GAS AND OIL ENGINES 



only thrust during which work is done ; the returning 

 piston expels the expanded gas, completing the cycle. 

 Thus there are three ineffective piston thrusts to one 

 effective thrust. Nevertheless, the engine has proved 

 a useful one for many purposes. 



This so-called Otto cycle has been adopted in almost 

 all gas and oil engines, the later improvements being 

 in the direction of still higher compression, and in the 

 substitution of lift for slide valves. There has been a 

 steady increase in the size and power of such engines, 

 the large ones usually introducing two or more working 

 cylinders so as to secure uniform driving. Cheap 

 forms of gas have been employed such as those made by 

 decomposing water by incandescent fuel, and it has 

 been proved possible thus to operate gas-power plants on 

 a commercial scale in competition with the most eco- 

 nomical steam installations. 



A practical modification of vast importance was in- 

 troduced when it was suggested that a volatile oil be 

 employed to supply the gas for operation in an internal 

 combustion engine. There was no new principle in- 

 volved in this idea, and the Otto cycle was still employed 

 as before; but the use of the volatile oil either a 

 petroleum product or alcohol made possible the com- 

 pact portable engine with which everyone is nowadays 

 familiar through its use in automobiles and motor boats. 

 The oil commonly used is gasoline which is supplied to 

 the cylinder through a so-called carburettor in which 

 the vapors of gasoline are combined with ordinary air to 

 make an explosive mixture. The introduction of this 

 now familiar type of motor is to a large extent due to 



