Patent GB-1411172-A (GB)
Title: Device for programmint the afterburning-initiation phase in a turbojet engine
IPC: F02K3/08
Filed: 1973-02-14
Abstract: 1411172 Gas turbine jet engine reheat control SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 14 Feb 1973 [18 Feb 1972] 7206/73 Heading F1J The invention relates to an arrangement for automatically controlling afterburner initiation in a gas turbine jet engine, the afterburner fuel being controlled by a metering device in dependence on a parameter #P2 where P2 is a compressor pressure such as compressor discharge pressure, and # is a coefficient less than one, there being means to modify the coefficient # so that it is reduced at least during the afterburner initiation phase, also means for automatically bringing the said means for modifying the coefficient # out of operation after the moment at which ignition of the afterburner fuel has occurred. A gas turbine jet engine with afterburner is shown in Fig. 1 and comprises an afterburner fuel pump 13, afterburner fuel metering device 17 and lines C, CR1, CR2, CR3 leading to fuel manifolds R1, R2, R3. Afterburner fuel also passes through line 27 to an afterburner ignition device 26 disposed in the main combustion equipment 2. Compressor discharge pressure P2 is directed through line 20 to a pressure reducer R, the reduced pressure #P 2  passing through line 22 to the fuel metering device 17. The engine is controlled by a lever M, the lever positions α1, α2 being non-afterburner positions and α3, α4, α5 being afterburner positions. An afterburner ignition detector 30 is provided. The pressure reducer R comprises a chamber 50 to which compressor discharge pressure P 2  is applied through line 20 and orifice 52, a further orifice 51 leading to atmosphere; the resulting pressure #P 2  is led to chamber 45 in which is disposed a bellows 46 which is connected to the fuel metering device 17. The arrangement shown in Fig.5 is modified in accordance with the invention as shown in Fig.6 in which the bellows 46 is disposed in a chamber 145 which is connected to the chamber 50 through an orifice 70 and which is connected to atmosphere through a further orifice 71 whereby the pressure in chamber 145 is #'P 2 , the coefficient #' being less than #; an electrically controlled valve ADF is disposed in the duct leading to the orifice 71, the valve being normally open but closed after afterburner initiation. The afterburner control system shown in Fig.7 is in accordance with the invention and automatically programmes afterburner fuel flow when the control lever is moved from the "dry" position α1 to the "full afterburner" position α5, such movement closing the switch 100, and opening the valve 80 in the air line 20 to the pressure reducer R. The transistor device 102 holds the circuit open until parameters X, Y such as engine rotational speed X and compressor discharge pressure Y attain values corresponding to the maximum "dry" operation; when these are attained the valve 19 is opened by the switch 65 and fuel flows to the afterburner pump 13 thence to the line 27 to the igniter device 26, also through the metering device 17 and line 15 to the afterburner manifolds R1, R2, R3. Current also flows through the switch 110 which is in the position shown, through the timed cut-out 120 to the electrically-controlled valve 29 which is thereby opened permitting fuel to pass to the igniter injector 26; this flow of fuel operates through a pressure sensitive device 64 to light a bulb 63 which indicates that fuel is passing to the igniter. The electrically-controlled valve ADF is in the open position so that the auxiliary pressure reducer 70, 145, 71 is in operation and the pressure in the chamber is the reduced pressure #'P 2 , so that a much reduced flow of after-burner fuel is passing from the metering device 17 to the line 15. Assuming that after burner ignition occurs, the detector 30 operates whereby current is passed through solenoid 111 so that the switch 110 is moved to its second position; thus the valve 29 is moved to its closed position stopping flow of fuel to the igniter injector 26; the signal lamp 63 is extinguished; the signal lamp 62 is lighted indicating that the afterburner is operating; and current passes through the timing device 130 to the electrically-controlled valve ADF which therefore closes so that the auxiliary pressure reducing device 70, 145, 71 no longer operates and the pressure in the chamber 145 returns to #'P 2 . Should after burner ignition not occur, the timing device 120 closes the valve 29 after a period of say 8 seconds, to prevent damage to the turbine. The timing device 130 causes a delay say 1.5 seconds, in the closing of the valve ADF so that the afterburner fuel flow is maintained at the reduced amount for a short period until after burning is stabilized.