mixture. Expansion of product , . . 0.8 ... 0.8 0.8 0 8 Sp. h e a t of product 2.2 ,. 2.2 ... 2 1 ,.. 2 2 Thus, with complete evapoResult, % h 102.8 100.8 104.2 113 2 102.8 106.4 102 2 I03 0 2.0 ... 8.6 :3 . 5 , . . 0.8 ration and the same mixture 100 284' 100 100 10i' 284 None Xune temperature, which necessiPer u n i t volume of correct mixture at a n y s t a n d a r d conditions, corrected for condition of fuel. b Results are computed as follows: tates 1% per cent heat Column 1: (1.006 X 1.022)lOO = 102.8 for the correct a l c o h o l - a i r Column 4 : (1.000 X 1.123 X 1.008)100 = 113.2 mixture, the correct gaso_ _ _ _ _ _ _ ~
2
'
,
;";E:tz;;f&%% Q
1098
I \ DUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 28, NO. 9
the a l c o h o l mixture and about 12-1 for the gasoline mixture. At these air-fuel r a t i o s the alcohol mixture temperature was about 30" F (17" C.) lower for the 0 w a t t s of heat input and about 65" F. (36" C.) lower for the 300 watts of heat input than for the gasoline mixture. VOLUMETRIC EFFICIENCY. The volumetric efficiencies (Figure 5)t were obtained by measuring the air and fuel, computing the theoretical gaseous volume of 4 8 IC I6 4 8 12 /6 20 8 themixtureatstandardconditions, and comparing with A/R-fUEL R A T / O AIR-FUEL RATIO CONP%€SS/O/Y RAT/O t h e e n g i n e disdacement. FIGCRE6. OPTIMUMSPARKADVANCE( C . F. R. ENGINE) This &dits t h e e n g i n e w i t h a h i g h e r volumetric volumes of correct gaseous mixtures of the two fuels, there efficiency than it deserves, if fuel enters the cylinder in would be 60 per cent more alcohol by weight. On a liquid liquid form, and consequently favors the alcohol mixture. volume basis the specific gravities indicate that 56 per cent If all of the fuel entered the cylinder in liquid form, the larger quantities of alcohol would be required. The results volumetric efficiency should be based on the air alone which of Table I indicate that these volumes might be increased 2.0 would decrease the values for alcohol from 5 to 13 per cent per cent in one case and reduced 8.6 per cent in another. and for gasoline from 1to 4 per cent, depending on the air-fuel Alcohol can be used in engines with higher compression ratios. Thus, the volumetric efficiencies represent the maxiratios, which will reduce the fuel consumption. Theomum attainable for this engine and conditions on the asretically, increasing the compression ratio from 5.45-1 to sumption that the fuel is vaporized when entering the cylin8-1 should increase the indicated efficiency about 18.7 per der. cent and should reduce the indicated fuel consumption by With rich mixtures and resultant low mixture tempera15.T per cent. tures, the higher volumetric efficiencies are obtained, the Compared to gasoline in a 5.45-1 compression ratio engine, alcohol mixtures showing greater increase with richness of the alcohol engine with 8-1 compression ratio would theomixture because of the greater percentage of fuel and higher retically require 35 per cent more fuel by weight and 31 latent heat. per cent more fuel by liquid volume. The volumetric efficiencies for maximum power air-fuel ratios and for no heat input and 300 watts of heat input to Single-Cylinder Tests the intake manifold are about 5 and 7 per cent higher, reThe procedure followed in the single-cylinder tests, all spectively, for the alcohol mixtures. of which were run a t 1200 r. p. m., was to run a series of tests SPARKADVANCE.The spark advance recorded in each with gasoline a t a given compression ratio, varying the aircase is that of optimum position, determined by runs with fuel ratio and mixture heat input. This was followed by various spark settings. The spark advance may be conthe same series of tests but with alcohol. Then the compressidered as an indication of the time of combustion, for acsion was changed, and the series of tests was run first with cording to Upton's rule the maximum power is obtained when alcohol and then with gasoline. This reversal of order was a definite part of the time of combustion has elapsed when used to eliminate the effect of any change in engine conditions the piston reaches top dead center. The optimum spark other than those under control. The jacket water and oil advance for the various test conditions (Figure 6 ) do not temperature were maintained at 212" F. (100' C.) and indicate any appreciable difference in minimum spark ad140" F. (60' C.), respectively, in all the tests on this engine. vance, although the gasoline mixtures appear to require TEMPERATURE CURVESOF INTAKE MANIFOLDMIXTURE. about 2' less spark advance. The mixture waa heated by an electric heater located in the POWERAND &EL CONSUMPTION.The power and fuel intake manifold between the carburetor and the mixture consumption results are plotted (Figure 7) using indicated temperature thermocouple which replaced the thermometer horsepower since the results are more significant on this shown in Figure 3. Four quantities of heat input were basis because of the high internal friction of a small singleu s e d 4 , 100, 200, and 300 watts. cylinder engine. On the average, about 1.5 and 3.2 per cent The manifold mixture temperature curves (Figure 4) show more power were obtained with the alcohol mixtures with the difference between room temperature and the manifold 0 and 300 watts of heat input to the manifold, respectively. mixture temperature as determined. With 0 and 100 watts The fuel consumption results indicate that heat input to of heat input the mixture temperature remains the same for the manifold mixture has no appreciable effect on the specific the alcohol mixture throughout the range of ab-fuel ratios. indicated fuel consumption. At the correct air-fuel ratios However, with 200 and 300 watts of heat input the alcohol of 8.45 for 190-proof alcohol and 15.11 for gasoline, and a t mixture temperature rises with the leaner mixtures. all compression ratios, the specific indicated fuel consumpThere is about 35" F,(19' C,) lower mixture temperature t The original curve for a 4-1 compression ratio and 300 watts of heat for no heat input to the manifold and about 60" F. (33' C.) input was found to be incorrect. A few check runs substantiated the other lower temperature with 300 watts of heat input for the correct data but showed these values to be low. Several tests at this condition alcohol mixture compared to the correct gasoline mixture. indicate that this curve should be as indicated by the dashed line with no points shown. Maximum power occurred a t about 7-1 air-fuel ratio for
,
SEPTEMBER, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
EXHAUSTGAS TEMPERATURES. The exhaust gas teni peratures (Figure 8) are not influenced appreciably by hear input to mixture in the intake manifold. Exhaust gas temperatures are slightly higher for the gasoline mixture; this indicates a higher maximum temperature, assuming other conditions to be the same during the expansion process in the engine, and checks a t least to some extent the theoretical aspect regarding specific heat of products.
