360 



APPLIED SCIENCE 



the gases, and the operation is then repeated. This method 

 of sparking is classified as a make-and-break system, and 

 should be distinguished from the spark-plug system. 



As the force is excited on but one side of the piston, and 

 only once in two revolutions, the gas engine is less steady 



than the steam 

 engine, which 

 has two impulses 

 for each revolu- 

 tion. This fault 

 is overcome to 

 some extent, 

 however, by the 

 use of heavy fly- 

 wheels. 



406. Types 

 of Gas Engines. 

 Most gas en- 

 gines are of the 

 four-cycle type 

 used in many 

 motor car en- 

 gines. It differs 



FIG. 176. Gas Engine with an Air Compressing from the two- 

 Outfit. Used for compressing air in a garage. The i fvrf> in 

 two large tanks or receivers in the rear are for C ^ C1 IV P e > 

 storing the compressed air. A gauge is on top that the explo- 

 of the tank to indicate the pressure in the tank. . 



sive mixture is 



admitted and ignited after every other revolution of the en- 

 gine, 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 



