1 Watson and others, J. Soc. Chem. Ind., 1916, 34, 266.

A good deal of experimentation with alcohol motors for agricultural work, creameries, pumping plants, and so on, and also for locomotive purposes, has been carried out both in this country and on the Continent, but especially in Germany. In the United States an extensive investigation has been made into the question of the comparative value of alcohol as a fuel, numerous experiments on gasoline (petrol) engines and alcohol engines having been undertaken.1 The general conclusions arrived at in these trials were: -

(1). That any petrol engine of the ordinary type can be run on alcohol without any material alteration in the construction of the engine.

(2). The chief difficulties likely to be met with are in the starting and in supplying a sufficient quantity of fuel.

(3). The maximum power is usually greater with alcohol, and the engines are more noiseless than with petrol.

(4). The fuel consumption per brake horse power with a good small stationary engine may be expected to be 1 lb. or a little more with alcohol, and 07 lb. with petrol (012 gallon and 010 gallon respectively).

In these United States experiments the engines were working under the best conditions, and very high efficiencies were obtained, both with alcohol engines and petrol engines, namely, 39 per cent. with the former fuel and 26 per cent. with the latter.

A special committee appointed to examine this question for the Australian Commonwealth Advisory Council on Science and Industry reports as follows.2

"When alcohol is used in an ordinary petrol engine the consumption of fuel per b.h.p. is about 50 per cent. greater than in the case of petrol. It appears, however, that the consumption of alcohol per b.h.p. in a specially designed alcohol engine will not exceed in volume the consumption of petrol in a petrol engine.

' The main alterations necessary in the ordinary design of petrol engines in order to fit them to work efficiently on alcohol are as

1 Bulletin No. 392, U.S. Geol. Survey, 1909.

2 Report of Executive Committee, C. 7963, 1917, follow, viz.: (a). An increased compression from about 75 lb. per square inch, which is the average for petrol engines, to about 180 lb. per square inch, both above atmospheric pressure; (b) a pre-heating of either the fuel or the air or of the mixture of fuel and air; and (c) an increase in the area of the fuel jets and fuel supply pipes.

"Though an alcohol engine designed in the above manner will run efficiently, it cannot generally be started from cold with alcohol. In order to overcome this difficulty some special means must be provided. For example, either the carburettor must be preheated by a torch or in some other way, or an arrangement must be provided whereby a small amount of petrol can be used at the start. When a temperature sufficient to vaporise the fuel is attained, the alcohol can be gradually turned into the carburettor and the preheating of the fuel maintained by the exhaust gases."

The following is a more detailed summary of the conclusions arrived at in the American experiments already referred to.

"Abstract of U.S.A. Geological Survey Bulletin No. 392, 'Commercial deductions from comparison of Gasoline and alcohol tests on internal combustion engines.'

"By R. M. Strong. Washington, Government Printing Office, 1909.

"1. Introduction. - The Bulletin furnishes a summary of the commercial results of 2,000 tests conducted by the U.S.A. Geological Survey at St. Louis and Norfolk in 1907 and 1908. The tests dealt primarily with gasoline and formed part of the investigation into mineral fuels. To determine the relative economy and efficiency of gasoline it was compared with denatured alcohol.

"2. Differences in Engines. - The only change required for the use of alcohol in a gasoline engine, if any, is in the size of the fuel passage-ways. With this change alone the consumption of alcohol will be from 1 1/2 to 2 times as much as the consumption of gasoline for the same power.

"(i) Special Engines for Alcohol. - By using alcohol in an alcohol engine with a high degree of compression (about 180 lb. per square inch above atmospheric pressure) the fuel consumption rate can be reduced to practically the same as the rate of consumption of gasoline for a gasoline engine of the same size and speed.

"When alcohol is used in a gasoline engine with the maximum degree of compression for gasoline, the available h.p. of the engine is increased about 10 per cent. An alcohol engine with the maximum degree of compression for alcohol will have an available h.p. 30 per cent. greater than a gasoline engine of the same cylinder size, stroke, and speed.

"(ii) Alteration of Gasoline Engines. - Some gasoline engines may be so changed that a sufficiently high compression is secured to make it possible to reduce the consumption of alcohol in gallons per h.p. per hour to an equality with that for gasoline before the engine was changed. The degree of compression may be most easily changed by lengthening the connecting rod. This may often be done by putting lines between the crank pin end of the connecting rod and the crank brasses. But if the cylinder is counterbored, or if there is not sufficient room at the head of the cylinder, a new cylinder should be cast with small clearance space. "3. Most Economical Degree of Compression. - A gasoline engine having a compression pressure of 70 lb., but otherwise as well suited to the economical use of denatured alcohol as gasoline, will, when using alcohol, have an available h.p. about 10 per cent. greater than when using gasoline.

"When the fuels for which they are designed arc used to an equal advantage, the maximum available h.p. of an alcohol engine having a compression pressure of 180 lb. is about 30 per cent., greater than that of a gasoline engine having a compression pressure of 70 lb., but of the same size in respect to cylinder diameter, stroke, and speed.

"When denatured alcohol is used in 10 to 15 h.p. four-cycle stationary engines having a compression pressure of approximately 180 lb., and the engines are operated at their maximum loads, the pressures during explosion or combustion reach 600 to 700 lb. Stationary gasoline engines, in which the compression pressure in some cases can be raised to 180 lb., are not usually built heavy enough to withstand such explosion pressures for any length of time.

"4. Consumption of Fuel. - A gasoline engine having the degree of compression ordinarily used for gasoline mixtures will in general require 50 per cent. more denatured alcohol than gasoline per b.h.p. "Gasoline and alcohol engines of similar construction having degrees of compression best suited to the fuel supplied will in general require equal volumes of gasoline and denatured alcohol respectively per b.h.p.

"When any of the usual methods of governing are used to control the speed of gasoline or alcohol engines, the rate of fuel consumption per b.h.p. per hour will ordinarily be about twice as great at one-third load as at maximum load. At the same time, an excessive rate of consumption of gasoline or denatured alcohol at any given load, if due to the incorrect adjustment of the mixture quality and time of ignition only, may be as great as, but not greater than approximately twice the minimum required before it will be noticeable from outward indications.

"5. Thermal Efficiency of Engines. - The thermal efficiency of alcohol and gasoline engines will in general increase with the pressure to which the charge is compressed when ignited.

"The maximum thermal efficiency of 10 to 15 h.p. four-cycle stationary engines of the usual type when operated with a minimum amount of throttling was found to increase with the compression pressure according to the formula} E=1 - (14.7/P).17 for gasoline and E= 1. (14.7/P).19 for alcohol, where E = the thermal efficiency

based on the indicated h.p. and low heating value of the fuel and P = the indicated pressure of the charge at the end of the compression stroke in lb. per square inch absolute.

"A high thermal efficiency and a rate of consumption of less than a pint per b.h.p. per hour, both for gasoline and for denatured alcohol, can often be obtained when the degree of compression, the load, the quality of the explosive mixture, and the time of ignition are carefully adjusted. A fair representation of the best economy values obtained, taken from the results of tests on 10 to 15 h.p. Nash and Otto stationary engines, and the corresponding thermal efficiencies, are given in the following table: -