Patent Publication Number: US-2017363292-A1

Title: Method of accessing a nozzle tip assembly of a fuel nozzle

Description:
TECHNICAL FIELD 
     The application relates generally to gas turbine engines, and more particularly to fuel nozzles for combustors of gas turbine engine 
     BACKGROUND 
     Gas turbine engine fuel nozzles which use a pressure atomizing nozzle tip, for providing the combustor with a pressurized spray of fuel and air, are known. The components that make up the nozzle tip are typically placed within a cavity in the stem of the fuel nozzle. It is often difficult or impossible to access the components of the nozzle tip within the cavity once the fuel nozzle has been assembled, which makes it difficult to perform repairs. This results in relatively new fuel nozzles or their components being scrapped prematurely. 
     SUMMARY 
     There is accordingly provided a method of accessing a nozzle tip assembly of a gas turbine engine fuel nozzle, the fuel nozzle having a stem and a heat shield enclosing at least part of the stem, the nozzle tip assembly being disposed within an inner cavity of the stem, a first end of the cavity being positioned opposite to a fuel nozzle exit from which fuel is sprayed from the fuel nozzle, the method comprising: forming an opening in at least the heat shield of the fuel nozzle, the opening providing access to the inner cavity of the stem via the first end thereof; accessing the nozzle tip assembly in the inner cavity via the opening; and closing the opening after accessing the nozzle tip assembly. 
     There is also provided a method of accessing a nozzle tip assembly of a gas turbine engine fuel nozzle, the fuel nozzle having a stem and a heat shield enclosing at least part of the stem, the nozzle tip assembly being disposed within an inner cavity of the stem, a first end of the cavity being positioned opposite to a fuel nozzle exit from which fuel is sprayed from the fuel nozzle, the method comprising: machining an opening through the heat shield and through the stem of the fuel nozzle, the opening providing access to the inner cavity of the stem via the first end thereof; accessing the nozzle tip assembly in the inner cavity via the opening; and closing the opening after accessing the nozzle tip assembly. 
     There is further provided a method of accessing a nozzle tip assembly of a gas turbine engine fuel nozzle, the fuel nozzle having a stem and a heat shield enclosing at least part of the stem, the nozzle tip assembly being disposed within an inner cavity of the stem, a first end of the cavity being positioned opposite to a fuel nozzle exit from which fuel is sprayed from the fuel nozzle, the method comprising: machining an opening through the heat shield and through the stem of the fuel nozzle, the opening providing access to the inner cavity of the stem via the first end thereof; accessing the nozzle tip assembly in the inner cavity via the opening; and covering the opening after accessing the nozzle tip assembly with a portion of the heat shield. 
     There may be alternately provided a fuel nozzle for a combustor of a gas turbine engine, comprising: a fuel nozzle stem extending between a nozzle head and an opposed nozzle tip; a nozzle sheath at least partially surrounding the stem, the nozzle sheath having a heat shield at least partially enclosing the nozzle tip, a portion of the heat shield being machinable to form an opening in the heat shield; and the nozzle tip having an inner nozzle tip assembly, the inner nozzle tip assembly being accessible via the opening in the heat shield. 
     There may be alternately provided a fuel nozzle for a combustor of a gas turbine engine, comprising: a fuel nozzle stem extending between a nozzle head and an opposed nozzle tip, the stem having an elongated inner cavity extending through a portion of the nozzle tip, the inner cavity extending between an open downstream end and an open upstream end; a nozzle sheath at least partially surrounding the stem, the nozzle sheath having a heat shield at least partially enclosing the nozzle tip and covering the inner cavity at the upstream end thereof, a portion of the heat shield adjacent to the upstream end of the inner cavity being machinable to form an opening in the heat shield providing access to the inner cavity via the upstream end thereof; and an atomizing nozzle tip having an inner nozzle tip assembly disposed within the inner cavity, and an outer nozzle tip assembly at least partially surrounding the inner nozzle tip assembly, the inner nozzle tip assembly within the inner cavity being accessible via the opening in the heat shield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIG. 2A  is a perspective view of a fuel nozzle and mounting support, according to an embodiment of the present disclosure; 
         FIG. 2B  is a cross-sectional view of the fuel nozzle of  FIG. 2A , taken along the line II-II of  FIG. 2A ; and 
         FIG. 3  is an enlarged, fragmentary cross-sectional view of the circled portion  3  in of  FIG. 2B ; 
         FIG. 4A  is an enlarged, fragmentary side cross-sectional view of the circled portion  3  in of  FIG. 2B ; 
         FIG. 4B  is another side cross-sectional view of the circled portion  3  in of  FIG. 2B , a nozzle tip assembly being shown removed from an inner cavity of the fuel nozzle; 
         FIG. 4C  is another side cross-sectional view of the circled portion  3  in of  FIG. 2B , showing a new nozzle tip assembly; 
         FIG. 4D  is another side cross-sectional view of the circled portion  3  in of  FIG. 2B , the new nozzle tip assembly being shown within the inner cavity; and 
         FIG. 5  is an enlarged, fragmentary cross-sectional view of a nozzle tip of a fuel nozzle, according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       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 compressor section  14  for pressurizing the air, a combustor  16  in 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. The gas turbine engine  10  has one or more fuel nozzles  20  which supply the combustor  16  with fuel which is combusted with the air in order to generate the hot combustion gases. 
