Gasoline and Alcohol-Gasoline Blends AND LEO M. CHRISTENSEN Iowa State College, Ames, Iowa
L. T. BROWN
HE reports of coniparative s t u d i e s of gasoline and alcoholgasoline blends clearly demonstrate that factors other than the heating values of the fuels have considerable bearing upon the relative specific fuel consumptions. Hubendick ( 3 ) and Ross and Ormandy (7) presented data which show the importance of the air-fuel ratio upon these relative values. With high air-fuel ratios the specific fuel consumption with alcohol blends w a s g r e a t e r t h a n that with gasoline, the difference being nearly proportional to the difference in the heating values. With the air-fuel ratio for greatest economy, the difference in specific fuel consumption was very small. With richer mixtures, such as those usually met in practice, the blends gave appreciably lower specific fuel consumption than did gasoline. The data presented by Wawrziniok (8), Gray (W), and Miller ( 5 ) indicate that engine speed and throttle opening also affect the relative fuel consumptions of alcohol blends and gasoline. Since the air-fuel ratio may also vary with engine speed and with throttle opening, i t is not possible from the reported data to evaluate the influence of these factors alone. The object of the tests here reported was to study the influence of the engine speed upon the relative fuel consumptions of gasoline and a blend containing 10 per cent of ethanol and 90 per cent of the same gasoline a t air-fuel ratios which might b e e m p l o y e d in p r a c t i c e . I n addition, the influence of the throttle
JET0.056 INCHIS GRAPH1. CARBURETOR DIAMETER AND FULL THROTTLE JET 0.058 INCHIN GRAPH2. CARBURETOR DIAMETER AND FULL THROTTLE JET0.061 INCHIX GRAPH3. CARBURETOR DIAMETER AND FULL THROTTLE JET0.064 INCHIN GRAPH4. CARBURETOR AND FULL THROTTLE DIAMETER
opening a t several speeds and with a carburetor setting which might be regarded as typical of practical operation, was also studied. A r e c o r d of p o w e r output, air-fuel ratio actually obtained, and carbon monoxide content of the exhaust gases was also made.
Equipment and Methods The tests were conducted with a six-cylinder truck or bus engine of 4-inch bore and 5inch stroke, developing its maximum power at about 2300 r. p. m.; the valves were located vertically in the head, and the combustion chamber was only slightly larger than the cylinder bore. The compression ratio of 4.85 to 1 used in these tests was as great as could be effective with the gasoline employed. Oil temperature was controlled by a cooler with a regulated supply of cooling water. A small fan and a few coils of copper tubing around the exhaust manifold were used to prevent excessive heating at this point at high speeds and full throttle. The engine was direct-connected to a 100-horsepower electric cradle dynamometer. A Sprague fuel-metering device for weighing the fuel and operating a stop watch and a revolution counter was p r o v i d e d . The air was m e a s u r e d t h r o u g h a wellrounded orifice, and records of barometric pressure, humidity, and temperature were maintained. The exhaust gases were sampled at a point in the exhaust pipe 8 feet from the engine, and a continuous flow through the sampling tube was maintained by means of a suction pump. The gases were passed through a cooler and brought to room temperature before being passed into the gas analysis apparatus. Three Williams gas analysis apparatus were used. The gasoline used throughout the tests was a 65-66 octane (C. F. R. Research m e t h o d ) Midcontinent “regular” grade without tetraethyllead. The blend contained 90 per cent of the same gasoline and 10 per cent by volume of anhydrous ethanol denatured with 1 per cent of aviation gasoline (formula S. D . 28-A) so that the blend actually contained 9.9 per cent of ethanol by volume. The octane rating of the blend was 75-76 (C. F. R. Research method). The gain in octane rating due to the addition of alcohol was somewhat greater than that reported by Kuhring (4). The distillation 650
Comparative Studies on Influence of AirFuel Ratio, Engine Speed, and Throttle Opening upon Relative Power Output, Specific Fuel Consumption, and Carbon Monoxide Production
characteristics of the two fuels are shown in Table I. The specific gravity 77/39.2" F. (25/4" C.) of the gasoline was 0.7237, and that of the blend, 0.7276. These factors were used to calculate volumetric fuel consumption from the measured consumption by weight. In making the tests the engine was first operated with gasoline at a desired speed and throttle opening and with a given carburetor jet, the spark being adjusted to give maximum power. When this adjustment had been made and the engine was operating at the desired speed, the test was run over a period of 4 to 6 minutes. Samples of exhaust gas were collected soon after the run wm started and analyzed for carbon dioxide and monoxide. Throughout the tests the jacket water t e m p e r a t u r e was maintained at 150" F. -~
TA4BLEI.
.Initial S. T. M. distn ., b. p. 30 60
Residue, 00. Vol. distd., cc. Barometer, mm. Room temp., F.
