1. Field of the Invention
The present invention relates generally to gas turbine engine combustor fuel injectors and, more particularly, such fuel injectors for use in staged fuel supply systems.
In order to lower emissions, gas turbine engines are using lean burning combustors which require turning on and off independent fuel circuits over a range of operating conditions including engine power level and environmental conditions. This is often referred to as fuel staging and is required to keep a local fuel/air ratio of the engine within a narrow range defined at its upper limit by NOx emissions and at its lower limit by a flame-out boundary.
Current engines use multiple individually controlled centralized staging valves with multiple fuel supply manifolds which deliver fuel to the fuel nozzles. There is one fuel supply manifold for each stage, thus, each fuel nozzle has multiple fuel supply connections, one for each stage. In order to prevent coking, fuel must be either drained from or continuously circulated in the unstaged manifold. These multi-manifold fuel systems are cumbersome and require many looped or bent fuel supply tubes of multiple shapes and sizes to feed the differential staged fuel nozzles. It is desirable to have a fuel system with a single fuel manifold and a fuel injector containing the differential staged fuel nozzles.
Fuel systems with multiple centralized staging valves are expensive and engine designers are always striving to build more reliable fuel systems with better operability response. Centralized staging fuel systems exhibit droop in speed during acceleration because unstaged fuel manifolds in such systems must be pressurized and empty volumes filled before fuel flow is attained in the circuit. It is highly desirable to reduce speed droop.
Fuel injectors, such as in gas turbine engines, direct pressurized fuel from a manifold to one or more combustion chambers. Fuel injectors also prepare the fuel for mixing with air prior to combustion. Each injector typically has an inlet fitting connected to the manifold, a tubular extension or stem connected at one end to the fitting, and one or more spray nozzles connected to the other end of the stem for directing the fuel into the combustion chamber. A fuel conduit or passage (e.g., a tube, pipe, or cylindrical passage) extends through the stem to supply the fuel from the inlet fitting to the nozzle. Appropriate valves and/or flow dividers can be provided to direct and control the flow of fuel through the nozzle. The fuel injectors are often placed in an evenly-spaced annular arrangement to dispense (spray) fuel in a uniform manner into the combustor chamber.
2. Brief Description of the Invention
A multi-staged gas turbine engine fuel supply system fuel injector includes at least first and second staged fuel injection circuits. Each of the first and second staged fuel injection circuits has first and second fuel injection points and at least first and second fuel nozzle valves controllably connected to the first and second staged fuel injection circuits, respectively. The first and second fuel nozzle valves are operable to open at different first and second crack open pressures, respectively. The first and second fuel nozzle valves are located in a valve housing of the injector which includes a single fuel supply connector connected in fuel supply relationship with the first and second fuel nozzle valves and a single fuel signal connector connected in pressure supply relationship with the first and second fuel nozzle valves.
In one embodiment of the fuel injectors, the first fuel injection points of the first staged fuel injection circuits are tip orifices in a fuel injector tips of pilot nozzles of the fuel injectors. The second fuel injection points of the second staged fuel injection circuits are spray orifices in main nozzles of the fuel injectors. The system may further include third staged fuel injection circuits having third fuel injection points in the fuel injectors. The third fuel injection points may also be in the main nozzles of the fuel injectors.