The United States Department of Agriculture has published in Farmers' Bulletin, No. 277, a very complete report, entitled "The Use of Acohol and Gasolene in Farm Engines," by Charles Edward Lucke, assistant professor of mechanical engineering, Columbia University, New York, and S. M. Woodward, irrigation engineer, office of experiment stations, Washington, D. C. The following abstracts are of general interest: The newest fuel for power purposes is alcohol. This is made from the yearly crop of plants. There is in existence no natural deposit of alcohol, but in a sense it may be said to be possible to produce inexhaustible supplies.
It is only within recent time that engineers have known how to build engines that would produce power from alcohol; and still more recent is the further discovery by engineers that this power can be produced at a cost which may permit its general introduction. The cost of fuel per unit of power developed depends first, on the market where it is to be used, and next, but by no means least, on the ability of the machinery to transform the fuel energy into useful work. If all the different kinds of machinery used for power generation could turn into useful work the same proportion of the energy in the fuel, coal would be almost universally used, because of the present low cost of energy in this form.
Anthracite coal in the neighborhood of New York can be bought in small sizes in large quantities for power purposes at about $2.50 per ton. This coal will contain about 12,500 B. T. U. per pound. This is equivalent to about 10,000,000 heat units per dollar. Large sizes, such as egg coal, containing about 14,000 B. T. U. per pound, can be bought in large quantities for about $6.25 per ton, which is equivalent to 4,500,000 B. T. U. per dollar. Other grades of anthracite coal and the various grades and qualities of bituminous coal will lie beween these two limits of cost. Illuminatin2 gas in New York costs $1 per 1,000 cubic feet, which is equivalent to about 500,000 heat units per dollar. Natural gas in the Middle States is sold for 10 cents per 1,000 cubic feet and upward. This fuel at the minimum price will furnish about 10,000,000 heat units for a dollar. Crude oil sells in the East at a minimum price of four cents per gallon, which is equivalent to about 4,000,000 heat units per dollar. Gasolene sells at a minimum price of ten cents per gallon, which is equivalent to about 1,200,000 heat units per dollar. Kerosene sells from ten to thirty cents per gallon, which is equivalent to 1,200,000 and 400,000 heat units per dollar, respectively. Grain alcohol, such as will be freed from tax under the recent legislation, will sell for an unknown price; but for the purpose of comparison, assuming thirty cents per gallon as a minimum, it will give 270,000 heat units per dollar. Gasolene, kerosene, crude oils, and, in fact, all of the distillates have about the same amount of heat per pound; therefore, at the same price per gallon, ignoring the slight difference in density they would deliver to the consumer about the same amount of heat per dollar, whereas the other liquid fuel, alcohol, if sold at an equal price, would give the consumer only about three-fifths the amount of heat for the same money. From the figures above given it apears that the cost of heat energy contained in the above fuels, at the fair market prices given, varies widely, lying between 200,000 heat units per dollar and 10,000,000 heat units per dollar. It is possible to buy eight times as much energy for a given amount of money in the form of cheap coal as in the form of low-priced gasolene, or twenty-five times as much as in the form of high-priced gasolene or kerosene. This being true, it might seem to a casual ob server as rather strange that gasolene should be used at all, and the fact that it is used in competition with fuel of one-eighth to one-twenty-fifth its cost shows clearly that either the gasolene engine has some characteristics not possessed by an engine or plant using coal, which makes it able to do things the other can not do, or that more of the heat it contains can be-transformed into energy for useful work. Both of these things are true.
Large steam plants in their daily work seldom use less than two pounds of poor coal per hour for each useful horse-power (known as a brake horse-power), which is equivalent to about 25,000 B. T. U. per hour, and which corresponds to about ten per cent thermal efficiency. Small steam plants working intermittently, such as hoisting engines, may use as high as seven pounds of coal per brake horse-power, or 2.5 per cent, thermal efficiency. Some plants will do better than the above with proper conditions, and some may do worse, but in general it may be said that the performances of steam plants lie between the limits of 2.5 and 10 per cent, thermal efficiency.
Plants consisting of gas-producers for transforming coal into gas for use in gass engines have in general a much higher thermal efficiency than steam plants doing the same work. They are, however, not built quite so small as steam plants, the smallest being about twenty-five horse power, and in general they have not been built so large, the largest being only a few thousand horse-power. Their efficiency, however, does not vary so much as is the case with steam plants. It may be fair to say that under the same conditions as above outlined these plants will use one and one-quarter to two pounds of coal of fair or poor quality per brake horse-power hour, which gives a thermal efficiency ranging from eighteen to ten per cent. These plants can be made to do much better than this, and perhaps may do worse, although the variation is not nearly so great as for steam plants.
Gas engines operating on natural gas or on illuminating gas from city mains will, on fluctuation of load with the regular work, average about 12,000 heat units per brake horse-power, or 20 per cent, thermal efficiency. Exploding engines operating on crude oil will average about 25,000 heat units per brake horse-power hour, which is equivalent to about 10 per cent, thermal efficiency. Exploding engines using gasolene should operate at a thermal efficiency of about 19 per cent, under similar operating conditions.