Systems and apparatus relating to downstream fuel and air injection in gas turbines

A gas turbine engine that includes: an interior flowpath defined through a combustor and a turbine; an aft frame forming an interface between the combustor the turbine, the aft frame comprising a rigid structural member that circumscribes the interior flowpath, wherein the aft frame includes an inner wall that defines an outboard boundary of the interior flowpath; a circumferentially extending fuel plenum formed through the aft frame; and outlet ports formed through the inner wall of the aft frame. The outlet ports may be configured to connect the fuel plenum to the interior flowpath.

BACKGROUND OF THE INVENTION

This present application relates generally to the combustion systems in combustion or gas turbine engines (hereinafter “gas turbines”). More specifically, but not by way of limitation, the present application describes novel methods, systems, and/or apparatus related to the downstream or late injection of air and fuel in the combustion systems of gas turbines.

The efficiency of gas turbines has improved significantly over the past several decades as new technologies enable increases to engine size and higher operating temperatures. One technical basis that allowed higher operating temperatures was the introduction of new and innovative heat transfer technology for cooling components within the hot gas path. Additionally, new materials have enabled higher temperature capabilities within the combustor.

During this time frame, however, new standards were enacted that limit the levels at which certain pollutants may be emitted during engine operation. Specifically, the emission levels of NOx, CO and UHC, all of which are sensitive to the operating temperature of the engine, were more strictly regulated. Of those, the emission level of NOx is especially sensitive to increased emission levels at higher engine firing temperatures and, thus, became a significant limit as to how much temperatures could be increased. Because higher operating temperatures coincide with more efficient engines, this hindered advances in engine efficiency. In short, combustor operation became a significant limit on gas turbine operating efficiency.

As a result, one of the primary goals of advanced combustor design technologies became developing configurations that reduced combustor driven emission levels at these higher operating temperatures so that the engine could be fired at higher temperatures, and thus have a higher pressure ratio cycle and higher engine efficiency. Accordingly, as it will be appreciated, novel combustion system designs that reduce emissions, particular that of NOx, and enable higher firing temperatures would be in great commercial demand.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a gas turbine engine that includes: an interior flowpath defined through a combustor and a turbine; an aft frame forming an interface between the combustor the turbine, the aft frame comprising a rigid structural member that circumscribes the interior flowpath, wherein the aft frame includes an inner wall that defines an outboard boundary of the interior flowpath; a circumferentially extending fuel plenum formed through the aft frame; and outlet ports formed through the inner wall of the aft frame. The outlet ports may be configured to connect the fuel plenum to the interior flowpath.

The present application further describes an annular structural member configured to wraparound an interior flowpath that extends between a combustor and a turbine within a gas turbine engine, the annular structural member including: connecting means by which the annular structural member connects to the combustor and the turbine; an inner wall that, in operation, defines an outboard boundary of the interior flowpath; a circumferentially extending fuel plenum formed within the annual structural member frame; a fuel inlet port formed through an outer wall of the aft frame; air inlet ports formed through the outer wall of the aft frame; and outlet ports formed through the inner wall of the aft frame that fluidly connect the fuel plenum to the interior flowpath.

These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

While the following examples of the present invention may be described in reference to particular types of turbine engine, those of ordinary skill in the art will appreciate that the present invention may not be limited to such use and applicable to other types of turbine engines, unless specifically limited therefrom. Further, it will be appreciated that in describing the present invention, certain terminology may be used to refer to certain machine components within the gas turbine engine. Whenever possible, common industry terminology will be used and employed in a manner consistent with its accepted meaning. However, such terminology should not be narrowly construed, as those of ordinary skill in the art will appreciate that often a particular machine component may be referred to using differing terminology. Additionally, what may be described herein as being single component may be referenced in another context as consisting of multiple components, or, what may be described herein as including multiple components may be referred to elsewhere as a single one. As such, in understanding the scope of the present invention, attention should not only be paid to the particular terminology, but also the accompanying description, context, as well as the structure, configuration, function, and/or usage of the component, particularly as may be provided in the appended claims.

Several descriptive terms may be used regularly herein, and it may be helpful to define these terms at the onset of this section. Accordingly, these terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate direction relative to the flow of a fluid, such as, for example, the working fluid through the compressor, combustor and turbine sections of the gas turbine, or the flow coolant through one of the component systems of the engine. The term “downstream” corresponds to the direction of fluid flow, while the term “upstream” refers to the direction opposite or against the direction of fluid flow. The terms “forward” and “aft”, without any further specificity, refer to directions relative to the orientation of the gas turbine, with “forward” referring to the forward or compressor end of the engine, and “aft” referring to the aft or turbine end of the engine, the alignment of which is illustrated inFIG. 1.

