Jet engines represent one of the most important propulsion systems used in modern aircraft. They operate by converting the chemical energy of fuel into thermal energy and then into kinetic energy that produces the thrust required for flight. The gas turbine forms the foundation of most jet engines, operating through a sequence of thermal and mechanical processes that convert the energy of fuel into a high-speed gas stream that is expelled backward, producing forward thrust for the aircraft. The engine operation begins when air enters through the engine inlet and is directed into the compressor, which consists of a series of rotating and stationary stages. The compressor increases the pressure of the air, which also causes its temperature to rise. The compressed air then enters the combustion chamber, where fuel is injected and mixed with the air before ignition takes place. Combustion releases a large amount of energy and converts the mixture into gases with high temperature and pressure. The hot gases then flow into the turbine, where they expand and lose part of their energy to rotate the turbine blades. The turbine is mechanically connected to the compressor through a rotating shaft, allowing the energy extracted from the gases to drive the compressor and maintain continuous engine operation. After passing through the turbine, the gases continue to expand and accelerate through the exhaust nozzle. The remaining energy is converted into a high velocity of the exhaust gases, producing thrust as a result of the change in momentum. The gas turbine in jet engines operates primarily according to the Brayton cycle, an ideal thermodynamic cycle consisting of four main processes. It begins with compression of the air in the compressor, followed by heat addition at approximately constant pressure inside the combustion chamber. The gases then expand through the turbine, followed by heat rejection at constant pressure under ideal conditions. Although actual engines differ from the ideal model because of friction, pressure losses, and heat transfer, the Brayton cycle provides an important basis for understanding the operation and performance of jet engines. The efficiency of a jet engine is affected by several factors, including the pressure ratio, the temperature of the gases entering the turbine, the efficiency of the compressor and turbine, and the design of the combustion chamber and exhaust nozzle. Improving these factors helps reduce fuel consumption, increase thrust, and enhance the overall performance of the engine. Through this integrated sequence, the jet engine operates as a continuous energy-conversion system that begins with air compression and ends with the acceleration of gases to high velocities. This thermal and mechanical principle forms the foundation that has enabled gas turbines to play a central role in modern aircraft and achieve high levels of speed, efficiency, and reliability. Lecturer. Boraq Hayder Mohsin