Patent Publication Number: US-8991192-B2

Title: Fuel nozzle assembly for use as structural support for a duct structure in a combustor of a gas turbine engine

Description:
This invention was made with U.S. Government support under Contract Number DE-FC26-05NT42644 awarded by the U.S. Department of Energy. The U.S. Government has certain rights to this invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a fuel nozzle assembly for use in a combustor apparatus of a gas turbine engine and, more particularly, to a fuel nozzle assembly that provides a direct structural connection between a duct structure and a fuel manifold. 
     BACKGROUND OF THE INVENTION 
     A conventional combustible gas turbine engine includes a compressor section, a combustion section including a plurality of combustor apparatuses, and a turbine section. Ambient air is compressed in the compressor section and directed to the combustor apparatuses in the combustion section. The pressurized air is mixed with fuel and ignited in the combustor apparatuses to create combustion products that define working gases. The working gases are routed to the turbine section via a plurality of transition ducts. Within the turbine section are rows of stationary vanes and rotating blades. The rotating blades are coupled to a shaft and disc assembly. As the working gases expand through the turbine section, the working gases cause the blades, and therefore the shaft, to rotate. 
     It is known that injecting fuel at two axially spaced apart fuel injection locations, i.e., via an upstream fuel injection system associated with a main combustion zone and a downstream fuel injection system downstream from the main combustion zone, reduces the production of NOx by a combustor apparatus. For example, if a significant portion of fuel is injected at a location downstream of the main combustion zone, i.e., by the downstream fuel injection system, the amount of time that second combustion products, created by the fuel injected by the downstream fuel injection system, are at a high temperature is reduced as compared to first combustion products, created by the fuel injected into the main combustion zone by the upstream fuel injection system. Since NOx production is increased by the elapsed time that combustion products are at a high combustion temperature, combusting a portion of the fuel downstream of the main combustion zone reduces the time the second combustion products are at a high temperature, such that the amount of NOx produced by the combustor apparatus is reduced. 
     SUMMARY OF THE INVENTION 
     In accordance with a first embodiment of the present invention, a fuel nozzle assembly is provided in combination with a duct structure in a combustor apparatus of a gas turbine engine comprising. The duct structure comprises an intermediate duct structure between a liner duct structure and a transition duct and defines a flow passage for combustion gases flowing from the liner duct structure to the transition duct. The intermediate duct structure is free to move axially with respect to each of the liner duct structure and the transition duct. The fuel nozzle assembly comprises an outer housing and a fuel injector. The outer housing is coupled to the intermediate duct structure and to a fuel manifold that defines a fuel supply channel therein in fluid communication with a source of fuel. The outer housing includes an inner volume and structurally supports the intermediate duct structure between the liner duct structure and the transition duct. The fuel injector is provided in the inner volume of the outer housing and defines a fuel passage therethrough. The fuel passage is in fluid communication with the fuel supply channel of the fuel manifold for distributing the fuel from the fuel supply channel into the flow passage of the intermediate duct structure. 
     In accordance with a second embodiment of the invention, a combustor apparatus is provided in a gas turbine engine. The combustor apparatus comprises a combustor device coupled to a main engine casing, a liner duct structure, an intermediate duct structure, and a fuel injection system. The combustor device comprises a flow sleeve for receiving pressurized air and a liner duct structure disposed radially inwardly from the flow sleeve. The liner duct structure has an inlet, an outlet, and an inner volume. The transition duct has an inlet section and an outlet section. The intermediate duct structure is disposed between the liner duct structure and the transition duct and defines a flow passage for combustion gases flowing from the liner duct structure to the transition duct. The intermediate duct structure has inlet and outlet portions, wherein the intermediate duct structure inlet portion is associated with the liner duct structure outlet such that movement may occur between the intermediate duct structure and the liner duct structure, and the intermediate duct structure outlet portion is associated with the transition duct inlet section such that movement may occur between the intermediate duct structure and the transition duct. The fuel injection system is associated with the intermediate duct structure and comprises a fuel manifold and a plurality of fuel nozzle assemblies. The fuel manifold is coupled to structure within the engine to provide structural support for the fuel injection system and for the intermediate duct structure. The fuel manifold defines a fuel supply channel therein that is in fluid communication with a source of fuel. The fuel nozzle assemblies each comprise an outer housing and a fuel injector. The outer housing of each fuel nozzle assembly defines an inner volume and spans between and is coupled to both of the fuel manifold and the intermediate duct structure to provide structural support for the intermediate duct structure via the fuel manifold. The fuel injector of each fuel nozzle assembly is provided in the inner volume of each respective outer housing. Each fuel injector defines a fuel passage therethrough that is in fluid communication with the fuel supply channel of the fuel manifold for distributing the fuel from the fuel supply channel into the flow passage of the intermediate duct structure. 
