Method and apparatus for actively controlling fuel flow to a mixer assembly of a gas turbine engine combustor

1. An apparatus for actively controlling fuel flow from a fuel pump to a mixer assembly of a gas turbine engine combustor, said mixer assembly including a pilot mixer and a main mixer, wherein said pilot mixer further includes an annular pilot housing having a hollow interior, a primary fuel injector mounted in said pilot housing and adapted for dispensing droplets of fuel to said hollow interior of said pilot housing, and a plurality of axial swirlers positioned upstream from said primary fuel injector, said fuel flow control apparatus comprising:

(a) at least one sensor for detecting dynamic pressure in a combustion chamber of said combustor;

(b) a fuel nozzle including:

(1) a feed strip with a plurality of circuits wherein the feed strip comprises a first circuit for supplying fuel to a fuel tube that is in flow communication with said primary fuel injector, a second circuit for supplying fuel to a first fuel manifold that is in flow communication with said pilot mixer, and a third circuit for supplying fuel to a second fuel manifold that is in flow communication with said main mixer; and

(2) a plurality of valves associated with said fuel nozzle and in flow communication with said feed strip thereof; and,

(c) a system for actively controlling fuel flow supplied to said pilot mixer and said main mixer of said mixer assembly by said fuel nozzle, wherein said control system activates said valves in accordance with signals received from said pressure sensor.

2. The apparatus of claim 1 , further comprising a plurality of pressure sensors spaced circumferentially around said combustion chamber.

3. The apparatus of claim 1 , wherein said control system activates said valves to increase fuel flow to said pilot mixer.

4. The apparatus of claim 1 , wherein said control system activates said valves so that fuel is pulsed through said primary fuel injector of said pilot mixer.

5. The apparatus of claim 1 , wherein a signal from said pressure sensor is indicative of incipient lean blow out in said combustion chamber.

6. The apparatus of claim 5 , wherein said signal from said pressure sensor has a frequency within a specified range.

7. The apparatus of claim 6 , wherein said specified frequency range is approximately 40 Hertz to approximately 50 Hertz.

8. The apparatus of claim 1 , wherein a signal from said pressure sensor is indicative of an unacceptable level of dynamic pressure instability in said combustion chamber.

9. The apparatus of claim 8 , wherein said signal from said pressure sensor has an amplitude greater than a specified level.

10. The apparatus of claim 9 , wherein said signal from said pressure sensor has an amplitude of at least approximately 0.5 psi peak to peak.

11. The apparatus of claim 4 , wherein fuel is pulsed to said primary fuel injector in a manner opposite of any pressure instabilities experienced by said combustion chamber.

12. The apparatus of claim 4 , wherein fuel is pulse to said primary fuel injector in a manner which is a subharmonic of any pressure instabilities experienced by said combustion chamber.

13. The apparatus of claim 1 , said pilot mixer further comprising a plurality of secondary fuel injection ports for introducing fuel into said hollow interior of said pilot housing and said feed strip including a circuit for providing fuel to the first fuel manifold that is in flow communication with said secondary fuel injection ports of said pilot mixer.

14. The apparatus of claim 13 , wherein said control system activates said valves to increase fuel flow to said secondary fuel injection ports of said pilot mixer.

15. The apparatus of claim 13 , wherein said control system activates said valves to increase fuel flow to said primary injector of said pilot mixer.

16. The apparatus of claim 13 , wherein said control system activates said valves so that fuel is pulsed through said primary injector of said pilot mixer.

17. The apparatus of claim 13 , wherein said control system activates said valves so that fuel is pulsed through said secondary fuel injection ports of said pilot mixer.

18. The apparatus of claim 14 , wherein a signal from said pressure sensor is indicative of incipient lean blow out in said combustion chamber.

19. The apparatus of claim 18 , wherein said signal from said pressure sensor has a frequency within a specified range.

20. The apparatus of claim 19 , wherein said specified frequency range is approximately 40 Hertz to approximately 50 Hertz.

21. The apparatus of claim 14 , wherein a signal from said pressure sensor is indicative of an unacceptable level of dynamic pressure instability in said combustion chamber.

22. The apparatus of claim 21 , wherein said signal from said pressure sensor has an amplitude greater than a specified level.

23. The apparatus of claim 22 , wherein said signal from said pressure sensor has an amplitude of at least approximately 0.5 psi peak to peak.

24. The apparatus of claim 17 , wherein fuel is pulsed to said secondary fuel injection ports in a manner opposite of any pressure instabilities experienced by said combustion chamber.

25. The apparatus of claim 17 , wherein fuel is pulsed to said secondary fuel injection ports in a manner which is a subharmonic of any pressure instabilities experienced by said combustion chamber.

26. The apparatus of claim 14 , wherein said control system activates said valves so that a predetermined amount of fuel flows to said primary fuel injector and said secondary fuel injection ports.

27. The apparatus of claim 1 , wherein said control system activates said valves so that a predetermined amount of fuel flows through said fuel nozzle to said pilot mixer and said main mixer during specified fueling modes of said combustor.

28. The apparatus of claim 27 , wherein said control system activates said valves so that fuel flowing through said fuel nozzle is supplied only to said pilot mixer during a first fueling mode for said combustor.

29. The apparatus of claim 28 , wherein said control system activates said valves so that approximately 20% of fuel flowing through said fuel nozzle is supplied to said pilot mixer and approximately 80% is supplied to said main mixer during a second fueling mode for said combustor.

30. The apparatus of claim 29 , wherein said control system activates said valves so that approximately 8% of fuel flowing through said fuel nozzle is supplied to said pilot mixer and approximately 92% is supplied to said main mixer during a third fueling mode of said combustor.

31. The apparatus of claim 27 , wherein a lower limit for said fueling modes of said combustor is defined by when lean blow out occurs.

32. The apparatus of claim 27 , wherein an upper limit for said fueling modes of said combustor is defined by a fuel pump limit associated with said fuel nozzle.

33. The apparatus of claim of claim 27 , wherein a lower limit for said fueling modes of said combustor is defined by an efficiency limit.

34. The apparatus of claim 1 , wherein fuel is supplied to said pilot mixer and said main mixer by said fuel nozzle to obtain specified temperature ranges of said combustor.

35. The apparatus of claim 1 , wherein fuel is supplied from said fuel nozzle to said pilot mixer of only specified mixer assemblies of said combustor to offset localized pressure instabilities experienced by said combustion chamber.