Abstract: An on/off surge prevention control and method for a gas turbine engine having a variable geometry diffuser is provided. This control receives exhaust gas temperature and compressor discharge pressure signals from the engine, and a signal from the aircraft indicative of a need for bleed air. When the aircraft signal is received, the control opens the diffuser to its maximum open setting, and when said aircraft signal is absent closes said diffuser to its minimum open setting. In the event that a faulty aircraft signal is received, the control senses changes in EGT, P3 and dP3/dt and compares these parameters to preselected values indicative of the compressor nearing surge. When the measured values reach the preselected values, the control closes the diffuser to it minimum open setting. By using a temperature signal in determining when to close the diffuser, unwanted closings due to operating transients in compressor discharge pressure are provided.

Abstract: A modulating surge prevention control and method for a gas turbine engine having a variable geometry diffuser is provided. The control calculates a maximum permissible compressor discharge pressure from a predetermined algorithim that is representative of the compressor discharge pressure when the compressor is operating at its minimum permissible surge margin with the diffuser in its maximum open position. The control also receives a signal from a sensor measuring the actual compressor discharge pressure. A error signal is formed by taking the difference between the measured pressure signal and the calculated signal. The control then continously adjusts the area of the diffuser so as to maintain the actual compressor discharge pressure at or below the calculated pressure. The calculated pressure is also corrected for variations in ambient temperature and altitude.