     An example of one such fuel nozzle  20  (or simply “nozzle”) is provided in  FIGS. 2A and 2B . In the depicted embodiment, the nozzle  20  typically has a nozzle head  24  located outside of a casing of the combustor, a nozzle tip  22  located within the casing, and a nozzle stem  23  connecting the head to the tip and providing fuel communication therebetween. The nozzle  20  atomizes a mixture of air and fuel to be combusted. The atomization of the fuel and air into finely dispersed particles occurs because the air and fuel are supplied to the fuel nozzle  20  under relatively high pressure, and mixed together within the nozzle tip  22 . The nozzle  20  therefore outputs a fine and uniformly-distributed mist mixture of the air and fuel. In providing such a fine mist, the nozzle  20  helps to ensure a more efficient combustion of the mixture. Fuel is supplied to the nozzle  20  via a manifold head  24 , and the nozzle  20  is secured to the engine via a mounting plate  25 . The manifold head  24  has and one or more fuel inlets  24 A which supply fuel to the nozzle  20 . 
     In the depicted embodiment of  FIG. 2B , the nozzle  20  has two nozzles within the same structure. One such nozzle is an inner fuel primary pressure atomizing nozzle tip assembly  30 , and the other nozzle is an outer, airblast air atomizing nozzle tip assembly  40 . Collectively, the nozzle tip assemblies  30 ,  40  form an atomizing nozzle tip  50 . Both nozzle tip assemblies  30 , 40  are contained in an outer nozzle sheath  26  which forms the outer shell of the fuel nozzle  20  and encloses both the inner and outer nozzle tip assemblies  30 , 40 . The nozzle sheath  26  directs air into the nozzle  20 , diverts water and other foreign materials away from the air passages, and provides support to help hold the combustor in place. The nozzle  20  and/or nozzle sheath  26  has a heat shield  27 . In the depicted embodiment, the heat shield  27  is not a part of the nozzle sheath  26 , but it can be. The protective heat shield  27  shields and at least partially insulates the inner and outer nozzle tip assemblies  30 ,  40  at the nozzle tip  22  from the hot combustion gases generated in the combustor. 
     The inner, or “primary pressure”, nozzle tip assembly  30  generally receives and outputs only fuel. Although used throughout all operating modes of engine operation, it is particularly useful during engine start-up or ignition, and employs a drop in fuel pressure to atomize the fuel by reducing the size of the fuel droplets. The inner nozzle tip assembly  30  is therefore able to generate a very fine mist of fuel for a relatively small flow capacity, which is ideal for engine start-up. During normal engine operation, the inner nozzle tip assembly  30  is used with the outer nozzle tip assembly  40  to meet the operating needs of the engine. The inner nozzle tip assembly  30  can thus be referred to as a “starting” nozzle. 
     The outer nozzle tip assembly  40 , in the depicted embodiment, provides the main airblast to the nozzle tip  22 , and also provides addition fuel to complement that provided by the inner nozzle tip assembly  30  for optimal normal engine operation. The body  41  of the outer nozzle tip assembly  40  is disposed about the inner nozzle tip assembly  30  so as to surround and enclose it. 
