GB1404501A - Reheat fuel systems for gas turbine engines - Google Patents

Abstract

1404501 Gas turbine jet engine - reheat fuel control ROLLS-ROYCE (1971) Ltd 5 Dec 1972 [4 Jan 1972] 217/72 Heading F1J The invention relates to a re-heat fuel system for a gas turbine jet engine which system is controlled conjointly with a variable area nozzle control system. The engine shown comprises a turbine 16, a reheat fuel system 18 and a variable area nozzle 20 controlled by actuator 38. Reheat control is by means of a pilot lever 22 which is connected to a schedule 24 to which signals such as engine speed and compressor pressure are supplied at 26, 28, the resulting signal passing through line 30 to an actuator 32 which opens fuel valve 34. The actual fuel flow through valve 34 is sensed and fed through line 46 to a comparator 50 where it is compared with the schedule flow, any flow error producing a flow error signal which causes the actuator 32 to adjust the fuel valve 34 to reduce the flow error. The actuator has limits set on its velocity or position which limits are calculated by a device 36 which operates in dependence on turbine pressure ratio error. The variable area nozzle actuator 38 is controlled by a control 40 which also acts to maintain the pressure ratio P3/P6 across the turbine substantially constant. The actual pressure ratio is determined by a sensing unit 44 and this is compared in a comparator 52 with the desired pressure ratio, any resulting pressure ratio error being fed to the nozzle actuator control 40 which causes the nozzle area to be adjusted to reduce the pressure ratio error. A bias term is added to the pressure ratio error signal supplied to the nozzle actuator control 40, the bias term being computed from the reheat fuel flow error in a bias term control 42. The bias term is proportional to the reheat fuel flow error and when added to the pressure ratio error signal produces a higher nozzle actuation signal. As the fuel flow error approaches zero, the bias term to the nozzle loop is removed.