Abstract:
A gas turbine component ( 20 ) with a layer of ceramic material ( 22 ) defining a wear surface ( 21 ), in which an array of cross-shaped depressions ( 26 A,  26 B) formed in the wear surface ( 21 ) define a continuous labyrinth of orthogonal walls ( 28, 30 ) of the ceramic material, and reduce the area of the wear surface ( 21 ) by about 50%. Within a representative area ( 36 ) of the wear surface ( 21 ), the depressions ( 26 A,  26 B) provide a ratio of a lineal sum of depression perimeters ( 27 ) divided by the representative area ( 36 ) of the wear surface of least 0.9 per unit of measurement for improved abradability characteristics of the wear surface ( 21 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to gas turbines, and more particularly to an igniter assembly used in conjunction with a gas turbine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Several conventional igniter assemblies for gas turbines have been developed.  FIG. 1  illustrates an example of such a conventional igniter assembly  110  used to control leakage of air flowing through an opening  118  within a combustion liner  119 . As illustrated in  FIG. 1 , the conventional igniter assembly  110  provides an igniter boss  115  which extends from the perimeter of the opening  118  and encircles an igniter  114  to minimize an air flow into the igniter cavity and through the opening  118 . 
         [0003]      FIG. 2  illustrates another example of a conventional igniter assembly  210  to control leakage of air flowing through an opening  218  within a combustion liner  219 . The conventional igniter assembly  210  provides an igniter  214  disposed within an igniter housing  216 . An igniter boss  215  extends from the perimeter of the opening  218  to a base  226  of the igniter housing  216 , to minimize the air flow into the igniter cavity and through the opening  218 . 
         [0004]    An additional example of a conventional igniter assembly is disclosed in U.S. Pat. No. 6,920,762 to Wells et al. As illustrated in  FIG. 2  of Wells et al., an igniter assembly  38  provides an igniter  36  with a tip  44  that passes through an opening  47  in an outer casing  30 , a pair of springs  42 , 52 , a first ring  46  and an opening  40  in a combustion liner  16  adjacent to a combustion chamber  14 . The igniter assembly  38  positions the igniter  36  between an outer casing  30  and the combustion liner  16  to maintain an alignment of the igniter  36  with respect to the combustion liner opening  40 . Since the outer casing  30  has a greater thermal growth characteristic than the combustion liner  16 , the outer casing  30  experiences thermal growth which exceeds that of the combustion liner  16 . During such thermal growth, the outer casing  30  and igniter  36  slide in a radial direction relative to the combustion liner  16 , and the springs  42 , 52  impart a predetermined load between the outer casing  30  and the liner  16  in order to maintain the alignment of the igniter  36  through the opening  40 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The invention is explained in the following description in view of the drawings that show: 
           [0006]      FIG. 1  is a sectional view of a conventional igniter assembly for a gas turbine; 
           [0007]      FIG. 2  is a sectional view of a conventional igniter assembly for a gas turbine; 
           [0008]      FIG. 3  is an exploded sectional view of an exemplary embodiment of an igniter housing, an igniter, and a top guide portion of an igniter assembly; 
           [0009]      FIG. 4  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 3 , including a cover portion of the igniter assembly; 
           [0010]      FIG. 5  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 4 , including a bottom guide portion of an igniter housing; 
           [0011]      FIG. 6  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 5 , where the top guide portion and bottom guide portion are welded together; 
           [0012]      FIG. 7  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 6 , including a spring of the igniter assembly; 
           [0013]      FIG. 8  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 7 , including a base portion of the igniter assembly; and 
           [0014]      FIG. 9  is a sectional view of the exemplary embodiment of the igniter assembly of  FIG. 8 , where the base portion and the cover portion are welded together. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The inventor has recognized that although the conventional igniter assembly  110  illustrated in  FIG. 1  is designed to reduce an airflow passing through the opening  118  within the combustion liner  119 , the positioning of the igniter boss  115  around the igniter  114  introduces a radial gap  117  between the igniter boss  115  and the igniter  114  to facilitate an undesired air flow to pass through the opening  118 . Additionally, the inventor has recognized that although the conventional igniter assembly  210  illustrated in  FIG. 2  is similarly designed to reduce an airflow passing through the opening  218  in the combustion liner  219 , the positioning of the igniter boss  215  proximate to the igniter housing base  226  introduces an axial gap  217  between the igniter boss  215  and the igniter housing base  226  to facilitate an undesired air flow to pass through the opening  218 . Thus, the inventor has recognized that there is a need to provide an igniter assembly with an air seal to eliminate radial gaps and axial gaps within the igniter assembly which facilitate the passage of an undesired air flow through the opening in the combustion liner. 
