Patent GB-720015-A (GB)
Title: A fuel and scavenging-air supply system for engine-starting gas turbines
Inventor: FLEMING WILLIAM
IPC: F02C7/264
Filed: 1951-06-11
Abstract: 720,015. Ignition systems. LUCAS (INDUSTRIES), Ltd., J. Sept. 8, 1952 [June 11, 1951], No. 13774/51. Class 7 (4). [Also in Group XXVI] An electrical system for automatically controlling the action of electric motors for driving the fuel and scavenging pumps and the ignition apparatus of a gas turbine used as a starter motor is shown in Fig. 1. On closing the switch k the electromagnet n of a cycle time mechanism is energized. The electromagnet energizes a spring which actuates a cam or other mechanism for operating switches o, p, q. The switch o is in series with the switch k and is opened by the mechanism immediately after the spring is energized. The operation of the switch k also energizes the electromagnet m which holds the push button closed and the electromagnet j which opens the switch i and closes the switch h. The fuel pump motor b then starts up. When the pressure at the discharge of the pump a reaches a predetermined value it acts on a diaphram t and closes the switches r, s. The switch s energizes the ignition apparatus e, f and the switch r the electromagnet u of a switch v with which is associated a time delay (not shown). If no ignition occurs in the combustion chamber, the switch v opens after a pre-arranged time interval and causes the electromagnets j, m, to release the associated switches. In the meantime the switch p will have closed and current will be supplied to the scavenging air pump motor d when the switch i is re-closed. Later the cycle-time mechanism completes its action, causing switches o, p, q to resume their initial positions. The apparatus is then ready for re-starting. If ignition occurs immediately the switch w operated by the pressure in the combustion chamber is closed and holds the system in operation until either the pressure in the combustion chamber falls and switch w opens or the switch q is opened by the cycle-time mechanism. Opening of either of these switches de-energizes the electromagnets j, m and releases the switches i, h, k. As the switch p has in the meantine closed, the motor d will be energized and will continue to run until the cycle-time mechanism opens the switch p and the system reverts to the condition shown. A switch y operated by a governor z driven by the turbine may be used to override the switches q, w, and opens when a predetermined speed is reached to cause the switch i to be closed and the scavenging pump to be started up. In a modification, the switch i is arranged separately from the switch h and is provided with a separate electromagnet under the control of the switch p in the cycle-time mechanism which is also provided with additional switches which control the electrical supply to the ignition apparatus and to an electromagnet controlling a throttle valve in the discharge of the fuel pump. In this arrangement, operation of the push button k causes scavenging air to be supplied to the combustion chamber and subsequently the throttle valve is opened for admitting fuel to the combustion chamber which causes the ignition apparatus to be energized.