Additionally, given a gas turbine engine's configuration about a central axis as well as this same type of configuration in some component systems, terms describing position relative to an axis likely will be used. In this regard, it will be appreciated that the term “radial” refers to movement or position perpendicular to an axis. Related to this, it may be required to describe relative distance from the central axis. In this case, for example, if a first component resides closer to the center axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. Additionally, it will be appreciated that the term “axial” refers to movement or position parallel to an axis. And, finally, the term “circumferential” refers to movement or position around an axis. As mentioned, while these terms may be applied in relation to the common center axis or shaft that typically extends through the compressor and turbine sections of the engine, they also may be used in relation to other components or sub-systems. For example, in the case of a cylindrically shaped “can-type” combustor, which is common to many machines, the axis which gives these terms relative meaning may be the longitudinal reference axis that is defined through the center of the cylindrical, “can” shape for which it is named or the more annular, downstream shape of the transition piece.

Referring now toFIG. 1, by way of background, an exemplary gas turbine10is provided in which embodiments of the present application may be used. In general, gas turbine engines operate by extracting energy from a pressurized flow of hot gas produced by the combustion of a fuel in a stream of compressed air. As illustrated inFIG. 1, the combustion turbine engine10includes an axial compressor11that is mechanically coupled via a common shaft to a downstream turbine section or turbine13, with a combustor12positioned therebetween. As shown, the compressor11includes a plurality of stages, each of which includes a row of compressor rotor blades followed by a row of compressor stator blades. The turbine13also includes a plurality of stages. Each of the turbine stages includes a row of turbine buckets or rotor blades followed by a row of turbine nozzles stator blades, which remain stationary during operation. The turbine stator blades generally are circumferentially spaced one from the other and fixed about the axis of rotation. The rotor blades may be mounted on a rotor wheel that connects to the shaft.

In operation, the rotation of compressor rotor blades within the compressor11compresses a flow of air which is directed into the combustor12. Within the combustor12, the compressed air is mixed with a fuel and ignited so to produce an energized flow of working fluid which then may be expanded through the turbine13. Specifically, the working fluid from the combustor12is directed over the turbine rotor blades such that rotation is induced, which the rotor wheel then translates to the shaft. In this manner, the energy of the flow of working fluid is transformed into the mechanical energy of the rotating shaft. The mechanical energy of the shaft then may be used to drive the rotation of the compressor rotor blades so to produce the necessary supply of compressed air, and, for example, to drive a generator to produce electricity.

FIG. 2is a section view of a conventional combustor in which embodiments of the present invention may be used. The combustor20, however, may take various forms, each of which being suitable for including various embodiments of the present invention. Typically, the combustor20includes multiple fuel nozzles21positioned at a headend22. It will be appreciated that various conventional configurations for fuel nozzles21may be used with the present invention. Within the headend22, air and fuel are brought together for combustion within a combustion zone23, which is defined by a surrounding liner24. The liner24typically extends from the headend22to a transition piece25. The liner24, as shown, is surrounded by a flow sleeve26, and, similarly, the transition piece25is surrounded by an impingement sleeve28. Between the flow sleeve26and the liner24and the transition piece25and impingement sleeve28, it will be appreciated that an annulus, which will be referred to herein as a “flow annulus27”, is formed. The flow annulus27, as shown, extends for a most of the length of the combustor20. From the liner24, the transition piece25transforms the flow from the circular cross section of the liner24to an annular cross section as it extends downstream toward the turbine13. At a downstream end, the transition piece25directs the flow of the working fluid toward the first stage of the turbine13.

It will be appreciated that the flow sleeve26and impingement sleeve28typically have impingement apertures (not shown) formed therethrough which allow an impinged flow of compressed air from the compressor12to enter the flow annulus27formed between the flow sleeve26/liner24and/or the impingement sleeve28/transition piece25. The flow of compressed air through the impingement apertures convectively cools the exterior surfaces of the liner24and transition piece25. The compressed air entering the combustor20through the flow sleeve26and the impingement sleeve28is directed toward the forward end of the combustor20via the flow annulus27. The compressed air then enters the fuel nozzles21, where it is mixed with a fuel for combustion.

The turbine13typically has multiple stages, each of which includes two axial stacked rows of blades: a row of stator blades16followed by a row of rotor blades17, as shown inFIGS. 1 and 4. Each of the blade rows include many blades circumferentially spaced about the center axis of the turbine13. At a downstream end, the transition piece25includes an outlet and aft frame29that directs the flow of combustion products into the turbine13, where it interacts with the rotor blades to induce rotation about the shaft. In this manner, the transition piece25serves to couple the combustor20and the turbine13.

