Patent Publication Number: US-7908863-B2

Title: Fuel nozzle for a gas turbine engine and method for fabricating the same

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to combustion systems for use with gas turbine engines and, more particularly, to fuel nozzles used with gas turbine engines. 
     Conventional gas turbine engines include secondary fuel nozzle assemblies that direct fuel into a flow of combustion gases that moves through a combustor assembly in a downstream direction along the secondary fuel nozzle. Some secondary fuel nozzle assemblies include fuel pegs that extend into the flow of combustion gases to facilitate directing the fuel into the combustion gas flow. In these conventional secondary fuel nozzle assemblies, the fuel pegs form openings that are oriented in the downstream direction to facilitate mixing the fuel with the flow of combustion gases as the combustion gases travel across the fuel pegs. As the fuel is directed into the flow of combustion gases, the fuel is carried with the combustion gases. However, in some conventional gas turbine engines, the fuel is not dispersed throughout the combustion gases but rather flows as a separate stream within the combustion gases. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method for fabricating a secondary fuel nozzle assembly is provided. The method includes providing a nozzle portion defining a passageway configured to supply fuel. At least one peg is operatively coupled in fuel flow communication with the passageway. The at least one peg extends radially outward from the nozzle portion and defines at least one opening configured to direct a flow of fuel in a substantially upstream direction. A disc is positioned about the nozzle portion upstream of the at least one peg. The disc is positioned in communication with the at least one opening and configured to interfere with the flow of fuel to facilitate fuel atomization. 
     In another aspect, a secondary fuel nozzle assembly is provided. The secondary fuel nozzle assembly includes a nozzle portion and at least one peg extending radially outward from the nozzle portion. The at least one peg defines at least one opening configured to direct a flow of fuel in a substantially upstream direction. A disc is positioned about the nozzle portion upstream of the at least one peg. The disc is positioned in flow communication with the at least one opening and configured to interfere with the flow of fuel to facilitate fuel atomization. 
     In another aspect, a combustor assembly for use with a gas turbine engine is provided. The combustor assembly includes a combustor liner defining a primary combustion zone and a secondary combustion zone. The combustor liner is configured to direct a flow of combustion gases substantially in a downstream direction. A primary fuel nozzle assembly extends into the primary combustion zone and a secondary fuel nozzle assembly extends through the primary combustion zone and into the secondary combustion zone. The secondary fuel nozzle assembly includes a nozzle portion and at least one peg extending radially outward from the nozzle portion. The at least one peg defines at least one opening configured to direct a flow of fuel in an upstream direction opposing the downstream direction. A disc is positioned about the nozzle portion upstream of the at least one peg, and configured to interfere with the flow of fuel to facilitate fuel atomization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is partial cross-sectional view of an exemplary gas turbine combustion system. 
         FIG. 2  is a cross-sectional view of an exemplary fuel nozzle assembly that may be used with the gas turbine combustion system shown in  FIG. 1 . 
         FIG. 3  is a partial view of the exemplary fuel nozzle assembly shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is partial cross-sectional view of an exemplary gas turbine engine  100  that includes a secondary fuel nozzle assembly  200 . Gas turbine engine  100  includes a compressor (not shown), a combustor  102 , and a turbine  104 . Only a first stage nozzle  106  of turbine  104  is shown in  FIG. 1 . In the exemplary embodiment, the turbine is rotatably coupled to the compressor with rotors (not shown) that are coupled together via a single common shaft (not shown). The compressor pressurizes inlet air  108  prior to it being discharged to combustor  102  wherein it cools combustor  102  and provides air for the combustion process. More specifically, air  108  channeled to combustor  102  flows in a direction generally opposite to the flow of air through gas turbine engine  100 . In the exemplary embodiment, gas turbine engine  100  includes a plurality of combustors  102  that are spaced circumferentially about an engine casing (not shown). In one embodiment, combustors  102  are can-annular combustors. 
