CHAPTER LV 



ENGINE OPERATION 



Essentials of Operation. Someone has said that there 

 are four features of the action of the gasoline or oil engine 

 which must be right or the engine will not run and furnish 

 power; and if they are right, the engine will run in spite of 

 everything, assuming for the time being that the working 

 parts are in such adjustment as to permit of free move- 

 ment. These essential features are: 



1. Proper mixture of gases. 



2. Compression. 



3. Ignition. 



4. Correct valve action. 



The Gas Mixture. During the suction stroke of the 

 piston the cylinder is drawn full of air mixed with a suffi- 

 cient amount of fuel vapor. The amount of air and fuel 

 vapor must be in about the correct proportion or the mixture 

 will not burn. For instance, if there be little fuel or if it be 

 improperly vaporized, the mixture will not be ignited by the 

 spark produced by the igniter. On the other hand, the mix- 

 ture will not burn if the proportion of fuel vapor be too large ; 

 oxygen of the air must be present to support combustion. 

 Pure fuel vapor or gas will not burn, nor will very rich mix- 

 tures. 



Now the range of proportions in which the air and fuel 

 vapor may be mixed and still give a combustible mixture is 

 quite limited, and the range of mixtures which will give a 

 good, strong working stroke is still more limited. The richest 

 mixture that will burn has been stated by one authority to 



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