FIG. 3illustrates a view of a combustor12that includes supplemental or downstream fuel/air injection. It will be appreciated that such supplemental fuel/air injection is often referred to as late lean injection or axially staged injection. As used herein, this type of injection will be referred to as “downstream injection” because of the downstream location of the fuel/air injection relative to the primary fuel nozzles21positioned at the headend22. It will be appreciated that the downstream injection system30ofFIG. 3is consistent with a conventional design and is provided merely for exemplary purposes. As shown, the downstream injection system30may include a fuel passageway31defined within the flow sleeve26, though other types of fuel delivery are possible. The fuel passageway31may extend to injectors32, which, in this example, are positioned at or near the aft end of the liner24and flow sleeve26. The injectors32may include a nozzle33and a transfer tube34that extends across the flow annulus27. Given this arrangement, it will be appreciated that each injector32bring together a supply of compressed air derived from the exterior of the flow sleeve26and a supply of fuel delivered through the nozzle33and inject this mixture into the combustion zone23within the liner24. As shown, several fuel injectors32may be positioned circumferentially around the flow sleeve26/liner24assembly so that a fuel/air mixture is introduced at multiple points around the combustion zone23. The several fuel injectors32may be positioned at the same axial position. That is, the several injectors are located as the same position along the center axis37of the combustor12. As used herein, fuel injectors32having this configuration may be described as being positioned on a common injection plane38, which, as shown, is a plane perpendicular to the center axis37of the combustor12. In the exemplary conventional design ofFIG. 3, the injection plane36is positioned at the rearward or downstream end of the liner24.

Turning to theFIGS. 4 through 19and the invention of the present application, it will be appreciated that the level of gas turbine emissions depend upon many operating criteria. The temperatures of reactants in the combustion zone is one of these factors and has been shown to affect certain emission levels, such as NOx, more than others. It will be appreciated that the temperature of the reactants in the combustion zone is proportionally related to the exit temperature of the combustor, which correspond to higher pressure ratios, and, further, that higher pressure ratios enable improved efficiency levels in such Brayton Cycle type engines. Because it has been found that the emission levels of NOx has a strong and direct relationship to reactant temperatures, modern gas turbines have only been able to maintain acceptable NOx emission level while increasing firing temperatures through technological advancements such as advanced fuel nozzle design and premixing. Subsequent to those advancements, late or downstream injection was employed to enable further increases in firing temperature, as it was found that shorter residence times of the reactants at the higher temperatures within the combustion zone decreased NOx levels. Specifically, it has been shown that, at least to a degree, controlling residence time may be used to control NOx emission levels.

Such downstream injection, which is also referred to as “late lean injection”, introduces a portion of the air and fuel supply downstream of the main supply of air and fuel delivered to the primary injection point within the headend or forward end of the combustor. It will be appreciated that such downstream positioning of the injectors decreases the time the combustion reactants remain within the higher temperatures of the flame zone within the combustor. Specifically, due to the substantially constant velocity of the flow of fluid through the combustor, shortening the distance via downstream injection that reactants must travel before exiting the flame zone results in reduced time those reactants reside at the high temperatures in the flame zone, which, as stated, reduces the formation of NOx and NOx emission levels for the engine. This has allowed advanced combustor designs that couple advanced fuel/air mixing or pre-mixing technologies with the reduced reactant residence times of downstream injection to achieve further increases in combustor firing temperature and, importantly, more efficient engines, while also maintaining acceptable NOx emission levels.

However, other considerations limit the manner in which and the extent to which downstream injection may be done. For example, downstream injection may cause emission levels of CO and UHC to rise. That is, if fuel is injected in too large of quantities at locations that are too far downstream in the combustion zone, it may result in the incomplete combustion of the fuel or insufficient burnout of CO. Accordingly, while the basic principles around the notion of late injection and how it may be used to affect certain emissions may be known generally, challenging design obstacles remain as how this strategy may be optimized so that to enable higher combustor firing temperatures. Accordingly, novel combustor designs and technologies that enable the further optimization of residence time in efficient and cost-effective ways are important areas for further technological advancement, which, as discussed below, is the subject of this application.

One aspect of the present invention proposes an integrated two stage injection approach to downstream injection. Each stage, as discussed below, may be axially spaced so to have a discrete axial location relative to the other within the far aft portions of the combustor12and/or upstream regions of the turbine13. With reference now toFIG. 4, a sectional portion of a gas turbine engine10is illustrated that, according to aspects of the present invention, shows approximate ranges (shaded portion) for the placement of each of the two stages of late injection. More specifically, a downstream injection system30according to the present invention may include two integrated axial stages of injection within a transition zone39, which is the portion of the interior flowpath defined within the transition piece25of the combustor12, or the interior flowpath defined downstream within the first stage of the turbine13. The two axial stages of the present invention include what will be referred herein to as an upstream or “first stage41” and a downstream or “second stage42”. According to certain embodiments, each of these axial stages include a plurality of injectors32. The injectors32within each of the stages may be circumferentially spaced at the approximately same axial position within either the transition zone39or forward portion of the turbine13. Injector32configured in this manner (i.e., injectors32being circumferentially spaced on a common axial plane) will be described herein as having a common injection plane38, as discussed in more detail in relation toFIGS. 5 through 7. Pursuant to preferred embodiments, the injectors at each of the first and second stages41,42may be configured to inject both air and fuel at each location.

