A turbojet compresses incoming air, mixes it with fuel, ignites it, and blasts the expanding gases out the back to create thrust. Unlike turbofan engines, all the air entering the intake passes through the combustion chamber. This design is highly inefficient at low speeds and extremely loud, but it excels at high altitudes and supersonic velocities where a narrow, high-speed exhaust plume is required.
You only see pure turbojets on older military fighters and supersonic drones where high-altitude speed matters more than fuel economy.
If a jet engine has a massive fan at the front that pushes air around the core, it is a turbofan, not a turbojet.
Related terms
Ramjet
An airbreathing jet engine that uses the vehicle's forward motion to compress incoming air.
Scramjet
An airbreathing jet engine that operates with supersonic airflow through its combustion chamber.
Airbreathing
An engine design that relies on atmospheric oxygen to burn its fuel.
Propulsor
A shrouded or ducted propeller system used to generate thrust.