Methods for shielding heat from a fuel nozzle stem of a fuel nozzle

Information

  • Patent Grant
  • 6622383
  • Patent Number
    6,622,383
  • Date Filed
    Thursday, September 28, 2000
    24 years ago
  • Date Issued
    Tuesday, September 23, 2003
    21 years ago
Abstract
A fuel nozzle including a nozzle stem having an annular overhang and a heat shield secured to the overhang is described. More specifically, and in one embodiment, the nozzle stem includes an upstream end and a downstream end. The annular overhang is intermediate to the upstream end and the downstream end of the stem. The heat shield includes a first end and a second end, and the heat shield is welded to the annular overhang at the heat shield first end. An annular air gap is between the nozzle stem and the heat shield.
Description




BACKGROUND OF THE INVENTION




This invention relates generally to gas turbine engines and, more particularly to a heat shield for a fuel nozzle.




Fuel nozzles in gas turbine engines provide fuel to a combustion chamber. The nozzles typically transport fuel through a compressor exit flow path. Temperatures around the fuel nozzle at the compressor exit flow path can exceed 1000 degrees Fahrenheit. The high temperatures around the fuel nozzle can cause the fuel passing through an inner passageway of the fuel nozzle to form granules of carbon on the walls of the inner passageway, which is undesirable. In addition, when the temperature of the fuel reaches approximately 300 degrees Fahrenheit, the fuel may begin to vaporize in the inner passageway, thereby resulting in intermittent or non-continuous fuel delivery to the downstream end of the fuel nozzle.




At least some known fuel nozzles include a heat shield which surrounds a nozzle stem of the fuel nozzle and which cooperates with the nozzle stem to define an annular air gap between the heat shield and the nozzle stem. One such known heat shield is described in U.S. Pat. No. 5,269,468, which is assigned to the present assignee. The heat shield and air gap insulate the fuel nozzle from the high temperatures. The heat shield may be attached to the fuel nozzle body by brazing. Low cycle fatigue (LCF) in braze attachments, however, adversely impacts the life of the shield.




BRIEF SUMMARY OF THE INVENTION




A fuel nozzle including a nozzle stem having an annular overhang and a heat shield secured to the overhang is described. More specifically, and in one embodiment, the nozzle stem includes an upstream end and a downstream end. The annular overhang extends from the upstream end of the stem.




The heat shield includes a first end and a second end, and the heat shield is welded to the annular overhang at the heat shield first end. An annular air gap is between the nozzle stem and the heat shield, and the heat shield second end cooperates with the downstream end of the nozzle stem to form an annular opening for permitting air to pass into and out of the air gap.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a side view of a fuel nozzle;





FIG. 2

is a fragmentary view of the fuel nozzle shown in

FIG. 1

;





FIG. 3

is an enlarged view of a section of the fuel nozzle shown in

FIG. 2

; and





FIG. 4

is a view of a weld between an overhanging section and a heat shield of the fuel nozzle shown in FIG.


3


.











DETAILED DESCRIPTION OF THE INVENTION





FIG. 1

is a side view of a fuel nozzle


10


. Nozzle


10


includes a nozzle stem


12


which is generally U-shaped and which has an upstream end


14


and a downstream end


16


. Nozzle stem


12


also includes a mounting bracket


18


integrally formed as part of nozzle stem


12


. Mounting bracket


18


includes an aperture


20


for mounting fuel nozzle


10


to a combustor apparatus (not shown) of a gas turbine engine. Upstream end


14


is configured to be coupled to a supply source of fuel (not shown) and downstream end


16


is configured to be positioned in an operative relationship with a combustor dome assembly (not shown) of the combustor apparatus.




Fuel nozzle


10


also includes a tubular heat shield


22


having a first end


24


which is secured to stem


12


intermediate upstream end


14


and downstream end


16


. Heat shield


22


also has a second end


26


operatively associated with downstream end


16


.





FIG. 2

is a fragmentary view of fuel nozzle


10


shown in FIG.


1


. As illustrated in

FIG. 2

, tubular heat shield


22


is generally cylindrical in shape and surrounds nozzle stem


12


. Shield


22


has a generally circular cross sectional shape. Nozzle stem


12


includes an outer surface


28


which cooperates with an inner surface


30


of heat shield


22


to define an annular air gap


32


about nozzle stem


12


. Second end


26


of heat shield


22


cooperates with downstream end


16


to define an annular opening


34


which opens into air gap


32


in order to permit air or other gases (not shown) to pass into and out of air gap


32


. Fuel nozzle


10


also includes primary and secondary fuel passageways


35


and


36


for permitting fuel to pass from upstream end


14


to downstream end


16


.




