Abstract:
A fuel nozzle guide and method of assembly/disassembly is disclosed with the nozzle guide having a frusto-conical hub section, an annular base, a pair of retaining tabs for securing the guide to the outer wall of a combustor bulkhead for limited movement relative to the bulkhead, and a radial inflow swirler. The method of assembly/disassembly comprises assembling/disassembling the nozzle guide in the bulkhead from the outer wall (cold) side of the bulkhead and mechanically connecting/disconnecting the nozzle guide to/from the outer wall of the bulkhead with mechanical fasteners.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/114,018, filed Dec. 29, 1998. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to gas turbine engine combustors and more particularly to a fuel nozzle guide for use in such a combustor. 
     BACKGROUND OF THE INVENTION 
     Gas turbine engine combustors include combustion chambers wherein compressed air is mixed with fuel sprayed into the combustion chamber by a fuel nozzle which extends into the combustion chamber through a hole in the chamber bulkhead. The air-fuel mixture is burned thereby increasing the kinetic energy of the resulting gases through the engine to produce useful power for the engine turbine and thrust for the engine. 
     Typically, a multicomponent fuel nozzle guide for receiving a fuel nozzle extends through an aperture in the chamber bulkhead to maintain the fuel nozzle and nozzle guide in proper alignment with the various other combustion chamber components such as the igniter plug and various air inlet apertures. The nozzle guide also aids in the insertion of the nozzle for combustor assembly and maintenance. Such a nozzle guide usually includes various air apertures for cooling and mixing. The environment within a gas turbine engine is extremely harsh. The air-fuel mixture burns in the combustion chamber at temperatures as high as 2100° C. causing extreme thermal gradients and thermal stresses in the chamber walls. The nozzle guide typically moves with the nozzle and slides with respect to the bulkhead to accommodate thermal growth of the components which might occur at different rates for the components. 
     In prior nozzle guides such as disclosed in Butler et al., U.S. Pat. No. 5,419,115 issued May 30, 1995 for Bulkhead and Fuel Nozzle Guide Assembly For An Annular Combustion Chamber, the nozzle guide comprises two components. In assembling the nozzle guide in the bulkhead aperture, one component is inserted from the upstream (or “cold”) side of the bulkhead and the other component is inserted from the downstream (or “hot”) side. The two components are then welded together. The nozzle is thereafter inserted in the nozzle guide from the upstream side. Any service or repair on the combustor which includes removal of the nozzle guide will require the cutting apart of the two nozzle guide components. Suliga, U.S. Pat. No. 4,870,818 issued Oct. 3, 1989 for Fuel Nozzle Guide Structure and Retainer For A Gas Turbine Engine discloses a similar nozzle guide configuration. 
     It would be desirable to provide a nozzle guide which is attached to the cold side of the bulkhead rather than the harsh, hot side environment. It would also be desirable to provide a nozzle guide that does not require the manufacturing step of welding the nozzle components together during assembly. Further, to facilitate disassembly of the nozzle guide, it would be desirable to eliminate the necessity of a cutting operation. 
     In addition to mounting the nozzle, the nozzle guide may contribute to fuel mixing in the combustion chamber in particular engine applications. Gas turbine engines emit various pollutants including oxides of nitrogen (“NOx”). NOx is primarily formed through the thermal fixation of nitrogen and results from the high temperature combustion of fuel and air in the gas turbine engine. Environmental concerns and more stringent governmental regulation of NOx emissions have prompted designers to pursue various methods for reducing the generation of NOx by gas turbine engines. Two basic approaches for a low NOx fuel injection system are (1) a locally lean stoichiometry system and (2) a locally rich stoichiometry system. Both approaches require good atomization, mixing and uniformity in the fuel-air mixture. It would be desirable to provide a nozzle guide that complements nozzles of the radial inflow design and that contributes to improved atomization, mixing and/or uniformity in low Nox applications. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a new and improved fuel nozzle guide which affords ease of assembly and disassembly relative to the combustor bulkhead. 
     Another object of the invention is to provide an integral, one-piece nozzle guide that is mountable to the combustor bulkhead from one side. 
     A further object of the invention is to provide a nozzle guide that is attached to the cold side of the combustor bulkhead. 