FIG. 4illustrates axially ranges within which each of the first stage41and the second stage42may be located according to preferred embodiments. To define preferred axial positioning, it will be appreciated that, given the sectional or profile view ofFIGS. 5 through 7, the combustor12and turbine13may be described as defining an interior flowpath extending about a longitudinal center axis37from an upstream end near the headend22of the combustor12through to a downstream end in the turbine13section. Accordingly, the positioning of each of the first and second stage41,42may be defined relative to the location of each along the longitudinal axis37of the interior flowpath. As also indicated inFIG. 4, certain reference planes formed perpendicular to longitudinal center axis37may be defined that provide further definition to axial positions within this region of the turbine. The first of these is a combustor mid-plane48, which is a perpendicular plane relative to center axis37which is positioned at the approximate axial midpoint of the combustor12, i.e., about halfway between the fuel nozzles21of the headend22and the downstream end of the combustor12. It will be appreciated that the combustor mid-plane48typically occurs near the location at which the liner24/flow sleeve26assembly gives way to the transition piece25/impingement sleeve28assembly. The second reference planes, which, as illustrated, is defined at the aft end of the combustor12, is referred to herein as the combustor end-plane49. The combustor end-plane49marks the far, downstream end of the aft frame29.

According to preferred embodiments, as shown inFIG. 4, the downstream injection system30of the present invention may include two axial stages of injection, a first stage41and a second stage42, that are positioned aft of the combustor mid-plane. More specifically, the first stage41may be positioned in the aft half of the transition zone39, and the second stage42may be positioned between the first stage41and the first row of stator blades16in the turbine13. More preferably, the first stage41may be positioned very late within the aft portions of the combustor12, and the second stage42near or downstream of the end-plane49of the combustor12. In certain cases, the first and second stages41,42may be positioned near each other so that common air/fuel conduits may be employed.

Turning now toFIGS. 5 through 10, several preferred embodiments are provided that illustrated further aspects of the present invention as it relates to a two staged system. Each of these figures includes a sectional view of an interior flowpath through an exemplary combustor12and turbine13. As one of ordinary skill in the art will appreciate, the headend22and fuel nozzles21, which may also be referred to herein as the primary air and fuel injection system, may include any of several configurations, as the operation of the present invention is not dependent upon any specific one. According to certain embodiments, the headend22and fuel nozzles21may be configured to be compatible with late lean or downstream injection systems, as described and defined in U.S. Pat. No. 8,019,523, which is hereby incorporated by reference in its entirety. Downstream of the headend22, a liner24may define a combustion zone23within which much of the primary supply of air and fuel delivered to the headend22is combusted. A transition piece25then may extend downstream from the liner24and define a transition zone39, and at the downstream end of the transition piece25, an aft frame29may direct the combustion products toward the initial row of stator blades16in the turbine13.

Each of these first and second stages41,42of injection may include a plurality of circumferentially spaced injectors32. The injectors32within each of the axial stages may be positioned on a common injection plane38, which is a perpendicular reference plane relative to the longitudinal axis37of the interior flowpath. The injectors32, which are represented in a simplified form inFIGS. 5 through 7for the sake of clarity, may include any conventional design for the injection of air and fuel into the downstream or aft end of the combustor12or the first stage within the turbine13. The injectors32of either stage41,42may include the injector32ofFIG. 3, as well as any of those described or referenced in U.S. Pat. Nos. 8,019,523 and 7,603,863, both of which are incorporated herein by reference, any of those described below in relation toFIGS. 14 through 19, as well as other conventional combustor fuel/air injectors. As provided in the incorporated references, the fuel/air injectors32of the present invention may also include those integrated within the row of stator blades16according to any conventional means and apparatus, such as, for example, those described in U.S. Pat. No. 7,603,863. For injectors32within the transition zone39, each may be structurally supported by the transition piece25and/or the impingement sleeve28, and, in some cases, may extend into the transition zone39. The injectors32may be configured to inject air and fuel into the transition zone39in a direction that is generally transverse to a predominant flow direction through the transition zone39. According to certain embodiments, each axial stage of the downstream injection system30may include several injectors32that are circumferentially spaced at regular intervals or, in other cases, at uneven intervals. As an example, according to a preferred embodiment, between 3 and 10 injectors32may be employed at each of the axial stages. In other preferred embodiments, the first stage may include between 3 and 6 injectors and the second stage (and a third stage, if present) may each comprises between 5 and 10 injectors. In regard to their circumferential placement, the injectors32between the two axial stages41,42may be placed in-line or staggered with respect to one another, and, as discussed below, may be placed to supplement the other. In preferred embodiments, the injectors32of the first stage41may be configured to penetrate the main flow more than the injectors32of the second stage42. In preferred embodiments, this may result in the second stage42having more injectors32positioned about the circumference of the flowpath than the first stage41. The injectors of the first stage, the second stage, and a third stage, if present, each may be configured that, in operation, injectors injects air and fuel in a direction between +30° and −30° to a reference line that is perpendicular relative a predominant direction of the flow through the interior flowpath.