     In accordance with a third embodiment of the invention, a fuel nozzle assembly is provided for use in a combustor apparatus of a gas turbine engine. An outer housing of the fuel nozzle assembly includes an inner volume and provides a direct structural connection between a duct structure and a fuel manifold. The duct structure defines a flow passage for combustion gases flowing within the combustor apparatus. The fuel manifold defines a fuel supply channel therein in fluid communication with a source of fuel. A fuel injector of the fuel nozzle assembly is provided in the inner volume of the outer housing and defines a fuel passage therein. The fuel passage is in fluid communication with the fuel supply channel of the fuel manifold for distributing the fuel from the fuel supply channel into the flow passage of the duct structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is a side cross sectional view of a combustor apparatus including a plurality of fuel nozzle assemblies according to an embodiment of the invention; 
         FIG. 2  is an enlarged cross sectional view illustrating one of the fuel nozzle assemblies shown in  FIG. 1 ; 
         FIG. 3  is a side cross sectional view of a combustor apparatus including a plurality of fuel nozzle assemblies according to another embodiment of the invention; and 
         FIG. 4  is a side cross sectional view of a combustor apparatus including a plurality of fuel nozzle assemblies according to yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring to  FIG. 1 , a combustor apparatus  10  forming part of a can-annular combustion system  12  in a gas turbine engine is shown. The engine further comprises a compressor section (not shown) and a turbine section (not shown). Air enters the compressor section where the air is pressurized. The pressurized air is then delivered to a plurality of the combustor apparatuses  10  of the combustion system  12 . In each of the combustor apparatuses  10 , the pressurized air from the compressor section is mixed with a fuel at two locations in the illustrated combustor apparatus  10 , i.e., an upstream location and a downstream location, which will both be discussed in detail herein, to create upstream and downstream air and fuel mixtures. The air and fuel mixtures are ignited to create hot combustion products that define working gases. The working gases are routed from the combustor apparatuses  10  to the turbine section. The working gases expand in the turbine section and cause blades coupled to a shaft and disc assembly to rotate. 
     As noted above, the can-annular combustion system  12  comprises a plurality of the combustor apparatuses  10 . Each combustor apparatus  10  comprises a combustor device  14 , a first fuel injection system  16 , a second fuel injection system  18 , a first fuel supply structure  20 , a second fuel supply structure  22 , a transition duct  24 , and, in the embodiment shown, an intermediate duct structure  26 . The combustor apparatuses  10  are spaced circumferentially apart from one another within the combustion system  12 . 
     Only a single combustor apparatus  10  is illustrated in  FIG. 1 . Each combustor apparatus  10  forming a part of the can-annular combustion system  12  can be constructed in the same manner as the combustor apparatus  10  illustrated in  FIG. 1 . Hence, only the combustor apparatus  10  illustrated in  FIG. 1  will be discussed in detail herein. 
     As shown in  FIG. 1 , the combustor device  14  of the combustor apparatus  10  comprises a flow sleeve  30  and a liner duct structure  32  disposed radially inwardly from the flow sleeve  30 . The flow sleeve  30  is coupled to a main engine casing  34  of the engine via a cover plate  36  and receives pressurized air from the compressor section through an annular gap  37  formed between the flow sleeve  30  and the second fuel injection system  18 . The flow sleeve  30  may be formed from any material capable of operation in the high temperature and high pressure environment of the combustion system  12 , such as, for example, stainless steel, and in a preferred embodiment may comprise a steel alloy including chromium. 
     The liner duct structure  32  is coupled to the cover plate  36  via support members  38 . As shown in  FIG. 1 , the liner duct structure  32  comprises an inlet  32 A, an outlet  32 B and has an inner volume  32 C, which inner volume  32 C at least partially defines a main combustion zone  40 . The liner duct structure  32  may be formed from a high-temperature material, such as HASTELLOY-X (HASTELLOY is a registered trademark of Haynes International, Inc.). 
