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I am working on an idea that involves a jet engine, but I don't quite know how the fuel system works. In a combustion engine like that in a car, you have nozzles that spray the fuel into the piston chambers (I think, correct me if I am mistaken), and then it's ignited when the piston compresses the chamber (sometimes using a spark plug, sometimes it doesn't). How is fuel mixed with air and ignited inside a jet engine? I know that compressed air comes from the intake system (the fan blades pull in and compress air and direct it into the part where it mixes with fuel), but how does fuel get mixed in?

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The place where air and fuel are mixed is the combustor, also known as the flame holder: Combustor #1

The diffuser takes in the compressed air and slows it down (remember that aircraft with jet engines are traveling extremely fast). If the air goes too fast, it won't burn enough; if it goes too slow, it won't provide enough thrust.

Air goes in through gaps in the liner. There are holes all along it, called primary holes, intermediate holes and dilution holes*. These further slow the air down, and help it enter the main part of the combustion chamber. However, most of the air goes through the swirler, which mixes the air as it enters. The dome is a related device.

Inside this chamber is an igniter, which creates the sparks needed for the fuel to burn. Next to it is the fuel injector, a pipe which inserts fuel into the chamber.

The air follows a series of complex paths inside the combustor:

Combustor #2

This picture should give you a good idea of them. Now you probably understand the names of the holes into the main chamber! They cool the combusted air (entering through the swirler) as it goes out the other end and into the next (and rear) section of the engine.

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  • $\begingroup$ What does the red line of the dome mean? Is that a metal sheet? Some special material? $\endgroup$ – Volker Siegel Mar 5 '15 at 0:27
  • $\begingroup$ @VolkerSiegel It's mostly just to highlight that specific section; materials can vary in the combustion chamber (e.g. see here). I also found a nice presentation here. $\endgroup$ – HDE 226868 Mar 5 '15 at 0:37
  • $\begingroup$ What I'm not understanding is the situation where the fuel arrow goes through the red dome: Is the fuel blocked by the dome, freely flowing into the combustion zone, or somehow interacting with the dome when penetrating it /crossing it/ passing through it? $\endgroup$ – Volker Siegel Mar 5 '15 at 0:43
  • $\begingroup$ @VolkerSiegel It has holes allowing the fuel to pass through. $\endgroup$ – HDE 226868 Mar 5 '15 at 0:44
  • $\begingroup$ Ah, thanks! Starting to understand the picture, I looked through en.wikipedia.org/wiki/Combustor - at first I thought it's just a structural element, letting the air pass in. But it seems to be far from that: it is "just a piece of sheet metal with holes for the air" - but it's shape is what controls most of the air flow and turbulence details of the whole thing. $\endgroup$ – Volker Siegel Mar 5 '15 at 0:57

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