EPR against TGT
 

Hi all,

anyone knows the actually relationship between EPR and TGT for a gas turbine engine?
any equation or formula to relate them?

Please help!!

Please give advices!:confused:

There is no single relationship. Each type of engine will be different (even those which dont use EPR as a control parameter have an EPR, they just dont bother displaying it), and each individual engine will be subtly different from its kin, and each individual engine will have a different TGT/EPR relationship as it ages.

Other than "EPR and TGT usually increase and decrease together" there's no real answer to your question.

Generally true, except near idle the TGT/ITT/EGT may see a "bucket" and be lower at part throttle than at idle. This is the result of efficiencies dropping off rapidly at low RPM. :8

The way EPR is measured is different with different manufaturers. I have flown the same type with two different engine options. They had very different EPR settings for the same speeds.

Part of EPR is measured at the same place as TGT. There's a thermodynamic relationship between the temperature of the gas stream and the pressure at the 4.5 station of the engine (where TGT, ITT, TOT, T5 etc is measured in modern jet engines). Put simply, more fuel goes into the burner can, it combusts thus increasng the engergy of the gas stream accelerating it. This energy is taken out of the gas stream as faster turbine speed and increased engine power. You'll see a rise in EPR and TGT and they're separated by (in very round terms) a constant (with some standard assumptions) that I can't recall right here and now. Sorry for the vagueity (if that's not a word I hereby claim it on behalf of the test community) but I don't have my references near to hand.

LGC :ok: