Patent Publication Number: US-8122727-B2

Title: Compliant metal support for ceramic combustor liner in a gas turbine engine

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     The instant application is a divisional application of U.S. patent application Ser. No. 11/117,599, filed Apr. 27, 2005, entitled COMPLIANT METAL SUPPORT FOR CERAMIC COMBUSTOR LINER IN A GAS TURBINE ENGINE, now U.S. Pat. No. 7,647,779. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a combustion system for an engine, such as a gas turbine engine, and more particularly, to a compliant metal support for a ceramic combustor liner used in the combustion system. 
     (2) Prior Art 
     A gas turbine engine consists of an inlet, a compressor, a combustor, a turbine, and an exhaust. The compressor draws in ambient air and increases its temperature and pressure. Fuel is added to the compressed air in the combustor to further raise gas temperature. The high temperature gas expands in the turbine to extract work that drives the compressor and other mechanical devices such as an electric generator. 
     To reduce NO x  produced in the combustor, it is desirable to reduce flame temperature. This requires a high percentage of the compressed air to be mixed with the fuel to produce a lean fuel air mixture. Such a lean combustion reduces the air available for combustor liner cooling and/or increases pressure loss during the cooling of the combustor liner. To lower the cooling air requirement and the attendant pressure loss, high temperature ceramic materials have been proposed for combustor liners. Although ceramic materials have excellent high temperature strength, their coefficients of thermal expansion (CTE) are much lower than those of metals. Thermal stress arising from the mismatch of the CTEs poses a challenge to the insertion of ceramic combustor liner into gas turbine engines. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a combustor system for an engine having a ceramic component and at least one metal component with a structure for controlling the thermal stresses which are produced. 
     It is a further object of the present invention to provide a structure as above which spreads the local contact stress in the attachment area by using a compliant interface layer. 
     It is yet a further object of the present invention to provide a structure as above which stops the reaction between the ceramic component and the metal component(s) by using an interface layer that is chemically non-reactive to both the ceramic component and the metal component(s). 
     The foregoing objects are attained by the present invention. 
     In accordance with the present invention, a combustion system for an engine is provided. The combustion system broadly comprises a ceramic component, at least one metal support component for providing radial and axial support to the ceramic component, and the at least one metal support component having means for minimizing stress and for increasing compliance of the metal support component with respect to the ceramic component. 
     Other details of the compliant metal support for a ceramic combustor liner in a gas turbine engine, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a ceramic combustor liner inside a metal casing; 
         FIG. 2A  is an exploded cut-away view of the inner combustion system; 
         FIG. 2B  is a perspective view of the metal support ring showing the main slots; 
         FIG. 3  is a sectional view of a portion of a ceramic liner attachment area; 
         FIG. 4  illustrates a double metal wall attachment method for a ceramic combustor liner; 
         FIGS. 5A-5H  illustrate the use of a U-shaped metal ring and corrugated strips as a compliant support; 
         FIG. 6  illustrates an alternative embodiment of a ceramic combustor liner inside a metal casing; 
         FIG. 7  is an exploded view of the inner combustion system of  FIG. 6 ; 
         FIG. 8  illustrates a portion of a ceramic liner attachment area in the embodiment of  FIG. 6 ; and 
         FIG. 9  illustrates an insulating ring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to the drawings,  FIGS. 1-3  illustrate a first embodiment of a portion of a combustion system of an engine, such as a gas turbine engine. Within the engine, the combustion system is positioned intermediate the compressor section(s) and the turbine section(s) of the engine. In the combustion section, pressurized air is received from the compressor section(s) and mixed with fuel in a known manner. 
     Referring now to  FIG. 1 , a combustion system  10  in accordance with the present invention may include an upper metal casing  12 , a lower metal casing  14 , a fuel air pre-mixer  16 , a fuel supply manifold  18 , a metal support ring  20  and a ceramic combustor liner  24 .  FIG. 2  depicts an exploded view of the combustion system  10  of  FIG. 1  without the upper and lower metal casings  12  and  14 . 
