Methods and apparatus for reducing gas turbine engine emissions

Information

  • Patent Grant
  • 6415594
  • Patent Number
    6,415,594
  • Date Filed
    Wednesday, May 31, 2000
    24 years ago
  • Date Issued
    Tuesday, July 9, 2002
    22 years ago
Abstract
A gas turbine engine includes a combustor system to reduce an amount of nitrogen oxide emissions formed by the gas turbine engine. The combustor system includes a combustor including a first annular dome. A centerbody is secured within the dome and includes at least one orifice for supplying fuel to the dome. An inner swirler is attached to the centerbody and an outer swirler is attached radially outward from the inner swirler such that a leading edge of the inner swirler and a leading edge of the centerbody are disposed upstream from a leading edge of the outer swirler.
Description




BACKGROUND OF THE INVENTION




This application relates generally to gas turbine engines and, more particularly, to combustors for gas turbine engine.




Air pollution concerns worldwide have led to stricter emissions standards. These standards regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO) generated as a result of gas turbine engine operation. In particular, nitrogen oxide is formed within a gas turbine engine as a result of high combustor flame temperatures. Making modifications to a gas turbine engine in an effort to reduce nitrogen oxide emissions often has an adverse effect on operating performance levels of the associated gas turbine engine.




In gas turbine engines, nitrogen oxide emissions can be reduced by increasing airflow through the gas turbine combustor during operating conditions. Gas turbine engines include preset operating parameters and any such airflow increases are limited by the preset operating parameters including turbine nozzle cooling parameters. For example, increasing airflows within domed combustors including inner and outer swirlers and premixers may cause wake recirculation to develop as airflows exiting the inner swirler separate from the swirler vanes. Furthermore, such wake recirculation permits fuel to dwell within the premixers and potentially autoignite within the premixers. Such autoignition increases emissions from the combustor and may potentially damage components within the combustor. As a result, to increase the airflow within the gas turbine combustor, the gas turbine engine and associated components often must be modified to operate at new operating parameters.




Because implementing gas turbine engine modifications is labor-intensive and time-consuming, users are often limited to derating the operating power capability of the gas turbine engine and prevented from operating the gas turbine engine at full capacity. Such derates do not limit the amount of nitrogen oxide formed as the engine operates at full capacity, but instead limit the operating capacity of the gas turbine engine.




BRIEF SUMMARY OF THE INVENTION




In an exemplary embodiment, a gas turbine engine includes a combustor system to reduce an amount of nitrogen oxide emissions formed by the gas turbine engine. The combustor system includes a combustor including a first annular dome that includes a premixer cup. A centerbody is secured co-axially within the dome and includes at least one orifice for supplying fuel to the dome. An inner swirler is attached to the centerbody and an outer swirler is attached radially outward to the inner swirler such that a leading edge of the inner swirler and a leading edge of the centerbody are disposed a distance upstream from a leading edge of the outer swirler relative to the dome. As a result, a premixing distance measured between the centerbody orifice and an exit of the dome is increased in comparison to known combustor assemblies.




During operation of the gas turbine engine, air and fuel are mixed in the dome prior to the fuel/air mixture exiting the dome for combustion. Although the premixing length is increased because the centerbody is positioned upstream from the outer swirler, because the inner swirler is also positioned upstream from the outer swirler, wake recirculation is reduced and fuel and air thoroughly mix prior to exiting the dome. As a result, nitrogen oxide emissions generated within the combustor are reduced. Furthermore, because wake recirculation is reduced, fuel is prevented from dwelling in the wake recirculation and a potential of fuel autoigniting within the combustor domes is reduced.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic illustration of a gas turbine engine;





FIG. 2

is a cross-sectional view of a combustor used with the gas turbine engine shown in

FIG. 1

;





FIG. 3

is an enlarged partial cross-sectional view of the combustor shown in

FIG. 2

; and





FIG. 4

is a partial cross-sectional view of an alternative embodiment of a centerbody that may be used with the combustor shown in FIG.


2


.











