Fuel injector heat shield

#The invention is directed to a method of inhibiting or completely preventing instability during operation of a gas turbine engine, instability being due to the uncontrolled interaction between the air filled gap defined by a heat shield and a fuel passage in a conventional fuel injector, particularly during low power operation.

#The invention relates to a method of inhibiting instability during operation of a gas turbine engine, where the instability is due to the uncontrolled interaction between the air filled gap defined by a heat shield and a fuel passage in a conventional fuel injector.

#Conventional fuel control systems are designed on the assumption that the fuel is incompressible and flows through a fixed volume conduit system to the injector tips. Therefore fuel control is based on supplying a known volume of incompressible fuel during a known time period.

#In order that the invention may be readily understood, one preferred embodiment of the invention will be described by way of example, with reference to the accompanying drawings wherein:

#FIG. 1 is a longitudinal cross-sectional view through a conventional fuel injector used in a gas turbine engine including an injector tip at the discharge end and an elongate stem with a tubular internal heat shield disposed within the fuel passage and spaced inwardly from the fuel passage thus defining an elongate annular air-filled thermal insulating gap between the fuel passage and the tubular heat shield.

#FIG. 2 is a detailed view of the end of the tubular internal heat shield illustrating the outward air-filled gap which serves as a thermal insulator to isolate the relatively cold fuel flowing through the internal heat shield from the fuel injector stem.

#FIG. 1 illustrates a longitudinal sectional view through a conventional fuel injector by which fuel is conveyed to the injector tip and sprayed into the combustor of the engine. Gas turbine engines include several elongate fuel injectors each having an injector stem 1 with an internal fuel passage 2 extending from an engine mount end 3 to an injector tip 4 at a discharge end 5.

#The injector stem 1 includes a tubular internal heat shield 6 disposed within the fuel passage 2. The heat shield 6 is secured to the fuel passage, by brazing for example, adjacent the mount end 3 and is spaced inwardly from the fuel passage 2 thus defining an elongate annular thermal insulating gap 7 between the fuel passage and the heat shield 6. The insulating gap 7 is used to thermally isolate the relatively hot injector stem 1 disposed within a flow of hot compressed air in the engine and the relatively cool fuel conducted through the heat shield 6 and fuel passage 2 into a plenum 8 in a downward direction as drawn in FIG. 1.

#The pressurized fuel from the plenum 8 is injected in a spray through the discharge end 5 into the engine combustor area (not shown) as atomized droplets thoroughly mixed with compressed air flowing through the central conduit 9 and orifices 10.