In regard to the axial positioning of the first stage41and second stage42of a downstream injection system30, in the preferred embodiments ofFIGS. 5 and 6, the first stage41may be positioned just upstream or downstream of the combustor mid-plane48, and the second stage42may be positioned near the end-plane49of the combustor12. In certain embodiments, the injection plane38of the first stage41may be disposed within the transition zone39, approximately halfway between the combustor mid-plane48and the end-plane49. The second stage42, as shown inFIG. 5, may be positioned just upstream of the downstream end of the combustor12or the end-plane49. Put another way, the injection plane38of the second stage42may occur just upstream of the upstream end of the aft frame29. It will be appreciated that the downstream position of the first and second stage41,42reduce the time for the reactants injected therefrom reside within the combustor. That is, given the relative constant velocity of the flow through the combustor13, the decrease in residence time relates directly to the distance reactants must travel before reaching the downstream termination of the combustor or flame zone. Accordingly, as discussed in more detail below, the distance51for the first stage41(as shown inFIG. 6, results in a residence time for injected reactants that is a small fraction of that for reactants released at the headend22. Similarly, the distance52for the second stage42results in a residence time for injected reactants that is a small fraction of that for reactants released at the first stage41. As stated, this decreased residence time reduces NOx emission levels. As discussed in more detail below, in certain embodiments the precise placement of the injection stages relative to the primary fuel and air injection system and each other may depend on the expected residence times given axial location and calculated flow rate through the combustor.

In another exemplary embodiment, as shown inFIG. 7, the injection plane38of the first stage41may be positioned in the aft quarter of the transition piece25, which, as illustrated, is slightly further downstream in the combustor12than the first stage41ofFIG. 5. In this case, the injection plane38of the second stage42may be positioned at the aft frame29or very near the end-plane49of the combustor12. In such a case, according a preferred embodiment, the injectors32of the second stage42may be integrated into the structure of the aft frame29.

In another exemplary embodiment, as shown inFIG. 8, the injection plane38of the first stage41may be positioned just slightly upstream of the aft frame29or the end-plane49of the combustor12. The second stage42may be positioned at or very near the axial position of the first row of stator blades16within the turbine13. In preferred embodiments, the injectors32of the second stage42may be integrated into this row of stator blades16, as mentioned above.

The present invention also includes control configurations for distributing air and fuel between the primary air and fuel injection system of the headend22and the first stage41and the second stage42of the downstream injection system. Relative to each other, according to preferred embodiments, the first stage41may be configured to inject more fuel than the second stage42. In certain embodiments, the fuel injected at the second stage42is less than 50% of the fuel injected at the first stage. In other embodiments, the fuel injected at the second stage42between approximately 10% and 50% of fuel injected at the first stage41. Each of the first and second stages41,42may be configured to inject an approximate minimum amount of air given the fuel injected, which may be determined by analysis and testing, to approximately minimize the NOx versus combustor exit temperature, while also allowing adequate CO burnout. Other preferred embodiments include more specific levels of air and fuel distribution the primary air and fuel injection system of the headend22and the first stage41and the second stage42of the downstream injection system. For example, in one preferred embodiment, the distribution of the fuel include: between 50% and 80% of the fuel to the primary air and fuel injection system; between 20% and 40% to the first stage41; and between 2% and 10% to the second stage. In such cases, the distribution of air may include: between 60% and 85% of the air to the primary air and fuel injection system; between 15% and 35% to the first stage41, and between 1% and 5% to the second stage42. In another preferred embodiment, such air and fuel splits may be defined even more precisely. In this case, the air and fuel split between the primary air and fuel injection system, the first stage41and the second stage42is as follows: 70/25/5% for the fuel and 80/18/2% for the air, respectively.

The various injectors of the two injection stages may be controlled and configured in several ways so that desired operation and preferable air and fuel splitting are achieved. It will be appreciated that certain of these methods include aspects of U.S. Patent Application 2010/0170219, which is hereby incorporated by reference in its entirety. As represented schematically inFIG. 9, the air and fuel supplies to each of the stages41,42may be controlled via a common control valve55. That is, in certain embodiments, the air and fuel supply may be configured as a single system with common valve55, and the desired air and fuel splits between the two stages may be determined passively via orifice sizing within the separate supply passages or injectors32of the two stages. As illustrated inFIG. 10, the air and fuel supply for each stage41,42may be controlled independently with separate valves55controlling the feed for each stage41,42. It will be appreciated that any controllable valve mentioned herein may be connected electronically to a controller and have its settings manipulated via a controller pursuant to conventional systems.

