In these engines, neither we have a carburettor nor there is any need to ignite the compressed mixture. At the time of suction only clean air comes into the cylinder. It is compressed at a high compression ratio in compression stroke. The temperature of the compressed air is from 600° to 800°F. In this air of such a high temperature, diesel oil is injected into the combustion chamber through a special type of injector at a pressure of 1500 ponds per sq.inch. For this purpose, a mechanically operated plunger pump is used, which is known as fuel injection pump. When the diesel comes into contact with the hot air it starts burning immediately because diesel starts burning even at a temperature of 450° to 500° F. The gases expand when they are burnt, pressure is exerted on the piston, which is obtained on the fly wheel in the form of power for performing other jobs.