330 Introduction to the Study of Science 



From this it should be evident that the voltage of an alter- 

 nating current may be stepped up as well as stepped down. 

 Explain how this can be done. 



IX. GASOLINE AS A MOTIVE POWER 



146. The gasoline engine. The remarkable increase in 

 travel and transportation on streets and highways in recent 

 years is due not only to the application of electricity, but also 

 to the development of the gasoline motor for use in vehicles of 

 all sorts. 



The gasoline motor is often described as an internal com- 

 bustion engine. This is because the fuel, a mixture of gasoline 

 vapor and air, is supplied directly to the cylinder where it is 

 ignited and by its expansion in combustion furnishes the working 

 power. The steam engine, for instance, receives through pipes 

 steam from a boiler under which a fuel has been burned. Both 

 types of engine are heat engines, for they convert heat energy 

 into working or mechanical energy. The chief difference be- 

 tween them is the place where the fuel is burned. 



Its operation. A gasoline motor may consist of a single 

 cylinder, or of two, four, six, eight, or twelve cylinders. But the 

 operation is the same for twelve as for one cylinder. If possible, 

 examine a gas engine and find out the important parts and the 

 work each does in operation. The main points of the common 

 motor may be illustrated in the diagrams of Fig. 109. In A, 

 the first stroke of the piston, the intake valve is open, the 

 piston is moving forward and drawing into the cylinder the 

 explosive mixture of gas and air. In B, the second or return 

 stroke, the piston is moving backward and compressing the 

 mixture. An electric spark, which is timed, ignites the mixture, 

 which, by exploding and expanding, drives forward the piston. 

 This, C, is the working stroke of the engine. The fourth step, 

 D, shows the piston moving backward, expelling the burned gas 

 through the exhaust valve, which is now opened. The working 

 energy, as illustrated in the diagrams, is applied only to alter- 



