the following article may give some of the details you are looking for: doi:10.3390/e17010244

In the case of power plants, combustion is the bigger process where lost work exists, for that reason, exergy analysis is very important, because the flue gases have a lot of ENERGY, but not EXERGY. It happens in the Brayton, Rankyne, Otto and Diesel Cycles, the combustion is most important process. By the way, to do that is neccesary to take into account chemical exergy.

To be specific to your question for DI Diesel engines, the following may be some of the reasons behind useful energy(exergy) loss :

- Abnormal combustion phenomena which occur when the delay period become longer.

- Unequal fuel distribution and bad mixing before combustion-.

- Gas frictional losses :Wall friction as the incoming gas pass through valves which is speed dependent .

- Residual exhaust gas from the previous cycle when scavenging during the overlap period is incomplete.

- Hot ambient conditions and bad engine cooling system.

thanx for the reply 

Kamal Nasreldin Abdalla  sir , how can i investigate these parameters experimentally ?

Dear Kamal

I found your answers interesting. I also think that the difference in temperature between the flame and combustion gasses if two large will lead to high entropy generation and thus high exergy losses. Unequal flame distribution may lead to high carbon formation (red heat)  away from the spark plug. This reduces the work transfer as part of the mixture is not burnt resulting to high exergy losses

Dear Fidelis

The question asked by Mr Chaudhary is about DI Diesel Engine which has no spark plug as combustion is known to start spontaneously due to high compression and high temperature in the combustion chamber.