What is the Brayton cycle in a gas-turbine engine?

The Brayton cycle is the thermodynamic cycle that describes the operation of a gas-turbine engine. It is defined as a cycle consisting of two adiabatic and two isobaric processes occurring in alternating order.12

In an idealized open-cycle gas-turbine engine, the process functions as follows:

• Compression: Air is drawn from the atmosphere and compressed to a higher pressure.1
• Heat Addition: Fuel is added and burned at an essentially constant pressure, significantly increasing the temperature of the air.1
• Expansion: The hot, high-pressure combustion gases expand through a turbine. This expansion produces work, most of which is used to drive the compressor, while the remainder provides useful shaft power or, in the case of a jet engine, is used to produce thrust.1

By modeling the engine on this cycle, engineers can calculate the theoretical thermal efficiency and power output of the system based on the pressure and temperature changes occurring throughout the process.1