Patent GB-983832-A (GB)
Title: Gas turbine engine fuel system
Inventor: JUBB ALBERT
IPC: F02K3/10
Filed: 1960-10-12
Abstract: 983,832. Gas turbine jet propulsion plant; centrifugal pumps. ROLLS-ROYCE Ltd. Sept: 29, 1961 [Oct. 12, 1960], No. 35000/60. Headings F1C, F1G and F1J. [Also in Division G3] A fuel system for controlling the supply of reheat fuel to the reheat combustion equipment of a gas turbine engine comprises a reheat fuel pump, means for metering the flow of reheat fuel, means for preventing flow of fuel when the engine rotational speed is below a predetermined speed which speed is substantially below the maximum engine speed, flow control means being provided which means may be set in an operative condition in which flow of fuel to the reheat combustion equipment is permitted and in an inoperative condition in which such flow is prevented. When the engine speed is between its maximum and the said pre-determined speed, reheat fuel may be supplied to the reheat combustion equipment whenever the flow control means is set in the operative condition, and when the engine speed is below the said pre-determined speed the supply of reheat fuel to the reheat combustion equipment will always be cut off. In Fig. 1 reheat fuel is supplied by a gear-type pump 10 to a line 12 which leads to a metering valve 16, the valve comprising a valve member 17 disposed within a valve body 15. The valve member 17 is shown in the position in which the annular recess 22 therein communicates with inlet ports 14 and with metering orifices 34 so that fuel can pass from the line 12 to the line 36 leading to the reheat burners. The system also comprises a needle valve 37 comprising a valve member 44 which controls communication between chamber 41 to which air at compressor delivery pressure P 2  is applied, and chamber 40, the position of the needle valve being dependent on the position of the engine throttle lever so that if the maximum engine speed is say 17,500 r.p.m. then the needle valve 44 is open only at speeds above say 14,000 r.p.m. In the open position of the valve shown, air at pressure P 2  passes through line 54 to act on the left-hand end of the metering valve member 17. Engine jet pipe pressure P 4  is applied through line 57 to act on the right-hand end of the valve member 17, a spring 27 also acting against this end of the valve member. The pressure P 2  in chamber 40 is also communicated through line 53 and restriction 56 to the line 57. A shut-off valve 87 is provided, the position of the valve member 85 being determined by the position of the engine throttle lever, the valve being shown in a position corresponding to an engine speed above 14,000 r.p.m. in which reheat fuel may be supplied. When the engine throttle lever is moved to a position corresponding to an engine speed below 14,000 r.p.m., the valve member 85 will be moved to a position in which high pressure fuel from the reheat fuel pump 10 passes through the line 90, the annular recess 88 in the valve member 85 to the line 93 and so back to the inlet of the pump. The valve 87 thus ensures that no reheat fuel can be supplied to the reheat combustion equipment at engine speeds below 14,000 r.p.m. The system also comprises a by-pass valve 60 which serves to maintain the pressure drop across the metering valve 16 at a constant value. The valve comprises a valve member 62 which is acted on at its at left-hand face by pressure of fuel delivered by the pump 10 through line 12, and at its right-hand face by pressure of fuel in the supply line 36, that is, the pressure of fuel downstream of the metering orifices 34, this pressure being communicated through line 71 containing restriction 72. The valve member 62 is also loaded at its righthand face by spring 70. The valve member 62 controls ports 76 so that there is always a bypass flow of fuel from the line 12 to the line 78 back to the inlet of the pump 10. The valve members 17 and 62 are arranged to be rotated during operation by means of gearing 23, 63, 64 so as to prevent sticking. A solenoid-operated valve 100 is also provided, the valve member 98 normally being held in the closed position by a spring 101, this being the reheat position. When the solenoid is energized however, the valve member opens and reheat fuel from the supply line 36 passes to the line 97 and back to the suction side of the pump 10. At the same time, the valve 62 will move to the right due to the reduced pressure at its right-hand face and so more fuel will be by-passed through the ports 76 back to the suction side of the pump. A pressurizing valve 82 is provided in the supply line 36 to the reheat