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Vaap
27th Sep 2005, 13:28
Why do some jet engines use ITT and some use EGT and how does this effect there management?

Thanks

Vaap

LME (GOD)
27th Sep 2005, 13:33
They're exactly the same thing...some engine manufacturers use inter-turbine temp some use exhaust gas temp. They work exactly the same way.:}

A-FLOOR
27th Sep 2005, 14:02
(Feel free to correct me on this as I'm not entirely sure)

ITT is not to be confused with TIT, which is the temp at the first turbine stage... as opposed to the EGT/ITT where the temperature is measured at the last stage.

rigpiggy
27th Sep 2005, 15:01
actually TIT=turbine inlet temp
ITT= interstage turbine temp
EGT=exhaust gas temp

same measurements at different parts of the engine
TIT normally temp before turbine
ITT normally between hi/lo pressure turbine
EGT tailpipe temp

barit1
27th Sep 2005, 19:11
Actually - I don't know of any engine in which TIT (i.e. combustor exit) is measured. Thermocouples would be lucky to last more than a few minutes in that environment.

EGT by rights is the exit of the last turbine stage, which made sense in the days of a pure turbojet. It's not so logical in a multi-rotor high-bypass machine, IMHO.

I think inter-turbine temp (HPT exit, LPT inlet) is the most common compromise. But the fog factor is that it's commonly labeled "EGT" - even though it's several stages upstream of the core exhaust. Lockheed labeled this same parameter ITT, which makes good sense.

A-FLOOR
27th Sep 2005, 19:46
TIT is used in the Kingair and for TSFC calculations on all gas turbines.

barit1
27th Sep 2005, 21:44
TIT is used in the Kingair and for TSFC calculations on all gas turbines.

In other PT6-powered aircraft it seems to be called ITT.

bobrun
27th Sep 2005, 21:56
On a twin otter PT6 it's called T5....same difference.

TR4A
27th Sep 2005, 22:51
barit1 said: Actually - I don't know of any engine in which TIT (i.e. combustor exit) is measured. Thermocouples would be lucky to last more than a few minutes in that environment The ALLISON T-56 used in the Lockheed C-130 and P-3 uses TIT.

barit1
28th Sep 2005, 00:09
The T56 was a late 40's design, and (w/ uncooled turbine) I'm sure it ran a much cooler TIT than later engines. So it may be the exception to the rule.

TR4A
28th Sep 2005, 02:03
barit1 said: Actually - I don't know of any engine in which TIT (i.e. combustor exit) is measured.Well I told you one and it happens to be a engine that was produced for over 40 years. Now you know of an engine that uses TIT. Even though it is "a late 40's design". :rolleyes:

The C-130A started production in 1955.

barit1
28th Sep 2005, 12:35
Thanks for the update.

Searching around the web, I found "The first flight of the YC-130 took place on August 23, 1954 at Lockheed's Burbank, California plant." So that pretty well dates the technology. Still a remarkable machine!

SR71
28th Sep 2005, 13:40
On a twin otter PT6 it's called T5....same difference.


Bloody hell. What about T1, T2, T3 & T4?

Normally the Brayton cycle denotes T3 as post-combustion, pre-expansion.

:ok:

barit1
28th Sep 2005, 21:26
Normally the Brayton cycle denotes T3 as post-combustion, pre-expansion.

That may be true in some conventions, but hardly universal. Over a 33-year career I've seen the numbering system change every few years.

But one thing that has remained (nearly) the same is P3 and T3 - it's compressor exit = combustor inlet. (In very new engines it may be called P30 & T30 - to permit a finer breakdown, pre- or post-diffuser)

Piltdown Man
29th Sep 2005, 13:04
Or ITT (Inter Turbine Temperature) on the PW125B. But I'm more of a TIT man myself! As for management of this engine, put the power levers in the detent and push the button on the ERP/PMP panel for the power rating you want. It also does the props for you as well, allowing you to get on with the important things of life - like breakfast.

pba_target
29th Sep 2005, 13:34
lol, who cares where its measured;) Just push the throttle forward until you make the needle line up with the red line;) unless you have an EMS/EEC etc etc etc, in which case, just push the throttle(s) all the way forward! (and wait for your thermocouple to fail, and your EMS to kill the fuel supply..... sporty just after takeoff!)

barit1
30th Sep 2005, 12:37
target, I know you're having a bit of laugh, but you bring up an interesting point: If a thermocouple fails, does is actually affect the engine operation?

I know some military engines where the thermocouples are part of the control loop (as in controlling the variable exhaust nozzle on an afterburner), but I can't think of a single commercial engine with such a feature. In fact I was told the airlines' engineering depts. would not accept such a system; the thermocouples are for readout only.

Enlighten, please!

PT6ER
30th Sep 2005, 15:37
Most systems I have seen use multiple probes with an averaging function.

I believe on some Pratt Canada engines, the ITT is "synthesized" (sp?) in as much as temperatures are taken at two discreet engine stations and an analog computation infers the temperature you are interested in. The engine I work with at the moment has three or five T5 probes (dependant on version) with an averaged readout to the flight deck. Should a probe go bad, your average becomes a little less accurate but is useable (in fact as an operator you wouldnt necessarily know a probe had gone down).

Also it is not used as part of the engine control loop until you introduce the pilot into the mix - Mark 1 eyeball and control of the N1 lever!!

westhawk
30th Sep 2005, 16:42
Cannot comment on all EEC, DEEC or FADEC controlled engines, but several I have had occasion to learn about use ITT or EGT inputs to perform a T5 limiting function. Loss of this input will not disable the engine control, but will generate an advisory message and/or log the occurance in memory in the digital units. This function does not remove responsibility for engine monitoring from the pilot, but will limit T5 exceedences by reducing fuel scheduling to an overtemping engine.

Best,

Westhawk

CV880
2nd Oct 2005, 02:24
To complicate things further airframe manufacturers may label the gauge with a generic name that does not reflect the actual thermocouples' location. For example on the 747 it is always labelled EGT when in many engine models it is not truly EGT.
On the JT9 series all engines except the -7Q and -7R were ITT however Pratt and Whitney relocated the probes on the -7Q and -7R to the LP turbine exit making them EGT rather than ITT. The result was max EGT on the earlier models was in the 900-1000 degree range but on the -7Q & -7R max EGT dropped to the 600-700 range in spite of being more powerful. engines.
With regard to TIT probes on the T56, having boroscoped many 501D13's (the civil equivalent on the Lockheed Electra) in my youth I can assure you finding melted/bent rearward thermocouples was not uncommon. Max TIT was in the high 900's and being a standard day engine it was always at max TIT if the OAT was above 15 celsius.