Mumbai University > Mechanical Engineering > Sem 5 > IC Engines

Marks: 5M

Year: Dec 2015

The combustion in a CI engine is considered to be taking place in four stages:

i) Ignition delay period/pre-flame combustion

ii) Rapid combustion/uncontrolled combustion

iii) Controlled combustion and

iv) After-burning

i) Ignition delay period: ignition delay (0.7-3ms) period is counted from the start injection to the point where the pressure time curve separates from the compression curve indicated as start of combustion. The delay period in the CI engine influence both engine design and performance

ii) Rapid combustion: the period of rapid combustion also called the uncontrolled combustion, is that phase in which the pressure rise rapid. The period of rapid combustion is counted from the beginning of the combustion to the point of maximum pressure on the indicator diagram.

iii) Controlled Combustion: The temperature and pressure in the second stage is already quite high. Hence the fuel droplets injected during the second stage burn faster with reduced ignition delay as soon as they find necessary oxygen and any father pressure rise is controlled by the injection rate. The period of controlled combustion is assumed to end at maximum cycle temperature.

iv) After burning: combustion does not cease with the completion of the injection process. The unburnt and partially burnt fuel particles left in the combustion chamber start burning as soon as they come into contact with the oxygen. The process continues for a certain duration called the after burning period.