     As best shown in  FIG. 2 , the metal support ring  20  has an upper annular member  32  and a lower annular member  34 . The upper member  32  and the lower member  34  are joined together by a plurality of spaced radial arms  36 . The upper annular member  32  has a shoulder portion  22 . The fuel manifold  18  is positioned so that it rests on the shoulder portion  22 . As shown in  FIGS. 1 and 3 , the upper metal casing  12  has a first flange portion  13  and the lower metal casing  14  has a second flange portion  15 . The fuel manifold  18  and the shoulder portion  22  are sandwiched between the first and second flange portions  13  and  15 . The flange portions  13  and  15  are fastened to each other. Any suitable means known in the art, such as bolts, may be used to fasten the flange portions  13  and  15  together and thereby maintain the fuel manifold  18  and the upper annular member in a fixed position. For example, bolts may pass through aligned openings in the flange portions  13  and  15 , the fuel manifold  18 , and the shoulder portion  22  if desired. 
     The pre-mixer  16  is positioned within the casings  12  and  14  so that a lower portion  17  passes through a central opening  21  in the lower annular member  34 . The pre-mixer is seated within a neck portion  25  of the ceramic combustor liner  24 . As can be seen in  FIG. 3 , the pre-mixer  16  has a C-shaped channel  26  adjacent its lower end. Seated within the C-shaped channel  26  is a sealing element  28 , such as a rope seal. The sealing element  28  which against an inner surface  30  of the neck portion  25  of the ceramic combustor liner  24  to create a seal between the pre-mixer  16  and the ceramic combustor liner  24 . 
     The metal support ring  20  provides both radial and axial support to the ceramic combustor liner  24 . The dimensional tolerance is set such that a slip fit exists between the metal support ring  20  and the ceramic combustor liner  24  at room temperature. At elevated temperatures, the metal support ring  20  expands more than the ceramic combustor liner  24  and results in interference between the two. The interference generates tensile hoop stress in the ceramic combustor liner  24  and is detrimental to the mechanical integrity of the ceramic combustor liner  24 . To minimize the stress and to increase the compliance, the metal support ring  20  has a plurality of spaced apart, axial slots  23  formed in the lower member  34 . As can be seen in  FIGS. 2A and 2B , the axial slots  23  are U-shaped and open at their bottom end. The provision of the U-shaped and open axial slots  23  allows relative movement between the metal support ring  20  and the ceramic combustor liner  24 . 
     The ceramic combustor liner  24  is provided with a plurality of spaced apart openings  38  in the neck portion  25 . Each opening  38  aligns with a respective one of the axial slots  23 . The ceramic combustor liner  24  may be joined to the metal support ring  20  by passing a plurality of fastening means  40  through the holes  38  and through the aligned axial slots  23 . Metal bushings  42  may be placed around the fastening means  40 , if needed, to spread the contact load between the fastening means  40  and the ceramic combustor liner  24 . Any suitable fastener known in the art, such as a bolt or a pin, that provide axial and circumferential support to the liner  24  may be used for the fastening means  40 . The fastening means  40  are preferably screwed on the metal support ring  20 . 
       FIG. 4  illustrates a variation of the combustion system shown in  FIGS. 1-3 . Instead of a single walled metal support ring, the metal support ring  20  has a double wall construction. At room temperature, the neck portion  25  of the ceramic combustor liner  24  is in contact with an outer wall  60  of the metal support ring  20 . At elevated temperatures, the ceramic combustor liner  24  is in contact with an inner wall  62  of the metal support ring  20 . The diameters of the inner and outer walls  62  and  60  respectively are such that a slide fit exists at room temperature and only slight interference exists at elevated temperatures. Both walls  60  and  62  may be provided with axial slots (not shown) to reduce stiffness. 
