Patent GB-934125-A (GB)
Title: Improvements in afterburner fuel control
IPC: F02K1/17
Filed: 1961-10-20
Abstract: 934,125. Jet propulsion engines. GENERAL ELECTRIC CO. Oct. 20, 1961 [Oct. 20, 1960], No. 37710/61. Class 110 (3). [Also in Group XXIX] In an after-burner fuel control for afterburner equipped jet-propulsion engines in which fuel is supplied to the after-burner through a metering valve, the metering valve comprises a piston and cylinder assembly, the piston being movable within the cylinder in both rotary and translatory modes, the piston and cylinder being formed with co-operating apertures which define a metering orifice. The rotary movement of the piston is controlled in accordance with the positioning of a throttle lever and the translatory movement is controlled in accordance with a measure of afterburner air flow as determined by the discharge pressure of the air compressor of the engine. A second and similar metering valve is provided for controlling the fuel supplied to an afterburner pilot burner, the pistons of the first and second metering valves being movable conjointly, and the first metering valve serving as a pressure-operated servomotor for the relative positioning of the piston of the second valve to supply fuel to the pilot burner. The afterburner main metering valve is indicated at 13 and comprises a piston 17 disposed in cylinder 18, the piston and cylinder being formed with ports 19 and 20 respectively which together define a fuel metering orifice. Fuel is supplied to the metering valve from an after-burner fuel pump through line 12 and discharges from the metering valve through the pressureregulating valve assembly 14 through the lines 52 and 16 to the after-burner fuel manifold. The after-burner pilot metering valve is shown at 57 and comprises a piston 62 movable within a cylinder 64, the piston 62 being conconnected to the piston 17 of the main metering valve by a pin 63. The piston 62 and cylinder 64 are formed with ports 65 and 66 respectively which co-operate to form an after-burner pilot fuel metering orifice. Fuel passes from the outlet port 20 of the main after-burner metering valve through line 58 to the inlet of the pilot metering valve and discharges therefrom through line 59, check valve 60 and line 61 to the afterburner pilot burner. Rotary movement of the piston valve 17 is caused by means of a rod 23 which is connected to the piston-rod 21 of the valve 17. The rod 23 is integral with the piston 25 of a bleed servo 24 to which after-burner fuel is supplied through line 27 as the servo fluid. The servo comprises a fixed orifice 28 and a variable orifice 29, the latter being controlled by the axial movement of the afterburner fuel control rod 11, axial movement of which to the left causes increase in afterburner fuel flow and movement of which to the right causes decrease in after-burner fuel flow. Axial movement of the piston 17 is also effected by a bleed servo device of which the piston 17 itself constitutes the servo piston. The valve piston is formed with a fixed orifice 30 which is in series flow with a variable orifice 31, the area of which is controlled by the position of a flapper element 32 pivotally mounted at 33. The flapper element is controlled by a pair of bellows 34, 35, the bellows 34 being connected to air compressor discharge pressure through line 36 and the bellows 35 being evacuated. If, say, compressor discharge pressure and so air flow through the after-burner, should increase, the flapper 32 will rotate in a clockwise direction opening the orifice 31 and so resulting in downward movement of the piston 17 with corresponding increase in size of the metering orifice 19, 20 and increase in fuel flow to the after-burner. Downward movement of the piston 17 causes the feedback lever 38 which is connected to the piston-rod 21 and is pivotally mounted at 39 to rotate in an anti-clockwise direction so increasing the loading of the spring 37 which acts against the loading of the sensing bellows 34 to restore the flapper element to its former position. A minimum fuel cam 48 is pivotally mounted on the feedback lever 38 and serves to position the element 47 in direct accordance with engine airflow. If the afterburner fuel control rod 11 is moved to the right in fuel flow decreasing direction, the lever 43 pivotally connected thereto and pivotally mounted at 45 will move in an anti-clockwise direction until the stop 46 engages the follower 47 and further movement of the rod 11 to the right is prevented. The pressure-regulating valve assembly 14 is provided to maintain the pressure drop across the metering orifice 19, 20 constant, the regulating valve comprising a piston valve 51 which is loaded at its left face by pressure of fuel upstream of the metering orifice, and at its right face by pressure of fuel downstream of the metering orifice, the position of the valve controlling the outlet to line 52. The after-burner pilot fuel metering valve piston being connected to the main metering valve piston moves conjointly therewith but the metering ports 65, 66 are shaped so that only axial movement of the piston 62 within the cylinder 64 produces variation in the area of the metering orifice, that is pilot fuel is metered in accordance with the air supply to the afterburner as determined by the compressor discharge pressure. Movement of the afterburner fuel control rod 11 has no effect on the area of the pilot fuel metering orifice. A check valve 15 is disposed between the afterburner main fuel lines 52 and 16, the valve comprising a valve member 67 connected to an actuator piston 69 which is spring-loaded in the closed direction. When after-burner fuel is supplied through line 12 a portion thereof passes through line 72 to act on the piston 69, causing the valve 67 to open. Means are also provided to ensure that at the start of afterburner operation, the fuel lines 16 and 61 are immediately filled with fuel. For this purpose fuel passing through line 72 at start of the afterburner operation passes also through ducts 73 and 75 into the fuel lines 16 and 59 respectively. As the valve 67 moves in the opening direction the ducts 73 and 75 are closed off; however, fuel then flows wholly through the metering valves. Means are also provided to purge the fuel lines 16 and 61 when the afterburner operation is completed such means comprising a valve assembly 79 which comprises a piston valve 81 disposed within a cylinder. When after-burner fuel is being supplied through line 12, fuel passes through lines 72, 84 and holds the valve 81 in the position shown. When after-burner fuel supply is cut-off however, air from the compressor discharge passing through line 80 moves the piston valve 81 to the right, whereby air flows from line 80 through lines 82 and 83 to purge the fuel lines 16 and 61. This air flow continues while the engine is in operation. Specification 934,124 is referred to.