Heat shield


22


includes a first section


38


and a second section


40


(shown in FIG.


1


). First section


38


is seam welded to second section


40


, as described below in more detail. Also, shield


22


is butt welded at shield first end


24


to a first end


42


of an annular overhang


44


intermediate ends


14


and


16


.




More specifically, and referring to

FIG. 3

which is an enlarged view of a section of fuel nozzle


10


shown in

FIG. 2

, a thickness of first end


42


of annular overhang


44


is less than a thickness of a second end


46


of overhang


44


at a main body section


48


of stem


12


. Heat shield


22


is welded to overhang


44


at overhang first end


42


.





FIG. 4

is a view of a weld


50


between overhang


44


and heat shield


22


of fuel nozzle


10


. As shown in

FIG. 4

, first end


42


of overhang


44


is adjacent first end


24


of shield


22


, and a suitable filler material


52


(such as Inconel


625


or Hastalloy X) is located between and overlaps first ends


24


and


42


. Shield first end


24


is spaced from overhang first end


42


by a distance D


1


. Filler material


52


extends within annular air gap


32


by a distance D


2


, and extends beyond outer surfaces


53


and


54


of shield


22


and overhang


44


, respectively, by a distance D


3


. Exemplary values of D


1


, D


2


, and D


3


are set forth below. Of course, the distance may vary depending on the particular application and materials utilized.




D


1


=0.025″




D


2


=0.030″




D


3


=0.030″




Machining an annular groove


56


in stem


12


forms overhang


44


. More specifically, groove


56


is formed by mounting stem


12


on a lathe and using a cutting tool to form groove


56


while stem


12


is spinning. Stem


12


typically is fabricated from Inconel


625


, and known trepanning machines can be used to form groove


56


in stem


12


. Heat shield


22


is then welded to overhang


44


by locating heat shield sections


38


and


30


adjacent end


42


of overhang


44


, and inserting a filler ring at the interface between ends


24


and


42


as shown in

FIG. 4. A

butt weld is then formed using an automated butt welding machine to secure shield


22


to overhang


44


. Automated butt welder machines are known. A seam welder is then utilized to weld first shield section


38


to second shield section


40


at the interfaces between sections


38


and


40


.




The overhang permits the maximum stress, which occurs in the weld and which results from thermal gradients generated during normal engine operation, to be relocated to overhang


44


which is a region of controlled geometry, parent metal properties, and away from the weld which has indeterminate geometry, reduced material properties, and inherent internal defects. By machining the overhang into the stem of the fuel nozzle, and by tapering the overhang thickness such that the end of the overhang welded to the shield is thinner than the end of the overhang at the stem main body, the thermal stresses in the overhang are minimized. Such lower stresses result in longer fatigue life. Further, the machined groove enables use of an automated butt weld, which is precise, controlled, and robust. In addition, the machined groove also enables control of thermal stresses around the machined trepan radius and the tapered overhang cross section. The machined trepan groove also facilitates precise centering of the heat shield on the fuel nozzle housing.




While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.



Claims
  • 1. A method for fabricating a fuel nozzle comprising a nozzle stem having an upstream end and a downstream end, said method comprising the steps of:machining an annular groove intermediate the upstream end and downstream end of the nozzle stem to form an overhang; and welding a heat shield to the overhang, wherein the heat shield has a thickness that is approximately equal to a thickness of the overhang, such that the overhang facilitates centering the heat shield with respect to the nozzle stem, and such that an annular air gap is defined between the nozzle stem and the heat shield.
  • 2. A method in accordance with claim 1 wherein the step of machining the annular groove comprises the step of trepanning the stem.
  • 3. A method in accordance with claim 1 wherein the heat shield comprises a first section and a second section, said method further comprising the step of welding the heat shield first section to the heat shield second section.
  • 4. A method in accordance with claim 1 wherein said step of welding a heat shield to the overhang further comprises the step of butt welding the heat shield to the overhang.
  • 5. A method in accordance with claim 1 wherein said step of welding a heat shield to the overhang further comprises the step of extending filler material from an outer surface of the heat shield and overhang into the annular air gap.
Parent Case Info

This application is a divisional of Ser. No. 09/390,973, now U.S. Pat. No. 6,149,075, filed on Sep. 7, 1999 and claims benefit thereto.

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