What is the Brayton cycle and how does it apply to gas turbine engines?

The Brayton cycle is the thermodynamic cycle for gas turbine engines consisting of four processes: isentropic compression (compressor), constant-pressure heat addition (combustor), isentropic expansion (turbine), and constant-pressure heat rejection (exhaust). The ideal cycle efficiency depends on the pressure ratio: higher compression ratios yield better efficiency. In real engines, component efficiencies, pressure losses, and temperature limits affect actual performance. Modern engines achieve pressure ratios of 40-50:1 with thermal efficiencies around 40-50% at cruise.