INDUSTRIAL AND ENGINEERING CHEMISTRY
222
When the liquid from the periphery of the glass tube is turned inward to constrict the core flowing in the axis, i t is sheared off and carried along through the orifice to form the jet which escapes into the downstream region. The shearing takes place at the upstream sharp edge of the orifice. The diameter of the sphincter-like ring of constricting liquid after shearing is less than that of the orifice. Thus i t seems certain that immediately adjacent to the periphery of the orifice there is a sheath of liquid moving very slowly and enveloping the rapidly flowing jet. That is the explanation proposed for the absence of images of illuminated particles between range wires W and the jet. When the upstream edge of the orifice is rounded, the constricting stream of liquid is bent into the orifice, and a thicker
VOL. 30. NO. 2
portion is sheared off by the rapidly flowing core. The combined masses of the core and the sheared liquid form a jet whose diameter is nearly that of the orifice. The enveloping sheath of slowly moving liquid adjacent to the peripheral surface of the orifice is thin. Thus the curvature of the upstream approach to the orifice dominates the size of the jet.
Acknowledgment The assistance of several students, particularly G. H. Cook, P. G. Ellis, and D. H. Gordon, in the construction and manipulation of the apparatus and in the making of photographic prints is gratefully acknowledged. RECEIVED August 2, 1937.
Gasoline-Alcohol Blends in \
c
Internal Combustion Engines
Y ONSIDERABLE interest in ethyl alcohol as a motor
fuel has existed in Europe for some time, especially in the countries which have no petroleum resources within their borders. Interest in this country and the Philippines (14) has been stimulated lately for various reasons, such as pessimistic forecasts (5) regarding the future of our petroleum supply and the problem of the recent surplus of farm products, which are a potential source for alcohol. There are also various technical reasons for the interest in alcohol. Ethyl alcohol with an octane number of about 90 (2) is a desirable fuel from an antiknock standpoint. This octane number is appreciably higher than that of commercial premium motor fuels. S a s h and Howes (IO, Article 419) state that “were it not for this desirable property, alcohol fuels would not possess a single redeeming feature as compared with petrols, with the possible exception of their high latent heat, which, in certain circumstances, has a beneficial effect upon Volumetric efficiency and power output.” Higher apparent or “blending” octane number is observed when small amounts of alcohol are blended with gasoline; but, as the data given here will show, this varies greatly with the base fuel and the amount of alcohol added, approaching the actual octane number as the amount of alcohol is increased. Considerably less energy is liberated either on a weight or a volume basis (36 and 31 per cent, respectively) in the combustion of ethyl alcohol than with gasoline. This is a distinct disadvantage where weight or volume of fuel is important. However, considerably less air (40 per cent) is required for a given weight of alcohol which results in approximately the same energy liberation per standard unit volume of correct air-vapor mixture for each fuel (9). The volatility and vaporization characteristics indicate theoretically lower mixture temperatures with ethyl alcohol than with gaeoline (9) and therefore higher volumetric efficiency and greater power output, which is confirmed experimentally. This indicates the possibility of increases similar but smaller in amount for blends of the two fuels. Based on heating value alone, the value of ethyl alcohol per gallon as a fuel is about two-thirds that of gasoline. Owing to better antiknock characteristics, alcohol can be used in engines with higher compression ratios than can gasoline; this
L. C. LICHTY AND c . W.PHELPS Yale University, New Haven, Conn. tends to put the two fuels on a more nearly equal basis when each is used in an engine with optimum compression ratio (10, paragraph 421). However, both theory (6’) and experiment (9, 12) show that present “standard” compression ratios would have to be more than doubled when using alcohol, before efficiencies would be reached to offset this difference in energy content per gallon. Also, it is generally believed that compression ratios for spark-ignition automotive engines will not reach a value much above 8 : l before some of the disadvantages of high compression will offset the gain in power and economy. Thus it appears that present compression ratios for spark-ignition automotive engines will not be doubled. Consequently, alcohol may always be a t a disadvantage compared to gasoline as a fuel for internal combustion engine use because of the low heating value of the alcohol, unless it is obtainable a t a lower cost than that of gasoline. Based on present costs, straight ethyl alcohol is a t a disadvantage as a motor fuel. Nevertheless, there has been considerable interest in and discussion of the possible use of small amounts blended with gasoline. The object of the tests reported here was to obtain data on the relative performance of gasoline and gasoline-ethyl alcohol blends as fuels under comparable conditions of internal combustion engine operation, extending the work previously done a t Yale (9)which compared ethyl alcohol and gasoline as separate fuels.
General Procedure Fuels and Apparatus The fuels used were a standard commercial gasoline, and blends of this gasoline with 5 , 10, and 20 per cent (by volume) anhydrous denatured ethyl alcohol. The gasoline, distributed in the New Haven district in June, 1936, was obtained from the stocks of the New Haven distributing plant. This gasoline is a nonleaded fuel with a specific gravity of 0.738 at 60” F. In some of the knock-rating and single-cylinder performance tests, the gasoline was leaded as indicated later.
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1938
A third-grade gasoline, used only in the octane rating tests, was obtained from the same source. The secondary reference fuel C-10, also used only in the octane rating tests, was obtained from the Standard Oil Development Company. Anhydrous ethyl alcohol, denatured according t o formulas 10 and IOM, was used for the alcohol blends. The specific gravity of the denatured alcohol was 0.799 a t 60' F. The 5 per cent alcohol-gasoline blend was used for octane rating tests only. Some comparative runs were made with pure absolute ethyl alcohol t o determine the effect of the denaturant. Tests were first run on a standard A. S. T. M.-C. F. R. singlecylinder engine t o determine the octane number of the various fuels. The same engine connected to an electric dynamometer was used for the single-cylinder performance tests. These tests were run at constant speed, at three compression ratios, and at three heat supplies to the intake manifold. In these tests a Cities Service Power Prover was connected to the exhaust and calibrated for each fuel by means of volume measurements of air-fuel ratios and Orsat analyses of the exhaust products. Multicylinder engine tests were run on a 1935 six-cylinder Chevrolet engine a t one com ression ratio, three speeds, and three loads. In these tests the eities Service Power Prover was connected t o the exhaust pipe as well as to the exhaust ports of the engine, which provided means of checking the air volume measurements and studying distribution (8).
