ALCOHOL vs. GASOLINE FOR POWER.
The Technologic Branch of the United States Geological Survey, under the direction of Mr. J. A. Holmes, has recently completed an elaborate series of tests on the relative value of gasoline and alcohol as producers of power. The tests, over two thousand in number, probably represent the most complete and exact investigation of the kind that has been made, either in this country or abroad, and includes much original research work.
Correspondingly well-designed alcohol and gasoline engines when running under the most advantageous conditions for each, will consume equal volumes of the fuel for which they are designed. This statement is based on the results of many tests made under the most favorable practical conditions that could be obtained for the size and type of engines and fuel used. An average of the minimum fuel consumption values thus obtained, gives a like figure of eight-tenths (.8) of a pint per hour per brake horsepower for gasoline and alcohol.
Considering that the heat value of a gallon of the denatured alcohol is only a little over six-tenths (.6) that of a gallon of the gasoline, this result of equal fuel consumption by volume for gasoline and alcohol engines probably represents the best comparative value that can be obtained for alcohol at the present time, as is also indicated by continental practice. Though the possibility of obtaining this condition in practice here has been thoroughly demonstrated at the Government Fuel-testing Plant, it yet remains with the engine manufacturers to make the “equal fuel consumption by volume” a commercial basis of comparison.
The gasoline engines that were used in these tests are representative of the standard American stationary-engine types, rating at 10 to 15 horsepower, at speeds of from 250 to 300 revolutions per minute, while the alcohol engines were of similar construction and identical in size with the gasoline engines.
The air was not preheated for the above tests on alcohol and gasoline, and the engines were equipped with the ordinary types of constant level suction lift and constant level pressure spray carburetters. Many special tests with air preheated to various temperatures up to 250° Fahrenheit, and tests with special carburetters were made, but no beneficial effects traceable to better carburation were found when the engines were handled under the special test conditions, including constant speed and best load.
The commercial completely denatured alcohol referred to is 100 parts ethyl alcohol plus 10 parts methyl alcohol plus one-half of one part benzol, and corresponds very closely to 94 per cent by volume or 91 per cent by weight ethyl alcohol (grain alcohol).
No detrimental effects on the cylinder walls and valves of the engines were found from the use of the above denatured alcohol.
The lowest consumption values were obtained with the highest compression that it was found practical to use; which compression for the denatured alcohol ranged from 150 to 180 pounds per square inch above atmosphere.
Eighty per cent alcohol (alcohol and water) for use in engines of the present types would have to sell for at least 15 per cent less per gallon than the denatured alcohol, in order to compete with it. The minimum consumption values in gallons per hour per brake horsepower for 80 per cent alcohol is approximately 17.5 per cent greater than for the denatured alcohol used, or for gasoline. A series of tests made with alcohol of various percentages by volume ranging from 94 per cent to 50 per cent, showed that the minimum consumption values in gallons per hour per brake horsepower increased a little more rapidly than the alcohol decreased in percentage of pure alcohol. That is, the thermal efficiency decreased with the decrease in percentage of pure alcohol. This decrease in thermal efficiency or increase in consumption referred to pure alcohol is, however, comparatively slight from 100 per cent alcohol down to about 80 per cent alcohol. Within these limits it may be neglected in making the calculations necessary to compare the minimum consumption values for tests with different percentages of alcohol.
The nearer the alcohol is to pure, the greater the maximum horsepower of the engine. The per cent reduction in maximum horsepower for 80 per cent alcohol as compared with that for denatured alcohol used, was less than one per cent, but the starting and regulating difficulties are appreciably increased.
With suitable compression, mixtures of gasoline and alcohol vapors (double carburetters) gave thermal efficiencies ranging between that for gasoline (maximum 22.2 per cent) and that for alcohol (maximum 34.6 per cent) but in no case were they higher than that for alcohol. The above thermal efficiencies are calculated from the brake horsepower and the low calorific value of the fuel, which for the gasoline was 19,100 British thermal units per pound, and for the denatured alcohol was 10,500 British thermal units per pound.
As has been previously published, alcohol can be used with more or less satisfaction in stationary and marine gasoline engines and these gasoline engines will use from one and one-half to twice as much alcohol as gasoline when operating under the same conditions. The possibilities, however, of altering the ordinary gasoline engines as required to obtain the best economies with alcohol are very limited; for the amount that the compression can be raised without entirely redesigning the cylinder head and valve arrangement is ordinarily not sufficient, nor are the gasoline engines usually built heavy enough to stand the maximum explosive pressures, which often reach six and seven hundred pounds per square inch. With the increase in weight for the same-sized engine designed to use alcohol instead of gasoline, comes an increase in maximum horsepower of a little over thirty-five per cent (35%), so that its weight per horsepower need not be greater than that of the gasoline engine, and probably will be less.
The work was taken up to investigate the characteristic action of fuels used in internal combustion engines with a detailed study of the action of each fuel (gasoline and alcohol) as governed by the many variable conditions of engine manipulation, design and equipment. These variables were isolated, so far as possible; their separate and combined effects were determined; worked out under practical operating conditions; and led up to the conditions required for minimum fuel consumption. The results show the saving that can be obtained over conditions for maximum consumption, and also establish a definite basis of comparison under conditions most favorable to each fuel. This latter is a point of much commercial interest, and a study of the comparative action of gasoline and alcohol may be of great service in solving some of the general internal-combustion-engine problems where other than liquid fuels are used.
A large number of fundamental tests were necessary in order to clearly define conditions and interpret results. In a way they follow the work conducted by the Department of Agriculture, supplementing to a certain extent, but not duplicating bulletin 191, which gives much data of general value.
Many of the tests of internal-combustion engines have been made, but most of them, especially in this country, were by private concerns, for a specified purpose, and the results are not generally available. Furthermore, as is generally recognized by those familiar with gas, and especially gasoline-engine operation, the conditions influencing engine performance are so numerous and varied as to make the value of offhand comparison very limited and oftentimes misleading, exact comparisons only being possible under identical conditions or with reference to the actual known differences in all conditions that influence the results.