DISTILL.ATION DATA F.:
Gasoline 101 125 138 161 186 213 237 259 284 314 350 382 3 95 734 80
10% Blend 101 123 131 141 149 167 225 252 278 308 348 380 3 95 734 80
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Immediately after the run with gasoline
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was completed, the fuel was changed to the blend, the engine was operated again for a
few minutes at the desired speed, and the ignition timing was again adjusted for maximum power. The test was then made as with gasoline. Engine speed and all engine operating conditions were duplicated as nearly as possible. Sets of comparativeruns were made over the speed range below peak power output and repeated with each of several carburetor jets. The smallest jet used was 0.056 inch in diameter and the largest, 0.068 inch. Comparative tests were also made at quarter- and at half-throttle, at several engine speeds but with only one carburetor jet. The 0.061-inch j e t was used because it gave the air-fuel ratio typical of that which might be met in practice. Results are shown in Graphs 1 to 7. 65 1
Discussion of Results The distillation data show the typical sag resulting from the formation of azeotropic binary mixtures of ethanol and those h y d r o c a r b o n s boiling between about 130" and 200" F. The initial and final boiling points were unchanged except through dilution. The higher latent heat of vaporization of the alcohol wa$ evidenced in the tempehture of the airfuel mixture in the intake manifold; the temperature was 11" F. lower with the 10 per cent alcohol blend than with gasoline, and this difference was constant throughout the tests. It is interesting to note that this is exactly the difference calculated by Christensen, Hixon, and Fulmer (I) from the data of Ricardo (6). Regularly, less cooling water was required with the blend than with the gasoline as the fuel to maintain an outlet temperature of 150' F. There was no significant difference in the temperatures in other parts of the engine in shifting from one fuel to the other. The operating crew were of the opinion that engine operation was somewhat steadier with the blend than with the gasoline. The air-fuel ratio with a given speed, throttle opening, and carburetor jet was practically identical with the two fuels. The ratio with the blend was slightly lower with the 0.056-inch jet and slightly higher with the 0.068-inch jet. Christensen, Hixon, and Fylmer (1) showed that the theoretically correct air-fuel ratio, for complete combustion, is 14.2 for a 10 per cent alcohol blend when that for the gasoline used in the blend is 14.8 (approximately the average for commercial gaso-
GRAPH5. CARBURETOR JET0.068 INCH IS DIAMETER AND FULL THROTTLE GRAPH6. CARBURETOR JET0.061 INCH IN DIAMETER AND QUARTER-THROTTLE GRAPH7. CARBURETOR JET0.061 INCH IN DIAMETER AND HALF-THROTTLE
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INDUSTRIAL AND ENGINEERING CHEMISTRY
lines). Since the blend was of slightly greater density than the gasoline, it isevident that the volume flowing through the jet was slightly less than the volume of gasoline flowing through the same jet under the same conditions. In effect, the substitution of the blend resulted in a mixtiire ratio slightly weaker than that obtained witlk gasoline under the same conditions. The air-fuel ratios varied from 11-1 to 1 C r l . Within this range the power output is ordinarily increased hy a decrease in the air-fuel ratio. Except at the higher speeds and with the highest air-fuel ratios, the hleod gave a greater power output than did the gasoline. This result was obtained in spite of the fact that the mixture ratio was, in effect,smaller with the gasoline. The blend gave appreciably less oarbon monoxide under a given set of conditions than did the gmoline, hilt there was no definite ratio. In general, the decrease in carbon monoxide production could he accounted for on the basis of the differencein oxygen requirements of the two fuels. That is, if the two fuels were used with mixture ratios containing the same ratio of oxygen required to oxygen present, the carbon monoxide content of the exhaust gas would be the same for the two fuels. The relsti>re power output with the gasoline and the hlend was affected by air-fuel ratio and engine speed, whereas the throttle position apparently had little or no influence upon the relative values. With the lrigbest air-fuel ratios (15 or 16 to 1) and the higher engine speeds (1600 to 2000 r. p. m.) the hlend was inferior to gasoline, but with the lower air-fuel ratios, and particularly a t low engine speeds, the hlend gave the greater power output. The relative specific fuel consumptioils show the influence of the air-fuel ratio previously reported by Hubendick (9)and by Ross and Ormandy (7). Engine speed and throttle opening also are factors and their influeiicc is not wliolly due to their effect upon the air-fuel rat.io. Iu general, the blend
was favored by low air-fuel ratio, low engine s p e d , and small throttle opening. Certainly there was no single relation between the relative specific fuel consumptions with the two fuels. The data indicate that the carburetor setting with t h e gasoline and the 10 per cent blend should be the same for satisfactory practical operat.ion. Operations at low speed and at part throttle mere part.irnilarly favorable as regards comparative advantage of the blend over gasoline, under which conditions the 10 per cent alcohol hlend gave slightly greater power output, appreciably lower specific fuel consumption, and a 30 to 50 per cent lower carbon monoxide production than was obtained with lire xasoline alone.
Acknowledgment The studies reported here were carried out as a part of the program of the Iowa State College Committee on the Use of Alcohol in Motor Fuel and were conducted by a crew consisting of G. E. Scott, I?. L. Spies, G. I,. Stoughton, E. F. Kelm, C . L. Vanatta, and M. K. Veldhuis.
Literature Cited (1) Chriatmsen, I,. M., Hixon, R. M . , and Fulmer, E. I., Zozoo State Coll. J . Sci., 8.245-50 (1934). ( 2 ) Gray, R. R., Anr. En$, 15, 106-9 (1934). (3) Hlnbondick. E., Trans. Fuel Con{., World Power Conf,,London, 1828,3, 7 2 4 4 8 (19%). (4) Kuhriiig, M. S., Can.J . Xesenmh, 11,48!4-504(1934). (5) Miller, Harry, Idrtho Agr. Ewt. St,&.,Bull. 204 (1934). (6) Rioardo, H. It.. "The High-Speed Internal Combustion Eneine." London. 1929. (7) Ross. .J. D., and Omandy, W. K.. Trans. Inat. Chm. Engrs. (London), 4,104-14 (1928). (8) Wawruiniok. Ot,Lo, Transportation Inst., Technionl Coll. of Saxony (Dreaden). Monograph I Y , Berlin, XiRsina and Co.. 1927.
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