Antiknock Characteristics All fuels were rated according to the A. S. T. M . 4 . F. R. motor method procedure (1). Standard reference fuels A-4, C-9, C-10, and F-1, obtained from the Standard Oil Development Company, were used. Three fuels- third-grade gasoline, regular gasoline, and C-10-were rated with alcohol in amounts of 0, 5, 10, and 20 per cent of the blend. The same fuels were also rated with 0.4, 1.0, 2.0, and 4.0 cc. of tetraethyllead added per gallon. Fuel C-10 was also rated against the primary reference fuels, octane and heptane.
TETRAETHYLLEAD, 0
5
IO
I5
"e*
ETHYL ALCOHOL, PERCENT
curves (left-hand side, Figure l), becomes less as more of the agent is added. TABLEI. COMPARISON OF ETHYL ALCOHOLAND LEADAS KNOCK INHIBITORS Third-Grade Gasoline Octane rating of fuel Per cent alcohol in blend 5 10 20
Tetraethyllead added, cc./ gal. 1 2 4 Per cent alcohol I n blend Added 5 5.3 11.1 10 20 25.0
OCTANE NUMBER
The fuels of higher octane number (Figure 1) show less increase in octane number with the addition of a given percentage of ethyl alcohol than do the fuels of lower octane number, with the exception of the 5 per cent blend with fuel C-10. However, the regular gasoline, with an octane rating about halfway between the third-grade and C-10 fuels, shows an increase in octane number, with the addition of alcohol, which is only slightly greater than that of fuel (2-10 and much less than that of the third-grade fuel. This indicates that some fuels are more sensitive than others to the addition of ethyl alcohol 8 s a knock inhibitor. A similar effect is noted with the addition of lead to these three fuels except that fuel C-10 is affected almost as much as the third-grade fuel. I n general, the sensitivity of these fuels to either of the knock-inhibiting agents, as indicated by the slope of the
Regular Fuel c-10 Gasoline 58 G7 78 Increase In octane number 5.0 2.7 3.4 4.4 9.7 4.9 18.9 8.7 6.9
10.7 6.2 10.0 15.2 9.1 13.0 20.8 11.8 18.3 Tetraethyllead equivalent t o alcohol, cc./gal. 0.4 0.4 0.2 0.9 0.8 0.3 2.5 1.8 0.6
Table I shows these results as well as the amount of lead needed in the fuel to match the octane number of the alcohol blends. These latter figures show that in the case of a fuel such as the third-grade, whose octane number increases markedly when alcohol is added, only 2.5 cc. of lead per gallon will result in as great an increase in octane number as occurs when 25 per cent alcohol is added.
Single-Cylinder Performance Tests Single-cylinder tests were run a t 1200 r. p. m.; optimum spark was used in each case. Three nominal compression ratios, 5.0:1, 6.2:1,and 6.8:1, were employed. The first represents approximately the lowest value found in the commercial engine of 1936. The second and third were the ratios which caused incipient detonation in the C. F. R. engine with the 10 and 20 per cent blends, respectively, a t maximum power air-fuel ratio, optimum spark setting, and 300 watts heat input to the mixture. The gasoline used a t 6.2:l and 6.8:l compression ratios contained 0.8 and 1.8 cc. of tetraethyllead per gallon, respectively, which increased the octane number of the gasoline to that of the 10 and 20 per cent blends, respectively. The order in which the fuels were tested, a t a compression ratio of 5 to 1, was gasoline, 10 per cent blend, and 20 per cent blend. This order was reversed for the tests a t the next compression ratio, 6.2:1, etc., in an endeavor to eliminate the possible effect of changing engine conditions. All temperatures were measured by means of either iron-constantan or chromel-alumel thermocouples
FIGURE 1. EFFECTOF ETHYL ALCOHOLAND TETRAETHYLLEAD ON
223
Mixture Temperatures
Figure 2 shows the difference in temperature between the mixture in the inlet manifold and the air a t the inlet of the air meter a t various air-fuel ratios. These curves show that the addition of alcohol to the gasoline results in a drop in mixture temperature of about 4" and 8 " F. for the 10 and 20 per cent blends, respectively, for any given heat input to the mixture. The drop in temperature increases with the heat input; i t is about 3", 4",and 5' F. for the 10 per cent blend a t 0, 150, and 300 watts heat input, respectively, owing to the difference in latent heats and volatility characteristics of the blends and the gasoline. Brown and Christensen (3, 4) reported a drop in mixture temperature of 11" F. for a 10 per cent blend, compared to gasoline, when used in a truck or bus engine. The mixture temperature for any given heat input increases with the air-fuel ratio. Less heat is required to vaporize the fuel, so that more is available to heat the mixture.
