Gas turbine fuel injector with metering cavity

A method of operating a gas turbine engine including a fuel injector, the fuel injector including a fuel gallery extending circumferentially around the fuel injector, an annular casing positioned circumferentially around the fuel gallery to define an insulating chamber around the fuel gallery, and a metering chamber spaced apart from the insulating chamber and circumferentially extending around the fuel injector, the insulating chamber and the metering chamber being fluidly coupled together by one or more purge holes, and the metering chamber being fluidly coupled to a compressed air space external to the fuel injector by one or more metering holes, the method comprising:

• mixing a fuel with compressed air and directing the resulting fuel-air mixture along a fuel flow path of the fuel injector;
• directing compressed air from the compressed air space to the metering chamber through the one or more metering holes at a first velocity;
• directing the compressed air from the metering chamber to the insulating chamber through the one or more purge holes at a second velocity lower than the first velocity;
• and
• exhausting the compressed air from the insulating chamber to the fuel flow path of the fuel injector.

A gas turbine engine, comprising:

• a compressor;
• a combustor positioned downstream of the compressor;
• and
• a fuel injector fluidly coupling the compressor and the combustor, the fuel injector being configured to direct a fuel-air mixture to the combustor through a flow path that extends longitudinally though the fuel injector, the fuel injector including:
• a gallery for liquid fuel at least partially encircling the flow path;
• one or more spokes fluidly coupling the gallery to the flow path;
• an annular casing extending circumferentially around the fuel injector to define an insulating chamber around the gallery;
• an annular cover extending circumferentially around the fuel injector to define a metering chamber spaced apart from the insulating chamber;
• one or more purge holes fluidly coupling the insulating chamber and the metering chamber;
• and
• one or more metering holes fluidly coupling the metering chamber to a compressed air space around the fuel injector.