578 



MACHINES, WORK, AND ENERGY 



piston moves from the 

 closed end of the cylin- 

 der to the open end. 

 This produces a partial 

 vacuum, and suction 

 causes air charged with 

 a spray of the liquid fuel 

 or a mixture of air and 

 gas to rush in through 

 the intake valve (Figs. 

 363 and 364). 



Second Stroke: The 

 piston moves from the 

 open end of the piston 

 FIG. 365. Second to the closed end. This 

 C m - "" charge 



of fuel and air to from P ression str ke. 

 one-fourth to one-fifteenth of its original volume, depending 

 upon the kind of fuel used (Figs. 365 and 366). 



Ignition: Just at the 

 end of the second 

 stroke the charge is 

 ignited, usually by an 

 electric spark. 



Third Stroke: This 

 is the expansion or 



WORDING STROKE. 



The burning gases 

 produce great pressure 

 upon the piston and 

 drive it toward the 

 open end of the cylin- 

 der (Figs. 367 and 

 368). 

 Fourth Stroke: The 



FIG. 367. Third 

 cycle, diagram. Work- 

 ing stroke. 



FIG. 368. Third 

 cycle, engine. Working 



exhaust valve is 8t roke. 



