The Brayton thermodynamic cycle models the open or closed continuous power cycle of gas turbine engines. The ideal cycle consists of four reversible internal processes: isentropic compression of air (1→2), constant-pressure (isobaric) heat addition in the combustion burner (2→3), isentropic expansion through the turbine extracting mechanical power (3→4), and isobaric heat rejection (4→1). Cycle thermal efficiency depends solely on pressure ratio.