GAS ENGINES 



495 



difference in these two gasolines is very apparent in cold 

 weather, although they may give about equal satisfaction 

 during the warm weather. The difficulty with the blended 

 gasoline is that the "tops" or high-test gasoline will evaporate 

 in handling and in storing, leaving the less volatile fuels in 

 excess. Volatility is the characteristic of gas-engine fuel 

 which is at a premium. 



Naphtha and kerosene are also products of crude petroleum 

 obtained by distillation. They are heavier than gasoline, but 

 are used as fuel in some gas engines. A special carbureting 

 provision is necessary for their use. 



GASOLINE SYSTEM 



Methods of furnishing fuel to carburetor. A supply tank 

 of a size proportionate to the demands of the engine fur- 

 nishes raw gasoline to the carburetor. There are several 

 methods of getting the fuel to the carburetor. 



Overflow system. In the over- 

 flow system (Fig. 383) a double 

 chamber is used. The gasoline 

 supply is within reach of an 

 engine-driven pump, which 

 delivers more gasoline than can 

 be used. The excess flows back 

 to the supply tank. The over- 

 flow system is used on many small stationary engines. 

 Gravity system. In the gravity system (Fig. 384) the 



gasoline supply is main- 

 tained above the carbu- 

 retor. The carburetor 

 is provided with a float 

 which operates a valve 

 regulating the flow of 

 gasoline. 

 Pressure system. Where 

 the pressure system is used, a pump is provided by which 

 an air pressure is placed upon an air-tight gasoline tank. 





Fig. 383. The overflow type of 

 gasoline supply to the carburetor 



Fig. 384. Gravity gasoline feed 



