Abstract:
A method and apparatus for internally mounting a fuel manifold within a surrounding casing in a gas turbine engine which involves inserting the fuel manifold into the casing with support elements positioned in a retracted position, displacing the support elements into an extended position, and fastening said support elements to mount the manifold to an inner surface of said casing.

Description:
TECHNICAL FIELD 
   The invention relates generally to fuel manifolds for gas turbine engines and, more particularly, to an improved structure and method for mounting fuel manifolds. 
   BACKGROUND OF THE ART 
   Annular fuel manifolds which distribute fuel to a plurality of fuel nozzles for injection into the combustion chamber of a gas turbine engine are typically supported within the surrounding structure of the engine by several radially extending support pins which are externally mounted and inserted through the engine casing for engagement with the fuel manifold. As such, the circumferentially spaced pins support the annular fuel manifold within the surrounding casing such that the fuel manifold is located in place adjacent a dome end of the combustor while nevertheless permitting sufficient displacement to accommodate any thermal growth mismatch between the fuel manifold and the supporting casing. 
   However such support pins are assembled from the outside of the engine casing and therefore assembly and installation of the pins to mount the fuel manifold in place can be time consuming and problematic due to obstruction by other engine components which surround the combustion section of the gas turbine engine. Removal and re-installation of the fuel manifold for inspection and/or maintenance purposes thus also becomes problematic. 
   Accordingly, there is a need to provide an improved method and structure to assemble and mount a fuel manifold using support pins. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of this invention to provide an improved structure and method for mounting fuel manifolds. 
   In one aspect, the present invention provides a method of installing a fuel manifold within a casing of a gas turbine engine comprising: providing the fuel manifold with attachment members fixed thereto, each of said attachment members defining an aperture for receiving a support element therein; mounting said support elements on said fuel manifold in a retracted position within said apertures such that said support elements project a first distance from said fuel manifold, said fuel manifold and said support elements mounted thereto in said retracted position forming a sub-assembly sized for receipt within said casing; inserting said sub-assembly into said casing; displacing said support elements outwards from retracted position into an extended position wherein the support elements project from the fuel manifold as second distance greater than said first distance, outer ends of said support elements being disposed proximate an inner surface of said surrounding casing when said support elements are disposed in said extended position; and fastening said outer ends of said support elements to said inner surface of said casing. 
   In another aspect, the present invention provides a method of internally mounting a fuel manifold within a surrounding casing in a gas turbine engine, the gas turbine engine including support elements mounted to at least one of the fuel manifold and the surrounding casing and movable relative thereto between at least a retracted and an extended position while mounted thereto, the method comprising: placing the support elements mounted in a retracted position; inserting the fuel manifold into the casing; and moving said support elements to the extended position to supportingly engage said fuel manifold to said casing. 
   In yet another aspect, the present invention provides a fuel manifold assembly for internal mounting within a surrounding casing of a gas turbine engine, comprising: an annular fuel manifold having mounting portions spaced about the circumference thereof; support pins engageable with said mounting portions and displaceable relative thereto between a retracted position, permitting said fuel manifold and said support pins to be inserted within the casing, and an extended position, in which said support pins project outwardly from said fuel manifold for engagement with said casing; and wherein said support pins are displaceable from said retracted position to said extended position once inserted into said casing for fastening to an inner surface thereof. 
   Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below. 

   
     DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying figures depicting aspects of the present invention, in which: 
       FIG. 1  is a partial cross-sectional view of a gas turbine engine; 
       FIG. 2  is a partial schematic cross-sectional view of an annular fuel manifold internally mounted within the gas generator case by support pin assemblies according to the present invention; and 
       FIG. 3  is a perspective view of the annular fuel manifold and a support pin assembly of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a multistage compressor  14  for pressurizing the air, a combustor  16  defining a combustion chamber  17  within which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. 
   Fuel is injected into the combustor  16  using a fuel injection system  20 , which comprises a fuel manifold ring  22  disposed outside the combustor  16  and n internally mounted within the surrounding engine casing. 
   Referring to  FIGS. 2 and 3 , the annular fuel manifold  22  is internally mounted within the gas generator casing  26  of the engine, adjacent to an upstream or dome end  19  of the combustor  16 . The fuel manifold  22  has a main ring body  23  defining at least one fuel flow passage  25  therein and preferably also includes an outer heat shield  27  which at least partially encloses the main ring body  23 . The fuel passage  25  of the annular fuel manifold ring  22  is disposed in fuel flow communication with a plurality of fuel injector spray tip assemblies (not shown), which typically project from the fuel manifold into the combustion chamber  17  for injecting fuel and combustion air therein. The fuel manifold  22  includes mounting portions disposed at several points thereabout for mounting the fuel manifold within the surrounding casing  26 . The mounting portions are preferably in the form of attachment lugs  24 , which are fixed to the main ring body  23  and project, preferably axially, therefrom such as to permit a support element  30  to be displaced therethrough without contacting or fouling on the main ring body  32  of the manifold. The main ring body  23  may also be provided with a recess formed therein in alignment with each attachment lug  24 , such that the support element may slide within the lugs as described in more detail below without contacting the main ring body. The surrounding heat shield  27  also preferably includes recesses  33  therein, such that displacement of the support elements  30  remains uninhibited. The recesses  33  in the heat shield  27  are circumferentially aligned with each of the attachment lugs  24 . The attachment lugs  24  may be either permanently fastened to the main ring body  23 , or alternately may be integrally formed therewith. Each attachment lug  24  define at least one aperture  32  therein for receiving a support element  30  which is fastenable to the gas generator case  26  in order to internally mount the fuel manifold  22  therewithin. The gas generator case  26  is preferably an annular casing defining circumferential inner and outer surfaces  38  and  39  respectively. 
