# Air fuel Mix Ambient psi vs. compressed energy ouput

Internal combustion engines, Ram Jet, Turban engines etc. require that the air fuel mix be compressed. Is the compression of the air fuel mixture required to give a higher or more efficient energy output? Otherwise if the air fuel mix were at a static or ambient pressure vs. compressed would the energy output be different?

rcgldr
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Is the compression of the air fuel mixture required to give a higher or more efficient energy output?
For piston engines higher compression is better (as long as the octane is high enough to avoid pre-detonation). I'm not sure about turbines, ram and scram jets. Compressing the air first increases the amount of oxygen available to mixs with the fuel in jet engines, so it's more efficient in terms of power versus size and/or weight to compress the air.

For rocket engines, it probably doesn't matter much, for example, solid fuel rockets are pressurized by the thrust from the engine, but the rate of compression is very small. For liquid fuel rocket engine, the nozzle pressure just has to be greater than the pressure due to thrust from the rocket engine.

FredGarvin