     The first fuel injection system  16  may comprise one or more main fuel injectors  50  coupled to and extending axially away from the cover plate  36 , and a pilot fuel injector  52  also coupled to and extending axially away from the cover plate  36 . The first fuel injection system  16  may also be referred to as a “main,” a “primary” or an “upstream” fuel injection system. The first fuel supply structure  20  is in fluid communication with a source of fuel  54  and delivers fuel from the source of fuel  54  to the main and pilot fuel injectors  50  and  52 . As noted above, the flow sleeve  30  receives pressurized air from the compressor through the gap  37 . After entering the flow sleeve  30 , the pressurized air moves into the liner duct structure inner volume  32 C where fuel from the main and pilot fuel injectors  50  and  52  is mixed with at least a portion of the pressurized air in the inner volume  32 C and ignited in the main combustion zone  40  to create combustion products defining first working gases. 
     The transition duct  24  may comprise a conduit having a generally cylindrical inlet section  24 A, a main body section  24 B, and a generally rectangular outlet section (not shown). The conduit may be formed from a high-temperature capable material, such as HASTELLOY-X, INCONEL 617, or HAYNES 230 (INCONEL is a registered trademark of Special Metals Corporation, and HAYNES is a registered trademark of Haynes International, Inc.). The transition duct outlet section includes structure that is coupled to a row  1  vane segment (not shown) of the turbine. 
     The intermediate duct structure  26  in the illustrated embodiment is located between the liner duct structure  32  and the transition duct  24  so as to define a flow passage  56  for the first working gases from the liner duct structure  32  to the transition duct  24 . 
     A plurality of secondary fuel injection openings  58  are formed in the intermediate duct structure  26 , see  FIGS. 1 and 2 . The secondary fuel injection openings  58  are each adapted to receive a corresponding downstream fuel nozzle assembly  60  of the second fuel injection system  18 . The second fuel injection system  18  may also be referred to as a “downstream” or a “secondary” fuel injection system. Additional details in connection with the second fuel injection system  18  will be described in greater detail below. 
     The intermediate duct structure  26  in the embodiment illustrated in  FIG. 1  comprises a generally cylindrical inlet portion  26 A, a generally cylindrical outlet portion  26 B, and generally cylindrical first and second mid-portions  26 C and  26 D, respectively, and an angled portion  26 E joining the first and second mid-portions  26 C and  26 D to one another. The first generally cylindrical mid-portion  26 C is proximate to the inlet portion  26 A and the second generally cylindrical mid-portion  26 D is proximate to the outlet portion  26 B. In the embodiment shown, the angled portion  26 E is located upstream from the secondary fuel injection openings  58  and defines a transition between differing inner diameters of the first and second mid-portions  26 C and  26 D. Specifically, the angled portion  26 E transitions between a first, larger inner diameter D 1  of the first generally cylindrical mid-portion  26 C and a second, smaller inner diameter D 2  of the second generally cylindrical mid-portion  26 D. The inlet portion  26 A has the same inner diameter D 1  as the first generally cylindrical mid-portion  26 C, while the outlet portion  26 B has the same inner diameter D 2  as the second generally cylindrical mid-portion  26 D. It is understood that the intermediate duct structure  26  may have a substantially constant diameter along its entire extent if desired, or the diameter D 2  of the second mid-portion  26 D could be greater than the diameter D 1  of the first mid-portion  26 C. 
     The inlet portion  26 A of the intermediate duct structure  26  is positioned over the liner duct structure outlet  32 B, see  FIG. 1 . An outer diameter D 3  of the liner duct structure outlet  32 B in the embodiment shown is smaller than the inner diameter D 1  of the intermediate duct inlet portion  26 A but is generally equivalent to the inner diameter D 2  of the intermediate duct mid-portion  26 D and to a diameter D 4  of the intermediate duct outlet portion  26 B, i.e., the liner duct structure outlet  32 B is generally coaxial with the intermediate duct mid-portion  26 D and the intermediate duct outlet portion  26 B, as clearly shown in  FIG. 1 . A contoured first spring clip structure  62  (also known as a finger seal) is provided on an outer surface  64  of the liner duct structure outlet  32 B and frictionally engages an inner surface  66  of the intermediate duct inlet portion  26 A such that a friction fit coupling is provided between the liner duct structure  32  and the intermediate duct structure  26 . The friction fit coupling allows movement, i.e., axial, circumferential, and/or radial movement, between the liner duct structure  32  and the intermediate duct structure  26 , which movement may be caused by thermal expansion of one or both of the liner duct structure  32  and the intermediate duct structure  26  during operation of the engine. Alternatively, it is contemplated that the first spring clip structure  62  may be coupled to the inner surface  66  of the intermediate duct inlet portion  26 A so as to frictionally engage the outer surface  64  of the liner duct structure outlet  32 B. 
