THE AUTOMOBILE 



2 73 



Power plant. The power plant consists of the following 

 parts : a gas engine, a carburetion system, an ignition sys- 

 tem, a lubrication system, and a cooling system. 



How the gas engine works. The gas engine is known as 

 an internal combustion machine, because the fuel is burned 

 inside the cylinder and the explosion thus formed forces 

 back the piston. Before entering the cylinder, the gasoline 

 is changed to a gas and mixed with air in the carburetor. 

 The mixture is set on fire by means of an electric spark. 



i er * * ^^O ' Carburetor 



. FIG. 102. Simple two-cylinder opposed water-cooled motor. 



The common gas engine is spoken of as a four-cycle 

 engine, as there are four distinct steps in the action of the 

 piston. The first stroke of the piston sucks in the mixture 

 of air and gas from the carburetor into the cylinder. The 

 second stroke compresses this mixture. At the beginning 

 of the third stroke, the explosion of the gases takes place 

 and the piston is forced back. On the fourth stroke the 

 burned gases are forced out of the cylinder through a valve. 

 These strokes are called respectively suction, compression, 

 combustion, and exhaustion. (See figures 103106.) 



Only once in four strokes, therefore, is the motive power 



T 



