Patent GB-838641-A (GB)
Title: Improved combustion system particularly suitable for gas turbine starters
IPC: F02C7/277
Filed: 1956-09-05
Abstract: 838,641. Gas-turbine plant. RIDDING, J. W. (General Electric Co.). Sept. 5, 1956, No. 27177/56. Class 110 (3). [Also in Group XII] Fuel and a combustionsupporting fluid are supplied under pressure to a combustion chamber in a mixture of a predetermined richness during an ignition period and in a second predetermined richness and a greater quantity during a subsequent period. A starter turbine 2 is connected to the engine to be started through a clutch 4 of the over-riding or unidirectional type and is driven by combustion products from a combustion chamber 3. Operation is initiated by manually closing a switch 75, which is then held closed by a holding coil 63, to energize a solenoid 33 and the ignition circuit 83. In addition, a solenoid 35 is energized through a normally-closed thermal time switch 82. Solenoids 33, 35 open valves 32, 34 to allow air, oxygen or other combustion-supporting fluid to flow from a storage bottle 7 by way of a pressure-regulating valve 30, a metering orifice 31 and the valve 32 to the chamber 14 of a regulator valve 9, and from chamber 14 to atmosphere by way of a metering orifice 38. The pressure in chamber 14 thereby takes up a value sufficient to move a diaphragm 11 and valve stem 12 downwards to open an orifice 13 and allow air from the bottle 7 to flow through orifice 13, chamber 15 and line 8 to the combustion chamber 3. The pressure in chamber 15 opposes the pressure in chamber 14 acting on diaphragm 11, and the resultant position taken up by valve stem 12 maintains a constant pressure in the line 8 downstream of the regulator valve 9. The air pressure downstream of valve 32 acts through line 46 to open a fuel shut-off valve 44 and is exerted against the diaphragm 29 of a fuel accumulator 23 to force fuel through lines 40, 40a to the combustion chamber 3. The richness of the mixture of fuel and air entering the combustion chamber is of a value necessary for ignition. After a period of three seconds, during which ignition should have occurred, the time switch 82 opens, causing the valve 34 to close. This stops the flow through the metering orifice 38, causing the pressure in chamber 14 to rise and produce an increased deflection of the diaphragm 11, resulting in an increase in the pressure and quantity of the air supplied through line 8 to the combustion chamber 3. In addition, closure of valve 34 causes the pressure in a line 36 to drop to atmospheric pressure, so that a valve 45 which had been held closed by the pressure in line 36 opens to allow fuel to flow through a line 40b to the combustion chamber 3, in addition to the existing flow through line 40a, so that the pressure and quantity of the fuel supplied to the combustion chamber are increased. The resultant fuel-air mixture entering the combustion chamber 3 is of the reduced richness and increased quantity appropriate for normal running of the turbine 2. After an elapse of time sufficient for the turbine 2 to bring the driven engine up to its starting speed, a time switch 76 opens to interrupt the current and stop the turbine 2. If overspeeding of the turbine 2 occurs, a centrifugal governor 59 opens a switch 71 to stop the turbine before the time has elapsed. In either case, the interruption of the current breaks the holding circuit of the switch 75, causing it to open so that the current remains interrupted until the switch 75 is again manually closed. The accumulator 23 is supplied with fuel from a tank 42 through a non-return valve 43. The tank may be located at a point higher than the accumulator to permit gravity feed. The starting cycle can be terminated at the will of the operator by manually opening a switch 74.