     In the exemplary embodiment, gas turbine engine  100  includes a transition duct  110  that extends between an outlet end  112  of each combustor  102  and an inlet end  114  of turbine  104  to channel combustion gases  116  into turbine  104 . Further, in the exemplary embodiment, each combustor  102  includes a substantially cylindrical combustor casing  118 . Combustor casing  118  is coupled to the engine casing using bolts (not shown), mechanical fasteners (not shown), welding, and/or any other suitable coupling means that enables gas turbine engine  100  to function as described herein. In the exemplary embodiment, a forward end  120  of combustor casing  118  is coupled to an end cover assembly  122 . End cover assembly  122  includes supply tubes, manifolds, valves for channeling gaseous fuel, liquid fuel, air and/or water to the combustor, and/or any other components that enable gas turbine engine  100  to function as described herein. 
     In the exemplary embodiment, a substantially cylindrical flow sleeve  124  is coupled within combustor casing  118  such that flow sleeve  124  is substantially concentrically aligned with combustor casing  118 . A combustor liner  126  is coupled substantially concentrically within flow sleeve  124 . More specifically, combustor liner  126  is coupled at an aft end  128  to transition duct  110 , and at a forward end  130  to a combustor liner cap assembly  132 . Flow sleeve  124  is coupled at an aft end  134  to an outer wall  136  of combustor liner  126  and coupled at a forward end  138  to combustor casing  118 . Alternatively, flow sleeve  124  may be coupled to casing  118  and/or combustor liner  126  using any suitable coupling assembly that enables gas turbine engine  100  to function as described herein. In the exemplary embodiment, an air passage  140  is defined between combustor liner  126  and flow sleeve  124 . Flow sleeve  124  includes a plurality of apertures  142  defined therein that enable compressed air  108  from the compressor to enter air passage  140 . In the exemplary embodiment, air  108  flows in a direction that is opposite to a direction of core flow (not shown) from the compressor towards end cover assembly  122 . 
     Combustor liner  126  defines a primary combustion zone  144 , a venturi throat region  146 , and a secondary combustion zone  148 . More specifically, primary combustion zone  144  is upstream from secondary combustion zone  148 . Primary combustion zone  144  and secondary combustion zone  148  are separated by venturi throat region  146 . Venturi throat region  146  has a generally narrower diameter D v  than the diameters D 1  and D 2  of respective combustion zones  144  and  148 . More specifically, throat region  146  includes a converging wall  150  and a diverging wall  152 . Converging wall  150  tapers from diameter D 1  to D v  and diverging wall  152  widens from D v  to D 2 . As such, venturi throat region  146  functions as an aerodynamic separator or isolator to facilitate reducing flashback from secondary combustion zone  148  to primary combustion zone  144 . In the exemplary embodiment, primary combustion zone  144  includes a plurality of apertures  154  defined therethrough that enable air  108  to enter primary combustion zone  144  from air passage  140 . 
     Further, in the exemplary embodiment, combustor  102  also includes a plurality of spark plugs (not shown) and a plurality of cross-fire tubes (not shown). The spark plugs and cross-fire tubes extend through ports (not shown) defined in combustor liner  126  within primary combustion zone  144 . The spark plugs and cross-fire tubes ignite fuel and air within each combustor  102  to create combustion gases  116 . 
     In the exemplary embodiment, at least one secondary fuel nozzle assembly  200  is coupled to end cover assembly  122 . More specifically, in the exemplary embodiment, combustor  102  includes one secondary fuel nozzle assembly  200  and a plurality of primary fuel nozzle assemblies  156 . More specifically, in the exemplary embodiment, primary fuel nozzle assemblies  156  are arranged in a generally circular array about a centerline  158  of combustor  102 , and a centerline  201  (shown in  FIG. 2 ) of secondary fuel nozzle assembly  200  is substantially aligned with combustor centerline  158 . Alternatively, primary fuel nozzle assemblies  156  may be arranged in non-circular arrays. In an alternative embodiment, combustor  102  may include more or less than one secondary fuel nozzle assembly  200 . Although, only primary fuel nozzle assembly  156  and secondary fuel nozzle assembly  200  are described herein, more or less than two types of nozzle assemblies, or any other type of fuel nozzle, may be included in combustor  102 . In the exemplary embodiment, secondary fuel nozzle assembly  200  includes a tube assembly  160  that substantially encloses a portion of secondary fuel nozzle assembly  200  that extends through primary combustion zone  144 . 
