Abstract:
Since a wall part of a combustor of a gas turbine engine includes a cylindrical flange projecting integrally from an outer periphery of a spark plug fitting hole, and a spark plug support device covering an extremity of a spark plug is welded or brazed to the flange, a welded or brazed site of the device is above the flange lower in temperature than the wall part, and it is possible to suppress decrease in strength at the welded or brazed site and to improve durability, and also to reduce cost since a shape of the device may be coincided with a simple shape of the flange and machining of the device becomes easy. Since the flange is formed integrally with the wall part, compared with a case where the flange is formed from a separate member, the number of components and machining steps is decreased, enabling further cost reduction.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a structure for supporting a spark plug for a gas turbine engine in which an extremity of the spark plug is covered with spark plug support means encircling a spark plug fitting hole formed in a wall part of a combustor of the gas turbine engine. 
       DESCRIPTION OF RELATED ART 
       [0002]    Such a structure for supporting a spark plug for a gas turbine engine is known from Japanese Patent Application Laid-open No. 2009-185821. With regard to this invention, one end of an annular hollow shaft  14  (flange) is fitted into and fixed by welding to an opening formed in a wall part of a combustor chamber  1 , a floating spark plug sleeve  120  (spark plug support collar) is supported in a floating state on the other end of the hollow shaft  14  via a hollow shaft sleeve  130  (collar support member), and an extremity of a spark plug  13  is made to extend through the floating spark plug sleeve  120 . 
         [0003]    In this conventional arrangement, since the hollow shaft  14  is directly welded to the opening formed in the wall part of the combustor chamber  1 , there is a possibility that strength of a peripheral edge of the opening will be degraded by heat of welding and a crack will occur. Moreover, in order to weld the hollow shaft  14  to the wall part of the combustor chamber  1 , which is formed with a complicated three-dimensional curved surface, it is necessary to machine a weld part of the hollow shaft  14  with good precision in conformity with the three-dimensional curved surface, and there is a problem that machining cost is high. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention has been accomplished in light of the above circumstances, and it is an object thereof to prevent durability from being degraded due to welding or brazing of spark plug support means to a combustor and to simplify a shape of the spark plug support means to thus cut machining cost. 
         [0005]    In order to achieve the object, according to a first aspect of the present invention, there is provided a structure for supporting a spark plug for a gas turbine engine in which an extremity of the spark plug is covered with spark plug support means encircling a spark plug fitting hole formed in a wall part of a combustor of the gas turbine engine, wherein the wall part of the combustor comprises a cylindrical flange projecting integrally from an outer periphery of the spark plug fitting hole, and the spark plug support means is welded or brazed to the flange. 
         [0006]    In accordance with the first aspect, the extremity of the spark plug is covered with the spark plug support means encircling the spark plug fitting hole formed in the wall part of the combustor of the gas turbine engine. Since the wall part of the combustor includes the cylindrical flange projecting integrally from the outer periphery of the spark plug fitting hole, and the spark plug support means is welded or brazed to the flange, the site of welding or the site of brazing of the spark plug support means is above the flange, which is at a lower temperature than that of the wall part of the combustor, and not only is it possible to suppress any decrease in the strength at the site of welding or the site of brazing and to improve the durability, but it is also possible to reduce the cost since the shape of the spark plug support means may be made to coincide with the simple shape of the cylindrical flange and machining of the spark plug support means becomes easy. Moreover, since the flange is formed integrally with the wall part of the combustor, compared with a case in which the flange is formed from a separate member, the number of components and the number of machining steps can be decreased, and it becomes possible to further reduce the cost. 
         [0007]    According to a second aspect of the present invention, in addition to the first aspect, a plurality of cooling holes for supplying air for cooling to an interior of the combustor are formed in a whole circumference of the spark plug fitting hole except for the flange in the wall part of the combustor. 
         [0008]    In accordance with the second aspect, since the plurality of cooling holes for supplying air for cooling to the interior of the combustor are formed in the whole circumference of the spark plug fitting hole except for the flange in the wall part of the combustor, the cooling hole can be formed in the wall part very close to the spark plug fitting hole without being hindered by the spark plug support means, thus ensuring the effect in cooling the area around the spark plug fitting hole and thereby preventing the strength from being degraded by heat. 
         [0009]    Note that a combustor main body part  12  of an embodiment corresponds to the wall part of the present invention. 
