The open Brayton cycle is commonly used in gas turbine engines for power generation, aircraft propulsion, and industrial processes. The Brayton cycle, named after American engineer George Brayton, who proposed it in 1872, converts fuel energy into mechanical work. The Brayton cycle became widely used in practical applications following the development of the gas turbine in the 1930s. Gas turbines were used extensively during World War II, and their efficiency and reliability improved significantly.
The Brayton cycle has numerous advantages for energy applications. For one, engineers can design it compactly, making it a strong fit for tight enclosures. With gas turbines being a common engine driver, the Brayton cycle is popular in modern applications. Since Brayton cycle engines are particularly efficient in gas turbine engines, they are useful for power generation, aircraft and marine propulsion, industrial processes, and more.
Additionally, Brayton cycle motors produce few emissions thanks to their efficient exhaust gas treatment systems, making them a greener choice than other fossil fuel systems. Coupled with their high efficiency from the isentropic compression and expansion processes that minimize energy loss, engineers continue to develop Brayton thermodynamic cycle systems to this day.
There are two main types of a Brayton cycle: open and closed. In an open Brayton cycle, the working fluid is continuously supplied to and exhausted from the system, and the process operates in an open loop. On the other hand, in a closed Brayton cycle, the working fluid is contained within the system and circulates in a closed loop. The schematics of a simple open-cycle gas turbine utilizing an internal-combustion process and a simple closed-cycle gas turbine using heat transfer processes are both shown in figure 1.
An ideal Brayton cycle consists of the following four processes:
- Isentropic compression: air is compressed to high pressure and temperature via an isentropic process that is adiabatic and reversible.
- Constant pressure heat addition: high-pressure air is fed into a combustion chamber where fuel is added and ignited.
- Isentropic expansion: high-temperature gases from the combustion chamber expand in the turbine in an isentropic process, producing mechanical work.
- Constant pressure heat rejection: the exhaust gases are expelled into the atmosphere.