Brayton (Joule) Gas Turbine Cycle

Thermodynamic cycle of gas turbines and jet engines featuring isentropic compression/expansion and isobaric heat transfer.

Specifications & Metrics

type: Internal Combustion Gas Cycle
processes: Isentropic compression (1→2), isobaric (constant-pressure) combustion (2→3), isentropic turbine expansion (3→4), isobaric heat rejection (4→1)
working fluid: Air and combustion gases (open cycle) or helium/supercritical CO₂ (closed cycle)
efficiency formula: η = 1 − 1 / (P₂ / P₁)^((γ − 1)/γ)
originator: John Barber (1791 turbine patent) & George Brayton (1872 'Ready Motor')
applications: Airbreathing turbojet/turbofan aircraft engines and gas-turbine electrical power plants

Named after American engineer George Brayton, who patented his constant-pressure piston 'Ready Motor' in 1872, the Brayton cycle is today executed continuously across an axial or centrifugal compressor, an open-flow combustion chamber, and a turbine.
Ideal Brayton efficiency rises with the compressor pressure ratio r_p = P₂/P₁ as η = 1 − r_p^((1−γ)/γ), while maximum specific power output is governed by the metallurgical temperature limit of the first-stage turbine rotor blades (~1,500 °C with single-crystal superalloys and film cooling).
Adding a recuperator heat exchanger, intercooling between compressor stages, or exhausting into a Rankine steam bottoming cycle (combined-cycle gas turbine) pushes overall plant thermal efficiency above 60%.