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Jet engine basic principle

Have you ever wondered how is it that jet engine works? I mean, it's a tube with an explosion inside it, but this explosion miraculously goes only in one direction.


Let us start with simple shape for combustion chamber.




The trick is that intake hole is smaller than exhaust hole!!!
Pressure times surface is force. You can imagine a balloon with one bigger hole on one side and one minute hole on the other side. Whill this balloon stay still or move?



Intake opening on the chamber is smaller then exhaust opening. Let's imagine that pressure in the chamber is uniform. That means that exhaust force is bigger than force at intake because pressure times surface is force. Obviously exhaust energy is higher than energy that is trying to push small thrust trough intake hole. Only thing now left to do is to use some of that exhaust energy to overcome force at intake hole of combustion chamber.This is what turbines and shaft do.

Small portion of thrust energy is converted by exhaust turbine and transferred by shaft to compressor(intake turbine). Intake turbine has to overcome force at intake opening on the combustion chamber and supply enough air.



If you somehow supply oxygen to combustion chamber until velocity is high enough, you don't even need turbines and shaft. This is how RamJet Works.