tion was about 70 per cent higher with alcohol than with gasoline. At maximum-power air-fuel ratios of 7-1 for alcohol and 12-1 for gasoline the specific indicated fuel consumption was about 60 per cent higher with alcohol than with gasoline. Comparing the indicated specific fuel consumption for a 12-1 air-gasoline mixture a t a 5.45-1 compression ratio with a 7- 1 air-alcohol mixture a t a compression ratio of 8-1 shows about 50 per cent increase in fuel consumption when using alcohol. Thus, the gain in efficiency with increase in compression ratio possible with alcohol does not begin to offset the lower heating value of alcohol. The specific indicated fuel consumption curves approach a minimum as the air-fuel ratio is increased. The increase in compression ratio also decreases the specific fuel consumption, approximately 20 per cent in the case of both mixtures in going from a compression ratio of 4-1 to 8-1. Analysis of the ideal cycle for these compression ratios indicates that the ideal gain for this increase in compression ratio would be about 28 per cent.
4
8
12
Multicylinder Engine Tests The standard 1935 Chevrolet engine was changed as follows for these tests: 1. The air cleaner was removed, and an air box was connected to the carburetor inlet for measuring the air induced. An electric heater in the air box maintained a constant air temperature of 100" F. (38" C.). 2. A needle valve was fitted to the main fuel nozzle of the carburetor to control the air-fuel ratio. 3. The vacuum spark control as well as the automatic ad-
I6
4 4
4
8
/?
AIR-f UfL
1099
/6
RA T l 0
8
/2
/6
8
/2
/6
20
20
20
AIR-FU€L RATIO
CONPR€SS/Ofl E A T l 0
F I G ~ R7.E INDICATED POWER AND SPECIFIC INDICATED FUELCONSUMPTION (C. F. R. ENGINE)
1100
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 28. NO. 9
POWER OUTPUT.The maximum power output (Figure 9) a t wide-open throttle is about the same a t all speeds for both fuels varying from about 3 per cent more power for the alcohol a t 2000 r. p. m. t o about 1 per cent more power for the gasoline a t 3000 r. p. m. The maximum power a t twothirds load ranges from about 3 per cent higher for gasoline a t 1000 r. p. m. to about 5 per rent higher for alcohol at 2000 r. p. m. The maximum power output a t one-third load ranges from about the same for both fuels at 1000 r. p. m. to about 5 per cent more for alcohol at 1500 r. p. m. The average increase in maximum power with alcohol as in--dicated by the curves in Figure A/R-FUEL RATIO A/R-FU€L R A T I O 9 is 1.1 per cent for full load, F I G C R E 8. EXH.AUST GAS TEMPERATURE6 1.8 per cent for two-thirds load, and 3.1 per cent for vance were disconnected so that the spark timing could he one-third load. This represents an average gain in maximum controlled manually. power a t all speeds and loads of about 2 per cent for alcohol, 4. Various thermocouples were attached to the engine to which is not much more than the experimental error involved determine the various temperatures of the air, mixture, exhaust, in such tests. water, and oil. FUEL COBSUMPTION.The fuel consumption results The tests rvere run at various speeds from 1000 to 3000 (Figure lo), when plotted on a basis of pounds per indicated r. p. in., at various air-fuel ratios and a t three loads. A defihorsepower hour, appear to be independent of load a t speeds nite manifold vacuum was chosen for one-third and txyoabove 1500 r . p , m . for gasoline and above 1000 r.p.m. for thirds load for each speed. The order of running the two alcohol. The specific fuel consumption a t the maximum fuels was reversed between speeds t'o eliminate the effect power air-fuel ratios of 7-1 for alcohol and 12-1 for gasoline of any change in engine conditions. The water and oil is about 63 per cent higher (by weight) for alcohol a t 1000 temperatures were controlled. The heat transfer from r. p. m. and decreases slightly with an increase in speed to exhaust to intake manifold was controlled automatically by 58 per cent more a t 3000 r. p. m. Thus, approximately 60 the thermostatic method standard with this model of Chevroper cent more alcohol by weight is required for a given let. output from the engine. 30
25
$ 20
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1?1Q 95
2
40 35 30
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25 20
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