     Primary fuel nozzle assemblies  156  partially extend into primary combustion zone  144 , and secondary fuel nozzle assembly  200  extends through primary combustion zone into an aft portion  162  of throat region  146 . As such, fuel (not shown) injected from primary fuel nozzle assemblies  156  is combusted substantially within primary combustion zone  144 , and fuel (not shown) injected from secondary fuel nozzle assembly  200  is combusted substantially within secondary combustion zone  148 . 
     In the exemplary embodiment, combustor  102  is coupled to a fuel supply (not shown) for supplying fuel to combustor  102  through fuel nozzle assemblies  156  and/or  200 . For example, pilot fuel (not shown) and/or main fuel (not shown) may be supplied through fuel nozzle assemblies  156  and/or  200 . In the exemplary embodiment, both pilot fuel and main fuel are supplied through both primary fuel nozzle assembly  156  and secondary fuel nozzle assembly  200  by controlling the transfer of fuels to primary fuel nozzle assembly  156  and secondary fuel nozzle assembly  200 , as described in more detail below. As used herein “pilot fuel” refers to a small amount of fuel used as a pilot flame, and “main fuel” refers to the fuel used to create the majority of combustion gases  116 . Fuel may be natural gas, petroleum products, coal, biomass, and/or any other fuel, in solid, liquid, and/or gaseous form that enables gas turbine engine  100  to function as described herein. By controlling fuel flows through fuel nozzle assemblies  156  and/or  200 , a flame (not shown) within combustor  102  may be adjusted to a pre-determined shape, length, and/or intensity to effect emissions and/or power output of combustor  102 . 
     In operation, air  108  enters gas turbine engine  100  through an inlet (not shown). Air  108  is compressed in the compressor and compressed air  108  is discharged from the compressor towards combustor  102 . Air  108  enters combustor  102  through apertures  142  and is channeled through air passage  140  towards end cover assembly  122 . Air  108  flowing through air passage  140  is forced to reverse its flow direction at a combustor inlet end  164  and is channeled into combustion zones  144  and/or  148  and/or through throat region  146 . Fuel is supplied into combustor  102  through end cover assembly  122  and fuel nozzle assemblies  156  and/or  200 . Ignition is initially achieved when a control system (not shown) initiates a starting sequence of gas turbine engine  100 , and the spark plugs are retracted from primary combustion zone  144  once a flame has been continuously established. At aft end  128  of combustor liner  126 , hot combustion gases  116  are channeled through transition duct  110  and turbine nozzle  106  towards turbine  104 . 
       FIG. 2  is a cross-sectional view of an exemplary secondary fuel nozzle assembly  200  that may be used with combustor  102  (shown in  FIG. 1 ).  FIG. 3  is a partial sectional view of a portion of secondary fuel nozzle assembly  200 . 
     In the exemplary embodiment, secondary fuel nozzle assembly  200  includes head portion  202  and a nozzle portion  204  described in greater detail below. Head portion  202  enables secondary fuel nozzle assembly  200  to be coupled within combustor  102 . For example, in one embodiment, head portion  202  is coupled to end cover assembly  122  (shown in  FIG. 1 ) and is secured thereto using a plurality of mechanical fasteners  168  (shown in  FIG. 1 ) such that head portion  202  is external to combustor  102  and nozzle portion  204  extends through end cover assembly  122 . In the exemplary embodiment, head portion  202  includes a plurality of circumferentially-spaced openings  205  that are each sized to receive a mechanical fastener therethrough. Head portion  202  may include any suitable number of openings  205  that enable secondary fuel nozzle assembly  200  to be secured within combustor  102  and to function as described herein. Moreover, although an inner surface  206  of each opening  205  is shown as being substantially smooth, openings  205  may be threaded. In addition, although each opening  205  is shown as extending substantially parallel to centerline  201  of secondary fuel nozzle assembly  200 , openings  205  may have any orientation that enables secondary fuel nozzle assembly  200  to function as described herein. Alternatively, head portion  202  is not limited to being coupled to combustor  102  using only mechanical fasteners  168 , but rather may be coupled to combustor  102  using any coupling means that enables secondary fuel nozzle assembly  200  to function as described herein. 
