Patent Publication Number: US-10767863-B2

Title: Combustor tile with monolithic inserts

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority from U.S. Patent Application No. 62/195,669, filed on Jul. 22, 2015, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to ceramic matrix composite tiles and support structures therefor, and more particularly to ceramic matrix composite tiles for gas turbine engines. 
     BACKGROUND OF THE DISCLOSURE 
     A gas turbine engine typically includes a compressor, a combustor, and a turbine. The gas turbine engine may also comprise an augmenter or afterburner. The combustor receives compressed air from the compressor and fuel from a fuel injector and includes a combustion chamber where the compressed air and the fuel are mixed and ignited. The combustion chamber may experience temperatures greater than 1,900° F. during the combustion process. Combustion gases flow out of the combustor and cause the turbine to rotate thereby performing work. Combustion reaction products include carbon dioxide (“CO 2 ”) and nitrous oxide (“NOx”). The combustion efficiency and amount of these reaction products depend on the combustion temperature. 
     The combustor includes a liner structured to shield components external of the combustion chamber from the heat produced in the combustion chamber. The liner may be comprised of or coated with insulation materials. Traditional liners comprised metals and alloys. Ceramic matrix composite (“CMC”) liners can withstand higher temperatures than metals and alloys, which enable the gas engine turbines to achieve higher efficiencies. In addition to combustors, CMC structures may be used to line any surface of the gas turbine engine in contact with combustion gases, including exhaust liners, augmenter liners, and blade tracks. 
     The liners are supported by a support structure which is, typically, metallic. Due to the temperature difference between the liner and the support structure, and the forces generated by the products of combustion, the support structure may thermally expand at a different rate than the liner, creating additional structural stresses. These stresses increase in proportion to the temperature of combustion and the power generated therefrom. Therefore, there is a need to provide an improved liner support structure and an improved method of making the improved liner support structure. 
     SUMMARY OF DISCLOSED EMBODIMENTS 
     Embodiments of an annular assembly for a gas turbine engine and a method of making same are provided herein. In one embodiment, the annular assembly comprises a supporting member comprising metal and including a support hole therethrough, and a liner tile made of ceramic matrix composite material. The liner tile is disposed adjacent the supporting member. A plurality of the liner tile form an annular liner to shield hot combustion gases produced by the gas turbine engine. A connecting member comprising ceramic material has a base element and a stem. The base element is embedded in the liner tile during construction of the liner tile to form an integrated structure therewith. A distal end of the stem is configured to pass through the support hole of the supporting member. A retaining member is configured to mate with the distal end of the stem to retain the liner tile adjacent the supporting member. In variations thereof, the annular liner comprises one of a combustor liner, an exhaust liner, an augmenter liner, and a blade track, of the gas turbine engine. 
     In one variation thereof, the ceramic matrix composite material comprises fibers, and the base element is surrounded by the fibers. In another variation thereof, the connecting member is sized and configured to maintain a distance between a supporting member facing side of the liner tile and an internal surface of the supporting member between about 0.030 and 0.090 inches. In one example, a section of the liner tile corresponding to a surface area of the base element protrudes from the supporting member facing side of the liner tile surrounding the base element and contacts the internal surface of the supporting member to maintain the distance. In another example, the stem of the connecting portion comprises a first section connected to and extending from the base element, a second section including the distal portion, and a transition portion therebetween contacting the internal surface of the supporting member to maintain the distance. 
     In a further variation, the integrated structure comprises at least two connecting members, the supporting member comprises at least two support holes therethrough, and the two support holes are shaped to permit lateral movement of the stems of the at least two connecting members to limit structural stresses caused by thermal expansion of the supporting member and the liner tile caused by the hot combustion gases. In one example, two of the at least two support holes have a short axis and a long axis in their cross-sections. The long axis of one of the two support holes is oriented differently than the long axis of the other of the two support holes to permit movement of the stems radially and axially relative to each other. 
