All About Engines

The Gas Engine 201 vide for an explosion every revolution, two of these operations must be carried out in such a way that they do not occupy a stroke, and this is achieved by arranging ports in the cylinder walls which shall be uncovered by the piston on its outward stroke. Through these ports a blast of compressed air is driven, which sweeps out the waste gases and leaves sufficient air for the next explosion. Towards the end of the stroke gas is admitted, so that by the time the piston is ready to return the new charge is there to be compressed. From the two-stroke to the double-acting engine is only a step. Using a piston of the ordinary type, like that of a steam engine, with a piston rod and cross head, and putting a front cover on the cylinder, the operations of a two-stroke engine can then be performed both in front of and behind the piston. The engine then looks—and acts—more like a steam engine, but explosions replace the steady, persistent force of expanding steam. The large gas engine has been an attractive field for inventors, and numerous attempts have been made to overcome the disadvantages produced by high temperatures, suddenly applied pressures, and the great weight of the parts. In several engines, for example, the explosion does not take place between the fixed end of a cylinder and a moving piston, but between two pistons, free to move in opposite direc- tions and each communicating its energy to the same or a neighbouring crank. Attempts have also been made to produce a gas turbine, but so far the problem