     As shown in  FIG. 4 , the lower portion  17  of the pre-mixer  16  is positioned within a central opening  21  in the support ring  20 . The pre-mixer  16  has a C-shaped channel  26  in an outer surface  64 . A sealing element  66 , such as a piston ring, is located within the C-shaped channel  26 . In use, the sealing element  66  forms a seal against an inner surface  68  of the metal support ring  20 . 
     To fasten the metal support ring  20  to the ceramic combustor liner  24 , a plurality of threaded bores  70  may be provided about the circumference of the outer wall  60  of the metal support ring  20 . The neck portion  25  may have a plurality of openings  38  which align with the bores  70 . A fastener  40  may be inserted into each bore  70  and into each opening  38 . If desired, each fastener  40  may have an external thread which mates with an internal thread in the a respective bore  70 . Each fastener  40  may be a metal bolt or any other suitable fastener known in the art. If desired, a bushing  42  may be placed around the fastener  40 . 
       FIGS. 5A-5H  illustrate still other embodiments of a combustor system in accordance with the present invention. In the embodiment of  FIG. 5A , there is a mixer  72  and a ceramic combustor can or liner  24 . As shown in more detail in  FIGS. 5B ,  5 C, and  5 H, the mixer  72  may have an inclined surface  74 . A shaped metal support ring  120  may be used to support an inside diameter of the ceramic combustor liner  24 . The metal support ring  120  may have a planar member  76  that has a surface  78  which rests against an undercut  80  in the mixer  72 . The support ring  120  may further have an outer metal lip  82  that contacts the ceramic combustor liner  24 . Within the metal lip  82 , there is a C-shaped channel  84  and a plurality of compliant taps  86  placed over the channel  84 . Each of the taps  86  is provided with an opening  88 . The openings  88  about the support ring  120  align with the openings  38  in the neck portion  25  of the ceramic combustion liner  24 . To join the ceramic combustion liner  24  to the support ring  120 , a fastener  40  is placed through the openings  38  and the openings  88 . Each fastener may comprise any suitable fasteners known in the art, such as a metal bolt. The metal taps  86  behave like beams. When the taps  86  are loaded, they bend like beams. For a given load, the amount of bending is controlled by the tap material stiffness, tap length, width and height. Therefore to increase the degree of compliance of the taps  86 , one can choose a soft material, increase tap length and/or reduce tap width and height. Compliant taps  86  enable large deformation to accommodate thermal growth mismatch without creating high loading. Such an arrangement may be more compliant than the metal ring configurations shown in the embodiments of  FIGS. 1-4 . 
     Referring now to the embodiment of  FIGS. 5D through 5G , a metal support ring  220  may be positioned adjacent the surface  74  of the mixer  72 . Instead of using axial slots to provide compliance, a corrugated, outer spring element  90  may be placed between the metal support ring  220  and the inner surface  92  of the ceramic liner  24 . A corrugated, inner spring element  94  may be placed adjacent an outside surface  96  of the ceramic liner  24 . Each of the spring elements  90  and  94  may have an end cut so that they are free to extend under compression and are therefore segmented. Further, each of the spring elements  90  and  94  may have a plurality of spaced apart openings  98  and  100  respectively. An outer segmented clamping ring  102  is provided to hold the corrugated spring elements  90  and  94  and the combustor liner  24  together. As can be seen from  FIG. 5G , the clamping ring  102  also has a plurality of spaced apart openings  104 . When properly positioned, the openings  104  align with the openings  98  and  100  and the openings  38  in the neck portion  25  of the ceramic combustor liner  24 . A plurality of fasteners  40  may be used to join the clamping ring  102  to the spring elements  90  and  94  and to the ceramic combustor liner  24 . The fasteners  40  may comprise any suitable fastener known in the art, such as metal bolts. The axial support for the ceramic combustor liner  24  comes from the fasteners  40 , and friction resulting from the interference at temperature between the liner  24  and the metal support ring  220 . Metal bushings (not shown) may be inserted into the openings to spread the contact load between the fasteners  40  and the ceramic combustor liner  24 . The metal bushings may be sized to be smaller than the diameter of the openings so that no interference situation exists between the bushings and the openings in the ceramic liner  24  at elevated temperatures during engine operation. 
