All About Engines

234 All About Engines would extend higher up the scale. Its place has been taken, however, by The Diesel Engine, which embodies another new principle in its mode of working. Engineers who experimented with gas engines had discovered that the efficiency increased as the compression rose ; but the compression could not be increased beyond a certain point lest the mixture should be prematurely ignited. In the early nineties it occurred to Dr. Rudolph Diesel that if the fuel could be kept out of the cylinder until the air within had been fully compressed—that is, until after the piston had reached the end of the com- pression stroke—the advantages of high compression might be secured and all risk of premature explosion avoided. Moreover, it might be possible to use a cheaper variety of oil which is less easily converted into vapour, since it would be burnt immediately it entered the cylinder instead of having to wait while the engine made from one to two strokes before ignition occurred. Dr. Diesel’s experiments were carried out first in France and then in Germany, where, with the financial aid of the powerful Krupp firm, he con- structed an engine according to the plan he had con- ceived, and took out a patent in 1895. But it was not all plain sailing. The compression was higher than had hitherto been employed—reaching 500 lb. on the square inch—and there were many difficulties of construction to be overcome. Engines of fifty and