Kerosene has advanced to the front rank as a fuel for the farm tractor within a decade. A heavily preponderating majority of tractors burn kerosene. The history of early oil engines is reviewed and some comparative costs of kerosene and gasoline fuel for tractors, obtained from tests made in January, 1920, are given. Kerosene tractor-engine development is then discussed. The conditions required for complete combustion are the same in principle for both kerosene and gasoline, but in actual practice a wider latitude in providing ideal conditions is permissible for gasoline than for kerosene.
The four classes of commercial liquid fuels usable in internal-combustion engines are the alcohols, the gasolines, the common kerosenes and the low-cost heavy-oil fuels. The alcohols rank lowest in heating value per pound of combustible. Under existing economic conditions neither alcohol nor the fuel oils require consideration as available fuels for the tractor. The problem of producing an acceptable oil-burning tractor has been solved. The oil engine is no longer inferior to the gasoline engine, but the oil-burning tractor of the future must burn oil without waste. In some 1919 tests the average fuel consumption of seventeen kerosene tractors was 0.963 lb. of kerosene per b-hp-hr. and the average of four gasoline tractors was 0.951 lb. of gasoline. Six tractors used more than 1 lb. of fuel per b.hp-hr. But in the 1920 tests, twenty-eight tractors showed an average consumption of 0.889 lb. per b.hp-hr. The 1912 record performance of an oil-burning tractor was 0.700 lb. but the 1920 performance at Columbus was 0.606 lb. of kerosene per b.hp-hr. Private tests of tractors of the same type have shown results as low as 0.550 lb. of kerosene per b.hp-hr.
The kerosene tractor should consume less fuel than the gasoline tractor because of the greater heating value per gallon of kerosene. The problem of using oil for fuel in the throttle-governed engine is complicated because the controlling factors become variables whenever there is a change in power or in engine speed. After analysis of the chemical merits of kerosene and gasoline and their respective boiling-points, it is stated that because kerosene is heavier, is comparatively non-volatile and has a higher viscosity coefficient than gasoline, engineering authorities have assumed that difficulties encountered in burning kerosene at higher loads are almost wholly attributable to the heterogeneous nature of the compounds composing kerosene.
Regarding ignitibility of fuel mixtures, rate of flame propagation, preignition and cracking in throttle-governed engines, experience shows that internal temperature conditions suitable or permissible for gasoline are impracticable for kerosene. The effects of compression and temperature on the fuel-to-air ratio have been recognized for many years. The quality, quantity, compression and temperature of fuel mixtures are controlling factors in the operation of all gas engines, but in throttle-governed oil engines the regulation of all these factors in coordination demands greater consideration than is necessary for ordinary gasoline engines. These considerations are then elaborated.
Water is an efficient and suitable medium for regulating heat conditions in a throttle-governed oil engine. Water can be used internally as well as in the water-jacket. This is amplified in some detail. The art of burning kerosene is comprehended in that all controlling factors of combustion, including the proportions of the fuel mixture and its temperature at the time of ignition and during the working stroke, must always be kept in physical correlation with the density of the air. When the compression is a variable, the other controlling factors must also be varied in coordination with the compression, so as to maintain efficient working relations between compressions, mixture ratios and temperatures during varying load. Thorough mechanical admixture of fuel, air and water is essential in using kerosene.