ALCOHOL MOTOR FUEL RESEARCH.
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The Result of Investigation Demonstrates the Differences Between Alcohol and its Admixtures on the One Hand and Petrol Mixtures on the Other.
THE FOLLOWING interim report of the Engineering Sub-committee of the Empire Motor Fuels Committee of the Imperial Motor Transport Council is published after reference to the Committee of Counoil of the Department of Scientific and Industrial Research, which committee make .a, grant to this branch of the Empire Motor Fuels Committee's investigations:—
It was decided by the Empire Motor Fuels Committee that a comprehensive and complete scientific investigation should be made of the behaviour of alcohol in internal-combustion engines, and that a complete range of experiments should be carried out with 95 volumes per cent. alcohol, as this was the strongest alcohol produced in commerce by the patent still. Through the kindness of the AngloAsiatic Petroleum Co., the committee were allowed to make use of the Ricardo variable compression engine, which had been designed and built for that company. The Government authorities gave permission for the experiments to be carried out with pure alcohol, so that there should be no difficulties introduced in this fundamental work by the presence of denaturants. In these and all other tests the committee have readily obtained the willing cooperatioR of the' Government Departments concerned.
The Nature of the Experiments That Have Been Conducted.
The experiments which it was decided to carry out with 95 volumes per cent. alcohol were divided into four series:— Series 1.—Tests for power output and consumption over the complete available range of mixture • strength with open throttle at four different piston speeds from 800 ft. to 2,000 ft. per minute and at compression ratios of 3.8 to 1 and 7 to 1 with constant heat to the carburetter.
Series 2.—Tests of power and efficiency over complete range of mixture strength of 0.8. 0.6, and 0.4 of full load, with piston speeds of 1,200 ft. and 2,000 ft. per minute and a compression ratio of 5 to 1, with constant heat to the carburetter. Series 3.—Tests over complete range of mixture strength at piston speed 2,000 ft. per minute, compression ratio 6 to 1, constant heat to carburetter, but with the circulating water at the outlet varied from 30 degrees C. to 90 degrees C.
Series 4.—Tests over the complete range of mix ture strength at 2,000 ft. per minute piston speed, at a compression of 5 to 1, varying the heat input to the carburetter from nil to 2,000 watts. This work has entailed many thousands of readings, but the results are of the greatest value. It was found that at all speeds, both with high and low compression, the thermal efficiency obtained with alcohol was higher than that obtainable with petrol or benzole at any compression which could be employed with them. Even at the low compression of 3.8 to 1, the thermal efficiency with alcohol is substantially greater than that obtained with petrol under similar conditions. In both cases the efficiency is almost independent of speed. The heat delivered to the circulating water is less in proportion with alcohol than with petrol. It was further found that, compared to petrol or benzole, the thermal efficiency obtained with alcohol is equally high at high or ism compression. The tendency to pre-ignition began to be evident at 7 to 1 compression ratio.
B20 Owing to the lower heat value of alcohol, the fuel consumption is much higher than is the case with petrol, in spite of the higher thermal efficiency, if they are used at the same compression, but the fuel consumption can be reduced much further in the case of alcohol than in that of petrol by increase of compression ratio. The throttle tests (Series 2) have shown that the behaviour of alcohol and petrol under variations of throttle conditions was identical.
The Question of Jacket Water Temperature.
The influence of, jacket water temperature was investigated (Series 3), and showed that the power output from the-engine was slightly diminished with increasing jacket temperature. The efficiency also fell slightly, as is the case with ail other volatile fuels investigated. The reputed increased power obtainable with alcohol engines with hot-water jacket is probably much more due to the diminished piston friction in the warm cylinder than to any other cause.
The e-xperiments in Series 4 have sho'wn that the maximum output from the engine is obtained when no heat is supplied to the ingoing air, but the thermal efficiency is slightly increased with increase of heat to the carburetter.
It has been proved that under all conditions. of compression, speed, or throttle, alcohol-driven engines run more sweetly and more smoothly than when running on petrol. Detonation never occurred under any compression employed, but at 7 to 1 compression, corresponding to a pressure of 185 lb. per sq, in., there was a tendency to pm-ignition.; 64. to 1 is probably the maximum compression to be aimed for.
There have been no evidences whatever of any corrosioirof valves.
Fundamental Facts and Figures Accumulated.
It must be remembered that these experiments have been carried out on a single-cylinder engine and that, in practice, troubles and difficulties introduced by induction manifolds may render it desir. able to sacrifice efficiency in some directions to gain flexibility and acceleration. Nevertheless' the series of experiments which has been carried out has led to the accumulation of the most valuable fundamental facts and. figures, which must be of the greatest value to the industry in the near future. It was decided by the committee that further experiments should be carried out on similar lines to those above referred to, but with alcohol at 99 and 90 volumes per cent. strength. The results obtained with these fuels substantiated the earlier work and proved that the mean effective pressure increases as the water content is increased so long as the whole of the fuel and water is completely evaporated before the end of the compression stroke. The -power output was increasing slightly, even with the 90 volumes per cent. alcohol. The behaviour of the varying amounts of water was studied over compressions ranging from 3.8 to 1 to 7 to 1, and it was proved that the presence of water in all cases incremes the maximum power output and reduces the heat flow through the cylinder walls. In high-compression engines there is a substantial advantage in using alcohol containing a. reasonable amount of water.
In conclusion, it is impossible in a brief interim report to deal with all the points which our cxperi
mental work has already touched upon, but it has definitely been proved :— (1) That alcohol can be employed from the low compression employed on paraffin engines up • to a far higher compression than can be used on any petrol.
(2) That the thermal efficiency obtainable with akohol is higher than with petrol or benzole.
(3) That, under all conditions of throttle or mixture, alcohol requires the. spark more advanced than is the case with petrolor benzale, and much more advanced with the weak mixtures.
(4) That there was no evidence at any piston speed attained in the engine that the rate of combustion of alcohol under the conditions obtaining was too slow to obtain the maximum effect.
(5) That detonation does not occur at compressions up to S to 1, and pre-ignition does not occur at 6 to 1, even when running for long periods at the highest possible power output of the engine.
(6) That there were no evidences whatever of corrosion in the engine.
(7) That the power output and bfficiency are increased by low temperature of the circulating water.
(8) That supplying heat to the carburetter reduces the.,power output but slightly increases the thermal efficiency.
(9) That increase in the water contents up to 10 volumes per cent. is=fan advantage, particularly in very high compression engines.
These brief conclusions require to be interpreted in the light of the fuller knowle,dge obtainable from the complete reports. A new series of experiments is now in hand, with a view to investigating the influence of-ether on, alcohol and the influence of alcohol on petrol, benzoic, paraffin, and ,tha. like. It is believed that this work will prove of considerable value to the motor industry, as it is probable that the first introduction /of alcohol onany scale as a motorfuel will be in the form of an admixture of the same with other ingredients.
A further series of investigations: into the behaviour of mixtures of alcohol and ether in varying proportions is now approaching completion and will form the subject of the next interim report of the Engineering Sub-Committee. Dr. W. R.
Ormandy, D.Sc., the chairman of the subcommittee, signs the interim report -reproduced above.
It is understood that the interim report of the Denaturation Sub-Committee will be available shortly.