Combustion staging system

Abstract

A combustion staging system is provided for fuel injectors of a multi-stage combustor of a gas turbine engine. The system has a splitting unit which receives a metered total fuel flow and controllably splits the metered total fuel flow into out-going pilot and mains fuel flows to perform pilot-only and pilot-and-mains staging control of the combustor. The system further has pilot and mains fuel manifolds which respectively receive the pilot and mains fuel flows, the mains fuel manifold being split into a primary line and a servo line such that each line receives a respective portion of the mains fuel flow. The system further has a plurality of mains flow control valves which distribute the mains fuel flow from the mains fuel manifold to mains discharge orifices of respective injectors of the combustor, both the primary line and the servo line extending to the mains flow control valves before reuniting. The system further has a servo pump operable to change the pressure in the servo line relative to the pressure in the primary line. Each mains flow control valve has a chamber containing a movable piston, the chamber to a primary side of the piston being fed by the primary line, and the chamber to a servo side of the piston being fed by the servo line. The piston is biased towards a closed pilot-only position which prevents flow out of the primary side of the chamber to the mains discharge orifice of the respective injector. The piston is movable under an increase in pressure in the servo line relative to the primary line to an open pilot-and-mains position which allows flow out of the primary side of the chamber to the mains discharge orifice of the respective injector.