Most gas engines are of the four-cycle type used in many motor car engines. It differs from the two-cycle type, in that the explosive mixture is admitted and ignited after every other revolution of the engine, instead of after every revolution as in the two-cycle type (Fig. 178). To get a more constant turning effect, certain machines, like motor cars, have engines composed of two, three, four, six, and sometimes eight cylinders. The six-cylinder engines are the most popular for touring cars.
Fig. 176. - Gas Engine with an Air Compressing Outfit. Used for compressing air in a garage. The two large tanks or receivers in the rear are for storing the compressed air. A gauge is on top of the tank to indicate the pressure in the tank.