224
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0, 150, and 300 watts heat input to the mixture, a n d t h e brake horsepower with the same heat inputs. The maximum power!or a given h e a t input and compression ratio was approximately the same for all three fuels. However, the average airfuel r a t i o s * a t AIR-FUEL RATIO which these FIGURE 2. MIXTURE TEMPERATURE (SINQLE-CYLINDER ENGINE) maxima occurred 0 gasoline. A 10 per cent blend. 0 20 per cent blend. were not t h e same; they were Compression ratio has no appreciable effect on mixture approximately 14.0:1, 13.2:1, and 12.5:l for the gasoline, 10, temperature, as would be expected from theoretical analysis and 20 per cent blends, respectively. This decrease in maximum power air-fuel ratio with the increase in the percentage (13). of alcohol in the blend was fairly consistent throughout the exVolumetric Efficiency periments. These mixtures are, respectix-ely, 8, 7, and 9 per Apparent volumetric efficiencies' obtained with the 20 per cent richer than those for complete combustion, indicating that cent blends were about 2 per cent higher than with the 10 per for maximum power the alcohol blends and the gasoline rec e n t blends. A t 6 . 2 : l comp r e s s i o n ratio and all heat inputs, as well as LL a t 5:l compression ratio and 52 300 watts heat Q input, the voluF metric efficiencies w i t h t h e gasoline w e r e 9 48 about 1 per AIR-F U E L RATIO cent lower than those obtained FIGURE 3. VOLUMETRIC EFFICIENCYI(SINGLE-CYLINDER ENGINE) with the 10 per 0 gasoline. A 10 per cent blend. 0 20 per cent blend. cent blend. I n all t h e other quire approximately the same percentage of excess fuel above cases the volumetric efficiencies appear 1to 3 per cent too high for gasoline relative to the blends, assuming that the blends that required for complete combustion. should result in higher volumetric efficiencies than those obSince the addition of alcohol decreases the maximum power tained with gasoline (see footnote 8). The decrease in manifold air-fuel ratios, the use of gasoline results in higher output, on mixture temperature with the addition of alcohol indicates the average, for air-fuel ratios greater than 13.2:l in the case a possible increase of about 1 and 2 per cent in volumetric of the 10 per cent blend and 12.5:l in the case of the 20 per efficiencies with the 10 and 20 per cent blends, respectively. cent blend. The apparent volumetric efficiency (Figure 3) decreased The addition of heat to the mixture in the inlet manifold aPProximatelY 4.5 Per cent for each 150 watts heat input $0 reduced the power output at any given air-fuel ratio. This the mixture, regardless of the fuel. This decrease is due to reduction amounted to about 5 and 10 per cent for an input the increase in both the percentage of fuel evaporated and the of 150 and 300 watts, respectively, a t maximum power air-fuel specific volume of the mixture with heat addition. ratio. The power output a t any given air-fuel ratio increased with Power Output an increase in the compression ratio. This increased output is due to the greater thermal efficiency of the cycle* This Figure 4 shows the indicated and brake horsepower plotted efficiency would continue to increase until a compression against air-fuel ratio for the three fuels with three heat inputs from ratios' to the mixture and three 2 The &-fuel ratios are based upon the same measurements as are used top to bottom, the S ~ Xgroups of curves at each compression in computing volumetric efficiencies. Inspection of the volumetric efficiencies suggests a possible error of 1 to 3 per cent in the case of some of the ratio represent, respectively, the indicated horsepower with 1
Apparent volumetric efficiency = vol. of air at room temp. and atm. pressure induced per hr. piston displacement X (revolutions per hr./2)
gasoline curves (see footnote 9. This indicates that the air-fuel ratios used to plot some of the gasoline curves may be too high in relation to those used for the blends. This might reduce the average value of 14.0 for maximum power air-fuel ratio for gasoline t o about 13.8.
FEBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
ratio was reached that would cause the fuel to detonate so severely that satisfactory operation of the engine a t optimum spark advance would be prevented. The increases in maximum indicated power were approximately 6 and 11.5 per cent in going from a compression ratio of 5.0:l to compression ratios of 6.2:l and 6.8:1, respectively. This compares with 10.2 and 14.5 per cent increases indicated by theoretical analysis (6, 1.3) for 10 per cent rich mixtures of octane and air.
TABLE11. SINGLE-CYLINDER INDICATED SPECIFIC FTJEL CONSUMPTION
Fuel consumption curves are plotted (Figure 5 ) without indicating heat input to mixture, since Ziurys (9) found that this factor did not appreciably affect the indicated specific fuel consumption. I n general, the specific fuel consumption is higher with alcohol blends than with gasoline a t any airfuel ratio except rich mixtures of gasoline. A better comparison of this difference with the various fuels is presented in Table 11, where the specific fuel consumptions a t both the correct and maximum power air-fuel ratios are listed. The fuel consumption for all the fuels decreased with an increase in compression ratio. The decrease for the leaded gasoline a t 15.1:l air-fuel ratio amounted to about 6.6 and 9.9 per cent when the compression ratio was increased from 5.0:l to 6.2:l and 6.8:1, respectively. The fuel consumption3 for the 20 per cent blend at 6.8:l compression ratio is identical with that for the gasoline a t 5.0:l compression ratio, showing that a n increase in compression ratio of 36 per cent was required in this case to offset the lower heating value of the alcohol in the 20 per cent blend. a Although power and specific fuel consumption values are plotted against air-fuel ratio in Figures 4 and 5 , respectively, their relation is independent of air-fuel ratio measurements, since for any power output there is a definite fuel consumption rate. Therefore, possible errors i n air measurement, indicatedin footnote * do not affect the maximum-power specific fuel consumptions listed in Table 11, which are the fuel rates corresponding t o the leanest mixture resulting in maximum power. The specific fuel consumptions listed under “Correct Air-Fuel Ratio,” Table 11, were obtained from Figure 5 a t the theoretical air-fuel ratios and thus would be affected by any error in air measurement. The volumetric efficiency curves for the blends a t a compression ratio of 6.2 t o 1 (Figure 3) are higher than those for gasoline, as would be expected. Hubendick and others (IO) called attention t o the higher latent heat of the alcohol in the blends which increases the air consumption and volumetric efficiency of the engine with the blends. Thus i t might be inferred t h a t the air measurements