     In an alternative embodiment, the liner duct structure  32  and the intermediate duct structure  26  are generally coaxial and the first spring clip structure  62  is eliminated. In such an embodiment, an inner diameter of the intermediate duct inlet portion  26 A may be slightly larger than the outer diameter of the liner duct structure outlet  32 B. Hence, the intermediate duct structure  26  may be coupled to the liner duct structure  32  via a slight friction fit or a piston-ring type arrangement. The intermediate duct angled portion  26 E may also be eliminated, such that the intermediate duct structure  26  may comprise a substantially uniform inner diameter along generally its entire extent. 
     The inlet section  24 A of the transition duct  24  is fitted over the intermediate duct outlet portion  26 B, see  FIG. 1 . An outer diameter of the intermediate duct outlet portion  26 B in the embodiment shown is smaller than an inner diameter of the transition duct inlet section  24 A. A second contoured spring clip structure  68  is provided on an outer surface  70  of the intermediate duct outlet portion  26 B and frictionally engages an inner surface  72  of the transition duct inlet section  24 A such that a friction fit coupling is provided between the intermediate duct structure  26  and the transition duct  24 . The friction fit coupling allows movement, i.e., axial, circumferential, and/or radial movement, between the intermediate duct structure  26  and the transition duct  24 , which movement may be caused by thermal expansion of one or both of the intermediate duct structure  26  and the transition duct  24  during operation of the engine. Alternatively, it is contemplated that the second spring clip structure  68  may be coupled to the inner surface  72  of the transition duct inlet section  24 A so as to frictionally engage the outer surface  70  of the intermediate duct outlet portion  26 B. 
     Because the intermediate duct structure  26  is provided between the liner duct structure  32  and the transition duct  24 , and the first and second spring clip structures  62  and  68  frictionally couple the liner duct structure  32  to the intermediate duct structure  26  and the intermediate duct structure  26  to the transition duct  24 , two joints are defined along the axial path that the working gases take as they move into the transition duct  24 . That is, a first joint is defined where the intermediate duct structure  26  engages the liner duct structure  32  and a second joint is defined where the intermediate duct structure  26  engages the transition duct  24 . These two joints accommodate axial, radial and/or circumferential shifting of the liner duct structure  32  and the transition duct  24  with respect to the intermediate duct structure  26  due to non-uniformity in temperatures in the liner duct structure  32 , the transition duct  24 , the intermediate duct structure  26  and structure mounting the liner duct structure  32  and the transition duct  24  within the engine casing. 
     As more clearly shown in  FIG. 2 , each fuel nozzle assembly  60  of the second fuel injection system  18  extends through a corresponding one of the secondary fuel injection openings  58  formed in the intermediate duct structure  26  so as to communicate with and inject fuel into the flow passage  56  defined by the intermediate duct structure  26 , which flow passage  56  is defined at a location downstream from the main combustion zone  40  (see  FIG. 1 ). 
     Each fuel nozzle assembly  60  comprises an outer housing  82  and a fuel injector  84 . The outer housing  82  of each fuel nozzle assembly  60  spans between the intermediate duct structure  26  and a fuel manifold  86  of the second fuel injection system  18  to provide a direct structural connection between the intermediate duct structure  26  and the fuel manifold  86 . The fuel manifold  86  defines a fuel supply channel  88  therein for delivering fuel to the fuel injector  84 , as will be described in detail herein. In the embodiment shown, the outer housing  82  comprises a generally cylindrical and rigid member and includes an inner volume  89  in which the fuel injector  84  is provided. 
     The outer housing  82  is coupled to the intermediate duct structure  26  and structurally supports the intermediate duct structure  26  between the liner duct structure  32  and the transition duct  24  via the fuel manifold  86 , as will be described herein. The coupling comprises an engagement of an outer surface  90  of the outer housing  82  with structure  92  of the intermediate duct structure  26  that defines the corresponding secondary fuel injection opening  58 . The outer housing  82  is slidably received in its corresponding secondary fuel injection opening  58  such that the outer housing  82  and the intermediate duct structure  26  can move radially independently of each other, which radial movement may occur during operation of the engine as will be discussed further herein. However, the engagement between the outer surface  90  of the outer housing  82  with the structure  92  of the intermediate duct structure  26  permits the intermediate duct structure  26  and the outer housing  82 , and, thus, the fuel nozzle assembly  60 , to move axially and circumferentially together. 
