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Afterburning Turbojet


Computer animation of pressure variation through an afterburning turbojet

Button to Make Engine Button to Display Low Speed Rotation Button to Display High Speed Rotation Button to Stop Action Button to Display Flow Button to Display Temperature Variation Button to Display Pressure Variation

This page shows the pressure variation through an afterburning turbojet. The pressure value has been color-coded as described on another page. The mathematics describing the thrust of an afterburning turbojet is given on a separate slide.

To move an airplane through the air, thrust is generated by some kind of propulsion system. Most modern fighter aircraft employ an afterburner on either a low bypass turbofan or a turbojet. On this page we will discuss some of the fundamentals of an afterburning turbojet.

In order for fighter planes to fly faster than sound (supersonic), they have to overcome a sharp rise in drag near the speed of sound. A simple way to get the necessary thrust is to add an afterburner to a core turbojet. In a basic turbojet some of the energy of the exhaust from the burner is used to turn the turbine. The afterburner is used to put back some energy by injecting fuel directly into the hot exhaust. In the diagram, you'll notice that the nozzle of the basic turbojet has been extended and there is now a ring of flame holders, colored yellow, in the nozzle. When the afterburner is turned on, additional fuel is injected through the hoops and into the hot exhaust stream of the turbojet. The fuel burns and produces additional thrust, but it doesn't burn as efficiently as it does in the combustion section of the turbojet. You get more thrust, but you burn much more fuel. When the afterburner is turned off, the engine performs like a basic turbojet.

Afterburners are only used on fighter planes and the supersonic airliner, Concorde. (The Concorde turns the afterburners off once it gets into cruise. Otherwise, it would run out of fuel before reaching Europe.) Afterburners offer a mechanically simple way to augment thrust and are used on both turbojets and turbofans.

Button to Display Propulsion Index

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by Tom Benson
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Last Updated Thu, Jun 12 04:47:01 PM EDT 2014 by Tom Benson