A jet engine is a reaction engine that produces thrust by expelling high-velocity gases through a nozzle. Turbojet engines operate on the open Brayton cycle, which consists of four continuous processes: intake, compression, combustion, and expansion (exhaust). Atmospheric air is drawn into the engine and compressed by the compressor, mixed with fuel, and burned at approximately constant pressure in the combustion chamber. The resulting high-temperature and high-pressure gases expand through the turbine, which supplies the power required to drive the compressor. The gases then pass through a nozzle, where they are accelerated to a high velocity to produce thrust.
The Armfield CM14 turbojet engine is a small-scale educational gas-turbine system designed to demonstrate the fundamental principles of jet propulsion. The engine is instrumented to measure thrust, rotational speed (RPM), exhaust gas temperature, compressor pressure ratio, and fuel consumption. These measurements allow direct comparison between theoretical jet-propulsion equations and actual engine performance. The system also enables the study of the effects of RPM on thrust, the function of the exhaust nozzle, and the evaluation of key performance parameters such as specific fuel consumption and thermal efficiency.
Thrust generation in a turbojet engine follows Newton’s Third Law of Motion, which states that for every action there is an equal and opposite reaction. As the engine accelerates a mass of air and combustion products rearward, an equal and opposite force is produced in the forward direction, resulting in thrust.
The thrust developed by a turbojet engine is given by:where
= mass flow rate of air and fuel,
= exhaust jet velocity,
= inlet (flight) velocity,
= exhaust pressure,
= ambient pressure,
= nozzle exit area.
