IC Engine Output vs Boost Pressure

[ryandias]

Is there a rough estimate of power output vs boost pressure?

I drive a turbo diesel jetta, and am curious what the unboosted engine output would be vs the 100Hp when boosted to ~15 psi above atm.

Is there a rough equation to input the boost pressure and get a ratio or % power number for unboosted engine output?

 

[patprimmer]

Yes power output is approximately proportional to absolute manifold pressure within certain parameters.

The main parameters against this are charge temperature and ability of the engine to withstand the cylinder pressure generated. Another parameter is increased exhaust blow down pressure but this tends to be less prominent.

The impact of charge temperature can be calculated by the combined gas laws.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[tbuelna]

ryandias,

The relationship between simple manifold pressure and brake horsepower in a diesel engine is somewhat tenuous, as patprimmer seems to indicate.

A better approach would be to compare brake horsepower figures at the two air mass flow conditions with similar smoke limits, and not manifold pressures. A diesel engine will continue to make more power as more fuel is injected, until there is no longer sufficient oxygen mass present in the intake charge. This is the smoke limit.

Of course this assumes that all other operating parameters are equal, which they're not. The relationships between air densities, trapping efficiencies, cycle temperatures and pressures, ignition delays, combustion heat release rates, etc. are very complex in a diesel engine.

So to answer your question, no there is no simple way to compare the two engines.

Hope that helps.
Terry

 

[BrianPetersen]

I am going to surmise that the 100 hp power output means that this is a "pumpe-duse" TDI because that's a common power output for those.

The "SDI" (non-turbo) version of that engine in Europe makes 64 horsepower stock. It can be chipped to low-seventies. One of the options when chip-tuning a diesel engine (increasing the boost pressure) isn't available in that case.