COMBUSTION STAGING SYSTEM

A combustion staging system for fuel injectors of a multi-stage combustor of a gas turbine engine. The system includes plural fuel injectors, each having respective pilot and mains injection stages. The system further includes a splitting unit which, to perform staging control of the combustor, receives a metered fuel flow and, for pilot and mains operation, controllably splits the received fuel flow into a pilot flow for injecting at the pilot stages of the injectors and a mains flow for injecting at the mains stages of the injectors, and for pilot-only operation, controllably splits the received fuel flow into a first part of the pilot flow for injecting at the pilot stages of a first portion of the injectors and a second part of the pilot flow for injecting at the pilot stages of a second portion of the injectors. The system further includes pilot and mains fuel manifolds distributing respective fuel flows from the splitting unit to the injectors. Each of the fuel injectors has a respective first solenoid valve which is movable between (i) a pilot-only operation position which shuts off the mains fuel manifold from the injector's mains stage, and (ii) a pilot and mains operation position which opens a path from the mains fuel manifold to the injector's mains stage. The system further includes additional solenoid valve means which is configured such that (i) for each injector of the first portion of the fuel injectors during pilot-only operation the pilot fuel manifold is shut off from the injector's pilot stage, and a path is opened from the mains fuel manifold to the injector's pilot stage, and (ii) for each injector of the first portion of the fuel injectors during pilot and mains operation a path is opened from the pilot fuel manifold to the injector's pilot stage, and the mains fuel manifold is shut off from the injector's pilot stage. Each injector of the second portion of the fuel injectors has a path from the pilot fuel manifold to the injector's pilot stage. The splitting unit is operable to direct the first part of the pilot flow into the mains fuel manifold and the second part of the pilot flow into the pilot fuel manifold for pilot-only operation, and is operable to direct the pilot flow into the pilot fuel manifold and the mains flow into the mains fuel manifold for pilot and mains operation.