     The outer housing  82  is also coupled to the fuel manifold  86 , such as, for example, by welding, such that the outer housing  82  is rigidly attached to and structurally supported by the fuel manifold  86 . As the fuel manifold  86  in the embodiment shown is structurally affixed to the flow sleeve  30 , which is in turn structurally affixed to the engine casing  34 , the fuel manifold  86  provides structural support for the fuel nozzle assembly  60 , and, thus for the intermediate duct structure  26 , via the affixation of the fuel manifold  86  to the flow sleeve  30 . It is noted that the fuel manifold  86  may be structurally supported by other structure within the combustor apparatus  10 , as will be described herein with reference to  FIGS. 3 and 4 . 
     The fuel nozzle assembly  60  according to this embodiment is not structurally affixed to the liner duct structure  32  or the transition duct  24 , but, rather, is structurally affixed to the intermediate duct structure  26 . Since the intermediate duct structure  26  can move independently from both the liner duct structure  32  and the transition duct  24 , as discussed above, the fuel nozzle assembly  60 , and also the fuel manifold  86 , which is structurally affixed to the fuel nozzle assembly  60 , can also move independently from the liner duct structure  32  and the transition duct  24 . Thus, relative movement between the intermediate duct structure/fuel nozzle assembly/fuel manifold and the liner duct structure  32  will not result in stress imparted on these structures, which might otherwise result if the fuel nozzle assembly/fuel manifold were directly affixed to the liner duct structure  32 . Similarly, relative movement between the intermediate duct structure/fuel nozzle assembly/fuel manifold and the transition duct  24  will not result in stress imparted on these structures, which might otherwise result if the fuel nozzle assembly/fuel manifold were directly affixed to the transition duct  24 . 
     It is noted that any relative radial movement between the fuel nozzle assemblies  60  and the intermediate duct structure  26  may be accommodated by the slidable engagement of the outer housings  82  of the fuel nozzle assemblies  60  within the secondary fuel injection openings  58  in the intermediate duct structure  26 . However, any axial or circumferential movement of the intermediate duct structure  26 , the fuel nozzle assemblies  60 , the fuel manifold  86 , or the flow sleeve  30  will result in all of these structures moving axially or circumferentially together. 
     As noted above, the fuel manifold  86  delivers fuel to the fuel injector  84  via the fuel supply channel  88  defined by the fuel manifold  86 . The fuel manifold  86 , which may comprise an annular manifold, extends completely or at least partially around a circumference of the intermediate duct structure  26 . The fuel supply channel  88  of the fuel manifold  86  receives fuel from the source of fuel  54  via the second fuel supply structure  22 , which, in the embodiment shown, comprises a pair of fuel supply tubes  94 , but may comprise additional or fewer fuel supply tubes  94 . Optionally, the fuel supply tubes  94  may comprise a series of bends defining circumferential direction shifts to accommodate relative movement between each fuel supply tube  94  and the fuel manifold  86 , such as may result from thermally induced movement of one or both of the fuel supply tubes  94  and the fuel manifold  86 . Additional description of a fuel supply tube having circumferential direction shifts may be found in U.S. patent application Ser. No. 12/233,903, filed on Sep. 19, 2008, entitled “COMBUSTOR APPARATUS IN A GAS TURBINE ENGINE,” the entire disclosure of which is incorporated herein by reference. 
     The fuel injector  84  defines a fuel passage  96  therein in fluid communication with the fuel supply channel  88  of the fuel manifold  86 , which fuel passage  96  receives fuel from the fuel supply channel  88 . The fuel passage  96  is in fluid communication with a fuel injection port  98  defined at distal end  100  of the fuel injector  84 , which fuel injection port  98  distributes the fuel into the flow passage  56  defined by the intermediate duct structure  26 . It is noted that the fuel injector  84  in the embodiment shown in  FIGS. 1 and 2  extends radially past the outer housing  82  and into the flow passage  56  defined by the intermediate duct structure  26 , while the outer housing  82  extends only up to the intermediate duct structure  26 . 
