OIL AND VOLATILE HYDROCARBON ENGINES
Although this book is devoted primarily to a discussion of street-gas and producer-gas engines employed in various industries, a few words on oil and volatile hydrocarbon engines may not be out of place.
Oil-engines are those which use ordinary petroleum as a fuel or illuminating oil of yellowish color, having a specific gravity varying from 0.800 to 0.820 at a temperature of 15 degrees C. (59 degrees F.), and boiling between 140 and 145 degrees C. (284 to 297 degrees F.). Volatile hydrocarbon engines are those which employ light oils obtained by distilling petroleum. These oils are colorless, have a specific gravity that varies from 0.680 to 0.720, and boil between 80 degrees and 115 degrees C. (176 to 257 degrees F.). Among these "essences," as they are called in Europe, may be mentioned benzine and alcohol.
In general appearance, and the way in which they are controlled, oil-engines differ but little from gas-engines. Their usual speed, however, is 20 to 30 per cent. greater than that of gas-engines. Except in some engines of the Diesel and Banki types, the compression does not exceed 43 to 71 pounds per square inch. In volatile hydrocarbon engines, on the other hand, the speed is very high, often running from 500 to 2,000
revolutions per minute, while the speed of gas or oil engines rarely exceeds 250 or 300 revolutions per minute.
Oil-Engines.—Oil-engines are employed chiefly in Russia and in America. Because of the high price of oil in other countries they are to be found only in small installations in country regions and are used mainly for driving locomobiles and launches. The improvements which have been made of late years in the construction of gas-engines supplied by suction gas-producers for small as well as for large powers, have hindered the general introduction of oil-engines.
The characteristic feature in the design of many of the oil-engines of the four-cycle type now in use (to which type we shall confine this discussion) is to be found in the controlling mechanism employed. The underlying principle of this mechanism lies not in acting upon the admission-valve, but in causing the governor to operate the exhaust-valve in such a manner that it is held open whenever the engine tends to exceed its normal speed. Some engines, however, are built on the principle of the gas-engine, with an admission-valve so controlled by the governor that it is open during normal operation and closed whenever the speed becomes excessive.
The necessity of producing a mixture of air and oil capable of being ignited in the engine-cylinder has led to the invention of various contrivances, which cannot be used if illuminating-gas or producer-gas be employed. These contrivances are the atomizer, the
carbureter, the oil-pump, the air-pump, the oil-tank, and the oil-lamp. In some oil-engines all of the elements may be found, but for the purpose of simplifying the construction and of avoiding unnecessary complications, manufacturers devised arrangements which rendered it possible to discard some of them, particularly those of delicate construction and operation. It is not the intention of the author to enter into a detailed description of these various devices, since the limitations of this book would be considerably surpassed. The reader is referred to books on the oil-engine, published in the United States, England, and France. [B]
Most of the observations which have been made on the construction and installation of gas-engines, as well as the precautions which have been advised in the conduct of an engine, apply with equal force to oil-engines. It will therefore be unnecessary to recur to this phase of the subject so far as oil-engines are concerned. One point only should be insisted upon—the necessity of very frequently cleaning the valves and moving parts of the engine.