     Another object is to provide an alternate embodiment of nozzle guide that can provide swirling air to the fuel-air spray from the nozzle. Included within this objective is the provision of a design that may be used to mount a nozzle of the type having a radial inflow swirler. 
     A further object is to provide a new and improved method of assembling a nozzle guide to a combustor bulkhead and disassembling the nozzle guide therefrom. 
     Other objects will be in part apparent and in part pointed out more in detail hereinafter. 
     Accordingly, it has been found that the foregoing and related objects and advantages are attained in a fuel nozzle guide having a frusto-conical hub section forming a central mounting aperture to receive a fuel nozzle, an annular base, a radial inflow swirler, and a pair of retaining tabs extending from the base for mounting to the outer bulkhead wall of a combustor. In one embodiment each tab has an elongated aperture to mount a bushing secured to the bulkhead wall so as to allow limited movement relative to the bulkhead. In another embodiment, each tab is configured to be received in a slot formed at the bulkhead wall by a retainer secured to the bulkhead wall so as to allow limited movement relative to the bulkhead. 
     In the method of the present invention, the nozzle guide is inserted into the bulkhead mounting aperture from the cold side of the bulkhead and mechanically secured to the bulkhead wall so as to allow predetermined limited movement relative to the bulkhead to accommodate thermal expansion during operation and fuel nozzle installation. In the method of disassembly, the nozzle guide is mechanically disconnected from the cold side of the bulkhead and withdrawn from the bulkhead mounting aperture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a broken away, partly sectional view of a nozzle guide in accordance with the present invention mounted in a combustor bulkhead. 
     FIG. 2 is an enlarged elevation view of the guide of FIG.  1 . 
     FIG. 3 is a sectional view seen on line  3 — 3  of FIG.  2 . 
     FIG. 4 is a broken away, enlarged elevation view seen on line  4 — 4  of FIG.  1 . 
     FIG. 5 is an elevation view of seen on line  5 — 5  of FIG.  4 . 
     FIG. 6 is a partly diagrammatic sectional view similar to FIG. 1 with a fuel nozzle mounted in the nozzle guide. 
     FIG. 7 is an enlarged elevation view of an alternate embodiment of the nozzle guide of the present invention. 
     FIG. 8 is a sectional view of a bushing for retaining the nozzle guide of FIG. 7 to the bulkhead. 
     FIG. 9 is a sectional side view, partly broken away, of the guide of FIG. 7 with a fuel nozzle mounted in the guide. 
     FIG. 10 is a partly diagrammatic sectional side view of the nozzle and guide assembly of FIG. 9 mounted in a gas turbine engine combustor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although specific forms of the present invention have been selected for illustration in the drawings, and the following description is drawn in specific terms for the purpose of describing these forms of the invention, the description is not intended to limit the scope of the invention which is defined in the appended claims. 
     Referring initially to FIG. 1, the nozzle guide of the present invention is generally designated by the numeral  10  and is shown mounted in the combustor head  12  of a combustion chamber of a gas turbine engine. 
     The combustion chamber includes an outer liner  14  which extends circumferentially about the axis of the engine and an inner liner (not shown) radially spaced therefrom to form a combustion zone  16  therebetween. The combustor head  12  is at the upstream end of the combustion chamber and includes a circumferentially extending dome  18  and a radially extending bulkhead  20  defining a region  15 . A plurality of fuel nozzles (not shown in FIG. 1) are spaced circumferentially about the interior of the engine with each nozzle extending into the combustor head and through the bulkhead  20  to deliver fuel to the combustion zone  16 . Each nozzle is received in a nozzle guide  10  which extends through an aperture  22  in the bulkhead. A heat shield  19  is disposed on the downstream or hot side surface  13  of bulkhead  20  about the aperture  22 . The heat shield has four bolt members extending axially to engage corresponding holes in the bulkhead. A plurality of additional heat shields  25  (only some of which are shown)are disposed about the interior of the combustion chamber. Additional detail concerning the combustion chamber structure may be found in Butler et al., U.S. Pat. No. 5,419,115 issued May 30, 1995 for Bulkhead and Fuel Nozzle Guide Assembly For An Annular Combustion Chamber which is incorporated herein by reference. 