The number of injectors32and each injector's circumferential location in the first stage41may be chosen so that the injected air and fuel penetrate the main combustor flow so to improve mixing and combustion. The injectors32may be adjusted so penetration into the main flow is sufficient so that air and fuel mix and react adequately during the brief residence time given the downstream position of the injection. The number of injectors32for the second stage42may be chosen to compliment the flow and temperature profiles that result from the first stage41injection. Further, the second stage may be configured to have less jet penetration in the flow of working fluid than that required for the first stage injection. As a result, more injection points may be located about the periphery of the flow path for the second stage compared to the first stage. Additionally, the number and type of first stage injectors32and the amounts of air and fuel injected at each may be chosen so to place combustible reactants at locations where temperature is low and/or CO concentration is high so to improve combustion and CO burnout. Preferably, the axial location of the first stage41should be as far aft as possible, consistent with the capability of the second stage42to foster reaction of CO/UHC that exits the first stage41. Since the residence time of the second stage42injection is very brief, a relatively small fraction of fuel will be injected there, as provided above. The amount of second stage42air also may be minimized based on calculations and test data.

In certain preferred embodiments, the first stage41and the second stage42may be configured so that the injected air and fuel from the first stage41penetrate the combustion flow through the interior flowpath more than the injected air and fuel from the second stage42. In such cases, as already mentioned, the second stage42may employ more injectors32(relative to the first stage41) which are configured to produce a less forcible injection stream. It will be appreciated that, with this strategy, the injectors32of the first stage41may be configured primarily toward mixing the injected air and fuel they inject with the combustion flow in a middle region of the interior flowpath, while the injectors32of the second stage42are configured primarily mixing the injected air and fuel with the combustion flow in a periphery region of the interior flowpath.

Pursuant to aspects of the present invention, the two stages of downstream injection may be integrated so to improve function, reactant mixing, and combustion characteristic through the interior flowpath, while improving the efficiency regarding usage of the compressed air supply delivered to the combustor13during operation. That is, less injection air may be required to achieve performance advantages associated with downstream injection, which increases the amount of air supplied to the aft portions of the combustor13and the cooling effects this air provides. Consistent with this, in preferred embodiments, the circumferential placement of the injectors32of the first stage41includes a configuration from which the injected air and fuel penetrates predetermined areas of the interior flowpath based on an expected combustion flow from the primary air and fuel injection system so to increase reactant mixing and temperature uniformity in a combustion flow downstream of the first stage41. Additionally, the circumferential placement of the injectors32of the second stage42may be one that compliments the circumferential placement of injectors32of the first stage41given a characteristic of the expected combustion flow downstream of the first stage41. It will be appreciated that several different combustion flow characteristics are important to improving combustion through the combustor, which may benefit emission levels. These include, for example, reactant distribution, temperature profile, CO distribution, and UHC distribution within the combustion flow. It will be appreciated that such characteristics may be defined as the cross-sectional distribution of whichever flow property within the combustion flow at an axial location or range within the interior flowpath and that certain computer operating models may be used to predict such characteristics or they may be determined via experimentation or testing of actual engine operation or a combination of these. Typically, performance improved when the combustion flow is thoroughly mixed and uniform and that the integrated two-stage approach of the present invention may be used to achieve this. Accordingly, the circumferential placement of the injectors32of the first stage41and the second stage42may be based on: a) a characteristic of an anticipated combustion flow just upstream of the first stage41during operation; and b) the characteristic of an anticipated combustion flow just downstream of the second stage42given an anticipated effect of the air and fuel injection from the circumferential placement of the injectors32of the first stage41and the second stage42. As stated, the characteristic here may be reactant distribution, temperature profile, NOx distribution, CO distribution, UHC distribution, or other relevant characteristic that may be used to model any of these. Taken separately, per another aspect of the present invention, the circumferential placement of the injectors32of the first stage41may be based on a characteristic of an anticipated combustion flow just upstream of the first stage41during operation, which may be based on the configuration of the primary air and fuel injection system30. The circumferential placement of the injectors32of the second stage42may be based on the characteristic of an anticipated combustion flow just upstream of the second stage42, which may be based on the circumferential placement of the injectors32of the first stage41.