     In the exemplary embodiment, head portion  202  is substantially cylindrical and includes a first substantially planar end face  207 , an opposite second substantially planar end face  208 , and a substantially cylindrical body  210  extending therebetween. 
     Head portion  202  includes, in the exemplary embodiment, a center passageway  214  and a plurality of concentrically aligned channels  216 ,  218 , and  220 . More specifically, center passageway  214  extends from first end face  207  to second end face  208  along centerline  201 . Further, in the exemplary embodiment, channels  216 ,  218 , and  220  each extend partially from second end face  208  towards first end face  207 , as described in more detail below. 
     In the exemplary embodiment, a plurality of concentrically aligned channel divider walls  222 ,  224 , and  226  in head portion  202  define center passageway  214 , channels  216 ,  218 , and  220 . More specifically, in the exemplary embodiment, center passageway  214  is defined by a first divider wall  222 , first channel  216  is defined between first divider wall  222  and a second divider wall  224 , second channel  218  is defined between second divider wall  224  and a third divider wall  226 , and third channel  220  is defined between third divider wall  226  and body  210 . 
     In the exemplary embodiment, head portion  202  also includes a plurality of radial inlets. A first radial inlet  228  extends through body  210  to center passageway  214 , a second radial inlet (not shown) extends through body  210  to first channel  216 , a third radial inlet  230  extends through body  210  to second channel  218 , and a fourth radial inlet (not shown) extends through body  210  to third channel  220 . Although in the exemplary embodiment only one radial inlet is in flow communication with corresponding center passageway  214 , or channel  216 ,  218 , or  220 , in alternative embodiments, more than one radial inlet may be in flow communication with center passageway  214 , or corresponding channel  216 ,  218 , or  220 . 
     In the exemplary embodiment, each radial inlet, such as first radial inlet  328  and/or third radial inlet  230 , has a substantially constant diameter along its respective inlet length. Alternatively, each radial inlet may be formed with a non-circular cross-sectional shape and/or a varied diameter. More specifically, the radial inlets may be configured in any suitable shape and/or orientation that enables combustor  102  and/or secondary fuel nozzle assembly  200  to function as described herein. Further, in the exemplary embodiment, first radial inlet  228  includes a corresponding radial port  232  and third radial inlet  230  includes a corresponding radial port  234 . Each port  232  and/or  234  may be a tapered port, a straight port, or an offset port. Alternatively, ports  232  and/or  234  may be configured in any suitable shape and/or orientation that enable combustor  102  and secondary fuel nozzle assembly  200  to function as describe herein. 
     Head portion  202  also includes, in the exemplary embodiment, a plurality of axial inlets  240 ,  242 , and  244 . Although only three axial inlets  240 ,  242 , and  244  are described, head portion  202  may include any number of axial inlets that enables secondary fuel nozzle assembly  200  to function as described herein. In the exemplary embodiment, axial inlet  240  extends from first end face  204 , through radial inlet  228 , to radial inlet  230 . Although, in the exemplary embodiment, axial inlet  240  extends through radial inlet  228 , axial inlet  240  may extend from first end face  204  to any radial inlet, with or without extending through another radial inlet such that secondary fuel nozzle assembly  200  functions as described herein. 
     In the exemplary embodiment, axial inlets  240 ,  242 , and/or  244  have a substantially constant diameter. Alternatively, axial inlets  240 ,  242 , and/or  244  may have a non-circular cross-sectional shape and/or a variable diameter. Moreover, in the exemplary embodiment, axial inlets  240 ,  242 , and/or  244  include a tapered port. Alternatively, the port may have any suitable shape that enables combustor  102  and/or secondary fuel nozzle assembly  200  to function as describe herein. 
     In the exemplary embodiment, nozzle portion  204  is coupled to head portion  202  by, for example, welding nozzle portion  204  to head portion  202 . Although in the exemplary embodiment nozzle portion  204  is cylindrical, nozzle portion  204  may be any suitable shape that enables secondary fuel nozzle assembly  200  to function as described herein. 