     Referring to  FIG. 3 , the inner nozzle tip assembly  30  has a fuel distributor  31 , which is generally an elongated annular body which is coaxial about the fuel nozzle center axis  28 . It extends along a length between an upstream end  32  of the inner nozzle tip assembly  30  and a downstream end  33 . The fuel distributor  31  receives a supply of fuel from an upstream supply in the fuel nozzle  20 , increases the velocity of the fuel, and outputs via an outlet  34  as a fine spray. The inner nozzle tip assembly  30  generally has a convergent outer member  35  which encloses the fuel distributor  31 , when present, and which is a hollow annular member being coaxial about the nozzle center axis  28 . The outer member  35  has a convergent extremity  36  or cone at the downstream end  33  which channels the fuel from the fuel distributor  31  to a relatively small exit from the inner nozzle tip assembly  30 . 
     The inner nozzle tip assembly  30  is located, at least partially, within an elongated inner cavity  29  in the stem  23 . The inner cavity  29  provides a housing for the inner nozzle tip assembly  30  within the stem  23  so that the inner nozzle tip assembly  30  can be secured thereto. In the depicted embodiment, the inner cavity  29  is a through bore which forms an annular passage extending through the stem  23  at the nozzle tip  22 . More particularly, the inner cavity  29  extends between a first and open upstream end  29 A, and a second and open downstream end  29 B. The terms “upstream” and “downstream”, when used to describe the ends  29 A,  29 B of the inner cavity  29 , refer to the direction of fuel flow through the nozzle  20 . Stated differently, the downstream end  29 B of the inner cavity  29  is closer than the upstream end  29 A to the outlet  34  of the inner nozzle tip assembly  30  from which the fuel is sprayed. In the depicted embodiment, the upstream end  29 A can therefore be referred to as a “rear” end of the inner cavity  29 . The open upstream end  29 A is open, which allows the inner cavity  29  (and the inner nozzle tip assembly  30  disposed therein) to be accessed. As will be discussed in greater detail below, the inner cavity  29  can have different configurations, and may be closed at one of its ends  29 A,  29 B. 
     Whether open or closed, the upstream end  29 A is covered and protected by a portion of the heat shield  27 . Therefore, to access the inner nozzle tip assembly  30  via the upstream end  29 A to repair or replace the inner nozzle tip assembly  30 , access must be provided in the heat shield  27 . 
     Referring to  FIGS. 4A to 4D , a method of accessing at least the inner (primary) nozzle tip assembly  30  within the inner cavity  29  will now be described in greater detail. The method allows for a technician to access the inner nozzle tip assembly  30  within the inner cavity  29  without having to uninstall the entire nozzle  20  and/or nozzle tip  22 . The technician may then repair or replace the nozzle tip assembly  30  and close off the access, thereby helping to extend the service life of the nozzle  20 . 
     Referring to  FIG. 4A , the method includes the step of forming an opening  27 A in at least the heat shield  27  to access the inner cavity  29 . The expression “at least” refers to the possibility that another opening may also be formed in other components of the nozzle  20 , such as in the stem  23 , or that the opening  27 A can be extended through other components of the nozzle  20 . One such embodiment is discussed in greater detail below. The opening  27 A is of sufficient size and adequately shaped so that the technician can access the inner cavity  29  via the opening  27 A to repair or replace the inner nozzle tip assembly  30 . More particularly, the opening  27 A in at least the heat shield  27  is adjacent to the upstream, or first, end  29 A of the inner cavity  29 . This allows the technician to access the inner nozzle tip assembly  30  via the opening  27 A in the heat shield  27 , and through the open “rear” upstream end  29 A of the inner cavity  29 . 
     The opening  27 A in at least the heat shield  27  can be formed by any suitable technique. For example, the opening  27 A can be machined. Some machining operations include drilling, grinding, reaming, and boring, and other machining operations using machining tools are also within the scope of the present disclosure. It will thus be appreciated that a portion  27 B (see  FIG. 3 ) of the heat shield  27  adjacent to the upstream end  29 A of the inner cavity  29  is machinable. This machinable portion  27 B allows the opening  27 A in the heat shield  27  to be formed. 
