All About Engines

2i4 All About Engines now leave the general principles and proceed shortly to examine engines for motor-cars, motor-boats, and aeroplanes. The enormous extension of motor traffic during the last fifteen years has made heavy demands upon the world’s supply of petrol, and the price of this fuel rose from 8d. to is. gd. a gallon even before the war. It was natural, therefore, for owners of petrol engines to look around for a cheaper fuel, and among those most easily obtainable were paraffin, benzol or benzene, and alcohol. Paraffin is ordinary illu- minating oil, such as is used in lamps. Benzol is produced when coal is distilled, in the manufacture of coal gas, and alcohol is obtained when vegetable matter ferments. All are inflammable, but do not vaporise so easily as petrol, while there is such a heavy duty on alcohol that the price is prohibitive. Before the war benzol, which was only two-thirds the price of illuminating oil, and paraffin, which was still cheaper, were both used. The only disadvantage is that the engine will not start with them. Once, however, the carburettor has become warmed up they work very well. Many engines are made to start on petrol and then work with paraffin or benzol. Other engines are made to work with paraffin or benzol altogether, and are provided with a vaporising chamber which can be heated up by a lamp. This is surrounded by a jacket through which the exhaust gases pass, so that when once it has been heated it remains hot enough to vaporise the fuel as long as the engine is working.