     The fuel injected by the fuel injectors  84  into the flow passage  56  defined by the intermediate duct structure  26  mixes with at least a portion of the remaining pressurized air, i.e., pressurized air not ignited in the main combustion zone  40  with the fuel supplied by the first injection system  16 , and ignites with the remaining pressurized air to define further combustion products defining second working gases. 
     It is noted that injecting fuel at two axially spaced apart fuel injection locations, i.e., via the first fuel injection system  16  and the second fuel injection system  18 , may reduce the production of NOx by the combustor apparatus  10 . For example, since a significant portion of the fuel, e.g., about 15-30% of the total fuel supplied by the first fuel injection system  16  and the second fuel injection system  18 , is injected at a location downstream of the main combustion zone  40 , i.e., by the second fuel injection system  18 , the amount of time that the second combustion products are at a high temperature is reduced as compared to first combustion products resulting from the ignition of fuel injected by the first fuel injection system  16 . Since NOx production is increased by the elapsed time the combustion products are at a high combustion temperature, combusting a portion of the fuel downstream of the main combustion zone  40  reduces the time the combustion products resulting from the second portion of fuel provided by the second fuel injection system  18  are at a high temperature, such that the amount of NOx produced by the combustor apparatus  10  may be reduced. 
     The fuel nozzle assemblies  60  may be substantially equally spaced in the circumferential direction, or may be configured in other patterns as desired, such as, for example, a random pattern. Further, the number, size, and location of the fuel nozzle assemblies  60  and corresponding openings  58  formed in the intermediate duct structure  26  may vary depending on the particular configuration of the combustor apparatus  10  and the amount of fuel to be injected by the second fuel injection system  18 . However, in a preferred embodiment, the number of fuel nozzle assemblies  60  employed in a given combustor apparatus  10  is at least 3, and in a most preferred embodiment is at least 8. 
     Referring to  FIG. 3 , a combustor apparatus  110  constructed in accordance with a second embodiment of the present invention and adapted for use in a can-annular combustion system  112  of a gas turbine engine is shown. The combustor apparatus  110  includes a combustor device  114 , a first fuel injection system  116 , a second fuel injection system  118 , a first fuel supply structure  120 , a second fuel supply structure  122 , a transition duct  124 , and an intermediate duct  126 . 
     The combustor device  114  comprises a flow sleeve  128  and a liner duct structure  130  disposed radially inwardly from the flow sleeve  128 . The flow sleeve  128  is coupled to a main engine casing  132  via a cover plate  134 . The liner duct structure  130  is coupled to the cover plate  134  via support members  136 . 
     The second fuel injection system  118  includes a fuel manifold  138  and a plurality of fuel nozzle assemblies  140  that extend through corresponding openings  142  in the intermediate duct structure  126 . The fuel nozzle assemblies  140  comprise fuel injectors  144  that inject fuel into a flow passage  146  defined by the intermediate duct structure  126  at a location downstream from a main combustion zone  148  defined by the liner duct structure  130 . 
     The fuel manifold  138  according to this embodiment is not directly affixed to the flow sleeve  128  as in the embodiment described above for  FIGS. 1-2 . Rather, the fuel manifold  138  in this embodiment is structurally affixed to a mounting structure  150  that is coupled to other structure within the combustor apparatus  110 . In the embodiment shown in  FIG. 3 , the fuel manifold  138  is diagrammatically illustrated as being structurally affixed to the main engine casing  132  via the mounting structure  150  and a structural member  152 . The structural member  152  is shown in dashed lines in  FIG. 3  to represent a possible structural attachment between the fuel manifold  138  and the main engine casing  132 . However, the structural member  152  may structurally attach the fuel manifold  138  to other structures within/proximate to the combustor apparatus  110 , and may take on any suitable shape, size, configuration, etc. Other suitable structures to which the structural member  152  may be attached to structurally support the fuel manifold  138  include the flow sleeve  128 , the cover plate  134 , or other structure within the combustor apparatus  110  capable of structurally supporting the fuel manifold  138 , the fuel nozzle assemblies  140 , and the intermediate duct structure  126 , which, as described above with reference to  FIGS. 1-2 , is structurally affixed in axial and circumferential directions to outer housings  154  of the fuel nozzle assemblies  140 , but is capable of moving radially with respect to the outer housings  154  as a result of the outer housings  154  being slidably received in their corresponding openings  142  in the intermediate duct structure  126 . It is noted that the structural member  152  can preferably accommodate some amount of relative movement between the fuel manifold  138  and the other structure to which the structural member  152  is attached, such as may result from thermal expansion of the intermediate duct structure  126 , the fuel nozzle assemblies  140 , the fuel manifold  138 , and/or the other structure to which the structural member  152  is attached. 
