Engine Exhaust Gas Temperature (EGT)

An introduction to Engine Exhaust Gas Temperature (EGT) and why issues with it are important in trend monitoring.

EGT is a measurement of temperature that is taken at the back of the engine. The location can differ for manufacturers where the EGT is measured, and each engine type will have its own limits and norms so an EGT range is specific to that engine type and not across the board.

In the illustration below you can see how the basic internal engine works (Red Line) is cold air being drawn in by the fan 1, through the compressor where the air is compressed (temperature rises) 2, then into the combustion chamber where we add fuel and ignite it 3, then the very hot and compressed air expands through the turbine forcing it to rotate 4, we measure the EGT at some stage in the turbine.

The turbine is how the compressor and fan is driven. The fan rotating creates most of the thrust and this is simply sucked in, compresses and forced out the back of the engine, it is called bypass air (blue line).

The reason this is important is due to the way the engine operates internally.

When parts become worn such or suffer damage then parts like the turbine blades can not harvest the energy form the hot compressed air expanding as efficiently as they should. As a result then the engine will have less power being taken from the turbine to the compressor, which can lead to a slower speed or less thrust.
In order to counteract this the engine will put more fuel in so more energy is created and the turbine can extract the required torque to maintain thrust.
This will see and EGT rise as more fuel is being burned to create the same level of thrust or core operating speed.
EGT can rise or fluctuate for other reasons also and this is introduction is just an example, but typically EGT is an important factor in trend monitoring to indicate issues internally.

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