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Afterburner
provide the extra thrust needed by an aircraft without adding to the design
complexity of the engine. Afterburner is based on the concept that the majority
of combustion that take place in the combustion chamber, has air or oxygen in
excess. So the exhaust from such combustion has oxygen molecules in it.
We know that for fire we require fuel, heat and oxygen. We already have heat
and oxygen in the exhaust gas, we just require fuel. And this is what is
exactly done in afterburner. Fuel is added to the hot exhaust. Now thrust can
be increased in two ways. One by increasing the volume of air molecules and
other by increasing the velocity of air molecules. Afterburner increases the
thrust by increasing the velocity of the air molecules. Now the question
arises, is afterburner really helpful? Here are some features of afterburner
that will help you decide.
Firstly,
afterburner is helpful if it's a military aircraft. The reason being military
aircrafts are often involved in dog fights as well as in missions where after
completing their tasks they have to quickly disappear from the target. The
aircraft in this scenario can be in subsonic or transonic speed and when they
have to disappear from the scene, they can activate the afterburner and achieve
supersonic speed. This could change the entire scenario of the battle.
Secondly,
military aircrafts have to be sleek and light. Sleek because they have to
achieve high speed and do unbelievable manoeuvrings. Light because they have to
carry different weapons. Afterburner help to keep the military aircraft sleek
because it only increase the length of the engine whereas the diameter of the
engine more or less remains the same. Afterburner has a very simple design, so
does add much weight to the aircraft, keeping it light in weight.
Thirdly,
afterburner is not meant for transport aircraft. The reason is transport
aircraft is all about saving fuel. And afterburner uses a lot of fuel, making
the engine less fuel efficient. Besides, transport aircraft are mostly
subsonic. And the turbofan and the turboprop engines of these subsonic
transport aircraft were specifically designed to save fuel. These engines
increase the thrust by increasing the volume of the air molecules, thus making
them fuel efficient. As long as fuel efficiency is the priority of transport
aircraft, afterburner will not be used.
Fourthly,
afterburner has a very simple design. With just few minor changes to turbojet
engine, like provision for adding fuel to the exhaust and variable exhaust
nozzle, an afterburner can be incorporated. This simplicity makes it easy to
adopt and use.
Fifthly,
however afterburner is not for continuous use. Even the military aircraft don't
use afterburner continuously. The reason being that it burns a lot of fuel.
So we can see that afterburner is a mixture of advantages and disadvantages. Its application is completely based on intended use of the aircraft. However, one thing is clear, using afterburner consumes a lot of fuel.
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