     Nozzle portion  204 , in the exemplary embodiment, includes a plurality of substantially concentrically-aligned tubes  250 ,  252 ,  254 , and  256 . Tubes  250 ,  252 ,  254 , and  256  are oriented with respect to each other such that a plurality of substantially concentric passageways  260 ,  262 ,  264 , and  266  are defined within nozzle portion  204 . More specifically, in the exemplary embodiment, a center passageway  270  is defined within a first tube  250 , a first passageway  260  is defined between first tube  250  and a second tube  252 , a second passageway  262  is defined between second tube  252  and a third tube  254 , and a third passageway  264  is defined between third tube  254  and a fourth tube  256 . Although the exemplary embodiment includes four concentrically-aligned tubes  250 ,  252 ,  254 , and  256 , nozzle portion  204  may include any number of tubes that enables secondary fuel nozzle assembly  200  and/or combustor  102  to function as described herein. In the exemplary embodiment, the number of tubes is such that the number of passageways defined by the tubes is equal to the number of head channels and head center passageway. 
     In the exemplary embodiment, channels  216 ,  218 , and  220  are substantially concentrically-aligned with passageways  260 ,  262 , and  264 , respectively. Moreover, nozzle center passageway  270  is aligned substantially concentrically with head center passageway  214 . As such, first tube  250  is substantially aligned with head first divider wall  222 , second tube  252  is substantially aligned with head second divider wall  224 , and third tube  254  is substantially aligned with head third divider wall  226 . In the exemplary embodiment, fourth tube  256  is aligned such that an inner surface  273  of fourth tube  256  is substantially aligned with a radially outer surface  274  of head channel  220 . 
     In the exemplary embodiment, nozzle portion  204  includes a tip portion  280  coupled to tubes  250 ,  252 ,  254 , and/or  256 . More specifically, in the exemplary embodiment, tip portion  280  is coupled to tubes  250 ,  252 ,  254 , and/or  256  using, for example, a welding process. In the exemplary embodiment, tip portion  280  includes a tube extension  282 , an outer tip  284 , and an inner tip  286 . Alternatively, tip portion  280  may have any suitable configuration that enables secondary fuel nozzle assembly  200  to function as described herein. In the exemplary embodiment, tube extension  282  is coupled to third tube  254  and fourth tube  256  using, for example, a coupling ring  288 . Coupling ring  288  facilitates sealing third passageway  264  such that a fluid (not shown) flowing within third passageway  264  is not discharged through tip portion  280 . Alternatively, third passageway  264  is coupled in flow communication through tip portion  280 . 
     In the exemplary embodiment, inner tip  286  includes a first projection  290  and a second projection  292 . Inner tip  286  further defines a center opening  294  and a plurality of outlet apertures (not shown). Inner tip  286  is coupled to first tube  250  and second tube  252  using first projection  290  and second projection  292 , respectively. As such, in the exemplary embodiment, a fluid (not shown) flowing within center passageway  214  and/or center passageway  270  is discharged through center opening  294  and/or the outlet apertures, and a fluid (not shown) flowing within first passageway  260  is discharged through the outlet apertures. Further, in the exemplary embodiment, outer tip  284  includes a plurality of outlet apertures (not shown) and is coupled to inner tip  286  and tube extension  282 . As such, a fluid (not shown) flowing within second passageway  262  is discharged through the outlet apertures defined in outer tip  284  and/or inner tip  286 . 
     In the exemplary embodiment, nozzle portion  204  also includes at least one peg  300  (also referred to herein as “vanes”) that extends radially outwardly from fourth tube  256 . As shown in  FIG. 2 , each peg  300  is in fuel flow communication with nozzle portion  204  through fourth tube  256 . Alternatively, pegs  300  may extend obliquely from nozzle portion  204 . Further, although only two pegs  300  are shown in  FIG. 2 , nozzle portion  204  may include more or less than two pegs  300 . In the exemplary embodiment, pegs  300  are positioned at a downstream end  302  of third passageway  264  proximate to coupling ring  288 . Alternatively, one or more pegs  300  may be positioned at any suitable location relative to third passageway  264 . 
