Abstract:
A fuel nozzle includes a fuel plenum, an outer body surrounding the fuel plenum, and bore holes that extend longitudinally through the outer body. The fuel nozzle also includes means for fixedly attaching the fuel plenum to the outer body and passages that provide fluid communication between the fuel plenum and the bore holes. A method for manufacturing a fuel nozzle includes drilling bore holes longitudinally through an outer body and drilling passages in the outer body to the bore holes. The method further includes inserting a fuel plenum into the outer body, wherein the passages provide a fluid communication between the bore holes and the fuel plenum, and attaching the fuel plenum to the outer body.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a fuel nozzle in a combustor and a method for making such a fuel nozzle. 
     BACKGROUND OF THE INVENTION 
     Combustors are widely used in commercial operations. For example, a typical gas turbine includes at least one combustor that injects fuel into the flow of a compressed working fluid and ignites the mixture to produce combustion gases having a high temperature and pressure. The combustion gases exit the combustor and flow to a turbine where they expand to produce work. 
       FIG. 1  provides a simplified cross-section of a combustor  10  known in the art. A casing  12  surrounds the combustor  10  to contain the compressed working fluid. Nozzles are arranged in an end cover  16 , for example, with primary nozzles  18  radially arranged around a secondary nozzle  20 , as shown in  FIG. 1 . A liner  22  downstream of the nozzles  18 ,  20  defines an upstream chamber  24  and a downstream chamber  26  separated by a throat  28 . The compressed working fluid flows between the casing  12  and the liner  22  to the nozzles  18 ,  20 . The nozzles  18 ,  20  mix fuel with the compressed working fluid, and the mixture flows from the nozzles  18 ,  20  into the upstream  24  and downstream  26  chambers where combustion occurs. 
     During full speed base load operations, the flow rate of the fuel and compressed working fluid mixture through the nozzles  18 ,  20  is sufficiently high so that combustion occurs only in the downstream chamber  26 . During reduced power operations, however, the primary nozzles  18  operate in a diffusion mode in which the flow rate of the fuel and compressed working fluid mixture from the primary nozzles  18  is reduced so that combustion of the fuel and the compressed working fluid mixture from the primary nozzles  18  occurs in the upstream chamber  24 . During all operations, the secondary nozzle  20  operates as a combined diffusion and premix nozzle that provides the flame source for the operation of the combustor. In this manner, fuel flow through the primary and secondary nozzles  18 ,  20  can be adjusted, depending on the operational load of the combustor, to optimize nitrous oxide NOx emissions throughout the entire operating range of the combustor. 
     Various efforts have been made to design and manufacture fuel nozzles with improved premixing and diffusion capabilities, especially for higher reactivity fuels. For example, direct metal laser sintering, braising, and casting are manufacturing techniques previously used to fabricate fuel nozzles that premix the fuel and compressed working fluid prior to combustion. However, these manufacturing techniques are relatively expensive, time-consuming, and otherwise less than optimum for large-scale production. Therefore, an improved fuel nozzle that can pre-mix the fuel and compressed working fluid prior to combustion would be desirable. In addition, an improved method for making such a nozzle that utilizes less expensive machining techniques rather than other more costly techniques would be desirable. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     One embodiment of the present invention is a fuel nozzle that includes a fuel plenum and an outer body surrounding the fuel plenum. The outer body includes a plurality of bore holes that extend longitudinally through the outer body. The fuel nozzle further includes means for fixedly attaching the fuel plenum to the outer body and a plurality of passages in the outer body between at least some of the plurality of bore holes and the fuel plenum, wherein the plurality of passages provide fluid communication between the fuel plenum and at least some of the plurality of bore holes. 
     Another embodiment of the present invention is a fuel nozzle that includes an outer body, wherein the outer body includes a plurality of bore holes that extend longitudinally through the outer body. A fuel plenum is inserted into the outer body, and a connection is between the outer body and the fuel plenum, wherein the outer body is fixed to and removable from the fuel plenum. A plurality of passages is in the outer body between at least some of the plurality of bore holes and the fuel plenum, wherein the plurality of passages provide fluid communication between the fuel plenum and at least some of the plurality of bore holes. 
     A still further embodiment of the present invention is a method for manufacturing a fuel nozzle. The method includes drilling a plurality of bore holes longitudinally through an outer body and drilling a plurality of passages in the outer body to at least some of the plurality of bore holes. The method further includes inserting a fuel plenum into the outer body, wherein the plurality of passages in the outer body provide a fluid communication between at least some of the plurality of bore holes and the fuel plenum, and attaching the fuel plenum to the outer body. 
     Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  shows a simplified cross-section of a combustor known in the art; 
         FIG. 2  shows a cross-section of a perspective view of a fuel nozzle according to one embodiment of the present invention; and 
         FIG. 3  shows a cross-section of a fuel nozzle according to an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Embodiments of the present invention may be machined and assembled to create a premixed direct injection (PDI) fuel nozzle design. In general, the fuel nozzle design comprises two components which may be separately machined or fabricated for subsequent assembly. One piece may be referred to as the tip or outer body, and the other piece may be referred to as the fuel cartridge or fuel plenum. The fuel plenum directs fuel downstream against a front wall of the outer body to provide impingement cooling to the front wall. After impinging against the front wall, the fuel then flows through passages to bore holes in the outer body where the fuel mixes with a fluid flowing through the bore holes before exiting the fuel nozzle and flowing into the combustion chamber. The fuel plenum and outer body, with their various bore holes and other passages, may be readily manufactured by machining instead of requiring more costly processes such as direct metal laser sintering. As a result, fuel nozzles according to various embodiments of the present invention may be less expensive to manufacture, while still providing improved cooling to the fuel nozzle and premixing the fuel prior to combustion. 
