44 



BULLETIN 119, U. S. NATIONAL MUSEUM. 



The engine is single-acting and when exerting its full power makes 

 one explosion or working stroke in every four strokes. Assuming the 

 piston to be at the end of its instroke and about to be moved through 

 its outstroke by the momentum of a flywheel, a slide valve opens to 

 admit air into the cylinder. As the outstroke proceeds, the air sup- 

 ply is cut off, and the combustible gas intimately mixed with air is 

 drawn in until the piston has arrived at the end of its outstroke. 

 The gas port then closes and the piston is caused, by the momentum 

 of the flywheel, to perform its instroke, whereby the charge of gaseous 

 mixture and air that filled the cylinder at atmospheric pressure will 

 be compressed. About the time for the beginning of the second out- 



FIG. 18. OTTO GASOLINE ENGINE. THE FIRST FOUK-CYCLE MOTOK, 1877. 



stroke the gas is ignited and the gradual expansion of the gases 

 causes the piston to complete its second outstroke. The second in- 

 stroke then expels the products of combustion through an exhaust 

 valve which remains open during this second instroke. The next 

 outward stroke then commences a fresh cycle by taking in a new 

 charge of air and gas. 



By compressing the charge before firing it, nearly double the 

 amount of air that otherwise would be permissible can be present in 

 the mixture without preventing its being ignited, this additional 

 cushion moderating the violence of the explosion and giving a more 

 sustained pressure during the working stroke. 



The cylinder is water- jacketed and the gas and air are admitted 

 by a slide valve which serves also as an igniting valve, carrying a 

 pocket of flame from an external light to a small port. The exhaust 



