US Patent 7811050 Operating line control of a compression system with flow recirculation

A system for controlling the operating lines of a gas turbine engine comprising a compression system which compresses an incoming flow of a gas, a bleed system which extracts gas from a bleed location in the compression system prior to the gas entering a throttling orifice, a recirculation system which reintroduces at least a portion of the gas extracted by the bleed system into a feed location in the compression system or upstream from it, a control system which controls the recirculated gas such that the operating lines of the compression system are changed such that the stall margin of the compression system is increased.