         [0016]    The inventor has recognized that although the igniter assembly  38  of the Wells et al. patent provides an air seal for a radial gap  40  in the combustion liner  16 , the air seal is limited to the igniter tip  44  being in an extended position beyond the combustion liner  16 . The inventor has recognized that if the igniter tip  44  of the Wells et al. patent were to retract through the combustion liner  16 , a noticeable undesired air flow would be generated through the opening  40  and into the combustion chamber  14 . Accordingly, the inventor has developed an igniter assembly featuring an air seal which prevents an air flow from entering the opening of the combustion liner, regardless of whether the igniter is in a retracted position or an extended position with respect to the combustion liner. 
         [0017]    Additionally, the inventor has recognized that even if the igniter tip  44  remains in the extended position beyond the combustion liner  16 , the igniter assembly  38  provides no structure to prevent an air flow from passing through an axial gap in the igniter assembly  38  attributed to thermal growth properties in the axial direction of the outer casing  30  and the combustion liner  16 . For example, the lone pair of springs  42 ,  52  surrounding the igniter do not provide an adequate air seal to prevent such an air flow. Accordingly, the inventor has developed an igniter assembly with an air seal having the appropriate structural features to prevent an air flow from passing through a respective radial gap or axial gap within the igniter assembly attributed to thermal expansion properties. 
         [0018]    The inventors have additionally recognized that the pair of springs  42 ,  52  in Wells et al. are positioned within an open area of the igniter assembly  38 , thereby posing a risk in the event that a portion of a spring  42 , 52  were to break away and fall through the opening  40  into the combustion chamber  14 , or to interfere with the motion of the igniter  36 . Accordingly, the inventor has developed an air seal featuring a spring which is captured within a stagnant volume, thereby reducing the risk posed by such a spring. 
         [0019]      FIG. 9  illustrates an exemplary embodiment of an igniter assembly  10  of a gas turbine  12 . The igniter assembly  10  includes an igniter  14  disposed within an igniter housing  16 , which encircles the igniter  14 . Although the exemplary embodiment of the igniter assembly  10  in  FIG. 3  features a circular igniter housing  16  and other circular components encircling the igniter  14  and the igniter cavity  13 , the igniter housing and the other components may be non-circular, polygon shaped components, for example. As illustrated in  FIG. 9 , the igniter tip  17  is positioned on a same side of a combustion liner  19  as the igniter housing  16 . The igniter  14  is extendable from the igniter housing  16  through an opening  18  in the combustion liner  19  to an extended position (not shown) on an opposite side of the combustion liner  19  than the igniter housing  16 . Subsequent to extending the igniter  14  through the opening  18  to the extended position, the igniter  14  is retractable from the extended position back through the opening  18  to a retracted position  22  ( FIG. 9 ) where the igniter tip  17  is positioned on the same side of the combustion liner  19  as the igniter housing  16 . The igniter assembly  10  of the present invention provides its notable advantageous features, including an air seal between the igniter housing  16  and the opening  18 , when the igniter  14  is in the extended position, the retracted position, and all positions in between. However, an exemplary embodiment of the igniter assembly  10  may exclusively provide the advantageous features for one or more particular igniter positions, for example. 
         [0020]    As illustrated in the exemplary embodiment of  FIG. 9 , the igniter assembly  10  further includes a compressible assembly  24  disposed between a base  26  of the igniter housing  16  and the combustion liner  19  to form a sealed interface  15  with a perimeter  28  of the opening  18  in the combustion liner  19 . The compressible assembly  24  collectively restricts an air flow from passing between the igniter housing base  26  and the perimeter  28  of the opening  18 . In an exemplary embodiment of the igniter assembly  10 , the compressible assembly  24  is variable in length to accommodate a respective variation in a separation between the igniter housing base  26  and the opening  18  within the combustion liner  19 . The structural features of an exemplary embodiment of the compressible assembly  24  are discussed in further detail below. 
