Turbine Pressure.

[Noah Zark.]

Hello Folks, can any give me an answer, please?
I am not in the aviation industry, merely an interested outsider. I was watching a prog on t.v. today, in which a cursory explanation was being given of how a turbine engine works, i.e. 'air is sucked into the engine by a set of turbine blades, which then compresses the air before fuel is added...etc. etc.
My question is, (and I don't need any mathematical breakdowns or whatever, it's only idle curiosity) what pressure does the air inside the engine reach before it is burnt?
I realise that it will probably be different for various types of engine, etc., but a general figure as a guide will be fine.
Thanks in advance.
N.Z.

[grounded27]

Sorry, that is not something we generally work with, not to say there is not someone out there with some insight. Suck, Bang, Blow... I am sure there is a large variance esp from older to newer aircraft, the prohibitive factor is operating the engine on the verge of a stall where the pressure becomes greater than can be sustained in flow and blows fwd out the inlet. Newer engines have better devices and materials to create better compression.

[Bye]

What you are referring to is the pressure ratio, or in piston engine terms the compression ratio.

In a typical Brayton cycle engine ( gas Turbine) the ratio at the outlet of the compressor has over the years increased and is in fact commercially sensitive in some instances these days but you can expect a minimum of 10:1 to a maximum of about 25:1 for certain engines.

so at say 10:1 your compressor would have an exit pressure of 10 bar.

as the above poster said you try to operate as close to the SURGE line as you can for maximum efficiency which is determined by the capability of the flame tubes / can to accept the total pressure of air being fed to it, with temperature being a factor. as a rule of thumb you can assume that if the ratio is 10:1 then the temperature at compressor outlet is also 10 times the ambient as well.

hope this helps, google it and you will get some good graphs of EPR for various engines over the years.

EDIT - just to clarify the compression ratio and Engine Pressure Ratio are different things, the numbers i have given are for compression ratio NOT EPR.

GB

[BluFin]

see for a jt8

JT8 Typical Temps and Pressures (http://boeing-727.com/Data/engine/Temps%20and%20Pressures.html)

[gas path]

For the RR RB211 at sea level take-off power the pressure at the back of the combustion chamber is about 430 psi. This pressure drops off rapidly down to about 25 psi at the exhaust as the power is extracted to drive the compressors and fan. The peak temperature reached is around 1400 deg C

[Noah Zark.]

That's excellent, guys! Thank you very much. That's plenty sufficient, as I said in my post, just a spot of curiosity.
N.Z.