     Remaining structure of the combustor apparatus  110  according to this embodiment is substantially the same as that described above with reference to  FIGS. 1-2 . However, since the fuel manifold  138 , the fuel nozzle assemblies  140 , and the intermediate duct structure  126  according to this embodiment are not structurally tied to the flow sleeve  128 , the flow sleeve  128  is free to move independently of the fuel manifold  138 , the fuel nozzle assemblies  140 , and the intermediate duct structure  126 , and vice versa. 
     Referring to  FIG. 4 , a combustor apparatus  210  constructed in accordance with a third embodiment of the present invention and adapted for use in a can-annular combustion system  212  of a gas turbine engine is shown. The combustor apparatus  210  includes a combustor device  214 , a first fuel injection system  216 , a second fuel injection system  218 , a first fuel supply structure  220 , a second fuel supply structure  222 , and a transition duct  224 . 
     The combustor device  214  comprises a flow sleeve  226  and a liner duct structure  228  disposed radially inwardly from the flow sleeve  226 . The flow sleeve  226  is coupled to a main engine casing  230  via a cover plate  232 . The liner duct structure  228  is coupled to the cover plate  232  via support members  234 . It is noted that, in this embodiment, since there is no intermediate duct structure, i.e., the intermediate duct structures  26  and  126  as described above with reference to  FIGS. 1-2  and  3 , a contoured spring clip structure  229  is provided in a radial gap between a liner duct structure outlet  228 A and a transition duct inlet  224 A, such that a friction fit coupling is provided between the liner duct structure  228  and the transition duct  224 . The friction fit coupling allows movement, i.e., axial, circumferential, and/or radial movement, between liner duct structure  228  and the transition duct  224 , which movement may be caused by thermal expansion of one or both of the liner duct structure  228  and the transition duct  224  during operation of the engine. 
     The second fuel injection system  218  includes a fuel manifold  236  and a plurality of fuel nozzle assemblies  238 , which, in this embodiment, extend through corresponding openings  240  formed in the liner duct structure  228 . The fuel nozzle assemblies  238  comprise fuel injectors  242  that inject fuel into a flow passage  244  defined by the liner duct structure  228 . The flow passage  244  is located downstream from a main combustion zone  246  defined by the liner duct structure  228 . 
     The fuel manifold  236  according to this embodiment is not directly affixed to the flow sleeve  226  as in the embodiment described above for  FIGS. 1-2 . Rather, the fuel manifold  236  in this embodiment is structurally affixed to the liner duct structure  228  via outer housings  250  of the fuel nozzle assemblies  238 . Specifically, as illustrated in  FIG. 4 , the outer housings  250  of the fuel nozzle assemblies  238  comprise rigid members that provide a direct structural connection between the liner duct structure  228  and the fuel manifold  236 . Thus, the fuel manifold  236  and its associated fuel nozzle assemblies  238  are structurally supported within the combustor apparatus  210  via the liner duct structure  228 , which, as noted above, is coupled to the cover plate  232  via the support members  234 . 
     The outer housings  250  of the fuel nozzle assemblies  238  are slidably received in the openings  240  of the liner duct structure  228  such that relative radial movement may occur between the fuel nozzle assemblies  238  and the liner duct structure  228 . Further, structure  252  of the liner duct structure  228  that defines the openings  240  that receive the fuel nozzle assemblies  252  engage outer surfaces  254  of the outer housings  250  such that the liner duct structure  228  and the outer housings  250 , and, thus, the fuel manifold  236 , can move axially and circumferentially together. 
     Remaining structure of the combustor apparatus  210  according to this embodiment is substantially the same as that described above with reference to  FIGS. 1-2 . However, since the fuel manifold  236  and the fuel nozzle assemblies  238  according to this embodiment are structurally tied to the liner duct structure  228  and not to the flow sleeve  226 , the flow sleeve  226  is free to move independently of the fuel manifold  236 , the fuel nozzle assemblies  238 , and the liner duct structure  228 , and vice versa. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.