   The support elements preferably comprise support pins  30 , which are slidably displaceable within the apertures  32  of the attachment lugs  24 , preferably along a center axis of the apertures  32  which is coaxial with the longitudinal axis  42  of the support pins  30 , between at least an inner or retracted position (depicted in  FIG. 2  with dotted lines  34 ) and an outer or extended position (depicted in  FIG. 2  with solid lines). When disposed in said retracted position, the fuel manifold with said support pins  30  mounted thereto defines an overall diameter which is sufficiently small to fit within an inner clearance diameter defined between the inner surfaces  39  of the surrounding gas generator casing  26 . Thus, the installation and internal mounting of the fuel manifold within the casing is possible without having to insert the support pins from the outside of the casing, as the sub-assembly formed by the annular fuel manifold  22  and the support pins  30  mounted therein in said retracted position, can be inserted directly into the casing for internal mounting therewithin. 
   Each support pin  30 , which includes a radially inner end  31  and a radially outer end  36 , therefore radially projects a first distance away from the attachment lugs  24  (and therefore the fuel manifold  22 ) when disposed in the retracted position and projects a second distance, greater than the first distance, when disposed in the extended position. This accordingly permits a sub-assembly formed by the fuel nozzle and the support pins  30  mounted thereon in the retracted position, to be inserted within the case together. Once located within the casing  26 , the support pins  30  can be slid radially outward along their longitudinal axes  42  (i.e. towards the inner surface of the casing) from their retracted position to their extended position, such that the outer ends  36  of the pins  30  can be fastened to the casing  26  from the inner side thereof. More particularly, the casing  26  preferably includes attachment bosses  28  disposed therein at points which correspond to the attachment lugs  24  of the fuel manifold, and which have threaded apertures  40  therethrough. The outer ends  36  of the support pins  30  are correspondingly threaded, such that the pins  30  can be threadably fastened within the apertures  40  of each of the bosses  28  in the casing  26 . Thus, so fastened to the surrounding casing  26 , the support pins radially project inwards towards the engine centerline  11 , in order to retain the annular fuel manifold  22  in place therewithin. Once mounted in place, some radial displacement between the fuel manifold  22  and the support pins  30  remains possible due to the sliding link between the apertures  32  in the attachment lugs  24  and the inner ends  31  of the pins  30 . Thus, any relative thermal growth between the fuel manifold and the support pins and casing can be accommodated. 
   Preferably, the pins  30  are translated outward along their longitudinal axis  42  between the retracted and the extended positions. In order to slide the pins  30  outwardly into the extended positions, an appropriate tool is preferably inserted through the apertures  40  and used to pull the outer ends  36  of the pins  30  outwards from the outer side of the casing  26 . The pins  30  can then be rotated in place about their longitudinal axis  42 , in order to threadably fasten them within the bosses  28 . Wrenching flats  44  may be provided on the body of the support pins  30  in order to permit the pins to be rotated by a suitable tool such as a torque wrench and torqued into place within threaded apertures  40 . A washer  48  is disposed about each support pin  30 , and is adapted to be squeezed between the projecting portion  43  of the pin  30  having the wrenching flats  44  thereon and the mating inner surface  29  on the casing bosses  28 . 
   When the annular fuel manifold  22  is inserted into the casing  26 , this is preferably done by aligning the center of the annular manifold with a main longitudinal axis of the casing  26 , which in the present case corresponds to the centerline axis  11  of the gas turbine engine  10 . The fuel manifold  22  is then displaced coaxially along this longitudinal center axis until the fuel manifold is located in a predetermined fore-aft position within the casing  26 , particularly adjacent the dome end  19  of the combustor  16 . The support pins  30  can then be radially outwardly displaced into their extended positions, as described above, for fastening within the casing  26 . 
   Thus, as the fuel manifold  22  is able to be installed and/or removed from the gas generator casing  26  of the gas turbine engine  10  from the inner side thereof, this enables the fuel manifold to be installed or removed from the casing, and therefore from the engine, regardless of any radially external obstructions which may be installed about the outside the casing. For example, once the bypass air duct is installed outside the gas generator casing  26  surrounding the combustor  16 , removal or installation of the fuel manifold  22  remains possible due to the internal mounting configuration thereof. This was previously not possible with externally mounted fuel manifolds of the prior art, which necessitated accessing the supporting pins from the outside of the gas generator casing, and therefore required complete removal of the bypass duct in order to do so. 
   The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without department from the scope of the invention disclosed. For example, although an annular fuel manifold is described and depicted, a non-annular fuel manifold may also be used. Further, although a number of support pins are preferably provided and equally distributed about the circumference of the fuel manifold, groupings of a number of support pins may also be used, and the distribution of support pins about the fuel nozzle may be unevenly distributed in order to provide additional support to areas predetermined to require additional support and localization within the surrounding gas generator case. Further still, although the support pins are preferably displaced linearly or translated by sliding between their retracted positions and their extended positions, the pins may be alternately displaced between the two positions. For example, the support pins may be hinge or otherwise interconnect with the fuel manifold, and simply pivoted or rotated from retracted position to the extended position. Although support pins have been described as “pins”, they need not be pins, per se, but rather any suitable support arrangement extending between manifold and surrounding structure. The manifold supports need not engage the gas turbine case directly. While the embodiments described above generally contemplate supports mounted to the manifold and which extend outwardly to engage the engine case surrounding support structure, the present invention also encompasses an inverse arrangement, wherein supports are mounted to the engine case or other support structure, retract generally outwardly and extend generally inwardly for engagement with the manifold. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.