DETAILED DESCRIPTION OF THE INVENTION





FIG. 1

is a schematic illustration of a gas turbine engine


10


including a low pressure compressor


12


, a high pressure compressor


14


, and a combustor


16


. Engine


10


also includes a high pressure turbine


18


and a low pressure turbine


20


. Combustor


16


is a lean premix combustor. Compressor


12


and turbine


20


are coupled by a first shaft


21


, and compressor


14


and turbine


18


are coupled by a second shaft


22


. A load (not shown) is also coupled to gas turbine engine


10


with first shaft


21


. In one embodiment, gas turbine engine


10


is an LM6000 available from General Electric Aircraft Engines, Cincinnati, Ohio.




In operation, air flows through low pressure compressor


12


and compressed air is supplied from low pressure compressor


12


to high pressure compressor


14


. The highly compressed air is delivered to combustor


16


. Airflow from combustor


16


drives turbines


18


and


20


and exits gas turbine engine


10


through a nozzle


24


.





FIGS. 2 and 3

are a cross-sectional view and an enlarged partial cross-sectional view, respectively, of combustor


16


used in gas turbine engine


10


(shown in FIG.


1


). Because a fuel/air mixture supplied to combustor


16


contains more air than is required to fully combust the fuel, and because the air is mixed with the fuel prior to combustion, combustor


16


is a lean premix combustor. Accordingly, a fuel/air mixture equivalence ratio for combustor


16


is less than one. Furthermore, because a gas and a liquid fuel are supplied to combustor


16


, and because combustor


16


does not include water injection, combustor


16


is a dual fuel dry low emissions combustor. Combustor


16


includes an annular outer liner


40


, an annular inner liner


42


, and a domed end


44


extending between outer and inner liners


40


and


42


, respectively. Outer liner


40


and inner liner


42


are spaced radially inward from a combustor casing


45


and define a combustion chamber


46


. Combustor casing


45


is generally annular and extends downstream from a diffuser


48


. Combustion chamber


46


is generally annular in shape and is disposed radially inward from liners


40


and


42


. Outer liner


40


and combustor casing


45


define an outer passageway


52


and inner liner


42


and combustor casing


45


define an inner passageway


54


. Outer and inner liners


40


and


42


extend to a turbine nozzle


55


disposed downstream from diffuser


48


.




Combustor domed end


44


includes a plurality of domes


56


arranged in a triple annular configuration. Alternatively, combustor domed end


44


includes a double annular configuration. In another embodiment, combustor domed end


44


includes a single annular configuration. An outer dome


58


includes an outer end


60


fixedly attached to combustor outer liner


40


and an inner end


62


fixedly attached to a middle dome


64


. Middle dome


64


includes an outer end


66


attached to outer dome inner end


62


and an inner end


68


attached to an inner dome


70


. Accordingly, middle dome


64


is between outer and inner domes


58


and


70


, respectively. Inner dome


70


includes an inner end


72


attached to middle dome inner end


68


and an outer end


74


fixedly attached to combustor inner liner


42


.




Each dome


56


includes a plurality of premixer cups


80


to permit uniform mixing of fuel and air therein and to channel the fuel/air mixture into combustion chamber


46


. In one embodiment, premixer cups


80


are available from Parker Hannifin, 6035 Parkland Blvd., Cleveland, Ohio. Each premixer cup


80


includes a centerbody


82


, an inner swirler


84


, an outer swirler


86


, and an axis of symmetry


88


extending from an upstream side


90


of dome


56


to a downstream side


92


of dome


56


. In one embodiment, inner swirler


84


and outer swirler


86


are counter-rotating. Each centerbody


82


is disposed co-axially with dome axis of symmetry


88


and includes a leading edge


100


and a trailing edge


102


. In one embodiment, centerbody


82


is cast within premixer cup


80


.




Each inner swirler


84


is secured to a centerbody


82


radially outward from centerbody


82


and includes a leading edge


104


and a trailing edge


106


. Each outer swirler


86


is secured to an inner swirler


84


radially outward from inner swirler


84


. Outer swirler


86


is attached such that inner swirler leading edge


104


is a distance


108


upstream from a leading edge


110


of outer swirler


86


. In one embodiment, distance


108


is approximately equal 0.25 inches. Furthermore, when outer swirler


86


is attached, centerbody


82


is positioned such that centerbody leading edge


100


is approximately co-planar with inner swirler leading edge


104


and distance


108


upstream from outer swirler leading edge


110


.




