Afterburner

An afterburner is an auxiliary device of a turbine jet engine, which can be used to increase the combustion of fuel injected after the turbine the thrust of the engine and the exit velocity of the working medium. The afterburner can often be controlled by the pilot in several power levels.

Since turbine jet engines are operated with excess air to keep the exhaust gas temperature to an acceptable for the materials of the turbine blades level, is in the exhaust gas after passing through the turbine enough oxygen available to burn additional fuel injected in the jet. The jetting temperature is no longer limited by the following components in the stream.

Since the fuel consumption when afterburner is up to a factor 10 above the normal consumption of the engine, it will be activated only in special situations when short term more thrust is needed. At subsonic speeds, the additional cost of fuel is in a bad relationship with the recovered thrust. With increasing Mach number of the afterburner is increasingly efficient.

Most supersonic aircraft rely on afterburners to achieve higher speeds exceeding Mach 1 in level flight. The ability to supersonic flight without afterburner is referred to as supercruise.

Operation

By increasing the temperature of the isobaric the density decreases, the speed increases to the same extent. The mass flow rate remains largely unaffected. With the use of the afterburner as an increase in jet velocity is achieved, without this, as in the nozzle spend the pressure of the compressor. The afterburner replaced the burden of the convergent nozzle at subsonic speed.

Constructive details

The afterburner has a generally separated by a small gap from the outer skin of the push tube inner tube. The gap serves to cool the inner Nachbrennerrohres by flow of flue gas or a mixture of flue gas and air. The injection of the fuel upon exit from the turbine ( " flame holder " ) generates local Rückströmgebiete and so stabilizes the flame (temperature up to 2,000 K).

The push rod cross-section is usually much larger than the nozzle cross-section and is intended to reduce the pressure loss in the flow. The ignition of the fuel takes place mainly by:

• Ignition catalyst by platinum elements;
• Spark plug or ignition torch (continuous fire );
• " Hot Shot ", ie additional injection of fuel into the combustion chamber. Consequently, the flame thus produced extends into the afterburner to; so that it ignites the fuel injected there in addition.
• Regulating the nozzle position or the supply of fuel in the afterburner, wherein an adjustment of the other parameter is such that the ratio of the (total ) pressure in the combustion chamber and turbine, will not be affected by the Nachbrennerbetriebszustand.

Afterburners are used almost exclusively in military aircraft. Two of the few civilian aircraft with afterburner were the Tupolev Tu- 144 and Concorde.

Is in first turbofan engines, the hot exhaust gas stream is mixed with the cold bypass flow and then directed into the afterburner, which is referred to as Nachbrennerart augmentor.

Saab 35 Draken zugeschaltetem with afterburner

Looking into the afterburner of a MiG -23