Explain different stages of combustion in C.I. engine with sketch.

1) Ignition delay period : During this fuel has already admitted but has not yer ignited. This is counted from start of injection to the point where P-O curve separates from pure air compression curve. 2) Rapid or uncontrolled combustion : In this stage pressure rise because of during the delay period the fuel droplet have time to spread over a wide area and fresh air around them. 3) Controlled combustion : The temperature and pressure rise in the second state is quite high, hence droplet of fuel injected in stage burn faster with reduced ignition delay as soon as they find necessary oxygen and further pressure rise is controlled by injection rate. 4) After burning : This sage may not be present in all cases. Because of poor distribution of fuel particles, combustion continues during part of the remainder of the expansion stroke.