Jet V Rocket engine explanations seem to be getting very complicated.
Try these analogies - they work for me
JET engine-
Sit on a kids skate board - pick up brick from ground - throw brick backwards - you go forwards. Repeat for continuous motion.
Bricks = AIR, energy used to throw brick = FUEL
Run out of either and you stop.
ROCKET engine-
Sit on the same skateboard, this time with a pile of bricks on your lap - throw bricks backwards one at a time - you go forwards.
In this case, Bricks and fuel need to be treated as one and the same - in a rocket engine, the fuel is both the energy source AND the accelerated mass. (OK-perhaps not in ION propulsion)
Too simple ?