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Jet Engine Question. Combustion in engine just used to expand air? Answered

Lately I have been researching Jet engines. I once heard that the gas combution process was just there to expand the air being sucked in. Is this true?



4 years ago

Yes, that is the main idea on gas turbine engines! Everything on the engine is just to support and direct the expansion of the hot gasses. The expanded gasses provide the thrust when they are ejected from the nozzle, and they are used to drive the turbines (which are for driving the compressors and any fuel pumps or generators). It is basically an air-breathing liquid-fueled rocket engine.

Check out this webpage on jet engines: http://www.ourbadscience.com/#!jet-engines/c1gse

You can also use other things than combustion for the heating. At the bottom of that page on jet engines there is an article on nuclear thermal jet engines.

Correct. The heated fuel products and the heated air take up a much larger volume than the cold products generating pressure.

This is why jet engines have to be so hot.ORK gives most of the details.


This may explain better

That's what it does in a piston-cylinder engine too: cause expansion, which then provides the force needed to run the engine.

In a jet, the force is used more directly, akin to a rocket (or, if you prefer, a balloon you've blown up and then released). Expansion produces pressure in all directions; the pressure is released toward the rear, which means the unbalanced pressure in front pushes the engine -- and the plane -- forward.

Pulse jet is closest to being a rocket; ramjet a bit less so, turbojet a bit less so -- but they're all using unbalanced force to drive the engine forward; the details lie in how the force is being contained.

BTW, if you want more detail on exactly how those different kinds of jet engines work, there's a LOT on the web.