     Referring further to  FIG. 3 , in the exemplary embodiment, each peg  300  defines at least one outlet aperture or opening  304  configured to discharge fuel flowing within third passageway  264  through openings  304  and direct the fuel in a substantially upstream direction opposing a flow of combustion gases in a downstream direction. 
     A disc  310  is positioned about nozzle portion  204  upstream of pegs  300 . Disc  310  is configured to interfere with the fuel to facilitate fuel atomization. More specifically, the collision of the fuel with an inner or downstream surface  312  of disc  310  facilitates atomization of the fuel. The atomized fuel  314  disperses and mixes with the flow of combustion gases and/or air that flows through combustor liner  126  in a substantially downstream direction, represented by arrows  316  in  FIG. 3 . 
     In the exemplary embodiment, disc  310  has a semi-toroidal shape, as shown in  FIG. 3 . The semi-toroidal shaped disc  310  is circumferentially positioned about and coupled to nozzle portion  204 . The semi-toroidal shaped disc  310  may be a continuous disc  310  or may include a plurality of disc segments (not shown) circumferentially positioned about nozzle portion  204 . Referring further to  FIG. 3 , in the exemplary embodiment, at least a portion of downstream surface  312  of disc  310  has an arcuate cross-sectional profile, such as a semi-circular or concave cross-sectional profile, as shown in  FIG. 3 , to facilitate directing the fuel in a direction of the flow of combustion gases upon contact with downstream surface  312 . 
     In an alternative embodiment, disc  310  includes a substantially planar downstream surface (not show) configured to interfere with the fuel to facilitate fuel atomization. In this alternative embodiment, the substantially planar surface is positioned at a perpendicular angle or an oblique angle with respect to a flow of fuel from pegs  300 . 
     In the exemplary embodiment, nozzle portion  204  is coupled to head portion  202  using a suitable process including, without limitation, a welding process. More specifically, each tube  250 ,  252 ,  254 , and/or  256  is coupled to head portion  202  such that nozzle passageways  260 ,  262 ,  264 , and  270  are substantially aligned with cooperating head channels  216 ,  218 ,  220 , and head center passageway  214 , as described above. In the exemplary embodiment, tip portion  280  is welded to tubes  250 ,  252 ,  254 , and/or  256  such that nozzle portion  204  is configured as described above. More specifically, in the exemplary embodiment, tube extension  282  is welded to tubes  254  and  256  using, for example, coupling ring  288 , inner tip  286  is welded to second tube  252  and first tube  250  using respective projections  292  and  290 , and outer tip  284  is welded to inner tip  286 . Alternatively, nozzle portion  204  may be fabricated using any other suitable fabrication technique that enables secondary fuel nozzle assembly  200  to function as described herein. 
     The above-described secondary fuel nozzle assembly includes fuel pegs that are oriented in an upstream direction to provide a flow or spray of fuel that contacts a semi-toroidal shaped disc of the secondary fuel nozzle assembly to increase fuel atomization and/or fuel mixing. More specifically, the semi-toroidal shaped disc interferes with the flow of fuel in the upstream direction to facilitate mixing the fuel with a flow of air through the secondary fuel nozzle assembly and redirecting the mixed fuel into a flow of combustion gases through the combustor assembly. The mixed fuel is redirected or sprayed into the flow of combustion gases rather than directly dumped into the flow of combustion gases, as in conventional secondary fuel nozzle assemblies. As a result, a fuel spray pattern is created using reflecting waves produced by the semi-toroidal shaped disc to facilitate fuel dispersion and/or atomization. 
     Exemplary embodiments of a secondary fuel nozzle assembly and methods for fabricating a secondary fuel nozzle assembly are described above in detail. The assembly and methods are not limited to the specific embodiments described herein, but rather, components of the assembly and/or steps of the method may be utilized independently and separately from other components and/or steps described herein. Further, the described assembly components and/or method steps can also be defined in, or used in combination with, other assemblies and/or methods, and are not limited to practice with only the assembly and methods as described herein. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.