Booting a turbine at altitude
 

Random brain fart - Would water/meth injection work well on a jet engine if it were EGT limited at (say) 30,000' ?

Yes, but water is HEAVY, so you can only carry enough for quick jobs, like take-off, not for long time applications, like cruising at altitude.

Hand me down stories suggest that some have tried this in the past.
Because they selected wter meth on with power already set they suddenly found themselves with an engine going past the power limit ie overtq or over thrust limit.

Not going to happen at 30,000' as you're already down a heap of power.

I can't edit the thread title sorry, it should be 'boosting' of course.

Was thinking about this today a little and I realised that up high you wouldn't be EGT limited but RPM limited instead, so decreasing the EGT by means of water/meth wouldn't achieve a great deal.
Would a dose of nitrous oxide gas help, as it'd boost the oxygen content of the incoming air?

It's been a while since turbo prop flying, but memory suggests that I've had turbo props on the temp limit at 30, hence the warning about tq/ power limits. In a jet however yes I agree that you aren't normally anywhere near the temp limit.

"Was thinking about this today a little and I realised that up high you wouldn't be EGT limited but RPM limited instead"

don,t think that much . it depends on the type of engine. and of course a turbofan can be EGT limited- i.e the ALF502 on bae146- we set the power according to EGT at cruise , that came first, not the permissible n1 or n2 rpm,s .

on a turboprop it also depends on the engine, even from the same family, one example :

the pt6a-11 on a cheyenne I is definitivly ITT limited at altitude , the pt6a-41 in a cheyenne III is gas generator speed limited at altitude .

Thanks aerobat, that is most interesting

Thanks, I'd have to find out more about the particular engine in question then.
But if EGT is limiting then water/meth should give more of a margin, and if RPM is limiting then nitrous should give a bit of a boost ... ?

Squirting a load of fuel into the jet pipe should do the job :ok: