Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-11-12
2001-08-21
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S039300
Reexamination Certificate
active
06276141
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fuel injectors for gas turbine engines of aircraft, and more particularly to heatshield structures for the fuel injectors.
BACKGROUND OF THE INVENTION
Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel spray nozzle located within the combustion chamber of the engine for receiving the fuel, a fuel spray nozzle located within the combustion chamber of the engine for atomizing (dispensing) the fuel, and a housing stem extending between and fluidly interconnecting the inlet fitting and the fuel nozzle. Appropriate check valves and/or flow dividers can be disposed within the fuel nozzle to control the flow of fuel through the nozzle. The fuel injector has an attachment flange which enables multiple injectors to be attached to the combustor casing of the engine in a spaced-apart manner around the combustor to dispense fuel in a generally cylindrical pattern.
Fuel injectors are typically heatshielded because of the high operating temperatures within the engine casing. High temperature gas turbine compressor discharge air flows around the housing stem of the fuel injector before entering the combustor. The heat shielding prevents the fuel passing through the injector from breaking down into its constituent components (i.e., “coking”), which occurs when the wetted wall temperatures of a fuel passage exceed 400° F. The coke in the fuel passages of the fuel injector can build up to restrict fuel flow to the nozzle.
One type of heatshield assembly for a fuel injector has an internal heatshield disposed within the fuel passage of the housing stem. The internal heatshield comprises a straight fuel conduit which is rigidly attached at one end to either the fuel nozzle or the inlet fitting, and is left unattached at the other end to allow for differences in thermal expansion between the relatively cooler inner heatshield and the hotter outer housing stem. The unattached end has a small clearance within the bore of the stem which allows for fuel to enter the cavity between the heatshield and the internal walls of the housing stem. Over time, the fuel in this cavity cokes to provide an insulating layer between the housing stem and the fuel conduit. While this technique for heatshielding is appropriate for some applications, the insulating coke layer can take a number of engine cycles to form, and the resulting coke layer can migrate into the fuel stream, which can affect downstream fuel passages.
Another type of heatshield assembly for a fuel injector has an external heatshield around the housing stem. This heatshield typically includes a pair of outer U-shaped heatshield members which are located on opposite sides of the housing stem, and extend axially herealong. The heatshield members are secured together along their opposite abutting side edges, and to the housing stem, such as by welding or brazing. The heatshield members define a stagnant air gap between the heatshield members and the outer surface of the housing stem. It is believed that the stagnant air gap between the heatshield members provides better insulating characteristics than a coke or carbon-filled gap. While this type of heatshield assembly can also be appropriate in certain applications, the use of external heatshield members increases the number of components for the fuel injector, which thereby increases material costs, assembly time, and hence the overall cost of the fuel injector. There can also be issues with the attachment of the heatshield members to the housing stem because of the thermal expansion characteristics of the outer heatshield members. This can limit the useful life of the fuel injectors over constant engine cycling.
It is known to provide an internal heatshield comprising a straight fuel conduit with both ends of the conduit sealed to the housing stem. In this case, a stagnant air gap is created between the conduit and the internal walls of the housing stem. To compensate for the thermal expansion characteristics of the heatshield and the housing stem, it is known that at least one end of the conduit can include a metal bellows or a slip-fit attachment with one or more O-ring seals to allow for thermal expansion of the conduit with respect to the housing stem. The other end of the conduit is typically rigidly attached to the housing stem. It is believed that both ends have not been rigidly attached to the housing stem in the past because of concerns of early fatigue failures over repeated engine cycling due to the thermal expansion characteristics of the conduit. While the stagnant air gap provides better insulating characteristics than a coke or carbon-filled gap, it is believed that a leak path can develop over time around the O-rings, particularly at elevated temperatures. Using O-rings and metal bellows can also increase the number of components associated with the fuel injector, and can be complicated and time-consuming to assemble, thereby also increasing the over-all cost of the fuel injector.
Thus it is believed there is a demand in the industry for a further improved fuel injector for gas turbine engines which maintains fuel passage wetted wall temperatures within the housing stem below the coking threshold, which has few components which are relatively straight-forward to manufacture and assemble, and which maintains reliable, leak-free operation over multiple cycles of the aircraft engine.
SUMMARY OF THE INVENTION
The present invention provides a novel and unique fuel injector for a gas turbine engine of an aircraft, and more particularly, a novel and unique heatshield structure for the fuel injector.
According to the principles of the present invention, the fuel injector has an inlet fitting for receiving fuel, a fuel nozzle for dispensing fuel, and a housing stem fluidly interconnecting and supporting the fuel nozzle on the fitting. An internal heatshield assembly comprising an internal fuel conduit extends within a bore formed in the housing stem. An upper end of the fuel conduit has a rigid, fluid-tight connection with a fuel inlet passage in the fitting, while the lower end of the fuel conduit has a rigid, fluid-tight connection with the nozzle. The internal walls of the bore closely surround the fuel conduit and provide a stagnant air gap between the bore and the outer surface of the fuel conduit. To allow for thermal expansion of the fuel conduit, the fuel conduit has a coiled or otherwise convoluted portion within an enlarged cavity in the bore. The coiled portion of the fuel conduit is preferably at a location in the fuel injector which is exterior to the engine casing when the fuel injector is mounted to the engine. The bore can be completely enclosed with a vacuum drawn in the bore, or can be open at its lower end to the prefilmer and the air swirler in the fuel nozzle. The fuel injector can be easily assembled with the engine combustor by a flange extending outwardly from the housing stem, and easily disassembled for inspection or replacement.
The internal coiled fuel conduit can include only a single fuel flow passage from the fuel inlet to the nozzle, or alternatively, can include a pair of fuel flow passages from the inlet to the nozzle. In the latter case, a pair of concentric fuel tubes are provided, each of which has a rigid fluid-tight connection at an upper end with the inlet fitting to receive fuel from one or more fuel inlet passages in the fitting, and a rigid, fluid-tight connection at the lower end with the nozzle to provide the fuel to fuel discharge passages in the nozzle. The tubes are evenly spaced apart along the length of the fuel conduit.
The present invention thereby provides an improved fuel injector which has a heatshield assembly which maintains the fuel passage wetted wall temperatures at a minimum, has relatively few components which are straight-forward to assemble and manufacture, and provides-reliable, leak-free operation over re
Freay Charles G.
Gartenberg Ehud
Hunter Christopher H.
Parker-Hannifin Corporation
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