     In another embodiment set forth herein, a combustor for a gas turbine engine comprises an annular shroud comprising metal and including a support hole therethrough, and a liner tile made of ceramic matrix composite material. A plurality of the liner tile form an annular liner to shield hot combustion gases produced in the combustor. The liner tile is disposed adjacent the annular shroud. A connecting member comprising ceramic material includes a base element and a stem. The base element is embedded in the liner tile during construction of the liner tile to form an integrated structure therewith. A distal end of the stem is configured to pass through the support hole of the annular shroud. A retaining member is configured to mate with the distal end of the stem to retain the liner tile adjacent the annular shroud. 
     In a further embodiment set forth herein, a method of making an annular assembly for a gas turbine engine comprises laying a first layer of fibers in a tool; positioning a base element of a connecting member on the first layer of fibers; laying a second layer of fibers over the first layer and the base element; infiltrating a ceramic matrix to form a ceramic matrix composite material; and densifying the ceramic matrix composite material to form a liner tile integrated with the base element. The connecting member includes a stem connected to and extending from the base element. The method also comprises inserting a distal end of the stem through a support hole of a supporting member comprising metal; securing a retaining member on the distal end to retain the integrated structure adjacent the supporting member; and repeating the inserting and securing steps to form an annular liner with a plurality of the liner tile for hot combustion gases produced by the gas turbine engine. 
     Additional embodiments encompass some or all the foregoing features, arranged in any suitable combination. Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. 
     The features and advantages of the present disclosure will become more readily appreciable from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of a gas turbine engine; 
         FIG. 2  is a partial cross-sectional view of an embodiment of an annular assembly; 
         FIG. 3  is an expanded partial cross-sectional view of the annular assembly of  FIG. 2 ; 
         FIG. 4  is an expanded partial cross-sectional view of a portion of the annular assembly of  FIG. 4 ; and 
         FIG. 5  is a perspective view of a portion of the annular assembly of  FIG. 4   
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. The exemplifications set out herein illustrate embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the claims in any manner. 
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings, which are described below. The embodiments disclosed below are not intended to be exhaustive or limit the claims to the precise form disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. It will be understood that no limitation of the scope of the claims is thereby intended unless specifically stated. Except where a contrary intent is expressly stated, terms are used in their singular form for clarity and are intended to include their plural form. 
     The disclosure relates to CMC tiles, support structures for CMC tiles, methods of supporting CMC tiles, and gas turbine engines including CMC tiles and supporting structures. CMC tiles exhibit good temperature resistance, fracture toughness under mechanical or thermo-mechanical loads, and lower weight than the structures they replace. These characteristics, and the capability to form CMC components in complex shapes, make CMC components suitable for use as tiles of liners in gas turbine engines. The CMC tiles are supported from support structures that comprise metal and have different thermal expansion coefficients, which can cause additional structural stresses at the high temperatures generated by the gas turbine engine. Embedding a support member in the CMC tile provides structural rigidity in a cost-effective process. The support member may be have a thermal expansion coefficient substantially similar to the thermal expansion coefficient of the CMC tile. A support arrangement that permits the CMC tiles to move relative to member of the support arrangement connected to and supporting the CMC tiles can limit the negative effect of operation at high temperatures, thereby enabling operation at even higher temperatures which may increase the efficiency of the gas turbine engine. Other advantages include reduced weight and reduced thermal expansion of the support arrangement. 
       FIG. 1  is a block diagram of a gas turbine engine  10  rotating a load  12  about a principal axis X and comprising, in the direction of air flow, an air intake assembly  14 , a compressor assembly  16 , a combustor  18  having an annular combustion chamber  40 , a turbine assembly  20 , and an exhaust assembly  22 . In operation, intake air  30  enters the air intake assembly  14 , is compressed in the compressor assembly  16 , and the compressed air is mixed with fuel and ignited in the combustion chamber  40 . A partial cross-sectional view of the combustion chamber  40  is shown in  FIG. 2 . Pressure generated by combustion of the fuel and compressed air mixture causes one or more turbines (not shown) in the turbine assembly  20 , and a turbine shaft  34  connected thereto, to rotate. The load  12  is connected to a load shaft  32  which is coupled to the turbine shaft  34  and rotated by it. Thus, combustion causes the gas turbine engine  10  to work by rotating the load  12 . The load  12  may comprise a fan propeller and be positioned within the air intake assembly  14 . 
