I'm trying to understand the difference between actual and theoretical indicator diagram for diesel engines. On a theoretical diagram, the compression stroke is a smooth curve due to adiabatic compression. However on the actual indicator diagram it sharply increases in gradient before the fuel is injected. This would make sense if there was a spark, but I know that there is no ignition until the end of the stroke when the fuel is injected. Could anyone explain the difference between the two curves?

Thank you


1 Answer 1


Although the air entering the gas is at surrounding temperature, as soon as it enters the cylinder, it gains heat from the cylinder at operating temperature.

So even before the fuel enters the scene, air is preheated.


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