     Referring to FIGS. 2 and 3, the nozzle guide  10  has a generally annular base  24  with an outwardly extending frusto-conical hub section  26  forming a central mounting aperture  28  dimensioned for snug slip-fit mounting of the head  30  of nozzle  32  (FIG.  6 ). The centerline of the guide (not shown) is concurrent with the centerline  34  of head  30  when it is mounted within the guide  10 . 
     The guide  10  includes a radial inflow swirler  36 . The swirler  36  has a frusto-conical air passage  38  formed in the hub section  26  concentric to centerline  34  (when nozzle head  30  is mounted in the guide  10 ) with an annular outlet end  40 . The outlet  40  is concentric about and adjacent to the outlet  42  of the swirler  44  of nozzle  32  when nozzle  32  is mounted in aperture  28  (FIG.  6 ). The inner end  46  of passage  38  is positioned in the annular base  24  and has a plurality of equi-spaced, circumferentially disposed air inlet ports  48 . The ports  48  open radially outwardly for the radial inflow of air into the passage  38 . As seen in FIG. 3, the frusto-conical passage  38  generally converges radially inwardly as the passage extends longitudinally from the inner end  46  to the outlet end  40  such that a progressively converging helical air pathway is followed by the swirled air. The swirled air from outlet  40  is directed into the fuel-air mixture from the nozzle head  30  producing a more uniform fuel-air mixture with rapid mixing. 
     The guide  10  also includes an additional air source into the fuel-air mixture in the form of a plurality of axial inflow air passages  50  in a flange portion  52  of base  24 . Each passage  50  has an inlet end  54  and an outlet end  56  (FIG. 3) and is disposed generally parallel to passage  38 , i.e., extending outwardly from the base and radially inwardly. The outlets  56  are disposed in a concentric array about the outlet  40  of swirler  36 . It is believed that air from the outlets purges the area about the nozzle and contributes to the mixing and flow of the fuel-air mixture. Alternately, the passages  50  can be disposed to provide some swirl to the discharged air. 
     The flange portion  52  of the base  24  has a planar surface  58  and a pair of radially-extending tabs  60 , 62  for retaining the guide in position within the bulkhead aperture. When the guide is mounted in assembly with the bulkhead  20 , the hub section  26  extends through the bulkhead aperture  22  with the array of air outlets  56  facing downstream and being disposed radially within the aperture  22 . The planar surface  58  has an annular area  64  radially outward from the array of air outlets that engages and rides on an upstream-facing annular pad or seal land  66  formed in the bulkhead  20  about the aperture  22  (FIG.  1 ). The start up pressure in the dome region  15  seats the annular area  64  against the annular pad for proper sealing between the guide and bulkhead. 
     Referring to FIGS. 4 and 5, the guide is retained to the bulkhead by pair of retainers or plates  68 , 70  so as to allow limited movement as described hereinafter. The retainers are positioned on opposed sides of the guide  10  generally orthogonal to the centerline  73  of aperture  22 . The retainer  68  is mounted to the upstream surface  72  of the bulkhead and has a stepped middle section  69  so as to form a slot  74  between the surface  72  and the section  69  which receives the tab  62 . Similarly, the retainer  70  has a stepped middle section  71  and is mounted to the surface  72  to form a slot  76  between the surface  72  and the section  71  to receive the tab  60 . The retainers  68 , 70  have bolt apertures (not shown) and are secured to the bulkhead by bolt members  21  and nuts  23  which also secure the heat shield  19  to the bulkhead. The slots  74 , 76  are dimensioned to receive the tabs  62 , 60  respectively and allow limited movement, i.e., the tabs  60 , 62  are deemed to “float” under the retainers  70 , 68  respectively. In the described embodiment, the bulkhead aperture  22  is dimensioned relative to the hub section  26  to allow the guide to move +/−0.180″ in the X direction and +/−0.200″ in the Y direction (as shown in FIG.  4 ). This gapping is desirable to allow for the considerations of detail part tolerances, fuel nozzle installation and thermal growth of the hardware during operation. The number of tabs and relative position may be varied according to application. 
