rocket engines produce thrust by the expulsion of an exhaust fluid that has been accelerated to high speed through a propelling nozzle.... ant got nothing to do with a 4 stroke internal combustion engine....DWB!
Yup. Momentum. High heat equals expansion, which is used to propel the mass of the spent fuel at a high speed.
M1v1=M2v2
Use a converging/diverging nozzle to reach supersonic speeds and the expansion results in even greater gains in exhaust velocity.
Since the available momentum is tied to the mass of the propellant, we get what's called "the tyrrany of the rocket equation" (the more mass you launch, the more fuel mass you need, which increases the mass and requires more fuel which..).
