Huffer

In aviation, a huffer is an external engine that creates large volumes of pressurized air used to start large gas turbine jet engines on some types of aircraft.

The huffer works by blowing compressed air via flexible hose to the aircraft's bleed air system. From there, the air flows via a pilot controlled valve to the engine's starter motor. The starter motor converts the energy of the moving air to rotational torque. The starter motor is linked via shaft to the N2 or core of the engine and spins the compressor and first stage turbine. Once there is enough air flowing through the compressor and the combustion chamber to light the engine, fuel in the form of vaporized kerosene starts flowing and an igniter similar to a spark plug ignites the fuel. Then fuel flow is increased to spin the engine up to its normal idle speed, at which point the engine is self-sustaining and no longer needs the support of the starter.

In some earlier jet engines, the air from the huffer acted directly on the compressor or turbine blades to cause them to spin without the need for the air starter motor.

Some aircraft turbine engines do not use compressed air to start, but instead are started using an electric starter motor. This is attached to the main turbine shaft and does the same job as the air starter motor. The application of the huffer is primarily seen when an aircraft's Auxiliary Power Unit is not working, or to military aircraft, many of which use a huffer to save on weight.

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Wikipedia