From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Report comparing the performance and consumption of petrol, benzole, and alcohol-based fuel mixtures.
| Identifier | ExFiles\Box 32\1\ Scan028 | |
| Date | 8th November 1913 | |
| THE AUTOCAR, November 8th, 1913. 10% of crude wood naphtha and about ½% petroleum naphtha to 90% of ethyl alcohol containing water, it is called methylated spirit, and it costs about 3s. 6d. per gallon. Without special permission it cannot be bought in quantities exceeding four gallons. We hope that in future alcohol will be denatured under Government permission with other ingredients, selected with an eye to their suitability for use in our engines, but in the meantime the industrial alcohol which we do get through ordinary trade channels is vicious to the kind of alcohol to experiment with, and that is methylated spirit. The following tests were made: (1.) A test of b.h.p. and consumption of the engine using petrol, Pratt's A motor spirit having a specific gravity of .710 at 60° Fahr. (2.) A test of b.h.p. and consumption of the engine using benzole 50-90's having a specific gravity of .875 at 60° Fahr. (3.) A test of b.h.p. and consumption of the engine using benzole 90's having a specific gravity of .885 at 60° Fahr. (4.) A test of b.h.p. and consumption of the engine using a mixture of 50% of benzole and 50% methylated spirit, the mixture having a specific gravity of .850. (5.) A test of b.h.p. and consumption of the engine using a mixture of 33.3% benzole and 66.6% of methylated spirit, the mixture having a specific gravity of .838. (6.) A test of b.h.p. and consumption of the engine using a mixture of 25% benzole 50-90's and 75% methylated spirit, the mixture having a specific gravity of .830. The engine ran even as slowly as 300 r.p.m. with all the mixtures, and was easily started from cold in the temperature of the test room, which was about 70° Fahr.; but on none of the mixtures of methylated spirit and benzole did it run steadily unless the jacket of the induction pipe was maintained at 160° Fahr. at least. The benzole took rather less air than petrol, as it commonly may be expected to do; and the alcohol mixtures took substantially less air than either. The greater the amount of alcohol in the mixture the greater is the reduction of the air needed. The satisfactory nature of this feature in the result is evident when we recall the fact, mentioned towards the beginning of this article, that less air in the cylinders means more fuel in the cylinder, and consequently the necessary opportunity for alcohol to make up for its low calorific value. Results. The whole range of the principal numerical results is roughly indicated by the following figures, which were obtained at an engine speed of 1,000 r.p.m.: Fuel. | Power. | Consumption. Compared with petrol in each case. 90's benzole ... 1.25% less ... 15.5% less 1-1 mixture of methylated spirit and benzole ... 1.0% less ... 3.7% less 2-1 mixture of methylated spirit and benzole ... 3.0% less ... 8.9% more 3-1 mixture of methylated spirit and benzole ... 8.5% less ... 24.5% more The curves in which these results have their places will be published with the letterpress of Dr. Ormandy's paper in Internal Combustion Engineering and The Automobile Engineer on November 12th, but, without giving these curves here, we may state the following generalisation which they carry. E54 The Possibilities of Alcohol Fuel. First, that from 700 to 1,500 r.p.m. the horse powers with different fuels took the following order. Petrol (greatest). 90's benzole. 1-1 mixture of benzole and methylated spirit. 1-2 mixture of benzole and methylated spirit. 1-3 mixture of benzole and methylated spirit. (least). This order was broken in one place, namely, below 1,000 r.p.m. the 1-1 mixture of benzole and methylated spirit gave slightly higher powers than benzole. Secondly, that from 700 to 1,500 r.p.m. the economy of consumption in pints per brake horse power per hour for the different fuels took the following order: Benzole (lowest consumption). 1-1 mixture benzole and methylated spirit. Petrol. 1-2 mixture benzole and methylated spirit. The one exception was that at about 1,440 r.p.m. and upwards the economy of petrol became better than that of the 1-1 mixture. The low position of the mixtures rich in methylated spirit confirms the expectation that the rate of propagation of flame in these mixtures under the conditions of the experiments would not be sufficiently rapid for efficiency. This is further borne out by the heated state of the exhaust valves, which was greater as the proportion of alcohol became greater. Alcohol burns slowly, as we understand slow burning in engine work, where it is all over in a small fraction of a second. But it does not follow that this must for ever be accompanied by diminished efficiency. Dr. Ormandy thinks, both as the results of his own experiments and those of Professor Junker, that the highest thermal efficiency—i.e., the best rate of work done to heat supplied—will be attained by that fuel which burns at a minimum rate in relation to the piston velocity. Rapid combustion gives very high temperatures at the beginning of the stroke, with tremendous radiant heat losses through the cylinder head. Professor Junker estimated that five out of seven units of lost heat passed through the cylinder head, and only two units through the walls. He was so impressed with the importance of this that he lays it down as an axiom that the temperature throughout the whole cycle should be as low as possible. In spite of the disadvantages of the low compression used in Dr. Ormandy's case, the high thermal efficiency of the alcohol mixtures strongly supports this view, and holds out a great hope for the future. Compression. An increasing compression gives an increasing rate of flame propagation for all kinds of volatile fuel. Alcohol, which has a slow rate of flame propagation, fortunately also permits a high compression without the risk of pre-ignition which there is with petrol or benzole. Had the compression of the Maudslay been increased for the alcohol mixtures, the results from them would undoubtedly have been better, but so far from being increased they actually fell off at high speed, where high compression is most wanted, and where it is most difficult to obtain. The cause, of course, is throttling in the carburetter, induction pipe, and valves. On this account Dr. Ormandy sought, and obtained, the permission of Mr. Coatalen and the Sunbeam Motor Car Co., Ltd., to repeat these experiments, to some extent at any rate, on a standard Sunbeam engine having a compression exactly equal to that of the Maudslay engine, but with cylinders 80 x | ||