When the engine is in motion, air from the atmosphere enters the inlet case at atmospheric pressure and passes through the compressor, which is driven by the turbine. In the combustion chamber, some of the compressed air is used to support combustion of the fuel. The fuel is supplied to this chamber by the fuel injectors.
In a turbojet engine, the compressed air sustains the burning of oil in the combustion chamber. When the gases produced by burning expand, they move with great velocity toward the back of the engine. The reaction force to the moving gases propels the engine forward.
The heat produced by combustion of the fuel causes all of the gases in the chamber to expand and to move through the chamber with a greater velocity. The force required to obtain this velocity develops a reaction that tends to propel the combustion chamber forward. This reaction helps to propel the entire engine.
Before the exhaust gases are discharged from the engine, they must strike the blades of the turbine. Since the turbine is mounted on the same shaft as the compressor, the rotation of the blades drives the compressor.
In some types of turbojet engines, the exhaust gases must also pass through an afterburner before they’re discharged through the exhaust nozzle. The afterburner is simply another combustion chamber. As a stream of gases enters the afterburner, it’s injected with fuel. The combustion of this fuel reheats the exhaust gases. These reheated gases pass through the exhaust nozzle with greatly increased velocity. As a result, the forward thrust on the turbojet engine is greater than it would have been without the afterburner.