     In assembling the guide  10  to the bulkhead  20 , the guide  10  is inserted through the aperture  17  in dome  18 . The aperture  17  is oblong to facilitate insertion, i.e., by tilting the guide and inserting it more or less sideways through the aperture  17  into the region  15 . The hub section  26  is positioned in the aperture  22  of the bulkhead such that the surface  58  of the flange portion  52  of the base  24  engages the raised pad  66  of the bulkhead. The guide is rotated so that the tabs  60 , 62  are generally aligned with the centerline  73 . The retainers  68 , 70  are then mounted on the bolt members  21  and secured with the nuts  23 . Welding is not required and simple hand tools (e.g., a wrench) may be utilized to secure the retainer and the guide in place. The head  30  of nozzle  32  is then inserted through aperture  17  in the dome and into the central aperture  28  of the guide  10  for snug, slip-fit mounting therein. 
     In disassembling for service or repair, the guide  10  is removed by first disengaging the nuts  23  from the bolt members  21 . Retainers  68 , 70  are then removed from the bolt members to free the guide from the bulkhead. The nozzle is first separated from the guide and the guide then removed from the bulkhead. Accordingly, disassembling for service or repair is easily and quickly accomplished without out the need for cutting. 
     Referring to FIG. 7, an alternate embodiment guide is shown and generally designated by the numeral  11  and wherein identical numerals are utilized to identify like or similar parts with guide  10 . The flange portion  52  has a pair of diametrically-opposed, radially-extending tabs  80 , 82 . Each tab  80 , 82  has an oblong aperture or slot  84 . In assembly, a bolt member  21  of a heat shield extends through each aperture  84  to secure the guide to the bulkhead. The bolt member  21  mounts a bushing  92  which is positioned in the slot  84  and secured by a nut  94 . Referring to FIG. 8, an example bushing is shown in cross section secured by the nut  94 . The apertures  84  and bushings  92  are dimensioned and positioned relative to the bulkhead to permit guide movement similar to the embodiment of FIG. 1, e.g., +/−0.080″ in the X direction, +/−0.200″ in the Y direction and +/−0.010″ in the Z direction. The limited movement in the X direction is attained from clearance between the bushing  92  and the aperture  84 . The limited movement in the Y direction is attained from the elongation dimension of the aperture  84 . The limited movement in the Z direction is attained from the clearance between the bushing and the nozzle guide. The retaining force of the nut and bushing must be sufficient to withstand any reverse flow conditions such as occurs during engine/compressor stall. Further, the guide  11  is sized to insure that the start-up pressure in the dome region  15  will be able to seat the guide  11  against the seal land of the bulkhead for proper sealing between the guide and the bulkhead. 
     Aerodynamically, the guide  11  is configured as guide  10  with an addition that each air inlet port  48  has an adjoining swirl vane surface  86  disposed at a predetermined swirl angle to impart swirl to the inflowing air. The angle of the vane surface determines the amount of swirl imparted to the inflowing air and the vane surfaces  86  may by positioned to provide either clockwise or counterclockwise swirl, i.e., co-swirl or counter-swirl relative to the swirl from the swirlers in the nozzle, depending upon application. 
     Referring to FIG. 10, the guide  11  is shown mounted in assembly with the nozzle  32 . The nozzle  32  is of the radial inflow swirler design having a radial inflow swirler  44  (in addition to an axial swirler  88 ). Referring to FIG. 9, an enlarged sectional view of the nozzle  32  is shown in assembly with the guide  11 . The ports  90  open radially outwardly for the radial inflow of air into the passage  96 . The passage  96  is an annular passage concentric to the centerline  104  with an outlet end  98  adjoining the fuel discharge outlet  100  and an inner end  102  connected to the ports  90 . As can be seen, the guide  11  is positioned downstream from the radial swirler inlet ports  90  so as not to interfere with air flow into the inlet ports  90 . Overall the guide  11  is aerodynamically configured to complement and contribute to the atomization and mixing action of the nozzle. A detailed description of the nozzle and operation is found in the commonly assigned U.S. patent application of Hoke et al., Ser. No. 000,897 filed Dec. 30, 1998 entitled Fuel Nozzle and Nozzle Guide For Gas Turbine Engine which is incorporated herein by reference. 
     As will be appreciated from the foregoing, a new and improved nozzle guide has been described which affords ease of assembly and disassembly without the need of welding or cutting respectively and which is mountable to the combustor bulkhead from one side. In this regard, a new and improved method of assembly/disassembly is also described. Further, an alternate embodiment can provide swirling air to the fuel-air spray from the nozzle to improve atomization, mixing and/or uniformity. 
     As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above-described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.