         [0010]    The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiment which will be provided below while referring to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  to  FIG. 4  show an embodiment of the present invention:  FIG. 1  is a longitudinal sectional view of a combustor of a gas turbine engine;  FIG. 2  is an enlarged view of part  2  in  FIG. 1 ;  FIG. 3  is a view in a direction of arrow  3  in  FIG. 2 ; and  FIG. 4  is a view, corresponding to  FIG. 3 , showing a comparative example. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    An embodiment of the present invention is explained below by reference to  FIG. 1  to  FIG. 4 . 
         [0013]    As shown in  FIG. 1 , a combustor  11  disposed so as to encircle an engine axis of a gas turbine engine includes an annular combustor main body part  12  and a dome part  13  blocking one end part of the combustor main body part  12 . A plurality of open flange parts  14  are disposed, at equal intervals on a circumference having the engine axis as the center, on the semicircular cross section dome part  13 , and the extremities of fuel nozzles  15  for injecting fuel into the interior of the combustor  11  via fuel supply holes  13 a formed in the center of the open flange parts  14  are covered with a nozzle guide  22  supported in a floating state by nozzle guide support means  16 . Furthermore, a plurality of spark plug fitting holes  12   a  are formed in an outer peripheral wall of the combustor main body part  12  at equal intervals in the circumferential direction, and the extremities of spark plugs  18  are inserted into spark plug support collars  20  supported in a floating state by spark plug support means  17  provided on the spark plug fitting holes  12   a.    
         [0014]    The combustor  11  is cantilever-supported on a casing of the gas turbine engine via an inner peripheral part thereof, and since base end parts of the fuel nozzles  15  and the spark plugs  18  are cantilever-supported on the casing, the fuel nozzles  15  and the spark plugs  18  move relative to the combustor  11  due to a difference in the amount of thermal expansion of each part accompanying change in temperature of the gas turbine engine. In order to allow this relative movement, the extremities of the fuel nozzles  15  are covered with the nozzle guide  22  supported on the nozzle guide support means  16  in a floating state, and the extremities of the spark plugs  18  are inserted into spark plug support collars  20  supported by the spark plug support means  17  in a floating state. Formed in the outer peripheral wall and an inner peripheral wall of the combustor main body part  12  are a plurality of air inlet holes  12   b  for introducing air for combustion into the interior of the combustor  11 . 
         [0015]    The structure of the spark plug support means  17  is now explained by reference to  FIG. 2  and  FIG. 3 . 
         [0016]    A cylindrical flange  12   c  is projectingly provided integrally with an outer peripheral face of the combustor main body part  12  by burring, and the spark plug fitting hole  12   a  is formed from the inner periphery of the flange  12   c . The spark plug support means  17 , which is disposed so as to encircle an axis L of the spark plug  18 , includes an annular collar support member  19  and the annular spark plug support collar  20 . 
         [0017]    The collar support member  19  integrally includes an annular support portion  19   a  that has a J-shaped cross section and opens inward in the radial direction and a cylindrical flange  19   b  that projects from the inner periphery of the support portion  19   a  toward the spark plug fitting hole  12   a  side along the axis L, the flange  19   b  being fitted around the outer periphery of the flange  12   c  of the combustor main body part  12  and joined by a weld w. 
         [0018]    The spark plug support collar  20  includes a disk-shaped flat portion  20   a  that is loosely fitted into the support portion  19   a  of the collar support member  19  and a guide portion  20   b  that enlarges conically from the inner periphery of the flat portion  20   a  in going radially outward along the axis L, the guide portion  20   b  covering the extremity of the spark plug  18 . Formed between the collar support member  19  and the spark plug support collar  20  are a gap α in the axis L direction and a gap β in the radial direction, the spark plug support collar  20  being supported in a floating state with respect to the collar support member  19  in the range of the gaps α and β. 
         [0019]    Formed in a wall part of the combustor main body part  12  are a large number of cooling holes  12   d  (see  FIG. 3 ) for introducing air for cooling into the interior of the combustor  11 . The cooling holes  12   d  are formed in the entire region of the wall part of the combustor main body part  12  except the flange  12   c  and are formed up to a position that is as close as possible to the whole circumference of the flange  12   c.    
         [0020]    The operation of the embodiment of the present invention having the above arrangement is now explained. 
         [0021]    During running of the gas turbine engine, air that has been compressed by a compressor is supplied to a space around the combustor  11  and is supplied therefrom to the interior of the combustor  11  after passing through the air inlet holes  12   b  of the combustor main body part  12  and the interior of the fuel nozzles  15 , and the air is mixed with fuel injected from the fuel nozzle  15  in the interior of the combustor  11 , thus carrying out combustion. Combustion gas generated by combustion is discharged from the combustor  11  and drives a turbine, and is then discharged via an exhaust nozzle and generates thrust. The spark plugs  18  ignite the mixed gas when the gas turbine engine is started, and combustion of the mixed gas continues automatically after starting the gas turbine engine. 
