Diesel Cycle Efficiency
The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber in a Diesel engine. In the Diesel cycle, the working medium in the combustion chamber is
- compressed adiabatically from
, to < , > , - expanded isobarically at
from to > , - expanded adiabatically from
, to and > , - cooled isochorically at
from to the initial pressure .
The heat absorbed by the medium is given by

P-V Diagram for idealized Diesel cycle.
Efficiency of the Diesel Cycle
Because the process
From the equation given above we can say that the heat gained
We can likewise deduce the heat lost as
The thermal efficiency is defined as1
Using the ideal gas law
From the diagram it can be seen that the volume V is the same in state 4 as in 1, i.e.
Dividing the fraction through by
where
For an adiabatic expansion,
Finally, putting these back in and playing with minus signs:
-
See MIT’s brief page about the Diesel cycle. It’s also whence I nicked my diagram. ↩︎