CHAPTER XXIX 

 GAS ENGINES 



405. Principles on Which Based. The gas engine (Fig. 

 176), which is coming gradually into use, requires but a small 

 amount of fuel. In a steam boiler, the energy is transmitted 

 to water inside the vessel. In the gas engine, the gas or oil is 

 brought in contact, mixed with the air, and exploded. Gas 

 engines are constructed in somewhat the same way as an 

 ordinary high-pressure steam engine, and are built both as 

 single and coupled engines. The cylinder is specially con- 

 structed and is surrounded by a water jacket provided with 

 an ample supply of water to keep it cool (Fig. 177). The 

 piston and rod, guards, connecting rod, crank, and fly-wheel 

 are the same as those of a steam engine. The propulsive 

 force of the gas engine is furnished by an explosion produced 

 by igniting within the cylinder a mixture of air with coal 

 gas, kerosene, gasoline, or alcohol vapor. To have complete 

 combustion, it is necessary to have sufficient air, as the oxy- 

 gen must combine with the hydrogen and carbon of the fuel. 

 The gas is admitted at every other revolution, since the prod- 

 ucts of combustion must first be expelled by the piston on 

 its first return stroke. During the second stroke the mixed 

 gases are admitted through a valve, which closes like a pump 

 valve when the piston shoots back. When the piston is at the 

 end of its stroke and has compressed the gases, it closes an 

 electric circuit, which is broken when the piston shoots on its 

 second outward stroke. This produces a spark which ignites 



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