Patent GB-1271940-A (GB)
Title: Pressure ratio control system for a gas turbine engine
Inventor: RIMMER RONALD
IPC: F02C9/32
Filed: 1968-07-18
Abstract: 1,271,940. Fluid regulation. DOWTY FUEL SYSTEMS Ltd. July 8, 1969 [July 18, 1968], No.34172/68. Heading G3H. [Also in Division F1] A gas turbine engine control system comprises a discharge nozzle and a receiver nozzle so dimensioned and coaxially spaced from one another that, in the region of a pre-selected critical ratio of inlet pressure to outlet pressure of the discharge nozzle, a change of the ratio of the discharge pressure of the receiver nozzle to the discharge nozzle inlet pressure, occurring with a change of the discharge nozzle pressure ratio, provides a controlling signal, control means operable, via restrictor means, on the discharge nozzle inlet and outlet pressures so that their ratio is a selected proportion of the pressure ratio of an engine compressor, and fluid-operated means regulating the fuel flow in response to the controlling signal in the sense that the selected proportion tends towards the critical ratio. A pressure intermediate the delivery pressure P4 and the inlet pressure P1 of a compressor of the gas turbine engine is selected by means of an air potentiometer 45, 73 controlled by a manual lever 75 and applied via a restrictor 48 to a discharge nozzle 49 which discharges across a vent 54 at the pressure P1 to a receiver nozzle 53 which is connected to a control passage 55 of a fluid switch 61, 62. The air potentiometer 45, 73 also supplies pressure air to the power jet 47 of the fluid switch and, via a further air potentiometer 51, 52, to a second control passage 56. When the pressures vary, the variation of the pressure recovered in the receiver nozzle 53 and the control passage 55 differs from that of the pressure in the control passage 56 whereby as the pressure ratio Ps/P1 across the discharge nozzle 49 passes through a critical value, there occurs a reversal of the difference of pressure between the control passages whereby the power jet from the nozzle 47 is deflected from an outlet passage 57 towards an outlet passage 58 or vice versa. To increase the fuel flow, the lever 75 is moved to enlarge the orifice 73. The resultant fall in pressure is less in the control passage 55 than in the control passage 56, so that the power jet from the nozzle 47 is deflected towards the outlet passage 58. The resultant increase in pressure in the outlet passage 64 of the fluid switch increases the vortex in a fluid amplifier 65 and thereby decreases the amplifier output pressure communicated via a pipe 42 to a capsule 39. This moves a beam 34 to increase the flow through a leak-off valve 32. The resultant drop in pressure in a chamber 26 reduces the opening of a valve 24 by-passing fuel from the outlet to the inlet of a fuel-pump 12, thereby increasing the flow through a metering valve 14 to the engine burners. The rate of acceleration is controlled by a fixed proportion a 1 of the pressure P4, tapped off by an air potentiometer 71, 72 and applied via a pipe 41 to a capsule 38. The increased fuel flow produces an increased pressure drop through the metering valve 14 which acts via capsules 36, 37 to bias the beam 34 towards a position of reduced opening of the valve 32 and thereby stabilize the fuel flow at the increased rate demanded by the lever 75. In a modification, Fig. 2 (not shown), the chamber (61) of the fluid switch has an outlet passage (80) acting upon the fluid amplifier (65) in opposition to the outlet passage (64) of the chamber (62). In a further embodiment, Fig. 3 (not shown), the fluid switch is omitted.