Air-Fuel Ratio-Max. PowerFuel conFuel consumosiimption tion lb./ in: Air-fuel lb./indicatdd Per cent d’icated Per cent ratio h. p. hr. increase h. p. hr. increase 5.0:l Compression Ratio 15.1 0.455 0.490 14.4 0.485 616 0.520 1 13.8 0.510 12.1 0.555 13.3 6 . 2 : l Compression Ratio 15.1 0.425 0.455 14.4 0.445 4:7 0.495 8:s 13.8 0.480 13.0 0.540 18.7 6.8:l Compression Ratio 15.1 0.410 0.435 13.8 0.455 ii:o 0.485 ii:5
-Correct
Gasoline 1 0 7 blend 20 blend
%
Fuel Economy
225
Gasoline 1 0 7 blend 20% blend Gasoline 20% blend
a:
It was found (Table I) t h a t 1.8 cc. of tetraethyllead were required to raise the rating of the standard gasoline to that of the 20 per cent blend so that each could be used at the same compression ratio. At 6.8:l compression ratio, which resulted in incipient detonation for both the 20 per cent blend and the leaded gasoline referred to, the specific fuel consumption with the blend was 11.0 and 11.5 per cent higher at the theoretically correct and maximum power air-fuel ratios, respectively. Also, 0.8 cc. of tetraethyllead was required to increase the octane rating of the standard gasoline used to that of the 10 per cent alcohol blend, which permitted operation of both fuels in the single-cylinder engine with incipient detonation a t a compression ratio of 6.2:l. The specific fuel consumption a t these conditions with the 10 per cent blend was about 7 per cent higher than with the leaded gasoline. It is obvious that for equal costs for alcohol and gasoline the cost of the increased fuel consumption with the blends must be balanced against the cost of tetraethyllead required to produce equal antiknock characteristics. Based upon a t 6.2:l compression ratio are relatively correct; those for almost all the gasoline curves a t the other compression ratios appear t o give volumetric efficiencies too high i n relation to the volumetric efficiency curves for the blends. However, any lowering of the volumetric efficiency curves for gasoline in these cases would result in shifting the gasoline fuel consumption curves to the left i n Figure 5 and increasing the differences noted in Table I1 for “Correct Air-Fuel Ratio” a t compression ratios of 5.0:l and 6.8:l.
0 W
!z 4 8 un z 44
a
:
40
0
a
w36
2.8
5 c.4 m 68:l C.R.
5.o:ICR.
2.0 9
II
13
15
FIQURE 4.
17
9
IS
II
AIR-F UEL RATIO INDICATED AND BRAKEHORSEPOWER (SIND-LE-CYLINDER EivaIm) 0 gasoline.
A 10 per oent blend.
0 20 per cent blend.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
for each speed. These pressures were selected to give one-third, twoa70 thirds, and full load a t i maximum power airW + 0.60 fuel ratio and optimum , a spark advance. The a -] 0.50 i n l e t a i r temperature w was m a i n t a i n e d a t 3 100' F., a n d the exG 040 h a u s t b a c k pressure 9 II within 2 inches of water AIR-FUEL RATIO of atmospheric p r e s FIGURE 5. INDICATED SPECIFIC FUELCONSUMPTION (SINGLE-CYLINDER ENQINE) sure. The three fuels were 0 gasoline. A 10 per cent blend. 0 20 per cent blend. u s e d i n t h e following o r d e r : a t 1000 and present cost of tetraethyllead, i t appears that alcohol must be 3000 r. p. m., gasoline, 10 per cent blend, and 20 per cent blend; a t 2000 r. p. m. the order was reversed. No tetraethylobtainable a t equal or less cost than gasoline to justify the use of 10 and 20 per cent blends in engines with optimum comlead was added in any of the multicylinder engine tests. pression ratios for the blends.
55
.$
Volumetric Efficiency
Exhaust Temperatures Exhaust gas temperatures have been plotted (Figure 6) without indicating heat input to the mixture, since Ziurys (9) found that this factor did not have an appreciable effect. These curves show that the maximum exhaust temperatures for a given compression ratio are about the same, regardless of fuel used. These maximum temperatures do not occur a t the same air-fuel ratio for each fuei, however, but appear to be approximately a t the theoretical ratio for perfect combustion-namely, 15.1:1, 14.4:1, and 13.8:l for the gasoline, 10 and 20 per cent blends, respectively. Incomplete combustion due to a deficiency of oxygen a t lower air-fuel ratios reduces the amount of energy liberated, while the excess air a t higher air-fuel ratios absorbs some of the energy liberated, which accounts for the shape of the curves. An increase in compression ratio decreases exhaust gas temperatures. However, the engine used in these tests was dismantled between runs a t the various compression ratios, and because of removal and replacement of the exhaust-gas temperature thermocouple the results are not comparable except for each compression ratio.
Multicylinder Performance Tests The multicylinder tests were run at three speeds-1000, 2000, and 3000 r. p. m.-and a t three inlet manifold pressures
The average apparent volumetric efficiencies for the multicylinder engine for full load a t three speeds and for the three fuels are as follows:
~.
Speed, p. m. 1000 2000 3000
Gasoline
10% Blend
86.7 83.5 77.4
87.6 84 0 77 2
These data show a n increase in volumetric efficiency of 0.6 and 1.6 per cent for the 10 and 20 per cent blends, respectively, a t 2003 r. p. m., an increase of 1.0 and a decrease of 0.6 per cent for the 10 and 20 per cent blends, respectively, a t 1000 r. p. m . ; and a decrease of 0.3 and 1.8 per cent for the 10 and 20 per cent blends, respectively, a t 3000 r. p. m. The increases in volumetric efficiencies obtained a t 2000 r. p. m. are approximately what would be anticipated from previous experiments dealing with ethyl alcohol alone (9).
