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Afterburning/Thrust Augmentation

Filed Under: Induction and Exhaust Systems

The terms afterburning and thrust augmentation generally pertain to military engine applications. The terms are used to describe the same system. Normally, this is used to increase the thrust of the engine up to double the original thrust.

The required additions to the exhaust nozzle for this system are a flame stabilizer, fuel manifold, flame holder, igniter, and a variable area exhaust nozzle. [Figure 3-50] After the engine has reached full power under normal operation, the power lever can be advanced to activate the afterburner. This allows more fuel to flow into the exhaust nozzle where it is ignited and burned.

Figure 3-50. An example of a variable area exhaust nozzle used to increase or decrease exhaust flow during afterburn.
Figure 3-50. An example of a variable area exhaust nozzle used to increase or decrease exhaust flow during afterburn.

As energy and mass is added to the gas flow, the exhaust nozzle must open wider to allow greater flow. As the power lever is moved back out of the afterburner, the exhaust nozzle closes down again. Some low-bypass turbofan engines used in military aircraft use bypass (fan air) to flow into the exhaust nozzle. Just as in a ducted fan, this air is used in the afterburner. It contains more oxygen and assists combustion in the afterburner. Since fuel is being burned in the exhaust nozzle, the heat buildup around the nozzle is a problem.

A special type of liner is used around the nozzle to up or down to increase flight maneuverability. allow cooler air to circulate around the nozzle. This operates somewhat like a single burner can combustion chamber. Operation in the afterburner mode is somewhat limited by high fuel consumption, which can be almost double normal consumption.

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