       FIG. 2  shows a cross-section of a perspective view of a fuel nozzle  30  according to one embodiment of the present invention. As will be explained, the fuel nozzle  30  generally includes two modular components, namely a fuel cartridge  31  that defines a or fuel plenum  32  and an outer body  34 , which may be separately machined or fabricated for subsequent assembly. The fuel cartridge  31  provides a chamber or conduit for fuel flow to and through the fuel nozzle  30 . For example, the fuel cartridge  31  may comprise a longitudinal passage  36  centrally located in the fuel nozzle  30 , as shown in  FIG. 2 . An inlet  38  to the fuel cartridge  31  may be connected to a fuel supply (not shown). Possible fuels supplied to and used by commercial combustion engines include, for example, blast furnace gas, coke oven gas, natural gas, vaporized liquefied natural gas (LNG), propane, and hydrogen. The fuel cartridge  31  may further include a plurality of apertures  40 . The apertures  40  may be located, for example, at the downstream portion of the fuel cartridge  31 , as shown in  FIG. 2 . The plurality of apertures  40  allow the fuel to flow through the fuel cartridge  31  and out of the fuel plenum  32 . 
     The outer body  34  includes a front wall  42  downstream of the fuel cartridge  31  and proximate to the plurality of apertures  40  in the fuel cartridge  31 . The front wall  42  is generally the closest portion of the fuel nozzle  30  to the combustion flame and therefore is subjected to higher temperatures than the remainder of the fuel nozzle  30 . Fuel flowing through the plurality of apertures  40  exits the fuel plenum  32  and impinges on the front wall  42  to provide impingement cooling to the front wall  42 . 
     The outer body  34  generally surrounds the fuel cartridge  31 , creating a space or annular plenum  44  between the fuel cartridge  31  and the outer body  34 . The outer body  34  further includes a plurality of bore holes  46  that extend longitudinally through the outer body  34 . The bore holes  46  may be arranged in any desired pattern. For example, as shown in  FIG. 2 , the bore holes  46  may be arranged in substantially concentric circles around the fuel cartridge  31 . The bore holes  46  are generally cylindrical in shape, although the present invention is not limited to any particular shape of bore holes  46 , unless specifically recited in the claims. Each bore hole  46  generally includes an inlet  48 , which may be beveled, as shown in  FIG. 2 , to facilitate an even distribution of fluid flow into and through the bore holes  46 . 
     The outer body  34  further includes a plurality of passages  50  between at least some of the bore holes  46  and the fuel cartridge  31 . The plurality of passages  50  provide fluid communication between the annular plenum  44  and at least some of the plurality of bore holes  46 . Specifically, fuel exiting the fuel cartridge  31  through the plurality of apertures  40  impinges on the front wall  42  to provide impingement cooling to the front wall  42 . The fuel then flows through the annular plenum  44  until it reaches one of the plurality of passages  50  where it flows into the associated bore hole  46 . In this manner, the fuel mixes with the fluid (e.g., compressed working fluid from a compressor) flowing through the bore hole  46  before exiting the bore hole  46  and entering the combustion chamber. 
     The fuel cartridge  31  and outer body  34  may be separately machined and manufactured for subsequent assembly. For example, the fuel cartridge  31  and/or outer body  34  may be cast from a molten metal. The various bore holes  46  and passages  50  in the outer body  34  may then be drilled to accurately and inexpensively position, size, and orient the various elements in the outer body  34 . If desired, the inlet  48  to various bore holes  46  may be further machined to include a beveled surface or otherwise increase the surface area of the inlet  48  for specific boreholes  46 , depending on particular design considerations. The fuel cartridge  31  may then be inserted into the annular plenum  44  defined by the outer body  34  and attached to the outer body  34 , 
     Various methods and means are known in the art for attaching or connecting the fuel cartridge  31  to the outer body  34 . For example, brazing, welding, complementary threads, seal rings, and other equivalent techniques and connections are known in the art for attaching or connecting the fuel cartridge  31  to the outer body  34 . Depending on the particular design needs, the connection between the fuel cartridge  31  and the outer body  34  may be permanent or temporary to allow for removal of the fuel cartridge  31  during maintenance or repair. The particular embodiment shown in  FIG. 2  includes a continuous weld bead  52  between the fuel plenum  32  and the outer body  34 . In addition, this particular embodiment also includes a threaded connection  54  between the fuel cartridge  31  and the outer body  34 . Alternate embodiments within the scope of the present invention may include only one of these means for attaching or connecting the fuel cartridge  31  to the outer body  34 , and/or other welding techniques, such as tack welding, and/or other mechanical fittings or connections between the fuel cartridge  31  and the outer body  34 . 
       FIG. 3  shows a cross-section of a fuel nozzle  56  according to an alternate embodiment of the present invention. The fuel cartridge  31  and outer body  34  in this embodiment are substantially similar to the embodiment previously described and illustrated in  FIG. 2 , and the same reference numbers are therefore used. In this particular embodiment, the means for attaching or connecting the fuel cartridge  31  to the outer body  34  again includes a continuous weld bead  52  around the perimeter of the fuel plenum  32 . In addition, the cross-section of this particular embodiment illustrates the plurality of passages  50  between bore holes  46  located at different distances from the fuel cartridge  31 . In this manner, the fuel may be more evenly distributed and mixed in specifically selected bore holes  46 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.