A hub


112


separates each inner swirler


84


from each outer swirler


86


and an annular mixing duct


120


is downstream from inner and outer swirlers


84


and


86


, respectively. Mixing duct


120


is annular and is defined by an annular wall


122


. Annular mixing duct


120


tapers uniformly from dome upstream side


90


to dome downstream side


92


to increase flow velocities within mixing duct


120


. Furthermore, because mixing duct


120


converges, a fuel/air mixture flowing within mixing duct


120


is accelerated which helps to minimize boundary layers from accumulating within mixing duct


120


and thus, minimizes flashbacks stemming therefrom.




Centerbody


82


also includes a cylindrically-shaped first body portion


13


Q and a conical second body portion


132


. Second body portion


132


extends downstream from first body portion


130


. Centerbody


82


has a length


134


extending from leading edge


100


to trailing edge


102


. Length


134


is sized such that centerbody trailing edge


102


is disposed in close proximity to a trailing edge


136


of premixer cup


80


.




Centerbody


82


is hollow and includes a first orifice


140


extending from an outer surface


142


of centerbody


82


to an inner passageway


144


. First orifice


140


is disposed at a junction between centerbody first body portion


130


and centerbody second body portion


132


. First orifice


140


is a fuel port used to supply fuel to premixer cup


80


and inner passageway


144


. Orifice


140


is in flow communication with a fuel nozzle


146


positioned at centerbody leading edge


100


. In one embodiment, fuel nozzles


146


are available from Parker Hannifin, 6035 Parkland Blvd., Cleveland, Ohio. A premixing length


148


, defined as a distance between first orifice


140


and dome downstream side


92


, ensures air and fuel thoroughly mix prior to the fuel/air mixture exiting dome


56


and entering combustion chamber


46


. Because centerbody leading edge


100


is positioned upstream from outer swirler leading edge


110


, premixing length


148


is increased in comparison to other known combustor premixing lengths.




A plurality of second passageways


150


extend through centerbody


82


and are in flow communication with an air source (not shown). Passageways


150


permit small amounts of air to be supplied to combustor


16


to prevent wake separation adjacent centerbody


82


.




Combustor domed end


44


also includes an outer dome heat shield


160


, a middle dome heat shield


162


, and an inner dome heat shield


164


to insulate each respective dome


58


,


64


, and


70


from flames burning in combustion chamber


46


. Outer dome heat shield


160


includes an annular endbody


166


to insulate combustor outer liner


40


from flames burning in an outer primary combustion zone


168


. Middle dome heat shield


162


includes annular heat shield centerbodies


170


and


172


to segregate middle dome


64


from outer and inner domes


58


and


70


, respectively. Middle dome heat shield centerbodies


170


and


172


are disposed radially outward from a middle primary combustion zone


174


.




Inner dome heat shield


164


includes an annular endbody


180


to insulate combustor inner liner


42


from flames burning in an inner primary combustion zone


182


. An igniter


184


extends through combustor casing


45


and is disposed downstream from outer dome heat shield endbody


166


.




Domes


58


,


64


, and


70


are supplied fuel and air via a premixer and assembly manifold system (not shown). A plurality of fuel tubes


200


extend between a fuel source (not shown) and domes


56


. Specifically, an outer dome fuel tube


202


supplies fuel to premixer cup


80


disposed within outer dome


58


, a middle dome fuel tube


204


supplies fuel to premixer cup


80


disposed within middle dome


64


, and an inner dome fuel tube (not shown) supplies fuel to premixer cup


80


disposed within inner dome


70


.




