Why does air have to be compressed in a jet engine?

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This has really got me confused lately. I’ve read online that it increases efficiency, the potential energy of the air and helps with combustion, but my question is:
If the same amount of air is passing through the engine regardless, why pressurise it? Wouldn’t the gain in PE of the air just be equal to the loss of KE of the aircraft due to the air hitting/dragging the aircraft back as it’s compressed? I’m almost certain I’m wrong here, but any explanation which could clear this up for me would be great thanks.

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Anonymous 0 Comments

The entire premise of a jet engine is that is has to eject mass out the back (due to Newton’s third law). Most of that with modern turbofans is just moving the air through it (it’s literally a giant freaking fan). But to spin that turbine, you need to move sufficient mass of exhaust gases (from air and fuel) out of the combustion chamber and through a smaller turbine. Since air and fuel need to be at a correct ratio to burn, you gotta squeeze a bunch of air into the combustion chamber to burn the required amount of fuel.

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