Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2001-10-09
2003-02-25
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C123S468000, C123S469000, C138S118000
Reexamination Certificate
active
06523350
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates generally to fuel injectors, and more particularly, to fuel conduits for fuel injectors and the injectors for gas turbine engine combustors.
Fuel injectors, such as in gas turbine engines, direct pressurized fuel from a manifold to one or more combustion chambers. Fuel injectors also prepare the fuel for mixing with air prior to combustion. Each injector typically has an inlet fitting connected to the manifold, a tubular extension or stem connected at one end to the fitting, and one or more spray nozzles connected to the other end of the stem for directing the fuel into the combustion chamber. A fuel conduit or passage (e.g., a tube, pipe, or cylindrical passage) extends through the stem to supply the fuel from the inlet fitting to the nozzle. Appropriate valves and/or flow dividers can be provided to direct and control the flow of fuel through the nozzle. The fuel injectors are often placed in an evenly-spaced annular arrangement to dispense (spray) fuel in a uniform manner into the combustor chamber. An air cavity within the stem provides thermal insulation for the fuel conduit. A fuel conduit is needed that can be attached to a valve housing and to the nozzle. The fuel conduit should be tolerant of low cycle fatigue (LCF) stresses caused by stretching of the stem which houses the conduit and which undergoes thermal growth more than the cold conduit. The attachment of the conduit to the valve housing should be a reliable joint which doesn't leak during engine operation. Fuel leaking into the hot air cavity can cause detonations and catastrophic over pressures.
A fuel injector typically includes one or more heat shields surrounding the portion of the stem and nozzle exposed to the heat of the combustion chamber. The heat shields are used because of the high temperature within the combustion chamber during operation and after shut-down, and prevent the fuel from breaking down into solid deposits (i.e., “coking”) which occurs when the wetted walls in a fuel passage exceed a maximum temperature (approximately 400° F. (200° C.) for typical jet fuel). The coke in the fuel nozzle can build up and restrict fuel flow through the fuel nozzle rendering the nozzle inefficient or unusable. One such heat shield assembly is shown in U.S. Pat. No. 5,598,696 and includes a pair of U-shaped heat shield members secured together to form an enclosure for the stem portion of the fuel injector. At least one flexible clip member secures the heat shield members to the injector at about the midpoint of the injector stem. The upper end of the heat shield is sized to tightly receive an enlarged neck of the injector to prevent combustion gas from flowing between the heat shield members and the stem. The clip member thermally isolates the heat shield members from the injector stem. The flexibility of the clip member permits thermal expansion between the heat shield members and the stem during thermal cycling, while minimizing the mechanical stresses at the attachment points.
Another stem and heat shield assembly is shown in U.S. Pat. No. 6,076,356 disclosing a fuel tube completely enclosed in the injector stem such that a stagnant air gap is provided around the tube. The fuel tube is fixedly attached at its inlet end and its outlet end to the inlet fitting nozzle, respectively, and includes a coiled or convoluted portion which absorbs the mechanical stresses generated by differences in thermal expansion of the internal nozzle component parts and the external nozzle component parts during combustion and shut-down. Many fuel tubes also require secondary seals (such as elastomeric seals) and/or sliding surfaces to properly seal the heat shield to the fuel tube during the extreme operating conditions occurring during thermal cycling. Such heat shield assemblies as described above require a number of components, and additional manufacturing and assembly steps, which can increase the overall cost of the injector, both in terms of original purchase as well as a continuing maintenance. In addition, the heat shield assemblies can take up valuable space in and around the combustion chamber, block air flow to the combustor, and add weight to the engine. This can all be undesirable with current industry demands requiring reduced cost, smaller injector size (“envelope”) and reduced weight for more efficient operation. Because of limited fuel pressure availability and a wide range of required fuel flow, many fuel injectors include pilot and main nozzles, with only the pilot nozzles being used during start-up, and both nozzles being used during higher power operation. The flow to the main nozzles is reduced or stopped during start-up and lower power operation. Such injectors can be more efficient and cleaner-burning than single nozzle fuel injectors, as the fuel flow can be more accurately controlled and the fuel spray more accurately directed for the particular combustor requirement. The pilot and main nozzles can be contained within the same nozzle stem assembly or can be supported in separate nozzle assemblies. Dual nozzle fuel injectors can also be constructed to allow further control of the fuel for dual combustors, providing even greater fuel efficiency reduction of harmful emissions.
A typical technique for routing fuel through the stem portion of the fuel injector is to provide a fuel conduit having concentric passages within the stem, with the fuel being routed separately through different passages. The fuel is then directed through passages and/or annular channels in the nozzle portion of the injector to the spray orifice(s). U.S. Pat. No. 5,413,178, for example, discloses concentric passages where the pilot fuel stream is routed down and back along the main nozzle for cooling purposes. This can also require a number of components, and additional manufacturing and assembly steps, which can all be contrary to desirable cost and weight reduction and small injector envelope.
U.S. Pat. No. 6,321,541 addresses these concerns and drawbacks with a fuel injector that includes an inlet fitting, a stem connected at one end to the inlet fitting, and one or more nozzle assemblies connected to the other end of the stem and supported at or within the combustion chamber of the engine. A fuel conduit in the form of a single elongated laminated feed strip extends through the stem to the nozzle assemblies to supply fuel from the inlet fitting to the nozzle(s) in the nozzle assemblies. An upstream end of the feed strip is directly attached (such as by brazing or welding) to the inlet fitting without additional sealing components (such as elastomeric seals). A downstream end of the feed strip is connected in a unitary (one piece) manner to the nozzle. The single feed strip has convolutions along its length to provide increased relative displacement flexibility along the axis of the stem and reduce stresses caused by differential thermal expansion due to the extreme temperatures in the combustion chamber. This reduces or eliminates a need for additional heat shielding of the stem portion of the injector.
The laminate feed strip and nozzle are formed from a plurality of plates. Each plate includes an elongated, feed strip portion and a unitary head (nozzle) portion, substantially perpendicular to the feed strip portion. Fuel passages and openings in the plates are formed by selectively etching the surfaces of the plates. The plates are then arranged in surface-to-surface contact with each other and fixed together such as by brazing or diffusion bonding, to form an integral structure. Selectively etching the plates allows multiple fuel circuits, single or multiple nozzle assemblies and cooling circuits to be easily provided in the injector. The etching process also allows multiple fuel paths and cooling circuits to be created in a relatively small cross-section, thereby, reducing the size of the injector.
The feed strip portion of the plate assembly is mechanically formed such as by bending to provide the convoluted form. In one embodiment the pl
Mancini Alfred A.
Mueller Peter W.
Andes William Scott
Belena John F
Freay Charles G.
Rosen Steven J.
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