ANNULAR PREMIXED PILOT IN FUEL NOZZLE
A combustor for a gas turbine engine has a head end portion that carries at least one fuel/air nozzle. Each fuel/air nozzle includes a premixed pilot nozzle having premix conduits where each premix conduit has an upstream end defining an opening and having a central axis and downstream end defining an outlet and having a central axis where the central axis of the downstream end is non-parallel with a central axis of a center body of the fuel/air nozzle. The premixed pilot nozzle can include an annular channel disposed radially outwardly from the premix conduits and may include air jets that direct air radially outwardly from the premix conduits.
The present application is a continuation application of U.S. application having Ser. No. 13/405,550 filed on Feb. 27, 2012, which is incorporated herein in its entirety by reference thereto for all purposes. Any disclaimer that may have occurred during prosecution of the above-referenced application(s) is hereby expressly rescinded.
FIELD OF THE INVENTIONThe present invention generally involves a gas turbine engine that combusts a hydrocarbon fuel mixed with air to generate a high temperature gas stream that drives turbine blades to rotate a shaft attached to the blades and more particularly to the engine's fuel nozzle having a pilot nozzle that premixes fuel and air while achieving lower nitrogen oxides.
BACKGROUND OF THE INVENTIONGas turbine engines are widely used to generate power for numerous applications. A conventional gas turbine engine includes a compressor, a combustor, and a turbine. In a typical gas turbine engine, the compressor provides compressed air to the combustor. The air entering the combustor is mixed with fuel and combusted. Hot gases of combustion are exhausted from the combustor and flow into the blades of the turbine so as to rotate the shaft of the turbine connected to the blades. Some of that mechanical energy of the rotating shaft drives the compressor and/or other mechanical systems.
As government regulations disfavor the release of nitrogen oxides into the atmosphere, their production as byproducts of the operation of gas turbine engines is sought to be maintained below permissible levels. One approach to meeting such regulations is to move from diffusion flame combustors to combustors that employ lean fuel and air mixtures using a fully premixed operations mode to reduce emissions of, for example, nitrogen oxides (commonly denoted NOx) and carbon monoxide (CO). These combustors are variously known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean Pre Mixed (LPM) combustion systems.
Fuel-air mixing affects both the levels of nitrogen oxides generated in the hot gases of combustion of a gas turbine engine and the engine's performance. A gas turbine engine may employ one or more fuel nozzles to intake air and fuel to facilitate fuel/air mixing in the combustor. The fuel nozzles may be located in a head end portion of the combustor, and may be configured to intake an air flow to be mixed with a fuel input. Typically, each fuel nozzle may be internally supported by a center body located inside of the fuel nozzle, and a pilot can be mounted at the downstream end of the center body. As described for example in U.S. Pat. No. 6,438,961, which is incorporated in its entirety herein by this reference for all purposes, a so-called swozzle can be mounted to the exterior of the center body and located upstream from the pilot. The swozzle has curved vanes that extend radially from the center body across an annular flow passage and from which fuel is introduced into the annular flow passage to be entrained into a flow of air that is swirled by the vanes of the swozzle.
Various parameters describing the combustion process in the gas turbine engine correlate with the generation of nitrogen oxides. For example, higher gas temperatures in the combustion reaction zone are responsible for generating higher amounts of nitrogen oxides. One way of lowering these temperatures is by premixing the fuel air mixture and reducing the ratio of fuel to air that is combusted. As the ratio of fuel to air that is combusted is lowered, so too the amount of nitrogen oxides is lowered. However, there is a trade-off in performance of the gas turbine engine. For as the ratio of fuel to air that is combusted is lowered, there is an increased tendency of the flame of the fuel nozzle to blow out and thus render unstable the operation of the gas turbine engine. A pilot of a diffusion flame type has been used for better flame stabilization in a combustor, but doing so increases NOx.
BRIEF DESCRIPTION OF THE INVENTIONAspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In theory, the closer one comes to having at every point in the combustion chamber, a stoichiometric relationship between the fuel and air that undergoes combustion at a given temperature of combustion, the closer one comes to minimizing the generation of nitrogen oxides as byproducts of the combustion. With a fuel nozzle configured as described below, it becomes possible to achieve a more uniform equivalence ratio across the plane of the center body tip of the outer nozzle and thus more closely approximate achieving in the combustion chamber of the gas turbine engine such theoretical conditions of the desired stoichiometric relationship between the fuel and air that undergoes combustion at a given temperature of combustion. Moreover, to overcome one of the drawbacks of a diffusion flame type of pilot, a premix pilot also can be used as a pilot to stabilize the pilot flame, even in low fuel to air ratio to prevent an increase in NOx.
