438 



Oil Engines. 



the heat so generated maintains the vapouriser thereafter at a 

 sufficiently high temperature without the aid of the external 

 heating lamp. This is in outline the method of the Hornsby- 

 Ackroyd engine. 



In other engines the oil simply drops into a passage some- 

 times heated by a lamp or by the heat due to explosive com- 

 bustion, through which it is drawn by the inrushing air supply 

 through the inlet valve. This system is adopted by several 

 makers, including Ruston, Proctor & Co., and Crossley Bros., 

 and by some the drops of oil are measured at each working 

 stroke, as in the Roots engine, in which the frequency of the 

 drops is determined by the hit-and-miss action of the governor. 



A few illustrations will serve to show the construction and 

 general principles of action of some of the engines which have 

 become favourably known. 



Fig. I is a diagram of the cylinder and valves of a Hornsby- 

 Ackroyd engine, but with the valves placed horizontally instead 

 of vertically for the purposes of explanation. 



In this diagram will be seen the piston, which may be assumed 

 to be moving in the cylinder in the direction of the arrow under 

 the pressure due to the combustion of working charge of oil 

 vapourised in the vapouriser and mixed with the required 

 quantity of air. The valves during this working stroke of the 

 piston would be closed as shown. When this stroke has been 

 completed the exhaust valve E will be lifted, and the engine 

 crank connected by the rod R to the piston will push the piston 

 back towards the vapouriser, and the products of the combustion 

 of the last charge will escape by the exhaust pipe. The piston 

 being then at the end of its instroke, the air admission valve A 

 is lifted, and the crank and connecting rod R pull the piston 

 outward again, and a charge of air is drawn into the cylinder by 

 it. A small quantity of oil is at the same time sent into the 

 vapouriser by an oil pump, the oil breaking up into a fine spray 

 as it enters. It is immediately vapourised, and the cylinder is 

 now full of air, mixed to a small extent with oil vapour, and the 

 vapouriser is full of oil vapour, mixed with a small proportion of 

 the products of combustion of the last working stroke. The 

 momentum of the fly-wheel, by means of the crank and con- 

 necting rod, now forces the piston back towards the vapouriser, 