     Referring now to  FIG. 2 , the combustion chamber  40  is formed by an internal annular assembly  50  and an external annular assembly  60 , both assemblies radially spaced from the principal axis X of the gas turbine engine  10 . The internal annular assembly  50  comprises an annular liner  52  and an annular shroud or supporting member  54 . The external annular assembly  60  comprises an annular liner  62  and an annular shroud or supporting member  64 . The annular liners  52 , 62  comprise discrete segments, or tiles,  70 , which are supported from the annular shrouds  54 , 64  by the connecting members  80 . Each tile  70  comprises or is substantially constructed of CMC materials. For example the CMC materials in a tile may comprise between about 50% and 100% of the weight of the tile. More preferably the CMC materials comprise between about 80% and 100% of the weight of the tile. As shown in  FIG. 2 , the annular shroud  64  has a plurality of support holes  66  corresponding to the plurality of connecting members  80 . A distal portion of each connecting member  80  passes through each support hole  66  and is secured to the annular shroud  64  by a retaining member (not shown). An embodiment of a retaining member, denoted by numeral  90 , is shown in  FIG. 3 . The annular liners  52 , 62  shield the annular shrouds  54 , 64  from the intense heat generated in the combustion chamber  40 . Thus, less cooling air may be required to operate with CMC liners supported as described herein, which may increase the gas turbine engines&#39; efficiency. 
     For example, when properly supported, CMC tiles can withstand temperatures near 2,200° F. and potentially as high as 2,350° F., where metallic and superalloy liners can only withstand about 1,900° F. Yet in spite of the thermal protection provided by the annular liners  52 , 62 , the annular shrouds  54 ,  64  expand as the temperatures rise. The coefficient of thermal expansion (“CTE”) of metal is about 9.5×10 −6  while the CTE of a CMC component is about 2.5×10 −6 . The annular shrouds  54 , 64  comprise metals, thus they may expand nearly four times as much as the CMC tiles. It is therefore advantageous to secure the tiles  70  to the annular shrouds  54 , 64  in a floating arrangement so that expansion of the annular shrouds  54 , 64  does not create undue structural stresses on the annular liners  52 , 62  or the connecting members  80 . A partial cross-sectional view of an embodiment of the connecting member  80  is shown in  FIG. 3 . A partial cross-sectional view of another embodiment of a connecting member, denoted by numeral  110 , is shown in  FIG. 4 . A floating arrangement is discussed with reference to  FIG. 5 . 
     Referring to  FIG. 3 , an expanded axial view of a section of the external annular assembly  60  of the combustion chamber  40  is shown. The internal annular assembly  50  is constructed in a similar manner. The annular shroud  64  includes, in addition to the support holes  66 , a plurality of cooling holes  92  configured to receive cooling air  94 . The annular liner  62  includes a plurality of cooling passages  96  formed between the tiles  70  to let the cooling air  94  pass therethrough. The cooling air  94  cools the shroud facing, or outer, surface  74  of the tiles  70  and then forms a cooling air layer adjacent the combustion chamber facing, or inner, surface of the tiles  70 . As used herein in connection with a tile  70 , “inner surface” may be used to refer to the surface facing the hot combustion gases and the “outer surface” may be used to refer to the surface facing the shroud or supporting member. Each tile  70  includes an environmental barrier coating (not shown) to prevent water vapor, another combustion reaction product, from reacting with the surface of the CMC tile thereby preventing surface recession in the CMC tile. Exemplary environmental barrier coatings include terbium disilicate and a combination of a doped rare earth disilicate bond coat and a porous rare earth silicate or barium-strontium-aluminosilicate top coat. In embodiments of the present disclosure the tiles  70  and  110  (discussed with reference to  FIGS. 4 and 5 ) have a length, disposed circumferentially, of between about 3 and 9 inches, a width, disposed longitudinally, of between about 1 and 3 inches, and a thickness, disposed radially, of between about 0.060-0.250 inches. However, the tiles may be smaller or larger, and may be longer axially than circumferentially. 
