Patent GB-854167-A (GB)
Title: Improvements in combustion gas generators and fuel control systems therefor
IPC: F02C7/277
Filed: 1957-04-08
Abstract: 854,167. Gas turbines. UNITED AIRCRAFT CORPORATION. April 8, 1957 [April 9, 1956], No. 11353/57. Class 110 (3). A turbine-driven starter motor has a turbine supplied with working fluid by a combustion gas generator comprising a combustion chamber, a fuel pump, a normally closed valve in the conduit connecting the pump to the combustion chamber, electrical means for opening the valve, an electric motor for driving the fuel pump through a releasable driving connection, a start switch for energizing this electric motor, an electrically-operated igniter in the combustion chamber, and a second turbine for driving the fuel pump supplied with working fluid from the combustion chamber has a first switch circuit arranged to de-energize the electric motor, an auxiliary circuit associated with said first switch circuit, to energize the electrical means for opening the valve and a second switch circuit responsive to the pressure in the fuel conduit to energize the igniter which circuit includes a time delay switch operable to deenergize the igniter at the end of the time delay. A turbine-driven starter comprises a turbine 26 which drives an output shaft 30 through a reduction gear 18. The turbine is supplied with working fluid from a combustion chamber 14 which is supplied with a monofuel such as propyl nitrate ignited at starting, by an electricallyoperated igniter 20. Before the fuel is injected the combustion chamber is scavenged with air supplied by a blower 34 driven by an electric motor 38. The electric motor also drives a flywheel 42 and through a one-way clutch 44 a turbine 48 which is connected to the fuel pump 50. When the start button 74, Fig. 2, is closed the circuits of a timer motor 76 driving two timing cams 78, 80 and a relay 82 are energized. The relay 82 closes a switch 86 in the circuit of a relay coil 88 which circuit also includes a switch 90 operated by the cam 78. The motor 76 and cam 78 are so arranged that the switch 90 will be closed at a selected interval (say, half a second) after the switch 74 is closed. Closing of the switch 90 energizes the relay coil 88 and causes the switches 92, 94 to be closed. Closing of the switch 94 causes the relay coil 96 to be energized through the normally closed switches 98, 100, 106, and the holding coil 97 for the startbutton 74 to be energized through the switches 98, 100. The relay coil 96 closes the switch 104 which causes the motor 38 to be energized. The motor 38 drives the blower 34 to purge the combustion chamber 14 during an acceleration period of known duration, say three to five seconds. Near the end of this period, the cam 80 operates the switch 106 to open the circuit of the relay coil 96 and to close the circuit of a solenoid 108. The solenoid 108 opens the valve 56 and allows fuel to enter the combustion chamber 14. When the fuel pressure in the line 24 reaches a preselected level the pressureresponsive switch structure 72 causes a switch 84 to be operated to de-energize the relay coil 82 and to close a circuit through a contact 110 in the circuit of the igniter or spark-plug 20. An electrical time delay is incorporated in the switch 86 so that when coil 82 is de-energized, a time delay of, say, two seconds elapses before the switch 86 opens. When coil 88 is de-energized, switch 92 is opened to de-energize the igniter 20. During the time delay period, combustion occurs in the combustion chamber 14 with a consequent pressure rise in the combustion chamber and fuel line 24. This pressure rise causes the mechanism 72 to close the switch 112 which completes a second circuit to the solenoid 108 so that the valve 56 is kept open to allow the fuel supply to the combustion chamber to be maintained. If the fuel fails to ignite, the switch 112 remains open and when the switch 94 opens at the end of the time delay, the coil 108 is deenergized and the valve 56 closed. The holding coil 97 is also de-energized so that the startbutton 74 opens to de-energize all of the control circuits. At this point of operation, assuming that combustion has started, only the circuits through the timing motor 76, the solenoid 108 and the holding coil 97 are energized. The motor 38 is de-energized but the pump 50 operates on the energy stored in the flywheel 42. Part of the combustion gases then flow to the turbine 48 which maintains the pump 50 running. The switches 98, 100 are responsive to the speed of the drive-shaft 30 and turbine 26, respectively. In a modification, Fig. 3 (not shown), the motor 38 is de-energized by a switch responsive to the motor speed.