         [0022]    Since the annular combustor  11  is cantilever-supported on the casing of the gas turbine engine via its inner peripheral part, and the base end parts of the fuel nozzles  15  and the spark plugs  18  are also cantilever-supported on the casing of the gas turbine engine, the fuel nozzles  15  and the spark plugs  18  move relative to the combustor  11  due to differences in the amount of thermal expansion accompanying change in temperature of the gas turbine engine. However, the spark plug  18  is inserted into and supported on the spark plug support collar  20 , which is supported by the spark plug support means  17  in a floating state on the flange  12   c  encircling the spark plug fitting hole  12   a  of the combustor main body part  12 , the spark plug support collar  20  supporting the spark plug  18  can move relative to the collar support member  19  in the axis L direction in the range of the gap α and in the radial direction in the range of the gap β, and the above relative movement is thereby allowed due to the action of the gaps α and β. 
         [0023]    In order to cool the combustor main body part  12 , whose temperature increases due to combustion of the air-fuel mixture, air is introduced through the cooling holes  12   d  extending through the wall face of the combustor main body part  12 , the air forms a thin film of air on the inner wall face of the combustor main body part  12 , and the combustor main body part  12  is thereby cooled effectively, thus preventing the durability from being degraded. 
         [0024]      FIG. 4  shows a comparative example of spark plug support means  17 ; with regard to the spark plug support means  17  of the comparative example, a collar support member  19  includes a large diameter flange  19   c  connected to a support portion  19   a , and this flange  19   c  is directly welded with a weld w to a section around a spark plug fitting hole  12   a  in a wall part of a combustor main body part  12 . Since a hole opening in a weld part is blocked during welding, there is the problem that a region of about a few mm long without a hole occurs around the weld part as the center, and if an attempt is made to machine cooling holes  12   d  after welding, the cost increases. 
         [0025]    On the other hand, with regard to the spark plug support means  17  of the present embodiment shown in  FIG. 3 , since the collar support member  19  is welded with a weld w to the cylindrical flange  12   c  encircling the spark plug fitting hole  12   a , the cooling holes  12   d  can be formed as close to the whole circumference of the spark plug fitting hole  12   a  as possible without being hindered by the spark plug support means  17 , thus improving the effect in cooling the combustor main body part  12 . 
         [0026]    Moreover, as in the comparative example shown in  FIG. 4 , if an attempt is made to weld the collar support member  19  of the spark plug support means  17  with a weld w directly to the wall part of the combustor main body part  12 , which has a three-dimensional curved face, there is the problem that machining for making the shape of the weld face of the collar support member  19  coincide with the shape of an outer surface of the combustor main body part  12  is difficult and becomes a main cause for an increase in cost, but in accordance with the present embodiment, since the collar support member  19  of the spark plug support means  17  is welded with the weld w to the flange  12   c , which has a simple cylindrical shape, it becomes unnecessary to subject the collar support member  19  to difficult machining, and it is possible to reduce the cost. 
         [0027]    Furthermore, the wall part of the combustor main body part  12 , which is directly exposed to flame during running of the gas turbine engine, attains a higher temperature than that of the flange  12   c , which projects from the wall part. As shown in  FIG. 4 , if the spark plug support means  17  is directly welded to the wall part of the combustor main body part  12 , the wall part of the combustor main body part  12  is degraded by the heat of welding, and if it attains a high temperature due to the heat of running of the gas turbine engine, there is a possibility that a crack, etc. will occur and the durability will be degraded. However, in accordance with the present embodiment, even if the flange  12   c  is degraded due to the heat of welding the spark plug support means  17 , since the flange  12   c  is maintained at relatively low temperature during running of the gas turbine engine, there is no possibility of a crack, etc. occurring and the durability being degraded. 
         [0028]    Moreover, since the flange  12   c  is formed integrally with the wall part of the combustor main body part  12  by burring, compared with a case in which the flange  12   c  is formed from a separate member, the number of components and the number of machining steps can be decreased, and it becomes possible to further reduce the cost. 
         [0029]    An embodiment of the present invention is explained above, but the present invention may be modified in a variety of ways as long as the modifications do not depart from the gist thereof. 
         [0030]    For example, in the embodiment the flange  12   c  is formed by burring, but it may be formed by press forming.