     Since the thermal stress produced by thermal growth differential is proportional to the structural stiffness, temperature rise and difference in the CTE, the ceramic combustor liner may be attached to metal cones, as will be discussed hereinafter, at a region that experiences lower temperatures compared to the rest of the ceramic combustor liner. Additionally, the metal support rings of the embodiments discussed hereinabove can be made of low CTE materials such as IN909 and IN783. To reduce structural stiffness of the metal support rings, axial slots may be introduced as discussed above. If a further reduction in structural stiffness is desired, a material with low Young&#39;s modulus, thin wall thickness, increased and longer slots can be considered for the metal support ring(s). Although low structural stiffness is critical in managing the thermal stress, high structural stiffness is required to maintain resistance to resonance in the ceramic combustor liner due to engine vibration. Therefore, caution should be exercised to strike a fine balance between resistance to thermal stress and resistance to structural resonance. 
     The ceramic combustor liner  24  illustrated in the embodiments of  FIGS. 1-5G  may consist of three segments—a neck portion  25  formed by a small diameter cylinder at the attachment area, a dome portion  106 , and a large cylinder portion  108 . Together, the three segments form an integral ceramic combustor liner. The neck portion  25  formed from the smaller cylinder could be locally thickened to provide extra strength at the attachment area. The rest of the ceramic combustor liner  24  may have a uniform thickness. 
     Referring now to  FIGS. 6-8 , there is shown another embodiment of a combustion system  10  in accordance with the present invention. The combustion system  10  includes an upper metal casing  12 , a lower metal casing  14 , a fuel air pre-mixer  16 , a fuel manifold  18 , and a ceramic combustor liner  24 . The attachment scheme for the ceramic combustor liner  24  includes an inner continuous metal cone  110  with radial slots  112 , and an outer segmented metal cone  114  with radial slots  116 . 
     The outer metal cone  114  is sandwiched between the fuel manifold  18  and the lower metal casing  14 . The outer metal cone  114  preferably has the same number of spokes  122  as the fuel manifold  18  so as to cause minimal disruption of the airflow external to the fuel air pre-mixer  16 . The outer metal cone  114  has a shoulder portion  118  attached to the spokes  122 . As can be seen from  FIG. 6 , the fuel manifold  18  may rest in whole or in part on the shoulder portion  118 . Further, the upper metal casing  12  has a first flange portion  13  and the lower metal casing has a second flange portion  15 . In a preferred embodiment, a portion of the fuel manifold  16  and the shoulder portion  118  are positioned between the first flange portion  13  and the second flange portion  15 . If desired, the flange portions  13  and  15  may be fastened to each other. For example, each of the flange portions  13  and  15 , the fuel manifold  18 , and the shoulder portion  122  may have aligned openings through which a fastener, such as a bolt, may be passed. 
     The outer cone  114  may consist of three segments to assist assembly of the combustion system  10 . More or fewer segments are possible if desired. The material for the outer cone  114  is preferably chosen to be the same as the material forming the lower metal casing  14  to minimize the thermal fight between the two components. 
     As can be seen from  FIGS. 6-8 , each of the cones  110  and  114  has a central opening  124 . This allows the fuel air pre-mixer  16  to be positioned against the ceramic combustor liner  24 . 
     As can be seen from  FIG. 8 , the ceramic combustor liner  24  has a flared-out cone portion  126  at the attachment area. The cone portion  126  is positioned between the inner metal cone  110  and the outer metal cone  114 . The inner metal cone  110  is preferably fastened to the outer cone  114 , using any suitable fastening means known in the art, after the ceramic combustor liner  24  is placed between the cones  110  and  114 . 