One embodiment of the present invention is directed to a fuel/air nozzle. The fuel/air nozzle includes a premixed pilot nozzle having an upstream end axially spaced from a downstream end with respect to an axial center line of a center body of the fuel/air nozzle. The upstream end is connected to a downstream end of the center body. The premixed pilot nozzle further defines a plurality of axially elongated, hollow premix conduits that are annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle. Each premix conduit has an upstream end that defines an entrance opening that communicates fluidly with an interior passage of the center body. Each premix conduit has at least one fuel hole that is in fluid communication with the pilot fuel nozzle portion. Each premix conduit includes a downstream end which defines an exit opening that allows fluid to discharge from the hollow premix conduit. Each downstream end of each premix conduit has a central axis that is not parallel to the central axis of the center body.
Another embodiment of the present invention is directed to a combustor. The combustor includes a head end portion and at least one fuel/air nozzle carried by the head portion. The fuel/air nozzle comprises a center body that defines a central axis of the fuel/air nozzle and an internal passage within the fuel/air nozzle. A fuel supply line extends axially within the center body and is in fluid communication with a source of fuel. A premixed pilot nozzle includes an upstream end that is axially spaced from a downstream end with respect to the axial center line of the center body. The upstream end is connected to a downstream end of the center body. The premixed pilot nozzle further defines a plurality of axially elongated, hollow premix conduits that is annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle. Each premix conduit has an upstream end that defines an entrance opening that is in fluid communication with the interior passage. Each premix conduit has at least one fuel hole that is in fluid communication with the pilot fuel nozzle portion. Each premix conduit includes a downstream end that defines an exit opening that allows fluid to discharge from the hollow premix conduit. Each downstream end of each premix conduit has a central axis that is not parallel to the central axis of the center body.
A further embodiment of the present invention is directed to a method of operating a fuel/air nozzle having a premix pilot nozzle including a plurality of premix conduits annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle. The method includes delivering a flow of pilot fuel to the premix pilot nozzle, delivering a flow of air through the center body to the premix pilot nozzle, and mixing the pilot fuel with the flow of air in a plurality of axially elongated, hollow premix conduits. Each premix conduit defines a central axis at the downstream end thereof that is not parallel to a central axis of the center body and that discharges the fuel/air mixture from the downstream end of the premix pilot nozzle. The method further includes expelling the fuel/air mixture from the exit openings of the premix conduits of the premixed pilot nozzle.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of embodiments of the invention.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. For instance, a range from 100 to 200 also includes all possible sub-ranges, examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and 187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to 5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes 7.
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While the fuel-air mix 62b tends to spread radially from each central axis 41c once the fuel-air mix 62b leaves the exit opening 66b of each premix conduit 41, applicants have shown that the radial spread is not very significant. Indeed, applicants' studies have shown that the equivalence ratio at the section of the burn exit plane 44 (
Various embodiments of the present invention include features that counteract this much higher equivalence ratio that exists at the section of the burn exit plane 44 (
As schematically shown for the embodiments of the premixed pilot nozzle 40 that are depicted in
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In another embodiment of the present invention depicted schematically in
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As schematically shown for the embodiment of the premixed pilot nozzle 40 that is depicted in
Each embodiment of the premixed pilot nozzle 40 provides a small well anchored premixed flame near the base of the fuel-air nozzle 12, thus anchoring the swirling fuel air mixture exiting the fuel-air nozzle 12. The improved flame stability enables lower fuel/air operations, thus extending LBO and the emissions operability window.
With fuel/air nozzles 12 such as the embodiments described above, it becomes feasible to implement advantageous methods of operating a fuel/air nozzle 12 for a gas turbine engine 10. One embodiment of such a method of operating a fuel/air nozzle 12 for a gas turbine engine 10 desirably includes the following steps schematically shown in
Another embodiment of such a method of operating a fuel/air nozzle 12 for a gas turbine engine 10 desirably includes the following steps schematically shown in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Claims
1. A fuel/air nozzle for a gas turbine engine, the fuel/air nozzle comprising:
- a premixed pilot nozzle having an upstream end axially spaced from a downstream end with respect to an axial center line of a center body of the fuel/air nozzle, wherein the upstream end is connected to a downstream end of the center body; and
- the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle, each premix conduit having an upstream end defining an entrance opening that communicates fluidly with an interior passage of the center body, each premix conduit having at least one fuel hole in fluid communication with the pilot fuel nozzle portion, each premix conduit including a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit;
- wherein each downstream end of each premix conduit has a central axis that is not parallel to the central axis of the center body.
2. The fuel/air nozzle as in claim 1, wherein each central axis of at least one premix conduit is disposed at an acute angle with respect to the central axis of the center body.
3. The fuel/air nozzle as in claim 1, wherein the premixed pilot nozzle further defines an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the center body, the annular channel defining a plurality of air jets, at least one of the air jets being disposed nearby one of the exit openings of at least one of the premix conduits and having a central axis.