It will be appreciated that the integrated two stage downstream injection system30of the present invention has several advantages. First, the integrated system reduces the residence time by physically coupling the first and second stages, which allows the first stage41to be moved further downstream. Second, the integrated system allows the use of more and smaller injection points in the first stage because the second stage may be tailored to address non-desirable attributes of the resulting flow downstream of the first stage. Third, the inclusion of a second stage allows that each stage may be configured to penetrate less into the main flow as compared to a single stage system, which requires the usage of less “carrier” air to get the necessary penetration. This means less air will be siphoned from the cooling flow within the flow annulus, allowing the structure of the main combustor to operate at reduced temperatures. Fourth, the reduced residence time will allow higher combustor temperatures without increasing NOx emissions. Fifth, a single “dual manifold” arrangement can be used to simplify construction of the integrated two stage injection system, which makes the achievement of these various advantages cost-effective.

Turning now to an additional embodiment of the present invention, it will be appreciated that the positioning of the stages of injection may be based on residence time. As described, positioning of downstream injection stages may affect multiple combustion performance parameters, including, but not limited to, carbon monoxide emissions (CO). Positioning downstream stages too close to the primary stage may cause excessive carbon monoxide emissions when the downstream stages are not fueled. Hence, the flow from the primary zone must have time to react and consume the carbon monoxide prior to the first downstream stage of injection. It will be appreciated that this required time is the “residence time” of the flow, or, stated another way, the time it takes the flow of combustion materials to travel the distance between axially spaced injection stages. The residence time between two stages may be calculated on a bulk basis between any two locations based on the total volume between the locations and the volumetric flow rate, which may be calculated given the mode of operation for the gas turbine engine. The residence time between any two locations, therefore, may be calculated as volume divided by volumetric flow rate, where volumetric flow rate is the mass flow rate over density. Expressed another way, volumetric flow rate may be calculated as the mass flow rate multiplied by the temperature of the gases multiplied by the applicable gas constant divided by the pressure of the gases.

Accordingly, it has been determined that, given the concern over emission levels, including that of carbon monoxide, the first downstream injection stage should be no closer than 6 milliseconds (ms) from the primary fuel and air injection system at the head end of the combustor. That is, this residence time is the period of time during a certain mode of engine operation in which combustion flow takes to travel along the interior flowpath from a first position defined at the primary air and fuel injection system to a second position defined at the first stage of the downstream injection system. In this case, the first stage should be positioned a distance aft of the primary air and fuel injection system that equates to the first residence time being at least 6 ms. Additionally, it has been determined that from a NOx emissions standpoint, delaying downstream injection has a beneficial impact, and that the second downstream injection stage should be positioned less than 2 ms from the combustor exit or combustor end-plane. That is, this residence time is the period of time during a certain mode of engine operation in which combustion flow takes to travel along the interior flowpath from a first position defined at the second stage to a second position defined at a combustor end-plane. In this case, the second stage should be positioned a distance forward of the combustor end-plane that equates to this residence time being less than 2 ms.

FIGS. 11 through 14illustrate a system with three injection stages.FIG. 11illustrates axially ranges within which each of the three stages may be positioned. According to preferred embodiments, as shown inFIG. 11, the downstream injection system30of the present invention may include three axial stages of injection, a first stage41, a second stage42, and a third stage43that are positioned aft of the combustor mid-plane. More specifically, the first stage41may be positioned in the transition zone39, the second stage42may be positioned near the combustor end plane49, and the third stage may be positioned at or aft of the combustor end plane49.FIGS. 12 and 14provide certain preferred embodiments at which each of the three injection stages may be located within those ranges. As shown inFIG. 12, the first and second stage may be located within the transition zone, and the third stage may be located near the combustor end plane. As illustrated inFIG. 13, the first stage may be located within the transition zone, while the second and third stages, respectively, are located at the aft frame and first row of stator blades. In certain embodiments, as discussed above, the second stage may be integrated into the aft frame, while the third stage is integrated into the stator blades.

The present invention further describes fuel and air injection amounts and rates within a downstream injection system that includes three injection stages. In one embodiment, the first stage, the second stage, and the third stage includes a configuration that limits a fuel injected at the second stage to less than 50% of a fuel injected at the first stage, and a fuel injected at the third stage to less than 50% of the fuel injected at the first stage. In another preferred embodiment, the first stage, the second stage, and the third stage comprise a configuration that limits a fuel injected at the second stage to between 10% and 50% of a fuel injected at the first stage, and a fuel injected at the third stage to between 10% and 50% of the fuel injected at the first stage. In other preferred embodiments, the primary air and fuel injection system and the first stage, the second stage, and the third stage of the downstream injection system may be configured such that the following percentages of a total fuel supply are delivered to each during operation: between 50% and 80% delivered to the primary air and fuel injection system; between 20% and 40% delivered to the first stage; between 2% and 10% delivered to the second stage; and between 2% and 10% delivered to the third stage. In still other preferred embodiments, the primary air and fuel injection system and the first stage, the second stage, and the third stage of the downstream injection system are configured such that the following percentages of a total combustor air supply may be delivered to each during operation: between 60% and 85% delivered to the primary air and fuel injection system; between 15% and 35% delivered to the first stage; between 1% and 5% delivered to the second stage; and between 0% and 5% delivered to the third stage. In another preferred embodiment, the primary air and fuel injection system and the first stage, the second stage, and the third stage of the downstream injection system may be configured such that the following percentages of a total fuel supply are delivered to each during operation: about 65% delivered to the primary air and fuel injection system; about 25% delivered to the first stage; about 5% delivered to the second stage; and about 5% delivered to the third stage. In this case, the primary air and fuel injection system and the first stage, the second stage, and the third stage of the downstream injection system may be configured such that the following percentages of a total air supply are delivered to each during operation: about 78% delivered to the primary air and fuel injection system; about 18% delivered to the first stage; about 2% delivered to the second stage; and about 2% delivered to the third stage.

