The turbojet engine thrust is created when the hot gas stream from the combustor chamber expands through the turbine and nozzle at great speed. However, to obtain this expanding gas, air must be compressed in the engine inlet and compressor, and then it must be mixed with fuel, which is burned in the combustor to produce the stream of gas that drives the turbojet turbine. The expanding hot gas is produced in the gas generator, which consists of the low pressure and high pressure compressor and the combustor.
In the compressor portion of a J79 engine, the pressure and temperature increase as a result of work being done in the air. The air temperature is sharply increased when burns in the combustor along with the fuel. In the turbine section of the engine, the gas stream energy is converted into rotatory energy which drives the shaft that turns the compressor. In the nozzle section, the gas stream is further expanded to produce a high exit kinetic energy which supplies the much needed thrust.
All the sections that make up the engine must perform in such a way as to efficiently generate the greatest amount of thrust for a minimum of weight. The need for more thrust at a relatively low speeds led to the adaptation of the turbojet to take the form of a turboprop, turbofan, and turboshaft engines.
Below, an schematic drawing of a turbojet engine, showing the different sections, with the combustor where the expanding gas stream is produced.