4. The fuel/air nozzle as in claim 3, wherein the central axis of the upstream end of at least one premix conduit is configured and disposed to extend in a direction parallel to the central axis of the center body.
5. The fuel/air nozzle as in claim 3, wherein the central axis of at least one of the air jets forms an acute angle with the central axis of the center body.
6. The fuel/air nozzle as in claim 3, wherein the annular channel is configured to taper as it proceeds in the downstream direction toward the air jets.
7. The fuel/air nozzle as in claim 1, further comprising a swozzle including a plurality of swirl blades extending radially across the primary air flow channel, at least one of the swirl blades defining a fuel conduit having an inlet at one end thereof and an outlet at an opposite end thereof in fluid communication with the primary air flow channel.
8. The fuel/air nozzle as in claim 1, wherein a downstream end of the pilot fuel nozzle defines a plurality of fuel jets oriented to direct a jet of fuel from the pilot fuel nozzle against a backside surface of the downstream end of the premixed pilot nozzle.
9. The fuel/air nozzle as in claim 1, further comprising a fuel plenum wall disposed radially outwardly from the pilot fuel nozzle and defining a fuel plenum between the pilot fuel nozzle and the fuel plenum wall, the fuel plenum wall further defining a plurality of fuel holes, at least one of the fuel holes being in fluid communication with at least one of the fuel jets via the fuel plenum, each premix conduit being disposed radially outwardly from the fuel plenum wall and in fluid communication with at least one of the fuel holes.
10. A combustor for a gas turbine engine, the combustor comprising:
- a head end portion;
- at least one fuel/air nozzle carried by the head portion, each fuel/air nozzle further comprising: a center body defining a central axis of the fuel/air nozzle and an internal passage within the fuel/air nozzle; a fuel supply line extending axially within the center body and in fluid communication with a source of fuel; a premixed pilot nozzle having an upstream end axially spaced from a downstream end with respect to the axial center line of the center body, wherein the upstream end is connected to a downstream end of the center body; and the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle, each premix conduit having an upstream end defining an entrance opening in fluid communication with interior passage, each premix conduit having at least one fuel hole in fluid communication with the pilot fuel nozzle portion, each premix conduit including a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit; wherein each downstream end of each premix conduit has a central axis that is not parallel to the central axis of the center body.
11. The combustor as in claim 10, wherein the premixed pilot further defines an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the center body, the annular channel defining a plurality of air jets.
12. The combustor as in claim 11, wherein at least one of the air jets is disposed adjacent to one of the exit openings of at least one of the premix conduits and has a central axis that is disposed at an acute angle with respect to the central axis of the nearby one of the exit openings of at least one of the premix conduits.
13. The combustor as in claim 11, wherein the annular channel tapers as it proceeds in the downstream direction toward the air jets.
14. A method of operating a fuel/air nozzle having a premix pilot nozzle including a plurality of premix conduits annularly arranged around a pilot fuel nozzle portion of the premixed pilot nozzle, the method comprising:
- delivering a flow of pilot fuel to the premix pilot nozzle;
- delivering a flow of air through the center body to the premix pilot nozzle;
- mixing the pilot fuel with the flow of air in a plurality of axially elongated, hollow premix conduits wherein each premix conduit defines a central axis at the downstream end thereof that is not parallel to a central axis of the center body and that discharges the fuel/air mixture from the downstream end of the premix pilot nozzle; and
- expelling the fuel/air mixture from the exit openings of the premix conduits of the premixed pilot nozzle.
15. The method as in claim 14, further comprising expelling the fuel/air mixture from the premix conduits of the premixed pilot nozzle in a direction that is radially away from the central axis of the center body.
16. The method as in claim 15, further comprising the step of diverting some of the flow of air to an annular channel that is disposed radially outwardly from the premix conduits of the premixed pilot nozzle.
17. The method as in claim 16, wherein the pressure of the air expelled from the annular channel exceeds the pressure of the air entering the annular channel.
18. The method as in claim 16, wherein the annular channel tapers as it proceeds in the downstream direction.
19. The method as in claim 16, further comprising the step of expelling air from the annular channel of the premixed pilot nozzle in a direction that is away from the exit openings of the premix conduits.
20. The method as in claim 19, wherein the air expelled from the annular channel is directed away from the central axis of the center body.
Type: Application
Filed: May 22, 2015
Publication Date: Sep 10, 2015
Inventors: Jong Ho Uhm (Yongin), Derrick Walter Simons (Greer, SC), Gregory Allen Boardman (Greer, SC), Bryan Wesley Romig (Simpsonville, SC), Kara Edwards (Greer, SC), Michael John Hughes (Pittsburgh, PA)
Application Number: 14/719,356