In IC engines, especially in diesels, compression pressure (CP) is key to thermal/indicated efficiency, the ratio of indicated power over fuel thermal energy.
Now, CP as measured in a motored, non-firing engine is changing over the engine life - due to wear it decreases over time - or engine tuners take measures to increase CP. I would like to estimate the impact on fuel efficiency/ brake power which would require the change in net indicated mean effective pressure related to a change in CP.
Is there a simple relationship for this?
Thanks!
Indicated efficiency is the ratio of indicated power over fuel energy input.
Thermal efficiency means brake thermal efficiency which is the ratio of brake power over fuel energy input.
I found this:
TTE=1 - 1/CR^(k-1) * (s^k - 1)/(k*(s-1))
TTE : theoretical thermal efficiency
CR : compression ratio
k : specific heat ratio
s : cut-off ratio
Can I assume that cooling and pumping losses are proportional to TTE for changes in CR up to 10%? Then I could get the change in compression pressure from the relationship CP=CR^1.4.
Does k=1.4 and s=2 make sense for a 2L TDI?
Thanks Pankaj. I suggested s=2 from literature but dont know if it is appropriate. Does it depend on the specifics of the engine's injection timing?
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