Brayton Cycle or Joule Cycle

Thermodynamic cycle refers to any closed system that undergoes various changes due to temperature, pressure, and volume, however, its final and initial state are equal.

A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and eventually return the system to its initial state.

Brayton Cycle

The Brayton Cycle is a thermodynamic cycle that describes how gas turbines operate. The idea behind the Brayton Cycle is to extract energy from flowing air and fuel to generate usuable work which can be used to power many vehicles by giving them thrust. The most basic steps in extracting energy is compression of flowing air, combustion, and then expansion of that air to create work and also power the compression at the same time.

This a thermodynamic cycle used in some heat engines. Notably, it is used for gas turbine engines and some jet engines. The cycle consists of compressing ambient air, mixing the air with fuel, then igniting the mixture, which expands, doing work. In many Brayton cycle engines, the hot air can then be recycled, heating the fresh air coming through.

A Brayton cycle with reheating and regeneration. Although it's not on a pressure volume diagram, this exemplifies the concept of the continuous loop, where the final and initial states are the same.

In 1872, an American engineer, George Bailey Brayton, advanced the study of heat engines by patenting a constant pressure internal combustion engine, initially using vaporized gas but later using liquid fuels such as kerosene. This heat engine is known as “Brayton’s Ready Motor”. The original Brayton engine used a piston compressor and piston expander instead of a gas turbine and gas compressor.

Today, modern gas turbine engines and airbreathing jet engines are also constant-pressure heat engines. Therefore we describe their thermodynamics by the Brayton cycle. In general, the Brayton cycle describes the workings of a constant-pressure heat engine.

It is one of the most common thermodynamic cycles found in gas turbine power plants or airplanes. In contrast to the Carnot cycle, the Brayton cycle does not execute isothermal processes because these must be performed very slowly. In an ideal Brayton cycle, the system executing the cycle undergoes a series of four processes: two isentropic (reversible adiabatic) processes alternated with two isobaric processes.