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Out of curiosity at what temperatures are the exhaust gasses are expelled from jet engines? A normal reciprocating engine from what I recall should be in the 700 - 1100 degrees Celsius range. Does this apply to turbofans/turboprops/turbojet engines also since the fuel properties should be similar? Or are the temperatures much lower as the engine is being used mostly at high altitudes?

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Turbofan without afterburner

In non-afterburning engines the exit temperature inside the nozzle is around 600°C at full continuous thrust. If the ambient temperature is low, less heating is needed for the same thrust, and exit temperatures are lower. The maximum temperature for a given engine is, however, independent of altitude and given by the materials inside the engine. In flight the continuous maximum can be higher than on the ground, when the cooling by the external flow is less effective.

Temperature profile at a distance

This report gives results of ground measurements on the Pratt & Whitney JT8D of the Douglas DC-9 and shows how quickly the temperature drops behind the aircraft due to mixing and radiation.

Jet temperature behind a DC-9 at take-off power
Jet temperature behind a DC-9 at take-off power. Picture source.

Jet temperature behind a DC-9 at idle power
Jet temperature behind a DC-9 at idle power. Picture source.

With afterburner

With full afterburner the engine uses approximately five times as much fuel as when running dry, and it shows in the exhaust gas temperature. This report details measurements of nozzle pressures and temperatures on one of the General Electric F-404 engines used in the X-29 program. The plot below is taken from the report and shows exhaust-jet temperature summaries in the horizontal centerline for various power settings (PLA = power level angle; 120° is full afterburner and 87° is military thrust).

Nozzle temperature survey of the GE F-404 afterburning engine
Nozzle temperature survey of the GE F-404 afterburning engine. Source.

The test conditions were 30.000 ft altitude and Mach 0.3, simulated in an altitude chamber. The temperatures were measured with a rake just a few inches aft of the engine nozzle. Note that the temperatures are given in Rankine; the maximum of 3800°R is 1838°C. The wake of the engine's center body causes lower temperatures in the center of the jet at XSRL = 0. The nozzle edge is at 12.7 inches from the center; due to symmetry only one half of the jet temperature profile is shown.

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  • $\begingroup$ @JanHudec: Sorry, but I removed the part on the GE-90 as it did not really fit here. $\endgroup$ – Peter Kämpf Sep 7 '15 at 20:03
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The exhaust gas temperature of a jet engine depends on a number of parameters like,

  • The operating conditions
  • Whether afterburner is used or not
  • The condition of the engine
  • Type of the engine (whether low or high bypass turbofan etc)

Without after burner, the exhaust gas temperature is around 600-650 $^{\circ}$ C, which goes upto 1500 $^{\circ}$C with after burner. The figure below shows the data for General Electric J79 low bypass turbofan engine.

GE J79

Source: www.aircraftenginedesign.com

In case of high bypass turbofan engines, the exhaust gas temperature is slightly lower, usually around 500-600 $^{\circ}$ C. For example, the figure shows the temperature variation in PW 4000 engine.

PW 4000

Source: web.mit.edu

The temperature of the engine is determined by the materials used, especially the turbine temperatures (and method of cooling), and not much on outside conditions. As such, the turbine gas temperature is the highest temperature in jet engines and the limiting factor.

The Exhaust gas temperature is a parameter to measure engine health. A high EGT for a given thrust (by a engine) is a sign that the engine required more fuel for the same thrust, due to wear out of rotating components, etc, and the engine may require inspection.

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