A turbojet is a type of gas turbine engine commonly used in airplanes. These engines are used in some aircraft, though many use turbofan engines instead. Turbojets are also used in some missiles. The turbojet, like all gas turbines, gathers the passing air to derive the oxygen necessary for combustion. The air is compressed, mixed with fuel, and then ignited. The force of exhaust gases moving through the nozzle at the rear of the engine creates the thrust that moves the craft.
At the front of the engine is the inlet, or intake. It gathers outside air in the most efficient and aerodynamically optimal way possible and feeds the air into the compressor. The compressor is most often a series of rotating blades, acting as airfoils, arranged in successive rows. As the air passes by each set of blades, its temperature and pressure build. In order to generate a substantial amount of thrust, the temperature and pressure of the air must be built up before entering the combustion chamber of the engine.
At the combustion stage, the oxygen in the air is ignited by adding fuel. The temperature of the air passing through this stage increases exponentially. It is forced through a turbine immediately following the combustion chamber, causing the turbine to spin. It is this section of the engine that powers the other parts. The turbine and compressor are connected via a central shaft. The energy gathered from the turbine is used to turn the compressor.
The last section of the turbojet is the nozzle. After the gasses have passed through the turbine, their temperature and pressure is still greater than that of the air passing outside of the turbojet. This heated and pressurized air is pushed through the nozzle which causes the gasses to accelerate and producing the thrust that moves the craft.
An afterburner can be added to the turbojet. This is a device in the exhaust section of the turbojet that adds additional fuel to the heated exhaust gases. The added fuel is rapidly burned, increases the temperature and pressure of the air and, accordingly, the amount of thrust.
The downside to a turbojet engine is its relative inefficiency at lower speeds compared to a turbofan. The turbojet reaches optimal working conditions after Mach 2 or twice the speed of sound. The sound that it creates is also quite disruptive for any nearby populations.