Fuel-air mixture distribution for gas turbine engine combustors

1. A fuel system for a gas turbine engine comprising:

a plurality of duplex fuel nozzles;

a plurality of simplex fuel nozzles, wherein said plurality of duplex fuel nozzles and said plurality of simplex fuel nozzles are arranged in alternating groups in a combustor and circumferentially around a central engine axis, said alternating groups defining local circumferential zones in said combustor;

a primary fuel manifold operable to communicate fuel to a primary flow jet in each of said plurality of duplex fuel nozzles;

a secondary fuel manifold operable to communicate fuel to a secondary flow jet in each of said plurality of duplex fuel nozzles and a secondary flow jet in each of said plurality of simplex nozzles;

a flow divider valve operable to proportion fuel flow to said primary fuel manifold and said secondary fuel manifold; and

an equalizer valve downstream of the flow divider valve and in communication with said primary fuel manifold and said secondary fuel manifold, said equalizer valve movable between an open position and a closed position, said closed position operable to permit supply of said primary fuel manifold with greater fuel pressure than said secondary fuel manifold and said open position operable to permit supply of said primary fuel manifold with essentially an equal fuel pressure as said secondary fuel manifold such that different fuel-air ratios are provided to said local circumferential zones.

2. The fuel system as recited in claim 1 , wherein said plurality of duplex fuel nozzles are arranged with respect to a fuel igniter.

3. The fuel system as recited in claim 1 , wherein at least one of said plurality of duplex fuel nozzles is arranged circumferentially opposite a fuel igniter.

4. The fuel system as recited in claim 1 , wherein said primary flow jet in each of said plurality of duplex fuel nozzles is surrounded by said secondary flow jet.

5. The fuel system as recited in claim 1 , wherein one of the groups of said plurality of duplex fuel nozzles is arranged circumferentially adjacent to a fuel igniter and another of the groups of said plurality of duplex fuel nozzles is arranged circumferentially opposite said fuel igniter.

6. The fuel system as recited in claim 1 , wherein said primary flow jet is defined along a fuel nozzle axis and said secondary flow jet is transverse to said fuel nozzle axis.

7. The fuel system as recited in claim 1 , wherein said equalizer valve bridges said primary fuel manifold and said secondary fuel manifold.

8. A method of noise control from a combustor of a gas turbine engine comprising:

proportioning fuel flow to a primary fuel manifold and a secondary fuel manifold using a flow diverter valve;

forming a plurality of local circumferential zones with different fuel-air ratios within the combustor using an equalizer valve located downstream of said flow diverter valve; and

alternating a plurality of duplex fuel nozzles and a plurality of simplex fuel nozzles to define the plurality of local circumferential zones.

9. The method as recited in claim 8 , further comprising: alternating the local circumferential zones with varied fuel-air ratios.

10. The method as recited in claim 9 , further comprising: forming the local circumferential zones as a high-low-high-low local fuel-air ratios.

11. The method as recited in claim 8 , further comprising:

locating at least one of the plurality of duplex fuel nozzles adjacent to a fuel igniter to form at least one high local fuel-air ratio within at least one of the plurality of local circumferential zones.

12. The method as recited in claim 11 , further comprising:

locating at least one of the plurality of duplex fuel nozzles opposite the fuel igniter to form at least one high local fuel-air ratio within a t least one of the plurality of local circumferential zones.

13. The method as recited in claim 8 , further comprising:

equalizing a fuel pressure between the primary fuel manifold and the secondary fuel manifold, the primary fuel manifold in communication with a primary flow jet in each of the plurality of duplex fuel nozzles and the secondary fuel manifold in communication with a secondary flow jet in each of the plurality of duplex fuel nozzles and a secondary flow jet in each of the plurality of simplex nozzles.

14. The method as recited in claim 13 , further comprising:

opening a valve between the primary fuel manifold and the secondary fuel manifold.

15. The method as recited in claim 8 , further comprising:

dividing a fuel pressure between the primary fuel manifold and the secondary fuel manifold, the primary fuel manifold in communication with a primary flow jet in each of the plurality of duplex fuel nozzles and the secondary fuel manifold in communication with a secondary flow jet in each of the plurality of duplex fuel nozzles and a secondary flow jet in each of the plurality of simplex nozzles.

16. The method as recited in claim 15 , further comprising:

closing a valve between the primary fuel manifold and the secondary fuel manifold.

17. The method as recited in claim 15 , further comprising:

forming the plurality of local circumferential zones with varied fuel-air ratios within the combustor in response to a low power condition.

18. The method as recited in claim 8 , further comprising:

locating one of the plurality of duplex fuel nozzles to be circumferentially adjacent to a fuel igniter and another of the plurality of duplex fuel nozzles to be circumferentially opposite said fuel igniter.

19. The method as recited in claim 8 , wherein the equalizer valve bridges the primary fuel manifold and the secondary fuel manifold.