Power Output The indicated horsepower of the Chevrolet engine for the three fuels a t three loads and three speeds is plotted against air-fuel ratio in Figure 7. The curves are similar to those of the single-cylinder engine tests (Figure 4). The average air-fuel ratios for maximum power, as determined from the torque curves (8), are approximately 13.0:1, 12.5:1, and 12.2:l for the gasoline, 10, and 20 per cent
AIR-FUEL
RATIO
ENQINE) GASTEMPERATURE (SINGLE-CYLINDER FIGURE 6. EXHAUST 0 gasoline.
20% Blend 86 2 84 8 76 0
A 10 per cent blend.
0 20 per cent blend.
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1938
blends, respectively. These mixtures are about 16, 15, and 13 per cent rich; those in the single-cylinder tests were about 8, 7, and 9 per cent rich, respectively. The richer mixtures are required in the multicylinder engine because of unequal mixture distribution to the cylinders. These figures indicate slightly better and appreciably better distribution for the 10 and 20 per cent blends, respectively, compared to gasoline. However, exhaust-gas analysis of the gases from the various ports of the engine led to the conclusion (8) that the distribution was not appreciably different for the fuels used. This variation is probably due to the difficulty of determining maximum power air-fuel ratios. The leanest mixture points plotted represent approximately the highest air-fuel ratios that could be used in the engine a t that speed and throttle setting without excessive missing or delayed firing. Therefore a comparison of these curves shows that the highest satisfactory air-fuel ratio increases with the throttle opening. This characteristic is especially noticeable a t 3000 r. p. m., where an air-fuel ratio less than 15:l is required for satisfactory operation with all fuels with a throttle setting to give approximately one-third load. This is due to the increased dilution of the charge with clearance products when the throttle opening is reduced
Fuel Economy The specific fuel consumption in pounds per brake horsepower hour is plotted (Figure 8) against brake mean effective pressure for one-third, two-thirds, and full load a t 1000,2000, and 3000 r. p. m. These “consumption loops,” a method of plotting used by Pye (11) and others, give a picture of the relation between fuel economy and power output; vertical and horizontal tangents to the curves indicate, respectively, the maximum power and maximum economy fuel rates given in Table 111. The fuel consumption for maximum power was lowest for gasoline and highest for the 20 per cent blend, as in the single-cylinder results. The fuel consumption for maximum economy shows the same trend as for maximum power, except that in several instances the increase in fuel consumption with the use of alcohol blends is more pronounced. The full-load fuel rates a t 2000 r. p. m. were lower than a t 1000 or 3000 r. p. m. for each fuel. At 1000 r. p. m. the spark setting had to be retarded to reduce detonation; a t 3000 r. p. m. a greater percentage of the total power produced was required to overcome friction loss. The increase in fuel consumption with the addition of alcohol was least in the full-load runs a t 1000 r. p. m., owing to detonation characteristicsof the fuels, as mentioned previously. The addition of alcohol decreased the tendency of the fuel to detonate. Therefore, the spark could be advanced more nearly to the optimum setting when the blends were used,
227
which compensated Dartlv for the lower Leati& value of the 90 blends. The fuel rate in80 c r e a s e d considerably when the load was d e c r e a s e d b y 70 I I throttling. This is due principally to the increase i n t h e percentage of total p o w e r required to overcome engine friction. The a v e r a g e increase in brake specific f u e l c o n sumption for maximum power conditions amounted to 4.7 and 8.5 per cent, and for maximum economy conditions, to 4.9 and 8.9 per cent for the 10 and 20 per cent blends, respectively. These results indicate the increases that might be expected when changing t o t h e s e alcohol blends and operating under 30 comparable c o n d i tions. T h e maximum b r a k e m e a n effective pressure a t wide-open throttle was approximately the same for all fuels used. A t 1000 AIR-FUEL RATIO r. p. m. the m a x i FIGURE 7. INDICATED HORSEPOWER mum for the gaso(MULTICYLINDER ENGINE) line was less than for 0 gasoline. A 10 per cent blend. 0 20 per cent blend. the blends because of the retarded spark to prevent excessive detonation. At 2000 r. p. m. the maximum for the 20 per cent blend was about 3 per cent greater than for the other fuels. I
-
Fuel Economy at Equal Power Outputs TABLE 111. BRAKESPECIFIC FUELCONSUMPTION (POUNDS PER BRAKEHORSEPOWER H O U R ) U N D E R COMPARABLE CONDITIONS --Max. 1000 r,p,m.
Power7 - Max. Economy2000 3000 1000 2000 3000 r.p.m. r.p.m. r.p,m. r.p.m. r.p,m. Full Load Gasoline 0.660 0.620 0.650 0.580 0.540 0.595 10 blend 0.670 0.640 0.700 0.590 0.560 0.640 20%. _blend 0.680 0.600a 0.720 0.595 0.675 0 . 6... 55 Two-Thirds Load Gasoline 0.670 0.690 0.720 0.590 0.625 0.705 0.720 0.710 0.770 0.640 0.650 0.740 0.750 0.760 0.790 0.655 0.700 0.750 One-Third Load .~ Qasoline 0.850 0.930 1.050 0.830 0.885 1.025 10 blend 0.900 0.990 1.085 0.855 0.955 1.035 2 0 % blend 0,900 1.020 1.140 0.900 0.990 1.130 5 Althoyghjhis figure appears to be in, error! the exce tionally good mirture distribution which occurred only with this run is Eelieved to acoount lor most of the apparent discrepancy (8).
