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I have a query concerning the turbine inlet temperature (TIT) in the context of various flight mission phases. Specifically, I'm trying to ascertain at which phase the gas turbine reaches the highest TIT.

My understanding is that maintaining consistent thrust as the aircraft gains altitude requires an increase in TIT. Consequently, it would seem plausible that the highest TIT occurs at high altitudes where the aircraft needs to maintain cruise thrust.

However, I'm also aware that the takeoff phase, which necessitates the most power, may also demand the highest TIT.

Could anyone with expertise or knowledge in this area clarify this for me? Any input would be greatly appreciated.

Thank you in advance, and I hope you're enjoying your Sunday!

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  • $\begingroup$ Are we to take into account effects of supersonic flight? $\endgroup$
    – Jpe61
    Jun 18 at 14:04
  • $\begingroup$ Do you count engine start as part of a flight mission? Because that’s when it peaks. $\endgroup$
    – Michael Hall
    Jun 18 at 14:31
  • $\begingroup$ No, my intention is to start counting from the taxi-out of a standard commercial aircraft not capable of supersonic flight. $\endgroup$
    – mumu
    Jun 18 at 14:41
  • $\begingroup$ Ok. Common sense says it would be during the takeoff roll. (High power setting, lower airflow). What sort of correlation to fact or data would make for an acceptable answer? $\endgroup$
    – Michael Hall
    Jun 18 at 18:19
  • $\begingroup$ Thank you for your input. Would you be able to provide any data sources or freely accessible journals that corroborate this? Specifically, I'm interested in information about standard commercial aircraft like B777 and so on. Your help would be much appreciated. $\endgroup$
    – mumu
    Jun 18 at 19:07

1 Answer 1

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The highest ITT/TIT/EGT is always seen as brief transient during start, during initial takeoff thrust setting, or during slam accelerations (go-arounds). On the General Electric CF-34-3B1 (the engine used on most Regional Jets and originally developed for the A-10), the max ITT is 900C, which is allowed for brief transients during starting, slam accelerations, or during takeoff (up to 2 minutes).

Outside of those conditions, you are limited to the Max Continuous Thrust temperature limitation (the normal climb thrust setting). On the CF-34, this is 874C.

On a fresh engine, temperatures seen will normally be well below these values when the fan RPM is at its limit (98.6% N1 for Max Continuous on the CF-34). This is called "ITT/TIT/EGT Margin" and is the main engine health condition indicator.

As the engine wears, temperatures creep closer to the limit values as efficiency declines, and eventually you start getting overtemps on start, or you can't achieve rated TO thrust or Max Cont thrust fan speeds without exceeding the temperature limits, and the engine is ready for overhaul.

But in any case, you will see the engine get pretty close to temperature redline during starting (less so with FADEC engines that manage the start fuel flow much more precisely, and will even auto-shutdown if there is an exceedance), and you may see it very close to that when setting TO thrust with a tired engine, but beyond that the temperature values are always lower for climb thrust, and lower still for cruise thrust, simply because you aren't putting as much fuel through.

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    $\begingroup$ Thank you very much for your detailed explanation. :) $\endgroup$
    – mumu
    Jun 19 at 8:35

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