GAS AND OIL ENGINES 



" (b) The charge is ignited by flame carried in by a 

 slide valve. 



"(c) Under the impulse of the explosion, the piston 

 shoots upward nearly to the top of the cylinder, the 

 pressure in which falls by expansion to about 4 Ibs. 

 absolute, while absorbing the energy of the piston. 



"(d) The piston descends by its own weight and the 

 atmospheric pressure, and in doing so causes a roller- 

 clutch on a spur-wheel gearing with a rack on the piston- 

 rod to engage, so that the fly-wheel shaft shall be driven 

 by the piston; during this down-stroke the pressure 

 increases from 4 Ibs. absolute to that of the atmosphere, 

 and averages 7 Ibs. per square inch effective throughout 

 the stroke. 



"(e) When the piston is near the bottom of the cylin- 

 der, the pressure rises above atmospheric, and the stroke 

 is completed by the weight of the piston and rack, and 

 the products of combustion are expelled. 



"(f) The fly-wheel now continues running freely till 

 its speed, as determined by a centrifugal governor, falls 

 below a certain limit when a trip gear causes the piston 

 to be lifted the short distance required to recommence 

 the cycle. 



"Ignition is performed by an external gas jet, near a 

 pocket in the slide valve by which the charge is admitted ; 

 this pocket carries flame to the charge, thus igniting it 

 without allowing any escape. The valve also connects 

 the interior of the cylinder with the exhaust pipe, and a 

 valve in the latter controlled by the governor throttles 

 the discharge, and so defers the next stroke until the 

 speed has fallen below normal. To run the engine empty 



[137] 



