Patent GB-1069872-A (GB)
Title: Engine fuel supply systems
Inventor: RIMMER RONALD
IPC: F02K1/17
Filed: 1963-02-19
Abstract: 1,069,872. Gas turbine jet engines; ramjet engines. BRISTOL SIDDELEY ENGINES Ltd. Feb.11, 1964 [Feb. 19, 1963], No.6680/63. Headings F1G and F1J. [Also in Division G3] The invention relates to an aircraft engine for flight at supersonic speeds, the engine comprising an air intake passage with a throat, a subsonic combustion zone, means for supplying fluid fuel to the combustion zone, and an exhaust nozzle with adjustable throat area; and including a control system comprising:- (a) fuel flow control means responsive to the position of a normal shock wave in the air intake so as to tend to return the shock wave to a predetermined position on departure therefrom, (b) means for producing a first signal which is a function of the supply of fuel to the engine, (c) means for producing a second signal which is a function of the mass flow of air through the engine, (d) exhaust nozzle throat area varying means responsive to the ratio of the first and second signals to reduce nozzle throat area upon increase of said ratio from a predetermined value, and vice versa, (e) means constituting a thrust selector for modifying one or both of the signals, or the response of the nozzle throat area varying means to their ratio. The invention is shown applied to a ramjet pro- - pulsion unit comprising an outer casing 1 and a centre body 3 which together define an air intake passage 6. The propulsion nozzle 8 is of convergent-divergent form, an axially-movable plug member 10 being disposed therein in order that the area of the nozzle throat may be varied, the plug member being movable by means of fluid pressure applied to one side or the other of the piston 11 disposed in cylinder 12. Fuel is supplied into the ramjet combustion chamber through spray nozzles 13 to which fuel is supplied through line 17. A pitot head 39 is mounted at the nose of the centre body 3 so as to sense the ram pressure at that point. The desired position of the normal shock wave within the intake passage is indicated at 7 and the pressure at this point is sensed by a reversed pitot system. Fuel is supplied to the engine through a line 14, through a servo-operated throttle valve 15 and a valve 16 having a linear pressure-flow characteristic to line 17 and hence to spray nozzles 13. The valve 15 comprises a double-ended piston 18 disposed within a cylinder 19 and affording servo pressure chambers 20, 21 therewith, the skirt portion 24 of the piston cooperating with inlet port 25 so as to control flow of fuel. Servo pressure fluid is supplied to the chambers 20, 21 from the line 14 through ducts having restrictions 22, 23 therein, the ducts terminating in nozzles 27, 28 from which fuel discharges through spill pipe 26, the nozzle outlets being controlled by a flap valve 29 pivoted within a casing 30. The flap valve is connected at its opposite end to a diaphragm 33 which divides the casing into two compartments 31, 32, the compartment 31 being connected by line 34 to the pressure sensed by the reverse pitot system 35, and the compartment 32 being connected by line 36 to the pressure in the pressure potentiometer 37 which comprises two restrictions 40, 41 disposed in the line 38 which is open to ram pressure PR at the pitot head 39 at its upstream end, and to atmospheric pressure at its downstream end, the restriction 41 being variable by means of an adjuster 41a which may be controlled for example by means of a Machmeter. Should the pressure within the ramjet casing increase, the normal shock wave may move forwardly, the reversed pitot system 35 would then sense the increased pressure downstream of the shock wave, the pressure in the chamber 31 would increase, the flapper valve would move to restrict the nozzle 27, the piston valve 18 would move downwardly so restricting the open area of the inlet port 25 and reducing the flow of fuel to the engine. The axial position of the plug 9 controlling the area of the nozzle throat 8 is controlled as follows: The fuel pressures P 1  and P 2  upstream and downstream of the valve 16 are communicated to bellows 53, 54 which are connected at opposite sides of the flapper valve 55 which is pivoted at 56, the pressure difference P 1 -P 2  being a measure of the fuel flow. Bellows 58, 59 are connected at opposite sides of the flapper valve 55 at the opposite side of the pivotal point 56 to bellows 53 and 54, the bellows 58 being subject to pressure P R  sensed by the pitot head 39 and communicated through duct 38 and the bellows 59 being subject to pressure KP R  which is the pressure in pressure potentiometer 60. The potentiometer 60 comprises a duct connected at its upstream end to the line 38a in which the pressure is P R  and at its downstream end to atmospheric pressure, there being a pair of restrictions 61, 62 within the duct, the pressure between the restrictions being KP R . The area of the restriction 62 is controlled by an adjuster 63. The end 64 of the flapper valve 55 co-operates with a pair of nozzles 65, 66 so as to control flow of servofluid through ducts 67, 68. Fluid is supplied to the ducts 67, 68 through supply port 86, ducts 71, 72 and ports 73, 74, flow through the ports 73, 74 being controlled by ports 75, 76 in skirt portions of a piston valve 70, the piston valve having also a pair of lands 78, 79 which co-operate with ports 80, 81 which lead to passages 82, 83 through which fluid may be supplied to or discharged from the spaces at either side of the piston 11 so controlling the piston of the adjustable plug 9. The ram pressure P R  gives a measure of the air flow through the ramjet engine. Thus the 'first signal' referred to at (b) above is that produced by the capsules 53, 54 and the 'second signal' referred to at (c) above is that produced by the capsules 58, 59. In the event that fuel flow to the engine is increased by the throttle valve 18 in response to a movement of the normal shock wave into the intake, that is supercritical pressure recovery condition, capsules 53, 54 will act on the flapper valve 64 to close the nozzle 65 and open the nozzle 66, the resulting increase in pressure in the chamber 67 causing the piston valve 70 to move upwardly whereby servofluid passes through duct 83 to move the piston 11 upwardly and thus the plug 9 is moved inwardly to reduce the exhaust nozzle throat area. The pressure within the combustion system therefore increases and the shock wave returns to its desired position, the pressure sensed by the reversed pitot system 35 acting to control the throttle valve 15 as previously described. A similar action will occur should the normal shock wave tend to move out of the intake, that is sub-critical operation. Engine thrust may be controlled by adjusting the needle 63 of the potentiometer 60, the needle may for example be adjusted by a device responsive to Mach number or by a device responsive both to flight Mach number and altitude. The invention is shown in Fig. 5 applied in the case of a gas turbine jet engine, the engine 101 being disposed within a duct 104 which has an engine air passage 107 defined between a fixed wall 105 and a series of movable members 108, 109, 110 at its upstream end and a variable area secondary nozzle 114 at its downstream end. The engine 101 has a variable area primary nozzle 103. A critical intake control, a fuel:air ratio control, and a primary nozzle throat area control operating in the manner as described with reference to Fig. 1 are provided.