FIGS. 14 through 19provide embodiments of another aspect of the present invention, which includes the manner in which fuel injectors may be incorporated into the aft frame29. The aft frame29, as stated, includes a framing member that provides the interface between the downstream end of the combustor12and the upstream end of the turbine13.

As shown inFIG. 14, the aft frame29forms a rigid structural member that circumscribes or encircles the interior flowpath. The aft frame29includes an inner surface or wall65that defines an outboard boundary of the interior flowpath. The aft frame29includes an outer surface66that includes structural elements by which the aft frame connects to the combustor and turbine. A number of outlet ports74may be formed through the inner wall of the aft frame29. The outlet ports74may be configured to connect the fuel plenum71to the interior flowpath67. The aft frame29may include between 6 and 20 outlet ports, though more or less may also be provided. The outlet ports74may be circumferentially spaced about the inner wall65of the aft frame. As illustrated, the aft frame29may include an annular cross-sectional shape.

As shown inFIGS. 15 through 19, the aft frame29according to the present invention may include a circumferentially extending fuel plenum71formed within it. As shown inFIG. 15, the fuel plenum71may have a fuel inlet port72that is formed through the outer wall66of the aft frame29and through which fuel is supplied to the fuel plenum71. The fuel inlet port72, thus, may connect the fuel plenum71to a fuel supply77. The fuel plenum77may be configured to circumscribe or completely encircle the interior flowpath67. As shown, once the fuel reaches the fuel plenum71, it may then be injected into the interior flowpath67through the outlet ports74. As shown inFIG. 16, in certain cases, air may be premixed with the fuel within a pre-mixer84before being delivered to the fuel plenum71. Alternatively, air and fuel may be brought together and mixed within the fuel plenum71, an example of which is illustrated inFIG. 17. In this case, air inlet ports73may be formed in the outer wall66of the aft frame29and may fluidly communicate with the fuel plenum71. The air inlet ports73may be circumferentially spaced about the aft frame29and be fed by the compressor discharge that surrounds the combustor in this region.

As also shown inFIG. 17, the outlet ports74may be canted. This angle may be relative to a reference direction that is perpendicular to a combustion flow through the interior flowpath67. In certain preferred embodiments, as illustrated, the cant of the outlet ports may be between 0° and 45° toward a downstream direction of the combustion flow. In addition, the outlet ports74may be configured flush relative to a surface of the inner wall65of the aft frame29, as shown inFIG. 17. Alternatively, the outlet ports74may be configured so that each juts away from the inner wall65and into the interior flowpath67, as shown inFIG. 19.

FIGS. 18 and 19provide an alternative embodiment in which a number of tubes81are configured to traverse the fuel plenum71. Each of the tubes81may be configured so that a first end connects to one of the air inlet ports73and a second end connects to one of the outlet ports74. In certain embodiments, as shown inFIG. 18, the outlet ports74formed on the inner surface65of the aft frame include: a) air outlet ports76, which are configured to connect to one of the tubes81; and b) fuel outlet ports72, which are configured to connect to the fuel plenum71. Each of these outlet ports may be positioned on the inner wall65in proximity to one another so to facilitate the mixing of air and fuel once injected into the interior flowpath67. In a preferred embodiment, as illustrated inFIG. 18, the air outlet ports76are configured to have a circular shape and the fuel outlet port75are configured to have a ring shape formed about the circular shape of the air outlet ports76. This configuration will further facilitate the mixing of fuel and air once it is delivered to the interior flowpath67. It will be appreciated that in certain embodiments the tubes81will have a solid structure that prevents a fluid moving through the tube81from mixing with a fluid moving through the fuel plenum71until the two fluids are injected into the interior flowpath67. Alternatively, as illustrated inFIG. 19the tubes71may include openings82that allow for air and fuel to premix before being injected into the interior flowpath67. In such cases, structure the promotes turbulent flow and mixing, for example, turbulators83, may be included downstream of the openings82so that premixing is enhanced.

As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.