The foregoing comparisons of brake specific fuel consumption wersmade without regard to the variations in power output. To drive a given motor vehicle a t a given speed requires a definite amount of power. Consequently, the brake specific fuel consumption data are plotted against brake horsepower (Figure 9) for the three loads a t each of the three speeds, and for the conditions resulting in maximum economy and maximum power, and also a t the arbitrary air-fuel ratios of 12:l and 11:l. From these curves the specific fuel consumptions can be determined for any given power requirement. The curves show that a 12:l air-fuel ratio is richer than maximum power mixtures for all fuels under all conditions of these tests. Curves for 13:l air-fuel ratio would lie in the same general region as the curves for maximum power and consequently have not been plotted, to avoid confusion with these curves.
INDUSTRIAL AND ENGINEERING CHEMISTRY
228 I .?
3 l/3 L A D
20
30
40
30
)
J
w
I
I
I
VOL. 30, NO. 2
Values from the curves in Figure 9 at equal powers and speeds FIGURE8. CONSUMPTION LOOPSare given in Table IV, which BRAKE SPECIFIC FUELCONSUMPTION also includes data for the 13:l us. BRAKEMEANEFFECTIVE PRESair-fuel ratio. A t maximum SURE (MULTICYLINDER ENGINE) economy conditions there was an 0 gasoline. A 10 per cent blend. 0 20 cent blend. average increase of 5.7 and 10.3 per cent in the brake specific fuel consumption for the 10 and 20 per cent blends, respectively; a t maximum power conditions the average increase was 5.5 and 8.5 per cent, respectively. At 13:l air-fuel ratio the average increase in gasoline consumption was 0.6 and 0.3 per cent compared with the consumption for the 10 and 20 per c e n t blends, respectively. At 12:l air-fuel ratio the average increase amounted to 0.6 and 1.2 per cent, respectively; a t 11:l a i r - f u e l ratio the average increase was 0.9 and 1.5 per cent, respectively. The 10 and 20 per cent alcohol blends have a specific gravity of I I I I I 1 1.0 and 2.0 per cent, respectively, greater than the gasoline. On a gallon basis this would c h a n g e the above percentages to 4.7 and 8.3 for maximum economy, 4.5 and 6.5 for maximum power, both in favor of gasoline; and to 1.6 and 2.3 for the 13:l air-fuel ratio, 1.6 and 3.2 for the 12:l air-fuel ratio, and 1.9 and 3.5 for the 11:l airfuel ratio, in favor of the alcohol blends.
IV
TABLEIV. FUELCONSUMPTION (POUNDSPER BRAKEHORSEPOWER HOUR)FOR EQUAL:POWER OUTPUTS --Max. Gasoline
Economy-? 10% 20% blend blend
---Max. Gasollne
10 h. p. % 0.720 Increase, 0 16 h. p. 0.605 Increase, % 0 22 h. p. 0.580 Increase, % 0 Av. increase, % 0
0.800 11.1 0.645 6.6 0.595 2.6 6.8
0.845 17.4 0.680 12.4 0.605 4.3 11.4
0.820 0 0.700
20 h. p. Increase, 70 32 h. p. Increase, 70 44 h. p. Increase, 70 Av. increase,
0.815 0 0.610 0 0.545 0
0.865 6.1 0.660 8.2 0.575 5.5 6.6
0.900 10.4 0.685 12.3 0.590 8.3 10.3
0.890 0 0.715 0 0.635
24 h. p. Increase, % 42 h. p. Increase, % 60 h. p. Increase, 70 Av. increase, Av. of all av. increases, %
0.990 0 0.715 0 0.605 0 0
1.010 2.0 0.740 3.5 0.640 5.8 3.8
1.095 10.6 0.765 7.0 0.665 9.9 9.2
0
5.7
10.3
,
0
0
0.665 0 0
0 0
1.040 0
0.750 0 0.655 0
0 0
-13: 1 Air-Fuel R a t i o PowerGaso10% 20% 10% 20y0 line blend blend blend blend 1000 Revolutions per Minute 0.880 0.880 0 880 0.890 0.875 6.7 7.3 1.1 0 0 0.735 0.765 0.780 9.3 11.4 1.4 0.675 0.700 0.710 5.3 6.8 1.6 7.1 8.5 1.3 '2000 Revolutions per 0.895 0.920 0.960 7.9 -0.6 3.4 0.736 0.785 0.730 9.8 -2.0 2.8 0.665 0.660 0.660 3.9 -1.5 4.7 3.6 7.2 -1.4 3000 Revolutions per 1.075 1.120 1.065 7.7 -1.8 3.4 0.790 0.820 0.830 5.3 9.3 3.8 0,710 0.735 0.715 8.4 12.2 1.4 5.7 9.7 1.1 5 5
8.5
0.3
0.730 0.725 0.7 0 0.670 0.665 0.8 0 0.5 0 Minute 0.900 0.880 -1.1 0 0.730 0.745 -2.0 0 0.660 0.670 -1.5 0 0 -1.5 Minute 1.070 1.085 -1.4 0 0.805 0.800 0.6 0 0.710 0.705 0.7 0
-12: 1 Air-Fuel RatioGaso10% 20% line blend blend
1.105 3.3 0.900 3.4 0.810 3.2 3.3
1.080 1.070 0.9 0 0.880 0.870 1.2 0 0.795 0.785 1.3 0 1.1 0
1.090 0 0.890 1.1 0.780 1.3 0.8
1.080 1.090 -0.9 0 0.890 0.880 1.1 0 0.775 0.770 0.6 0 0.3 L 1.270 1.270 0 0 0.965 0.965
0
1.285 1.2 0.955 -1.1 0.855 1.8 0.6
0
1.5
0.995 3.1 0.825 3.8 0.735 3.5 3.5
0.980 1.6 0.810 1.9 0.725 2.1 1.9
0.965 0 0.745
0.985 -1.5 0.805 -0.6 0.710 0.7 -0.5
0.975 -2.5 0.805 -0.6 0.715 1.4 -0.6
1,000 0 0.810
1.160 0.9 0.875 0 0.765 0 0.3 0.6
0
0
1.165 1.3 0.875 0 0.765 0 0.4
-0.3
0
1.2
-11: 1 Air-Fuel RatioQaso10% 20% line blend blend
0
0.710 0 0
0
0.705 0 0
1.150 0 0.875 0
0.765 0
0
0
0.850 0.840 1.2 0 0.4 0 0.6
0
FEBRUARY, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
