All About Engines

The Petrol Motor 213 for them to knock their heads off. In order to secure silence some engines have rotary valves, not unlike the Corliss valves shown in Fig. 76; others have piston valves; and in others there is a sliding, or sliding and turning, sleeve between the piston and cylinder, pro- vided with holes which at the right moment coincide with ports in the cylinder itself. Thus the Itala and Daracq are rotary valve engines, and the Argyll and Daimler companies make sleeve engines. There is, further, an engine open at both ends with two pistons between which the explosion takes place. But the most important departure in principle is the substitution of the two-stroke for the four-stroke cycle. The plan adopted is the same as in the two- stroke gas engine to which reference has already been made in Chapter VIL, except that the crank case is employed as a sort of receiver. In the dia- grammatic view in Fig. 120 it will be seen that the admission and exhaust ports are in the side of the cylinder and are opened and closed by the movement of the piston itself. As the crank case is air-tight the upward movement of the piston draws in the ex- plosive mixture from the carburettor. The down- ward movement first compresses this charge, and then, when the port is exposed, forces it into the upper half of the cylinder, where it displaces the waste gases from the previous explosion. The return of the piston closes both ports and compresses the mixture. Explosion then takes place and the whole process is repeated, the piston thus receiving an impulse for every revolution of the crank. We can