     Referring to  FIG. 4B , the method also includes accessing the inner nozzle tip assembly  30  (see  FIG. 4A ) in the inner cavity  29  via the opening  27 A in at least the heat shield  27 . As previously explained, the inner nozzle tip assembly  30  can be accessed to be repaired or replaced. An example of a repair operation that can be performed includes repairing brazed joints between the inner nozzle tip assembly  30  and an inner surface  29 C of the inner cavity  29 . Other repair operations are also possible. Some of these include removing carbon formation, accessing and inspecting external brazing joints/welds, and manipulating portions of the inner nozzle tip assembly  30  that may be deformed. It will thus be appreciated that the repair operations are more easily performed via the rear, or upstream end  29 A of the inner cavity  29  than via the front or downstream end  29 B as is done with some conventional techniques. This facilitates the repair process and helps to reduce the duration of servicing. Since repairs are made relatively easier to perform, they contribute to the service life of the nozzle  20  and help to reduce the number of inner nozzle tip assemblies  30  and/or nozzles  20  that are scrapped prematurely. 
     In the depicted embodiment of  FIGS. 4B to 4D , accessing the inner nozzle tip assembly  30  includes replacing it. The inner nozzle tip assembly  30  is not shown in  FIG. 4B  because it has been removed. In an embodiment, the inner nozzle tip assembly is removed by inserting a machining tool into the inner cavity  29  via the opening  27 A to destroy the inner nozzle tip assembly  30  therein. By “destroy”, it is understood that the inner nozzle tip assembly  30  mechanically demolished and put beyond use. This can be achieved, for example, by boring the inner nozzle tip assembly  30  out of the inner cavity  29 . The fragmented pieces of the inner nozzle tip assembly  30  are then removed from the inner cavity  29  via the opening  27 A in at least the heat shield  27 . The result is a substantially empty inner cavity  29 , as shown in  FIG. 4B . 
     Referring to  FIG. 4C , accessing the inner nozzle tip assembly  30  to replace it includes inserting a new nozzle tip assembly  30 ′ into the inner cavity  29  of the stem  23  via the opening  27 A in at least the heat shield  27 . The new nozzle tip assembly  30 ′ is inserted through the “rear” of the nozzle stem  30 , via the opening  27 A in at least the heat shield  27 , along direction D. Prior to being inserted into the inner cavity  29 , the components of the new inner nozzle tip assembly  30 ′ can be assembled, calibrated, and tested. This contributes to reducing the duration of servicing and installation because testing and calibration can be performed off-site. 
     Once inserted and properly positioned within the inner cavity  29 , and as shown in  FIG. 4D , an outer surface  37  of the new inner nozzle tip assembly  30 ′ is brazed to the inner surface  29 C of the inner cavity  29  to attach the new inner nozzle tip assembly  30 ′ to the stem  23 . Brazing forms brazing joints  38  between the inner surface  29 C and the outer surface  37 . 
     Once the inner nozzle tip assembly  30  has been repaired, inspected, or replaced, the method includes closing the opening  27 A. In the depicted embodiment of  FIG. 4D , closing the opening  27 A includes covering the opening  27 A with the machinable heat shield portion  27 B and securing the portion  27 B to the remainder of the heat shield  27  by any suitable technique. It will be appreciated that the heat shield portion  27 B can be the same portion of the heat shield  27  that was removed to form the opening  27 A, or may be a new piece of heat shield material. 
     As explained above, the configuration of the inner cavity  29  may vary from that described above. Referring to  FIG. 5 , the inner cavity  129  of the depicted embodiment extends between a closed upstream end  129 A, and an open downstream end  129 B. The open downstream end  129 B allows the inner nozzle tip assembly  30  to be placed within the inner cavity  129 , and the closed upstream end  129 A prevents the inner nozzle tip assembly  30  from being conveyed through the “rear” of the stem  123 . In order to access the inner cavity  129  of the depicted embodiment and the inner nozzle tip assembly  30  therein, the step of forming an opening  127 A in at least the heat shield  27  also includes extending the opening  127 A through the stem  123  adjacent to the upstream end  129 A of the inner cavity  129 . The extended opening  127 A through the heat shield  27  and through the rear of the stem  123  provides access to the inner cavity  129  via its upstream end  129 A. The extended opening  127 A can be formed using any suitable machining tool. Therefore, the method disclosed herein helps to provide access to inner cavities  29 , 129  that have both open and closed upstream ends  29 A,  129 A. 
     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 departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the appended claims 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 claims.