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The major components of am afterburner are the diffuser, in which the velocity of the gases leaving the turbine is decreased to a value suitable for combustion, the combustion chamber, in which fuel is added and combustion takes place, and the variable area exhaust nozzle.
A jet engine with an afterburner is a basic engine type. It differs from a simple jet engine in the following important characteristics.
1. Higher maximum thrust per unit frontal area.
2. Higher maximum thrust per unit airflow, thus it
requires smaller air intakes and ducts.
3. Higher fuel consumption at maximum thrust.
4. Lower fuel consumption for cruising thrust. This is true on most airplane designs, and is caused by the fact that on afterburner installation, the engine is cruised at a higher percent output and thus at a more favorable specific fuel consumption. In addition, the afterburner airplane can generally be designed to have a lover drag coefficient.
From the above characteristics, it is apparent that the jet engine with afterburning becomes the optimism power plant:
1. When the design maximum speed of the airplane is high, since at high speeds, the thrust per unit frontal area and thrust par unit airflow becomes increasingly important. In fact, there Is some speed, probably supersonic, above which an afterburner must be used, since a simple turbo-jet engine would produce insufficient thrust.
2. When the portion of the flight time, during which maximum power is used, is a small portion of the total flight time. This is, of course, caused by tha high fuel consumption with the afterburner in operation,
When heat is added in the afterburner, the volume of the exhaust gases increases, and it is necessary to increase the exhaust nozzle area to avoid excessive back pressure on the turbine. For optimum performance, the nozzle area is adjusted so that pressures end temperatures in the engine are the same with the afterburner operative or inoperative.
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