     While the inner cone  110  is preferred to be continuous, it too may be formed from a plurality of segments if desired. Insulating material  111 , as shown in  FIG. 9 , may be inserted between the cones  110  and  114  and the ceramic combustor liner  24  to prevent heat flow from the ceramic combustor liner  24  to the cones  110  and  114  and potential reaction between the ceramic combustor liner  24  and the cones  110  and  114 . Preferably, the insulating material  111  is compliant and easily deformable to distribute the clamping force uniformly onto the ceramic combustor liner  24 . 
     The initial gap between the cones  110  and  114  may be set to be smaller than the flared-out conical portion  126  of the ceramic combustor liner  24 . In this way, a compressive clamping force may be introduced during assembly and maintained during engine operation. The clamping force is preferably such that relative movement between the ceramic combustor liner  24  and the cones  110  and  114  is possible when the combustion system  10  cycles up and down in temperature. This relative movement relieves thermal stress build-up between the cones  110  and  114  and the ceramic combustor liner  24 . 
     The conical construction of this embodiment allows accurate locating of the ceramic combustor liner  24  during assembly and maintains ceramic combustor liner concentricity during engine operation. It also accommodates thermal expansion mismatch during engine operation. 
     The ceramic combustor liner  24  may consist of four segments—the flared-out cone portion  126  at the attachment area, a neck portion  25  formed by a smaller straight cylinder, a dome portion  128 , and a large cylindrical portion  130 . Together, they form an integral ceramic combustor liner  24 . The flared-out cone portion  126  may be thickened to provide extra strength. The rest of the ceramic combustor liner  24  may have a smaller thickness. It also provides a convenient means to balance the thrust load on the ceramic combustor liner  24  due to the pressure drop through the fuel air pre-mixer  16 . Such a design eliminates the need for fastening holes that can be sources of stress risers. 
     The fuel air pre-mixer  16  may be made of a high temperature alloy. Its high CTE compared to the ceramic combustor liner&#39;s CTE may lead to interference and overloading of the ceramic combustor liner  24  at temperature. Therefore, the initial gap needs to be sized such that no such interference and overloading will occur at all engine conditions. This is achieved by statistical component stack-up analysis. To plug this gap, a sealing element  132 , such as a piston ring, may be positioned within a C-shaped channel  134  in the wall  136  of the pre-mixer  16  and positioned within the fuel air pre-mixer  16  and the neck portion  25  of the ceramic combustor liner  24 . The fuel air pre-mixer  16  may be locally thickened where the sealing element  132  is situated. The extra thick portion of the pre-mixer  16  helps to reduce leakage through the gap. Ramps (not shown) may be introduced to facilitate the sealing element  132  sliding into its sealing channel  134 . 
     The exit end  138  of the fuel air pre-mixer  16  is exposed directly to the hot gas flame. To avoid overheating, the wall at the exit end  138  should be thin and cooled from the backside. The large number of holes  139  insures even distribution of cooling air. 
     The ceramic combustor liner  24  is supported at the flared out cone portion  126  only. The exit end  140  of the ceramic combustor liner  24  is free to slide in and out of a combustor transition duct with finger seals. This arrangement prevents jamming and other modes of deformation that could potentially damage the ceramic combustor liner  24 . Additionally, a sealing element, such as a piston ring, can be placed between the ceramic combustor liner  24  and the transition duct to reduce leakage of compressor discharge air into the duct, which is detrimental to the NO x  emission of the combustion system. 
     The various combustion system embodiments shown herein provide several advantages. For example, the embodiments have (1) means that control the thermal stress by structural members with predefined stiffness; (2) a predefined structural stiffness that can be the results of structure material and/or geometrical dimensions of the structural member; (3) means to spread the local contact stress in the attachment area by using a compliant interface layer; (4) means to stop the reaction between a ceramic member and a metal structure by using an interface layer that is chemically non-reacting to both the ceramic and the metal member; and (5) means to reduce the heat flow by a heat insulating interface layer between the ceramic member and the metal structure. 
     It is apparent that there has been provided in accordance with the present invention a compliant metal support for a ceramic combustor liner in a gas turbine engine which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other alternatives, modifications, and variations will become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.