How does a jet engine get started?

21 August 2011

Question

How does a jet engine get started?

Answer

Dave - A gas turbine jet engine is quite interesting in that it just doesn't work unless it's spinning - like a normal car engine. So basically, you've got to spin it up fairly fast, so you attach an electric motor into it - either it's integrated in there or you stick on the outside and spin it up. Then it gets going pretty fast, you inject some fuel, then you essentially have something like a spark plug inside it which ignites the fuel, then it starts it going and it basically then starts running, spins up to full speed, and you have a jet engine.

Chris - So it's not dissimilar to a diesel engine in a sense that you've got to get the engine spun up to start compressing air to get it hot so you can inject fuel to start it burning, and then once it's going, it's got its own ability to carry itself.

Dave - Yeah, pretty much! Also, there's nothing really to make the air explosion coming out of the back if the air is not coming in the front so you've got to have everything spinning for it to work at all.

Comments

In addition to electric start there are also compressed air starters. Some military aircraft use a cartridge starter that produces hot gas which is used to rotate the engine. This has the advantage that you don't need any ground equipment to start the engine so military aircraft such as the Harrier used this so it could operate away from bases with ground starters. A number of Quick Reaction Aircraft also used this so the engines could be started and the aircraft taxied without waiting for the ground power to be disconnected and people to get out the way. One example is the Vulcan that had cartridge starters so all 4 engines could be started at the same time.

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