         [0021]      FIGS. 3-9  illustrate exemplary embodiments of the respective structural assembly steps for a compressible assembly  24  of the igniter assembly  10 .  FIG. 3  illustrates an exemplary embodiment of the igniter  14  encircled by the igniter housing  16 , and a top guide portion  36  which is slid up around the igniter tip  17  and into contact with the igniter housing base  26  ( FIG. 4 ). As illustrated in the exemplary embodiment of  FIG. 3 , the top guide portion  36  includes an outer flange  40  to form a sealed interface  21  with the igniter housing base  26  ( FIG. 4 ), an upper longitudinal portion  42  slidably engaged with an inner portion  44  of the igniter housing  16 , and a lower longitudinal portion  46 . As illustrated in the exemplary embodiment of  FIG. 4 , once the top guide portion  36  forms the sealed interface  21  with the igniter housing base  26 , and the upper longitudinal portion  42  is slidably engaged with the inner portion  44 , a cover  52  is passed up around the lower longitudinal portion  46  of the top guide portion  36 . As illustrated in  FIG. 5 , upon passing the cover  52  around the lower longitudinal portion  46  of the top guide portion  36 , a bottom guide portion  38  is passed up inside the cover  52  and aligned with the top guide portion  36 . The bottom guide portion  38  includes a spring flange  48  extending outwardly from a longitudinal portion  50 . The top guide portion  36  and bottom guide portion  38  are welded together, as illustrated in  FIG. 6 , at opposing ends, where the respective opposing ends are slanted in opposite directions to accommodate the welding process, as appreciated by one of skill in the art. Upon welding the top guide portion  36  and bottom guide portion  38 , the cover  52  includes an outer portion  56  (discussed below) and a top portion  54  which is slidably engaged with an outer surface  58  of the longitudinal portion  50  of the bottom guide portion  38  and the lower longitudinal portion  46  of the top guide portion  36 . As illustrated in  FIG. 7 , a spring  66  is passed up into the cover  52  adjacent to an inner surface of the outer cover portion  56  and against the spring flange  48  of the bottom guide portion  38 . As illustrated in  FIG. 8 , upon positioning the spring  66 , a base  60  including a bottom portion  62  and a longitudinal portion  64  is passed upward, and the longitudinal portion  64  is passed into the cover  52  between the spring  66  and the longitudinal portion  50  of the bottom guide portion  38 . The bottom portion  62  is subsequently welded to the bottom end of the longitudinal portion  56  of the cover  52  ( FIG. 9 ), and the bottom portion  62  forms a sealed interface  57  with the opening  18 . As illustrated in  FIG. 9 , the spring flange  48 , the outer cover portion  56 , the bottom base portion  62  and the longitudinal base portion  64  form a variable stagnant volume  68  in which the spring  66  is disposed to impart an upward force on the spring flange  48  such that the compressible assembly  24  forms an effective seal between the igniter housing base  26  and the opening  18 . 
         [0022]    Although  FIGS. 3-9  illustrate an exemplary set of assembly steps for the exemplary embodiment of the compressible assembly  24  utilizing a particular set of components, these assembly steps may be rearranged or supplemented using the same components so to provide an additional exemplary embodiment of a compressible assembly. Additionally, the compressible assembly is not limited to the exemplary set of components illustrated in  FIGS. 3-9 , but may include any set of components which may be assembled using any set of steps, provided that the compressible assembly restricts an air flow from passing between the igniter housing base  26  and the perimeter  28  of the opening  18 , and is variable in length to accommodate a respective variation in a separation between the igniter housing base  26  and the opening  18  within the combustion liner  19 . 
         [0023]    In the exemplary embodiment of the igniter assembly  10  illustrated in  FIG. 9 , the spring flange  48  contacts a top end  70  of the spring  66  disposed within the stagnant volume  68 . A variation in the separation between the igniter housing  16  and the opening  18  causes the spring  66  to maintain an upward force on the spring flange  48  and vertically shift the spring flange  48  in the same relative shift direction as the igniter housing  16  during the separation variation. Thus, the spring flange  48  forms a variable top portion of the stagnant volume  68 . Additionally, the longitudinal base portion  64  disposed between the spring  66  and the longitudinal portion  50  of the bottom guide portion  38  forms an inner portion of the stagnant volume  68 . The stagnant volume  68  is further defined by the outer cover portion  56  positioned along an outer surface of the ring  66 , which forms an outer portion of the stagnant volume  68 . The bottom base portion  62  forms a bottom portion of the stagnant volume  68 . 
