What is the working principle of a turbojet engine ?
All gas turbine engines turbojets, turbofans and turboprops are based on the Brayton thermodynamic cycle.
Turbojet engines are used for the aircraft’s high speed subsonic and supersonic flight. A jet engine takes a mass of air and exhausts it at a higher velocity with the combustion products. A jet engine makes the intake air to exhaust faster from its back end. Jet engine consists of following parts inlet, diffuser, compressor, burner, turbine and the nozzle.
Air is inducted through inlet of the engine. After that the speed of airflow is reduced in diffuser to around low subsonic speed of Mach number 0.2. The diffusion process increases the static pressure. After diffuser, the air is passing through the compressor where it get compressed. In compression process, pressure is increased further. It increases the total pressure of the flow.
After compressor, air is passed through combustor. Here, fuel is injected and there is a burning at a constant pressure. After the combustor, hot gas is flowing through the turbine, where expansion takes place and pressure get decreased. Turbine is connected to the compressor through a shaft. Turbine drives the compressor through this shaft.
After turbine, flow passes through the nozzle, where pressure is further decreased, and the flow exists from the engine. If the turbojet engine is designed for a subsonic flight, exit velocity of flow is subsonic or at large sonic. For supersonic aircraft, the exhaust velocity of the flow is supersonic.