An example of a jet engine is a full balloon that is not held closed. It will release the air and push the balloon forward.
Turbojet engines are used on airplanes. Turbojet engines have a gas compressor, a kind of fan, at the front that takes in air. The engine burns fuel to make the air expand, and it blows a big wind out the back. On the way out, the hot air turns another fan (a gas turbine) which turns the rod that turns the fan at the front to make it go.
- Jet Engine at Citizendium