     The connecting member  80  comprises a base element  82 , a stem including a first section  84  connected to and extending from the base element  82 , a second section  88  extending from the first section  84 , and a transition portion, or shoulder,  86  therebetween. In the present embodiment, the annular shroud  64  contacts the transition portion  86  and thus the length of the first section  84  defines a separation distance “d” between the annular liner  62  and the annular shroud  64 . The separation distance is configured to maximize cooling. In one variation, the separation distance is between about 0.090 and 0.300 inches. The retaining member  90  keeps the second section  88 , and the tile  70 , in place. Exemplary embodiments of a retaining member include nuts, snap-rings, C-clips, and any known or future developed component configured to mate with a distal end of the stem to retain the connecting member. In embodiments of connecting members the distal end of the stem is threaded, includes a circumferential slot, or otherwise comprises a feature configured to mate with a corresponding retaining member. The base element comprises a length, a width, and a thickness. The length extends circumferentially and the width extends longitudinally. The base element may comprise geometric shapes including squares, rectangles, circles, ellipses, superellipses, and squircles, in each case exhibiting a curvature radius similar to the radius of the liner. The base element may comprise parallel surfaces that define the thickness of the base element. The base element may also comprise an ellipsoid. Preferably the base element is devoid of corners to avoid stress points. Preferably the rectangles and squares have rounded corners. 
     The connecting members are integrated with the tiles in the process of constructing the tiles. The connecting members may comprise any monolithic ceramic material, green body, reinforced ceramic, or CMC material (either partially or fully densified) that is compatible with the CMC process used to construct the tiles. To construct a tile, fibers are laid in a tool, and at least one connecting member is positioned over the fibers. Exemplary fibers comprise carbon (C), silicon carbide (SiC), alumina (Al 2 O 3 ), mullite (Al 2 O 3 —SiO 2 ), and silicon nitride (Si 3 N 4 ). Exemplary matrices can comprise the same materials, and free silicone. In one example, a connecting member comprises a SiC/SiC matrix composite. More fibers are then laid over the existing fibers and the base element of the at least one connecting member, trapping the base element between the fibers and forming a protruding section, denoted in  FIG. 3  by numeral  72 , corresponding to the surface area and thickness of the base element  82  and protruding from the outer or shroud facing surface  74  of the liner tile. The fibers are then infiltrated. Exemplary infiltration processes include melt, slurry, and chemical vapor infiltration. After infiltration the structure is further processed, for example by intensification. The structure prior to intensification will be referred to as a “green body”. After intensification, the connecting member is permanently mechanically secured in the CMC composite, forming an integrated structure. The connecting member may bond with the CMC matrix. The connecting member may be embedded in the fibers as a green body or as finally processed, and may be machined as a green body, after infiltration, or after densification of the integrated structure. 
     More than one connecting member may be integrated with each tile  70 . In addition to the connecting member  80 , shown in cross-section, a similarly constructed connecting member  78  is shown in  FIG. 3 , not in cross-section, to illustrate that the connecting member  78  is at a different longitudinal position (into the page) in the tile  70  relative to the connecting member  80 . Preferably, between two and seven connecting members  78 , 80  are integrated with each tile  70 , and more preferably three connecting members  78 , 80  are integrated with each tile  70 . However, in a variation of the present embodiment the connecting member includes one base element and at least two spaced-apart stems connected thereto and extending therefrom, the at least two stems passing through two supporting holes in the annular shroud. 