         [0024]    In an example of a variation in the separation between the igniter housing  16  and the opening  18 , when the separation is minimized as illustrated in  FIG. 9 , the spring flange  48  imparts a downward force on the spring  66  and compresses the spring  66  to a compressed length  78  within the stagnant volume  68  such that the stagnant volume  68  is minimized. Additionally, as the spring flange  48  is lowered to compress the spring  66  within the stagnant volume  68 , the top cover portion  54  slidably moves up and engages an upper portion  86  along the outer surface  58  of the longitudinal portion  50  and the lower longitudinal portion  46 , as illustrated in  FIG. 9 . From the minimal separation between the igniter housing  16  and the opening  18  illustrated in  FIG. 9 , the separation may be increased to a maximum separation (not shown), in which the downward force imparted on the spring  66  by the spring flange  48  is reduced, and the spring  66  varies in length to an uncompressed length (not shown). Additionally, as the spring flange  48  is raised to uncompress the spring  66  within the stagnant volume  68 , the top cover portion  54  slidably moves down and engages a lower portion  84  along the outer surface  58  of the longitudinal portion  50  and the lower longitudinal portion  46 , as illustrated in  FIG. 9 . Although  FIG. 9  illustrates one spring  66  disposed within one stagnant volume  68 , the present invention is not limited to this arrangement and may include multiple springs disposed within a single stagnant volume, or multiple springs disposed within respective multiple stagnant volumes. Additionally, the present invention may include the use of a non-spring compressible device disposed within the stagnant volume or within any portion of the compressible assembly, provided that the compressible device facilitates varying the compressible assembly length with the variance in the separation between the igniter housing and the opening in the combustion liner, and ensures that a sufficient minimal contact is maintained between the compressible assembly and the igniter housing and perimeter of the combustion liner opening, to maintain all sealed interfaces to prevent an undesired air flow from passing between the igniter housing and the combustion liner opening. 
         [0025]    Regardless of the degree of separation between the igniter housing  16  and the opening  18 , the top cover portion  54  forms a sealed interface  55  with the outer surface  58  to prevent air from passing between the top cover portion  54  and the top guide portion  36  or bottom guide portion  38 , depending on the separation between the igniter housing  16  and the opening  18 . For example, when the igniter housing  16  and the opening  18  are separated by the maximum separation, the top cover portion  54  slidably engages a lower portion  84  along the longitudinal portion  50  of the outer surface  58  and forms the sealed interface  55  between the top cover portion  54  and the longitudinal portion  50 . Thus, for the maximum separation between the igniter housing  16  and the opening  18 , the sealed interface  55  prevents an air flow from passing between the top cover portion  54  and the bottom guide portion  38 . In another example, when the igniter housing  16  and the opening  18  are separated by a minimum separation, the top cover portion  54  slidably engages an upper portion  86  along the outer surface  58 , and forms the sealed interface between the top cover portion  54  and the longitudinal portion  50 . Thus, for a minimum separation between the igniter housing  16  and the opening  18 , the sealed interface  55  prevents an air flow from passing between the top cover portion  54  and the top guide portion  36 . 
         [0026]    As illustrated in  FIG. 9 , the compressible assembly  24  is configured to form a seal in a direction parallel to a longitudinal axis  88  of the igniter  14 , where the seal extends from the igniter housing base  26  to the opening  18  to prevent the air flow from passing between the igniter housing base  26  and the opening  18  and through the opening when the igniter  14  is either in the retracted position ( FIG. 9 ) or the extended position (not shown). In addition to the compressible assembly  24  illustrated in  FIG. 9 , the igniter assembly  10  features a landing  23  positioned between the base  60  and the combustion liner  19  to form a sealed interface  15  around the opening  18 . 
         [0027]    The compressible assembly  24  is disposed between the igniter housing base  26  and the landing  23 , and the compressible assembly  24  maintains a respective minimum contact level with the igniter housing base  26  and the landing  23  for a range of separations between the igniter housing  16  and the opening  18  sufficient to maintain the sealed interface  21  between the top guide portion  36  and the igniter housing base  26 , a sealed interface  57  between the bottom base portion  62  and the landing  23 , and the sealed interface  15  between the landing  23  and the combustion liner  19 . The sealed interface  21  prevents air from passing between the igniter housing  16  and the top guide portion  36 , into the igniter cavity  13  and through the opening  18 . The sealed interface  57  prevents air from passing between the bottom base portion  62  and the landing  23  and entering the opening  18 . The sealed interface  15  prevents air from passing between the landing  23  and the perimeter  28  of the opening  18  and into the opening  18 . 
         [0028]    As illustrated in  FIG. 9 , an opening  90  is provided in the igniter housing  16  to selectively supply an air flow into an igniter cavity  13  of the igniter housing  16  to purge the igniter cavity  13 . The opening  90  may be selectively opened (using a controller or other control mechanism) to purge air from the igniter cavity  13 , particularly when the temperature of the air within the igniter cavity  13  exceeds a predetermined threshold (which may be measured by a temperature sensor, for example). Thus, purging the igniter cavity  13  through the opening  90  provides some protection against thermal damage to the interior of the igniter cavity  13  and the igniter assembly  24  when the air temperature within the igniter cavity  13  reaches a high level. 
         [0029]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.