20
229
28
36
A4
60
St
68
76
obtained, except under conditions where the addition of alcohol permitted the use of more nearly optimum spark advance. Table V shows the efficiencies for each fuel at each speed and load for maximum power and richest complete combustion mixtures. The maximum power air-fuel ratios were about 13.0:1, 12.5:1, and 12.2:l for the gasoline, 10, and 20 per cent blends, respectively, as determined from Figure 7; the corresponding richest complete combustion air-fuel ratios were approximately 15.3:1, 14.8:1, and 14.3:l. These latter values were obtained by extrapolating the curves (8, Figures 5, 6,7)for the richest cylinders and noting the air-fuel ratios a t which the carbon monoxide in the exhaust became zero. The values for gasoline in Table V average about 1 per cent higher than those for the 10 per cent blend but about 1 per cent lower than those for the 20 per cent blend. Thus the
These figures indicate, for motor vehicles, an average increase in fuel consumption on a gallon basis of 4.6 and 7.4 per cent for the 10 and 20 per cent blends when all fuels are run under comparable mixture conditions, and an average decrease of 1.7 and 3.0 per cent for the 10 and 20 per cent blends when all fuels are run a t the same air-fuel ratios. These air-fuel ratios, at which the use of alcohol blends results in the smaller fuel consumption, are equal to or richer than the maximum power air-fuel ratio for gasoline. A comparison of the fuel consumption at air-fuel ratios of 14:l and greater show less fuel consumption for the gasoline than for the blends; the difference increases with air-fuel ratio.
Brake Thermal Efficiency
t
t
The maximum efficiencies (Figure 10) for wide-open throttle operation were obtained a t air-fuel ratios leaner than the theoretically correct mixtures. These efficiencies decreased and occurred a t lower air-fuel ratios as the load on the engine was decreased. Thus, at one-third load these efficiencies were about two-thirds of those a t full load and occurred a t air-fuel ratios richer than the theoretically correct mixtures. This trend of maximum efficiencies is caused by the increase in the percentage of power required for friction and pumping losses a t decreased load, whereas the trend in air-fuel ratio is due to the increase in the dilution of the charge by clearance gases upon throttling the engine. The addition of alcohol to the fuel does not appear to have any appreciable effect on the maximum brake thermal efficiencies except to lower the air-fuel ratios a t which these were
TABLEV. BRAKETHERMAL EFFICIENCIES (IN PER CENT) AT COMPARABLE CONDITIONS
--
1000
3000
19.6 19.7 20.0
k:Rk::
20.3 20.7 21.4
21.4 21.2 22.0
Gasoline 1 0 7 blend 20% .. blend
18.9 18.8 19.5
18.7 18.8 19.0
Gasoline
14.1 14.0 14.4
14.1 13.9 13.9
1000
Combustion-
2000
3000
r.p.m.
r.p,m.
22.8 23.2 24.0
24.0 24.4 24.8
22.0 21.5 22.2
22.2 21.6 21.8
21.2 21.2 20.5
19.0 18.8 19.2
15.9 16.1 15.9
14.2 13.3 14.2
a
Two-Thirds Load 17.4 16.9 17.4 12.4 12.3 12.6
::g Mixture :b:bll too lean for satisfactory engine operation. a
U
AIR-F UEL
15
1
17
19
RATIO
FIGURE 10. BRAKE THERMAL EFFICIENCY (MULTICYLINDER ENGINE) 0 gasoline.
-Complete r.p.m.
One-Third Load
I
II
2000
r.p.m. r.p.m. Full Load
Gasoline
L
9
Max. Power----
r.p.m.
A 10 per cent blend.
0 20 per cent blend.
a
a
INDUSTRIAL AND ENGINEERING CHEMISTRY
230
brake thermal efficiency is practically the same for both the gasoline and alcohol blends a t comparable conditions.
Energy Distribution Energy supplied an engine eventually appears as mechanical work a t the crankshaft, heat to the cooling water, thermal and chemical energy in the exhaust products, and heat lost from the engine by radiation and convection (7). The percentage of energy supplied which appears as mechanical work has already been indicated in Figure 10 and Table V. The percentage of energy supplied which appears in the cooling water is given in Table VI for maximum-power and complete-combustion conditions. TABLE VI.
ENERGY TO COOLING WATER(IN PERCENTOF ENERGY SUPPLIED) -Max.
1000
r.p.m.
Power--
2000
3000
21.0 21.0 21.2
Gasoline 10 blend 20gblend ._
29.0 26.6 29.0
22.6 22.4 23.4
Gasoline 10 blend
31.0 31.0 32.0
26.0 26.0 27.2
20zblend
--Complete
r.p.m,r.p.m. Full Load
1000
Combustion-
2000
3000
33.8 31.8 33.0
26.6 26.2 27.4
25.0 25.2 25.4
38.6 37.8 36.9
30.8 30.8 30.4
28.5 28.7 28.6
44.5
36.2 36.4 37.0
34.40 33.W 34.70
r.p.m.
r.p.m.r.p.m.
Two-Thirds Load 24.4 24.2 24.6
One-Third Load Gasoline
37.6 36.4 37.4 These values are from
ig$kt%: 0
31.8 32.0 32.0
28.0 27.2 29.2
44.6 43.6
extrapolated data.
