Gasoline Engines. 523 



gines, ranging from 1 to 15 and 20 horse-power, are now 

 offered for sale by manufacturers. While it cannot be 

 said that these motors have in general earned for them- 

 selves the reputation for reliability that steam engines pos- 

 sess, it is now acknowledged that there are upon the mar- 

 ket gasoline engines which are efficient and quite satisfac- 

 tory for farm purposes. 



654. Gasoline and Steam Engines Contrasted. Gasoline 

 engines are widely different from the steam types de- 

 scribed in the last section. In those the power is derived 

 from a' steadily burning fire converting water into steam, 

 which transmits the power to the working parts of the en- 

 gine; in these the fire is an intermittent one which is al- 

 most instantaneous in duration and which begins and ends 

 like an explosion. Indeed, the gasoline engine may be 

 likened to a cannon which loads and fires itself at deter- 

 mined intervals and where the ball is a piston whose mo- 

 tion is arrested by a crank shaft and transformed into rot- 

 ary motion in the fly wheels of the engine, to be used as a 

 source of power. After the first charge has been fired a 

 portion of its energy is used to reload the piece again, 

 making it ready for a second explosion, to be repeated as 

 often as needed. 



655. Principal Parts of a Gasoline Engine. The gasoline 

 engine, like the steam engine, has its cylinder and piston, 

 and its fly wheel and governor, but it has no boiler or fire- 

 box and is much more simple in its construction and man- 

 agement. There are provisions for supplying the engine 

 with gasoline and air as needed for the explosions, for ig- 

 niting the charge when ready and for disposing of the 

 waste products after the explosion has taken place. 



656. The Working Cycle. The working cycle of most 

 gasoline engines consists of five operations : 



1. Charging the cylinder with the explosive mixture of 

 air and gasoline vapor. 