       FIGS. 4 and 5 , sectional and perspective views of a portion of an external annular assembly comprising the annular shroud  64  and embodiments of an annular liner including a CMC tile, illustratively tile  100 , having an outer surface  104  facing the annular shroud  64 . As shown in  FIG. 4 , the tile  100  is integrated with a connecting member  110  having a base element  112 , and a stem  114 , which is secured to the annular shroud  64  by a retaining member  116 . Retaining member  116  is similar to a retaining member  90  and serves the same function. A protruding section  102  of the tile  110  contacts the inner surface of the annular shroud  64  defining the distance d therebetween. The thickness of the base element  112  may be structured to control the distance d. The thickness may be substantially uniform, as shown in  FIG. 4 , or may vary in a uniform manner, for example by decreasing uniformly between the stem  114  and the periphery of the base element  112 . The thickness may also vary in a non-uniform manner, providing on the tile&#39;s surface a thick protruding area, a thin protruding area, and a transition therebetween, the thick protruding area defining the distance d. Preferably the thick protruding area surrounds the stem  114 . 
       FIG. 5  is a perspective view of the tile  100  and a portion of the annular shroud  64  before the tile  100  is secured thereto illustrating an exemplary floating arrangement. As used herein, a floating arrangement means a support structure in which a CMC tile has at least one degree of freedom to move relative to a supporting member to which it is attached. Preferably the floating arrangement provides axial and circumferential freedom of movement. Generally, freedom of movement is provided when one of two support holes has a larger cross-section than the other of two support holes. The larger cross-section may be provided by a larger diameter support hole or a larger axis of an ovoid-shaped support hole. In this embodiment, the tile  100  includes three connecting members denoted by numerals  110 ,  120 , and  130 . The connecting members are identical but denoted by different numerals to denote exemplary positioning of the connecting members on the tile, wherein the connecting members  110  and  120  are aligned on a common plane normal to the principal axis X and the connecting member  130  is on a plane spaced apart from the common plane. Protruding sections  102 ,  124 , and  134  are formed by the base elements of the connecting members  110 ,  120  and  130 , and represent base elements with rounded rectangular shapes, wherein the long axes of the rectangles are oriented circumferentially. The portion of the annular shroud  64  includes three support holes denoted by numerals  66 ,  122 , and  132 . In the present embodiment, each of the support holes  66 ,  122 , and  132  has a long axis and a short axis. In one example, each of the support apertures  66 ,  122 , and  132  comprise a slot with circumferential ends, the short axis of the slot is about 0.270 inches, and the long axis is about 0.300 inches. In the present embodiment the distal end of the stem is cylindrical, thereby providing at least 0.030 inches of potential movement of the tile relative to the supporting member. The long axes of the support apertures  66 , 122  are oriented along the circumference of the annular shroud  64  thereby enabling relative circumferential expansion or contraction of the annular shroud  64  (relative to the annular liner) without creating stress concentrations. The long axis of the support aperture  132  is oriented longitudinally thereby enabling relative longitudinal expansion or contraction of the annular shroud  64  (relative to the annular liner) without creating stress concentrations. In one variation of the present embodiment, a tile is supported by at least two stems, one of the at least two corresponding supporting holes is cylindrical, and the other of the at least two supporting holes is longer than it is wide. In another variation of the present embodiment, a tile is supported by at least two stems, both of the at least two corresponding supporting holes are cylindrical but one has a larger diameter than the other, the larger supporting hole enabling the tile to pivot about the first supporting hole. 
     Other variations of the disclosed embodiments may be implemented to improve upon known assemblies. For example the distance d between the supporting member and the tile may be constant or may vary. In one embodiment, a liner tile is supported by upstream and downstream supporting members (the terms “upstream” and “downstream” corresponding to the direction of air flow from upstream to downstream) and the length of the stem of the upstream connecting member is shorter than the stem of the downstream connecting member such that tiles are axially angled relative to the surface of the shroud. In another embodiment, the liner tile comprises a blade track segment, and the supporting member supporting the liner tile is connected to an annular blade track carrier of the gas turbine engine. The liner tile is supported by the supporting member as described hereinabove and the supporting member is connected to the annular blade track carrier in any manner know to a person of skill in the art of gas turbines. 
     While the invention herein disclosed has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.