During operation of gas turbine engine


10


, air and fuel are mixed in premixer cups


80


and dome premixing length


148


ensures air and fuel thoroughly mix prior to the fuel/air mixture exiting dome


56


and entering combustion chamber


46


. Although centerbody


82


is positioned upstream from outer swirler


86


to increase premixing length


148


, because inner swirler


84


is also positioned upstream from outer swirler


86


, wake recirculation is reduced and fuel and air mix thoroughly prior to exiting dome


56


. As a result, nitrogen oxide emissions from combustor


16


are reduced. Furthermore, because wake recirculation is reduced, fuel is prevented from dwelling in an inner swirler airflow separation and no autoignition of the fuel occurs within premixer cup


80


.





FIG. 4

is a partial cross-sectional view of an alternative embodiment of a centerbody


300


that may be used with combustor


16


(shown in FIGS.


1


and


2


). Centerbody


300


is secured within dome


56


(shown in

FIGS. 2 and 3

) co-axially with dome axis of symmetry


88


(shown in

FIGS. 1 and 2

) and includes a leading edge


302


and a trailing edge


304


. In one embodiment, centerbody


300


is cast within premixer cup


80


.




Centerbody


300


also includes a cylindrically-shaped first body portion


310


and a conical second body portion


312


. Second body portion


312


extends downstream from first body portion


310


. Centerbody


300


has a length


314


extending from leading edge


302


to trailing edge


304


. Length


314


is sized such that centerbody trailing edge


304


is disposed in close proximity to premixer cup trailing edge


136


(shown in

FIG. 3

) when centerbody


300


is secured within dome


56


. When centerbody


300


is secured within dome


56


, inner swirler


84


(shown in

FIGS. 2 and 3

) and outer swirler


86


(shown in

FIGS. 2 and 3

) are secured radially outward from centerbody


300


such that inner swirler leading edge


104


(shown in

FIGS. 2 and 3

) is upstream from both outer swirler leading edge


110


(shown in

FIGS. 2 and 3

) and centerbody leading edge


302


.




Centerbody


300


is hollow and includes a first orifice


320


extending from an outer surface


324


of centerbody


300


to an inner passageway


326


. First orifice


320


is disposed a distance


330


upstream from a junction


332


between centerbody first body portion


310


and centerbody second body portion


312


. In one embodiment, distance


330


is approximately equal 0.25 inches. First orifice


300


is a fuel port for supplying fuel to premixer cup


80


(shown in

FIG. 2

) and inner passageway


326


is in flow communication with fuel nozzle


146


(shown in

FIGS. 2 and 3

) positioned at centerbody leading edge


316


when centerbody


300


is installed within dome


56


. Dome premixing length


148


(shown in

FIG. 3

) is defined as a distance between first orifice


320


and dome downstream side


92


(shown in FIG.


2


). Because first orifice


320


is positioned distance


330


from dome downstream side


92


, dome premixing length


148


using centerbody


300


is increased in comparison to other known combustor premixing lengths.




A plurality of second passageways


340


extend through centerbody


300


and are in flow communication with an air source (not shown). Passageways


340


permit small amounts of air to be supplied to combustor


16


to prevent wake separation adjacent centerbody


300


.




The above-described combustor system for a gas turbine engine is cost-effective and reliable. The combustor system includes a combustor including a centerbody, an inner swirler, and an outer swirler positioned relative to each other to provide an increased area for fuel and air to mix thoroughly prior to being directed into the combustion chamber. Furthermore, the relative positioning of the centerbody, the inner swirler, and the outer swirler reduces wake recirculation within the combustor dome. As a result, fuel does not dwell in the wake recirculation and is not susceptible to autoignition. Furthermore, as a result, nitrogen oxide emissions are reduced.