burners so as to ensure that fuel is supplied to the burners only above a certain minimum pressure. An alternative embodiment is shown in Fig. 2 and comprises a reheat fuel pump 125 of the centrifugal type, a metering valve 142 and a shut-off valve 113, fuel passing into the control unit from a tank through the inlet 110 and discharging therefrom to the reheat burners through discharge line 160. There is a connection to engine compressor discharge pressure P 2  through line 172 and to engine jet pipe pressure P 4  through line 176. There is also a connection to the high pressure side of the main engine fuel pump through line 210 for use as a servo-fluid. The pinions 116, 182 which actuate the valve members 113, 170 respectively are connected to the engine throttle lever. The unit is shown in the reheat operative position and fuel passes from the inlet 110 to the shutoff valve 113 passing through the annular recess 117 in the valve member 114 to the chamber 123, through the valve sleeve 216 to the inlet 124 of the reheat fuel pump 125. Fuel is discharged from the pump into annular manifold 126, through the duct 138 which contains a pressurizing valve 139, to the metering valve 142. The fuel passes through the annular recess 167 in the valve member 143, through the metering orifices 165, the crosssectional area of which increases towards the right, and discharges through the line 160 which contains a pressurizing valve 159 to the reheat burners. Air at the compressor discharge pressure P 2  is passed through line 172 under the control of needle valve 171 to the left-hand end face of the metering valve member 143, while air at the engine jet pipe pressure P 4  is supplied through line 176 to the right-hand end face of the metering valve member 143. The right-hand end face of the valve member 143 is also acted on by a spring 180. The position of the metering valve member 143 and so the quantity of reheat fuel supplied to the burners is therefore dependent upon the valves of P 2  and P 4 , also on the position of the needle valve 171. The duct 172 conveying pressure P 2  is connected to the duct 176 conveying pressure P 4  by a duct containing a restriction 174. The metering valve member 143, also the sleeve valve 216, are arranged to be rotated continuously during operation by speed reduction gearing so as to prevent sticking. The sleeve valve 216 is positioned in dependence on the pressure drop across the metering orifice 165, so that the fuel flow through the pump inlet will be throttled in accordance with said pressure drop. The pressure drop is therefore maintained constant. The pressure at the discharge of the pump 125 is conveyed through line 206, through the annular recess 187 in the valve member 184 to the space 221 at the right-hand side of the piston 220 formed integral with the sleeve valve 216. The fuel pressure downstream of the metering orifice 165 is conveyed through duct 223 to the space at the left-hand side of the piston 220. The piston 220 is also loaded towards the right by the spring 222. The sleeve valve 216 therefore takes up a position which is dependent on the pressure drop across the metering orifice 165. When the solenoid valve 213 is energized, the valve 212 is opened against the force of spring 214 and the left-hand end face of the valve member 184 is placed in communication with the low pressure prevailing in the chamber 146, which chamber communicates with the fuel inlet 110 through line 149. The high pressure of fuel from the main engine fuel pump supplied through line 210 acts on the pressure face 186 of the valve member 184, and the valve member now moves to the left and the line 206 leading from the outlet of the pump 125 is now placed in communication through the annular recess 188 in the valve member 184, with the drain 207. At the same time the high pressure fuel in the line 210 will pass through the annular recess 187 in the valve member 184 to the space 221 at the right-hand face of the piston 220 and the sleeve valve 216 will therefore move to the left to close off the inlet 124 to the pump 125. When the shut-off valve 113 is actuated, that is, when the engine throttle lever is moved to a position corresponding to a speed of less than 14,000 r.p.m., the pinion 116 is rotated so as to move the valve member 114 to the right and the annular recess 117 is moved out of communication with the ports 121 so that fuel cannot pass from the inlet 110 to the inlet of the pump 125. Movement of the valve member 114 to the right also connects the pump outlet 126 to drain through the ducts 127, 132. Specifications 842,354, 914,105, and 983,831 are referred to.