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I assume that at some point giggling engineering students caused their instructor to change "turbine inlet temperature" from TIT to TET, but I wonder if anyone knows the real reason and history? Perhaps adapted from another language?

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The temperature in jet engine turbines is usually measured in one (or more) of these places:

As far as I know, TET is not used as an acronym for Turbine Inlet Temperature, where TIT is used.

There are however two different definitions for TET:

  1. In gas turbines for power plants, TET stands for Turbine Entry Temperature and is defined in ISO 11086:1996 (Gas Turbines - Vocabulary).

    It is very important for gas turbine calculations how the temperatures in the hot part of the gas turbine are defined:

    • TIT - Turbine inlet temperature is defined as the temperature that would occur before the nozzle guide vanes, if all cooling air was mixed into the flue gases at that point.
    • TRIT - Turbine rotor inlet temperature is the temperature before the first rotor stage, i.e. right before the work extraction begins.
    • TET - Turbine entry temperature is the actual temperature before the nozzle guide vanes.

    (Gas Turbine Cooling Modeling - Thermodynamic Analysis and Cycle Simulations by Kristin Jordal)

  2. TET is also sometimes defined as Turbine Exit Temperature, e.g. in this paper (also for power plant gas turbines) or in this patent (for a jet engine):

    We have found that the turbine inlet temperature (TIT) or turbine exit temperature (TET) are viable parameters for indicating stall [...]

To avoid confusion, always check the glossary of the document when encountering TET. If there is no definition, it might be difficult to tell what the author meant.

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  • $\begingroup$ Ahhh, excellent post. My confusion is from a 1970s article by the Olympus team that refers to TET without defining it - when I googled the term the resulting article was on TIT. I did not notice the fine print. $\endgroup$ Aug 17 at 14:51
  • $\begingroup$ The turbine inlet temperature is pretty much fixed, unless you have a flame-out, since the combustion temperature depends mainly on chemistry, not aerodynamics. On the other hand the exit temperature depends strongly on the mass flow through the turbine and the power it is producing, so it is a much more useful measure of "what the engine is doing" (not to mention that it is lower than the inlet temperature, and therefore easier to measure). $\endgroup$
    – alephzero
    Aug 17 at 21:38
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    $\begingroup$ Please note that the TIT cannot be measured as it is generally too high for cooled turbine engines. Also, the SOT is sometimes referenced, the Stator Outlet Temperature, i.e. the temperature behind the nozzle guide vanes. $\endgroup$
    – 0scar
    Aug 17 at 22:09

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