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 assembling a gas turbine engine combustor to reduce an amount of emissions from the gas turbine engine, said method comprising the steps of:providing a combustor including a plurality of annular domes, wherein each dome includes a premixer cup; securing an inner swirler to a centerbody within a first annular dome such that the inner swirler is radially outward from the centerbody; securing an outer swirler to the inner swirler such that the outer swirler is radially outward from the inner swirler and such that a leading edge of the outer swirler is downstream from a leading edge of the inner swirler; and securing the first annular dome within the gas turbine engine.
  • 2. A method in accordance with claim 1 wherein said step of securing the outer swirler further comprises the step of securing the outer swirler to the inner swirler such that a leading edge of the centerbody is upstream from a leading edge of the outer swirler.
  • 3. A method in accordance with claim 1 wherein said step of securing an outer swirler further comprises the step of securing the outer swirler to the inner swirler such that a leading edge of the centerbody is approximately 0.25 inches upstream from a leading edge of the outer swirler.
  • 4. A method in accordance with claim 1 wherein said step of securing an outer swirler further comprises the step of securing the outer swirler to the inner swirler such that a leading edge of the inner swirler is approximately 0.25 inches upstream from a leading edge of the outer swirler.
  • 5. A method in accordance with claim 1 further comprising the step of securing a second and a third annular dome to the first annular dome.
  • 6. A combustor for a gas turbine engine, said combustor comprising:a plurality of annular domes comprising at least a first annular dome comprising a premixer cup and an axis of symmetry; an inner swirler within said first dome and comprising a leading edge and a trailing edge; an outer swirler radially outward from said inner swirler and within said first dome, said outer swirler comprising a leading edge, said inner swirler leading edge upstream from said outer swirler leading edge; and a centerbody radially inward from said inner swirler along said annular dome axis of symmetry.
  • 7. A combustor in accordance with claim 6 further comprising a second and a third annular dome.
  • 8. A combustor in accordance with claim 6 wherein said centerbody comprises a leading edge and a trailing edge, said centerbody leading edge upstream from said outer swirler leading edge.
  • 9. A combustor in accordance with claim 6 wherein said inner swirler leading edge is approximately 0.25 inches upstream from said outer swirler leading edge.
  • 10. A combustor in accordance with claim 6 wherein said centerbody comprises at least one orifice configured to inject fuel into said first annular dome premixer cup.
  • 11. A combustor in accordance with claim 10 wherein said centerbody further comprises a conical first body portion and a cylindrical second body portion, said centerbody first body portion extending downstream from said centerbody second body portion.
  • 12. A combustor in accordance with claim 11 wherein said at least one orifice is disposed in said centerbody first body portion.
  • 13. A combustor in accordance with claim 10 wherein said at least one orifice disposed approximately 0.25 inches upstream from said first body portion.
  • 14. A gas turbine engine comprising a combustor system configured to reduce emissions from said gas turbine engine, said combustor system comprising a combustor comprising a plurality of annular domes comprising at least a first annular dome comprising a premixer cup, an inner swirler, and an outer swirler, said inner swirler disposed radially inward from said outer swirler and comprising a leading edge and a trailing edge, said outer swirler disposed within said annular dome and comprising a leading edge, said inner swirler leading edge being upstream from said outer swirler leading edge.
  • 15. A gas turbine engine in accordance with claim 14 further comprising a centerbody disposed radially inward from said inner swirler and comprising a leading edge and a trailing edge, said centerbody leading edge upstream from said outer swirler leading edge.
  • 16. A gas turbine engine in accordance with claim 14 wherein said inner swirler leading edge approximately 0.25 inches upstream from said outer swirler leading edge.
  • 17. A gas turbine engine in accordance with claim 15 wherein said centerbody further comprises a first body portion and a second body portion, said first body portion substantially cylindrical, said second body portion extending downstream from said first body portion and substantially conical.
  • 18. A gas turbine engine in accordance with claim 17 wherein said centerbody further comprises at least one orifice configured to inject fuel into said annular dome premixer cup.
  • 19. A gas turbine engine in accordance with claim 18 wherein said at least one orifice disposed within said centerbody first body portion.
  • 20. A gas turbine engine in accordance with claim 18 wherein said at least one orifice disposed approximately 0.25 inches upstream from said centerbody second body portion.
US Referenced Citations (9)
Number Name Date Kind
3764071 Carlisle Oct 1973 A
4092826 Pask Jun 1978 A
4222243 Mobsby Sep 1980 A
5323604 Ekstedt et al. Jun 1994 A
5675971 Angel et al. Oct 1997 A
5680766 Joshi et al. Oct 1997 A
5778676 Joshi et al. Jul 1998 A
5899075 Dean et al. May 1999 A
6141967 Angel et al. Nov 2000 A