Temperature Egt

Temperature Egt

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what is the EGT actually? is it the temperature of the gas just coming out of the turbine of the engine?

To answer your question I have provided answers for EGT on both turbine and engines with cylinders with references for each.

EGT (exhaust gas temperature) is a critical variable of turbine engine operation. The EGT indicating system provides a visual temperature indication in the cockpit of the turbine exhaust gases as they leave the turbine unit. In certain turbine engines the temperature of the exhaust gases is measured at the entrance to the turbine unit. This is usually referred to as a TIT (turbine inlet temperature) indicating system. The principal disadvantages of this method are that the number of thermocouples required become greater and the environmental temperatures in which they must operate are increased.

A gas temperature thermocouple is mounted in a ceramic insulator and encased in a metal sheath; the assembly forms a probe which projects into the exhaust gas stream. The thermocouple is made from chromel (a nickel/ chromium alloy) and alumel (a nickel/aluminum alloy). The hot junction protrudes into a space inside the sheath. The sheath has transfer holes in the end of it which allow the exhaust gases to flow across the hot junction.

Several thermocouples are used and are spaced at intervals around the perimeter of the engine turbine casing or exhaust duct. The thermocouples measure engine EGT in millivolts, and this voltage is applied to the amplifier in the cockpit indicator, where it is amplified and used to energize the servomotor which drives the indicator pointer.
(Reference AC 65-15)

EGT (exhaust gas temperature), TIT (turbine inlet temperature), tailpipe temperature, and turbine discharge temperature are one and the same. Temperature is an engine operating limit and is used to monitor the mechanical integrity of the turbines, as well as to check engine operating conditions. Actually, the turbine inlet temperature is the important consideration, since it is the most critical of all the engine variables. However, it is impractical to measure turbine inlet temperature in most engines, especially large models. Consequently, temperature thermocouples are inserted at the turbine discharge, where the temperature provides a relative indication of that at the inlet. Although the temperature at this point is much lower than at the inlet, it provides surveillance over the engine's internal operating conditions. Several thermocouples are usually used, which are spaced at intervals around the perimeter of the engine exhaust duct near the turbine exit. The EGT indicator in the cockpit shows the average temperature measured by the individual thermocouples.

Two of the most important factors affecting turbine engine life are EGT (exhaust gas temperature) and engine speed. Excess EGT of a few degrees will reduce turbine blade life as much as 50%. Low exhaust gas temperature materially reduces turbine engine efficiency and thrust. Excessive engine speed can cause premature engine failure.
(Reference AC 54-12A)

Many airplanes are equipped with an exhaust gas temperature (EGT) gauge. If properly used, this engine instrument can reduce fuel consumption by 10 percent because of its accuracy in indicating to the pilot the exact amount of fuel that should be metered to the engine.
An EGT gauge measures, in degrees Celsius or Fahrenheit, the temperature of the exhaust gases at the exhaust manifold. This temperature measurement varies with ratio of fuel to air entering the cylinders, and therefore can be used as a basis for regulating the fuel/air mixture. This is possible because this instrument is very sensitive to temperature changes.

Although the manufacturer's recommendation for leaning the mixture should be adhered to, the usual procedure for leaning the mixture on lower horsepower engines when an EGT is available is as follows:

The mixture is leaned slowly while observing the increase in exhaust gas temperature on the gauge. When the EGT reaches a peak, the mixture should be enriched until the EGT gauge indicates a decrease in temperature. The number of degrees drop is recommended by the engine manufacturer, usually approximately 25° to 75°. Engines equipped with carburetors will run rough when leaned to the peak EGT reading, but will run smooth after the mixture is enriched slightly.
(Reference AC 61-23)