All About Engines

The Gas Engine 191 While the cylinder of the steam engine had to be kept warm by means of a steam jacket, that of the gas engine must be kept cool by means of a water jacket. The walls of the cylinder are double, and cold water is maintained in constant circulation—some- times naturally and sometimes by the aid of a pump. If this were not done the valves would soon wear out, and the piston would expand and jam owing to the heat produced by the explosions. Moreover, the combustion chamber—the small space behind the piston into which the mixed gases are compressed —would become so hot that the mixture would explode immediately on admission, with the cer- tainty of damage to the engine, and probably also injury of the man in charge. With the steam engine the absence of steam in the jackets means merely a loss in efficiency ; with a gas engine even an interrup- tion to the flow of water means a smash. And even when the cooling system is working effectively the gases which escape from the exhaust are hot enough to render very useful service. In some cases they are employed to produce hot water. Thus about 2 gallons of boiling water can be obtained for each horse- power per hour, and the waste heat from a 50-horse- power engine will produce 100 gallons per hour. Having now learnt how a gas engine works, let us see what advantage it possesses over the steam engine. In the first place, it occupies less space. No boiler is required, and the heat is produced in the same chamber in which it is to be utilised. There is no loss of heat by radiation from the surface of