SOME COMMON MECHANICAL MOTORS 



577 



large power plants. During the World's Columbian Ex- 

 position at St. Louis in 1903 and for a few years following, 

 the United States Government maintained at St. Louis a 

 fuel-testing plant. The purpose was to determine the 

 relative values of fuels and the most economical use of fuel 

 for power production. As a result of a long series of ex- 

 periments, it was shown that the best modern steam engines 

 require about two and one-half times as much coal as do gas en- 

 gines producing the same amount of power in large power 

 plants. Of course the coal is first converted into producer gas 

 and this gas is used as fuel in the engine. Many recent power 

 plants are equipped with producer gas producers and gas 

 engines (see Figs. 82 and 295 and review Art.- 119). 



692. How the Gas Engine Works. Like Newcomen's air- 

 steam engine, the gas engine cylinder is closed only at one 

 end. The mixture of gas and air is admitted into the closed 

 end of the cylinder and then ignited. Rapid combustion 

 takes place, producing very high temperature thus expanding 

 the gases greatly. The pressure produced drives the piston 

 to the opposite end of the cylinder. 



693. The Four- 

 cycle Engine. Most 

 gas engines are of the 

 type known as FOUR- 

 STROKE Or FOUR- 

 CYCLE engines. By 

 this is meant that 

 the piston moves the 

 length of the cylinder 

 four times and the 

 flywheel makes two 

 revolutions for each 

 explosion of gas. The 

 operation of the en- 

 gine is as follows: 

 First Stroke: The 



FIG. 363. First 

 cycle, diagram. Suc- 

 tion stroke. 

 37 



FIG. 364. First 

 cycle, engine. Suction 

 stroke. 



