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A method and system for providing fuel to primary and secondary fuel nozzles in a gas turbine engine fuel system comprises generating a fuel flow and routing primary fuel from the fuel flow to a primary fuel nozzle. Backpressure on the fuel flow is maintained using a valve. The valve is opened at in

A method and system for providing fuel to primary and secondary fuel nozzles in a gas turbine engine fuel system comprises generating a fuel flow and routing primary fuel from the fuel flow to a primary fuel nozzle. Backpressure on the fuel flow is maintained using a valve. The valve is opened at increased fuel flow to route secondary fuel from the fuel flow to a secondary fuel nozzle. The valve is progressively opened under increasing fuel flows to reduce a pressure drop across the valve produced by the secondary fuel.

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1. A fuel system for dividing fuel between primary and secondary nozzles in a gas turbine engine, the fuel system comprising: primary and secondary fuel nozzles coupled to a combustor in the gas turbine engine;a fuel pump that generates a fuel flow;a first flow divider valve that receives the fuel f

1. A fuel system for dividing fuel between primary and secondary nozzles in a gas turbine engine, the fuel system comprising: primary and secondary fuel nozzles coupled to a combustor in the gas turbine engine;a fuel pump that generates a fuel flow;a first flow divider valve that receives the fuel flow and divides fuel to the primary and secondary fuel nozzles, the first flow divider valve comprising: a valve housing having an inlet for receiving the fuel flow;means for providing primary fuel to the primary fuel nozzles comprising a spring-actuated piston valve disposed within the valve housing to maintain a backpressure in the fuel flow that routes the primary fuel through a first fuel line extending between the inlet and the primary nozzles; andmeans for providing secondary fuel to the secondary fuel nozzles while progressively decreasing the pressure drop across the means for providing the secondary fuel to the secondary fuel nozzles, the means for providing secondary fuel to the secondary fuel nozzles comprises: a window in the valve housing disposed along the piston to route the secondary fuel through a second fuel line; anda second flow divider valve disposed within the valve housing and coupled to the second fuel line and a plurality of outlets fluidly coupled to the secondary nozzles. 2. The fuel system of claim 1 wherein the means for providing secondary fuel to the secondary fuel nozzles is configured such that pressure drop across the means for providing the secondary fuel to the secondary fuel nozzles is negligible when the spring-actuated valve is fully open. 3. The fuel system of claim 1 and further comprising means for routing fuel flow to a cavity behind the piston. 4. The fuel system of claim 3 wherein the means for routing fuel flow to the cavity behind the piston comprises: a fuel passage extending through the piston. 5. The fuel system of claim 3 wherein the means for routing fuel flow to the behind the piston comprises: a fuel line connecting the fuel flow to the cavity behind the piston. 6. The fuel system of claim 1 and further comprising: a fuel tank from which the fuel pump receives fuel; anda fuel metering unit disposed between the fuel pump and the flow divider valve to deliver a metered flow of fuel to the flow divider valve and to return unused fuel to a fuel ecology system. 7. The fuel system of claim 6 and further comprising a drain line for connecting the means for providing secondary fuel to the fuel ecology system. 8. A fuel system for dividing fuel between primary and secondary nozzles in a gas turbine engine, the fuel system comprising: primary and secondary fuel nozzles coupled to a combustor in the gas turbine engine;a fuel pump that generates a fuel flow;a flow divider valve that receives the fuel flow and divides fuel to the primary and secondary fuel nozzles, the flow divider valve comprising: a valve housing having an inlet for receiving the fuel flow;a piston disposed within the housing to maintain a backpressure on the fuel flow;means for providing primary fuel to the primary fuel nozzles comprising: a spring-actuated valve that maintains a back pressure in the fuel flow; anda window in the housing fluidly coupled to a first fluid line extending to the primary nozzles, wherein the window is contoured to achieve a linear relationship between valve position and primary fuel flow;means for providing secondary fuel to the secondary fuel nozzles while progressively decreasing the pressure drop across the means for providing the secondary fuel to the secondary fuel nozzles, the means for providing secondary fuel to the secondary fuel nozzles comprises: a slot on the piston that is in fluid communication with the first fuel line and a second fuel line in communication with the secondary fuel nozzles, wherein the slot is contoured to permit a first secondary fuel flow rate over a first length of the slot and a second secondary fuel flow rate over a second length of the slot. 9. The fuel system of claim 8 and further comprising means for routing fuel flow to a cavity behind the piston. 10. The fuel system of claim 9 wherein the means for routing fuel flow to the cavity behind the piston comprises: a fuel passage extending through the piston. 11. The fuel system of claim 9 wherein the means for routing fuel flow to the behind the piston comprises: a fuel line connecting the fuel flow to the cavity behind the piston. 12. The fuel system of claim 8 and further comprising: a fuel tank from which the fuel pump receives fuel; anda fuel metering unit disposed between the fuel pump and the flow divider valve to deliver a metered flow of fuel to the flow divider valve and to return unused fuel to a fuel ecology system. 13. The fuel system of claim 12 and further comprising a drain line for connecting the means for providing secondary fuel to the fuel ecology system. 14. A fuel system for dividing fuel between primary and secondary nozzles in a gas turbine engine, the fuel system comprising: primary and secondary fuel nozzles coupled to a combustor in the gas turbine engine;a fuel pump that generates a fuel flow;a flow divider valve that receives the fuel flow and divides fuel to the primary and secondary fuel nozzles, the flow divider valve comprising: a valve housing having an inlet for receiving the fuel flow;a piston disposed within the housing to maintain a backpressure on the fuel flow;means for providing primary fuel to the primary fuel nozzles comprising: a spring-actuated valve that maintains a back pressure in the fuel flow; anda first window in the housing coupled to a first fuel line extending from the valve housing to the primary nozzles; andmeans for providing secondary fuel to the secondary fuel nozzles while progressively decreasing the pressure drop across the means for providing the secondary fuel to the secondary fuel nozzles, wherein the means for providing secondary fuel to the secondary fuel nozzles comprises: a second window in the housing coupled to a second fuel line extending from the valve housing to the secondary nozzles;a third window in the housing positioned between the first and second windows, the third window coupled to a third fuel line extending to a cavity behind the spring-actuated piston;a fixed orifice positioned on the piston to receive fuel from the cavity;a fourth fuel line extending from the cavity to the second fuel line; anda variable orifice positioned between the orifice and the fourth fuel line. 15. The fuel system of claim 14 and further comprising means for routing fuel flow to a cavity behind the piston. 16. The fuel system of claim 15 wherein the means for routing fuel flow to the cavity behind the piston comprises: a fuel passage extending through the piston. 17. The fuel system of claim 15 wherein the means for routing fuel flow to the behind the piston comprises: a fuel line connecting the fuel flow to the cavity behind the piston. 18. The fuel system of claim 14 and further comprising: a fuel tank from which the fuel pump receives fuel; anda fuel metering unit disposed between the fuel pump and the flow divider valve to deliver a metered flow of fuel to the flow divider valve and to return unused fuel to a fuel ecology system. 19. The fuel system of claim 18 and further comprising a drain line for connecting the means for providing secondary fuel to the fuel ecology system.