How does an Afterburner work?

Animation of a 2-spool, high-bypass turbofan.
A. Low pressure spool
B. High pressure spool
C. Stationary components
1. Nacelle
2. Fan
3. Low pressure compressor
4. High pressure compressor
5. Combustion chamber
6. High pressure turbine
7. Low pressure turbine
8. Core nozzle
9. Fan nozzle 

Many military jets, like the F-18 and the SR-71 take off from short airstrips and aircraft carriers to aid with special missions. But, how do they gather enough speed in such a short distance? How do they fly without stalling? This is all thanks to the afterburner. So, here comes the real question: How does an afterburner work?

 First off, a jet engine, like many other engines, is a reactor engine. It works by absorbing air, compressing the air in a combustion chamber where the air expands greatly and then it is shot back out at the back of the engine as air and exhaust at about Mach 2 or about 1500 miles/hour. This is known as thrust. An engine absorbs air and shoots it out as a hot gas.

Modern jet engines use a turbine to improve the fuel efficiency of a jet engine. This allows the jet engine to work at lower speeds and therefore lower temperatures. The turbine compresses the air before fuel is injected in the combustion chamber. This modern engine is extremely efficient. For example, on a Boeing 747-400, the aircraft can earn up to 19 miles per passenger gallon.

An afterburner is a part of an engine that acts like a booster. The afterburner is another stage fitted on only a certain amount of their engines like that of a Rolls Royce/SNECMA Olympus 593 fitted on the Supersonic Concorde. The afterburner injects fuel directly into the exaust stream expanding the air even more and creating nearly 50% more thrust to the engines' thrust.

The advantage of an afterburner is it can significantly add more thrust without adding weight, complexity and higher speeds and temperature to the engine. An afterburner is basically just a number of fuel injectors to compress the air further and increase the thrust of an engine.

The disadvantage of the afterburner is that it uses a lot of fuel to generate its power.

 The afterburner was an amazing design for the 1970s to 1990s but now has come out of commercial service due to the retirement of the Concorde. Military aircraft like the F-18 and the SR-71 still has afterburner to aid with special missions or to take-off from a short airstrip.

To look at a much more thorough article, look at the article from HowStuffWorks. You can go there by clicking here.

Sources: HowStuffWorks, How does an afterburner work?, HowStuffWorks, How Jet Engines Work?

This was originally posted on Thursday, October 27th 2011 on Aerospot. The animation and photo that are part of this post are protected by the Creative Commons License. Click here for more details.