These and other data obtained in these tests indicate that the percentage of total energy that goes to the cooling water decreases with an increase in speed or load but increases as the mixture is made leaner, regardless of fuel. Increasing load and speed increases the rate of energy liberation in the cylinders, which tends to decrease the percentage to the cooling water. These increases also result in higher mean gas temperatures in the cylinder and higher rates of heat transfer which tend to increase the percentage of heat to the cooling water and thus partly compensate for the effect of increase in rate of energy liberation with increase in speed and load. Increasing the air-fuel ratio to the correct mixture ratio decreases the energy supplied and increases the percentage of heating value liberated, which increases the temperatures in the cylinder. Therefore the percentage in the cooling water should increase with air-fuel ratio, a t least up to the theoretically correct mixture ratio. Examination of all the data shows that this percentage continues to rise with air-fuel ratio until the mixture becomes very lean-i. e., 16:l or 17:l airfuel ratio. The percentage of the total energy that was rejected to the cooling water appeared to be practically the 4ame for the three fuels. The differences between the comparable values in Table VI, in most cases, are well within the limits of experimental error. The energy that left the engine through the oil cooler used to maintain constant oil temperature was only a small percentage of the total. The maximum values a t full load were about 1.3,2.4, and 2.8 per cent a t 1000,2000, and 3000 r. p. m., respectively. The sum of the brake thermal efficiency and the per cent to the cooling water may be subtracted fromunity to obtain the per cent of “exhaust, radiation, and unaccounted for.”
Conclusions The addition of ethyl alcohol to gasoline increases the octane number of the fuel. Ten and 20 per cent of alcohol, by volume, are equivalent to about 1 and 2 cc. of tetraethyllead per
VOL. 30, NO. 2
gallon of gasoline. However, the antiknock effect of both the alcohol and tetraethyllead depends upon the gasoline used. Volumetric efficiencydata do not show a consistent increase with the addition of ethyl alcohol to gasoline either in the single- or multicylinder tests. Considering only the singlecylinder engine data a t 6.2:l and 6.8:1, the addition of 10 and 20 per cent alcohol increases the volumetric efficiency about 1and 2 per cent, respectively. The power output, thermal efficiency, and heat loss to the cooling water, with comparable mixture conditions, does not change appreciably with the addition of ethyl alcohol to the gasoline, except where this addition reduces detonation and permits the use of optimum spark advance. An increase in indicated specific fuel consumption of 7 and 13 per cent for the single-cylinder engine and an increase in brake specific fuel consumption of 5 and 9 per cent for the multicylinder engine result from the use of 10 and 20 per cent blends of ethyl alcohol compared to gasoline, respectively, a t the sanie compression ratio and with the carburetor adjusted to give air-fuel ratios comparable for each fuel in regard t o maximum power or maximum economy. Applying the multicylinder power and fuel consumption data to motor vehicles on the highway (i. e., based on the same power output and with adjustment to maximum power or maximum economy air-fuel ratios for each fuel), the substitution of alcohol blends for gasoline should result in an increase in volumetric fuel consumption of about 5 and 7 per cent with comparable mixture ratios for the 10 and 20 per cent blends, respectively. Using air-fuel ratios equal to or richer than maximum power for gasoline and without adjustment ofair-fuel ratio on substitution of the 10 and 20 per cent blends, a decrease in volumetric fuel consumption of about 2 and 3 per cent, respectively, should be obtained. However, the lowest fuel consumption can be obtained with gasoline, rather than alcohol blends, by adjusting the carburetor for maximum economy mixture. Based on fuel consumption, ethyl alcohol should cost less than gasoline to warrant its use in 10 and 20 per cent blends in engines with optimum compression ratios for present “standard” gasolines; it should cost about the same as “standard” gasoline if both the blend and the gasoline are used in engines with optimum compression ratios suitable for each of the fuels; and the blends should cost less than gasoline with sufficient tetraethyllead to permit operation in engines with optimum compression ratios for the blends.
Literature Cited (1) Am. 800. Testing Materials, Standards, Part I1 (1936). (2) Bridgeman, IND.ENQ.CHEM.,28, 1102 (1936). (3) Brown, L. T., and Christensen, L M., Ibid., 28,650-2 (1936). (4) Christensen, L M.,Hixon, R. M., and Fulmer, E. I., Iowcp State CoZZ. J. Sci., 8,245-50 (1934). (5) Dearborn Conference Proc., pp. 99 and 125,May 12-14, 1936. (6) Goodenough and Baker, Univ. Ill. Eng. Expt. Sta., Bull. 160 (1927). (7) Lichty, Automothe I n d , 71, 354 (1934). (8) Lichty and Phelps, IND.ENQ.CIEEM., 29,495 (1937). (9) Lichty and Ziurys, Ibid., 28, 1094 (1936). (10) Nash and Howes, “Principles of Motor Fuel Preparation and Application,” New York, John Wiley & Sor,~,s, 1935. (11) Pye, D. R., “Internal Combustion Engine, Vol. I, p- 202, Oxford, Clarendon Press, 1934. (12) Ricardo, H. R.,“High Speed Internal Combustion Engine,” Table XI, London, Blackie and Son, 1931. (13) Streeter, R. L., and Lichty, L. C , ”Internal Combustion Engines,” 4th ed., pp. 76 and 139, New York, McGraw-Hill Book Co., 1933. (14) Teodoro. A. L., PhiEippine Agr., 24, Nos. 3, 4, 6, 9, and 10. (1936). R E C E I V ~August D 10, 1937. The tests reported here were rlzn in 1936 at Mason Laboratory and form part of the graduate work of C. W. Phelpb in the Mechanical Engineering Department of the School 05 Engineering, Yale University.
