Jet Engines

Hey everyone, just after a bit of help if at all possible.

I’m just writing an A-level piece of Physics coursework on jet engines, a 4000 word research project. I’ve stumbled a little and can’t quite get my head around a small principle…

I am talking about combustion chambers and how the process works, linking it to Boyle’s and Charles’ combined gas law.

Essentially, (P1 x V1)/ T1 = (P2 x V2)/ T2.

Say for example the pressure upon entering the chamber is 2, the volume is 10 and the temperature is 5 (it doesn’t matter which numbers, just to make a point).

Then fuel is injected and ignited, the volume is the same at 10, the temperature increases to say 10, therefore meaning that after a simple calculation, P2 must increase to 4.

But how does that work? I thought that the pressure must have to decrease as the gas expands, otherwise how/why does it travel out the rear of the engine?