Combustion in Piston aircraft and turbofans. EGT (Exhaust Gas Temperature) vs. ITT (Interstage Turbine Temperature). Which are the differences?

[wipeout01 0]

Hi, I'm trying to fly the King Air C90 GTX. This is a turbofan aircraft. My question is valid for all turbofans, for this reason I am not posting in a certain forum for this aircraft. Also, my question a general question.

I am wondering what are the differences (operational, not technical or mechanical) about the ITT vs. the EGT.

As you may know, pisto aircrafts, like the Bonanza A36... use a method to know if the engine combustion is ok.

Due the air is less dense as soon we ascend (that is we have less oxigen in it), things burn bad. You would burn better a match at 0 feet than in the acme of the Everest mountain (29,029 feet). So things high don't burn so well... because we don't have much oxigen.

Due aircrafts fly, and sometimes high, they need to change the mixture (air and fuel) inside the engine.

When we fly high, we need less fuel and more air (lean mixture), that is because we need more air to burn the fuel. Due the air have less oxigen... we need to put more air inside the engine, so the fuel would burn better.

When we fly low... we need more fuel and less air (rich mixture), that is because we have a lot of oxigen in the air... so we don't need a lot of air to burn our fuel.

However... how do we know if the things are burning as they should?

Very simple. With a termomether.

We put a thermometer in the exahust pipes of the aircraft, to measure the gases temperature. Measuring the gases temperature, we can know if the engine is burning well (we must have the highest temperature possible) or if the engine is burning bad... then we will have a low temperature in the gases... as a candle fainting.

The goal of the EGT peak is... to enrich or lean the mixture, moving the red levers in the aircraft...forward or rearward... until we get the higest temperature for the gases. We can see that in the cockpit, because we must have an indicator, called EGT, that show us a needle. The objective here is to have the EGT needle in its highest possition.

Then, we need to move again the red levers to enrich or lean the mixture to make the EGT needle drop a bit. The goal now is to make the EGT needle drop a bit... around 20º degrees or what is specified in the performances tables.

However, we have two options. We can reduce the temperurate enriching the mixture, we move the red lever forward or we can reduce the temperature leaning the mixture, we have move the red lever, rearward.

 

That is in essence, the EGT peak.

 

However, I am flying right now a turbofan... and it has ITT, Interstage Turbine Temperature...

I'm wondering if ITT is the same as EGT in an operational  mode?

I mean, I am not interested right now about mechanical things, such as were is the thermometer located or stuff like that.

 

What I need to know is how do I operate the ITT?

I must find also a peak, such as the EGT?

And then dropping the temperature?

 

If you could help me with this, I'd be grateful.

 

Cheers

[mcdw 0]

Propdriven aircraft doesn't has Interstage Turbine Temperature (ITT). 

 

Are you flying turbofan like B737 or turboprop like King Air with turbine engine....???  Because B737 didn't has ITT.... ;-)

[19dcavscout 39]

There is no ITT peak.  The ITT is an excellent measure of the health of the engine. Just fly below redline and you will be fine. The fuel control unit automatically measures the correct amount of fuel entering the engine. You on have to set the throttles and be fine. The only benefit of flying at a lower ITT is engine health, which doesn't matter in the sim.

Also the King Air is a turboprop, not a turbofan.  A turbofan is on something like a 737/777.

Also just for reference, you may also see something called TGT in other turboprops. It is essentially the same thing, just a different name.

[KevinAu 441]

The main thing you watch the itt for is to make sure they don't exceed the stated limitations.  And the most common operation where this becomes a factor is during engine start, wherd you havd to be on guard and ready to abort the start if you suffer a hot start.

Your concept of fuel mixture seems a little off.  When you fly high, you lean the fuel mixture in order to thin the fuel down to maintain an appropriate burn ratio with the thinner ambient air.