Axial fuel stage injector creating air curtain

Abstract

To provide an axial fuel stage (AFS) injector.MEANS FOR SOLVING THE PROBLEM: An AFS injector includes a mixing member and a high pressure air-fuel injection member. The injection member includes an HP air-fuel injector including an inner wall defining an inner air jet and an outer wall surrounding and concentric with the inner wall and defining an outer air jet loop. The inner wall and the outer wall are separated by a spacer member. A plurality of fuel injector passages extend from the outer wall through the spacer member and the inner wall to the inner air jet. Each fuel injector passage has an end including a fuel injector directed into the inner air jet. A fuel plenum is configured to deliver a fuel to each fuel injector. The inner air jet and the air jet loop are configured to direct a high-pressure air flow from a high-pressure air source with the fuel into an inlet of a mixing chamber.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates generally to turbomachine combustors, and more particularly to axial fuel stage (AFS) injectors that create an air curtain downstream of the fuel injector, and combustor and gas turbine systems including such AFS injectors. [Background technology]

[0002] A gas turbine system includes a combustion section that includes multiple combustors that combust fuel to generate a combustion gas flow that is converted to kinetic energy in a downstream turbine section. Current combustors include a head-end fuel nozzle assembly for burning the fuel in a primary combustion zone and axial fuel stage (AFS) injectors for burning the fuel in a secondary combustion zone downstream of the primary combustion zone. A portion of the supply air, for example from a compressor discharge casing, is delivered to the head-end fuel nozzle assembly and the AFS injectors through various flow paths. Current AFS injectors have challenges in adequately mixing highly reactive fuels, such as hydrogen, with air and achieving desirable low emissions and flame-holding capabilities. Summary of the Invention

[0003] All aspects, embodiments and features listed below may be combined in any technically possible manner.

[0004] One aspect of the disclosure encompasses an axial fuel stage (AFS) injector for a combustor of a gas turbine (GT) system, the AFS injector including: a mixing element defining a mixing chamber therein, the mixing chamber having an inlet and an outlet, the outlet configured to be in fluid communication with a combustion chamber of the combustor; and a high-pressure (HP) air-fuel injection element including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including an inner wall defining an inner HP air jet, a concentric outer wall surrounding the inner wall, the inner wall and outer wall defining an outer HP air jet loop therebetween, a spacer member spacing the inner wall from the outer wall, and an outer HP air-fuel injection element including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including an inner wall defining an inner HP air jet outlet ... spacer member spacing the inner wall from the outer wall, and an outer HP air-fuel injection element including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel a plurality of fuel injector passages extending from the outer surface of the wall through the spacer member and the inner wall to the inner HP air jet, each fuel injector passage having a first end open to the outer surface of the outer wall and a second end including a fuel injector directed toward the inner HP air jet defined by the inner wall; and a fuel plenum defined in the HP air fuel injection member and in fluid communication with the first end of each fuel injector passage, the fuel plenum configured to deliver fuel from a fuel source to each fuel injector, each inner HP air jet and each HP air jet loop configured to direct a flow of HP air from the HP air source along with fuel to an inlet of the mixing chamber.

[0005] Another aspect of the present disclosure includes any of the above aspects, wherein the HP air-fuel injection member further includes a plurality of HP air inlet openings downstream of the one or more rows of HP air-fuel injectors for directing a separate flow of HP air into the air-fuel mixture and to the inlet of the mixing chamber.

[0006] Another aspect of the present disclosure includes any of the above aspects, wherein the flow of HP air also entrains low pressure (LP) air from an LP air source to direct LP air into the inlet of the mixing chamber along with the HP air and fuel.

[0007] Another aspect of the present disclosure includes any of the above-described aspects, wherein the HP air-fuel injection member further includes a plurality of HP air inlet openings downstream of the one or more rows of HP air-fuel injectors for directing a separate flow of HP air into the air-fuel mixture and to the inlet of the mixing chamber, the HP air flow also incorporating low pressure (LP) air from an LP air source for directing LP air along with the HP air and fuel to the inlet of the mixing chamber.

[0008] Another aspect of the present disclosure includes any of the above aspects, wherein the fuel injector directed toward the inner HP air jet in the inner wall of each fuel injector passage includes an elongated slot.

[0009] Another aspect of the present disclosure includes any of the above aspects, wherein the inner HP air jet is elongated and includes a first end and a second end separated by an intermediate section, each of the first end and the second end being narrower than the intermediate section.

[0010] Another aspect of the present disclosure includes any of the above-described aspects, wherein the HP air injection loop has opposing sides each having a first longitudinal end and a second longitudinal end separated by an intermediate longitudinal portion, and wherein the first longitudinal end and the second longitudinal end on each of the opposing sides are narrower than the intermediate longitudinal portion.

[0011] Another aspect of the present disclosure includes any of the above aspects, wherein the one or more rows of HP air-fuel injectors include a first row of HP air-fuel injectors and a second row of HP air-fuel injectors.

[0012] Another aspect of the present disclosure includes any of the above aspects, wherein the one or more rows of HP air-fuel injectors include a first row of HP air-fuel injectors, a second row of HP air-fuel injectors, and a third row of HP air-fuel injectors between the first row of HP air-fuel injectors and the second row of HP air-fuel injectors.

[0013] Another aspect of the present disclosure includes any of the above-described aspects, wherein the HP air-fuel injectors of the third row of HP air-fuel injectors direct the air-fuel mixture in a direction parallel to the mixing chamber, and the HP air-fuel injectors of the first and second rows direct the air-fuel mixture at an acute angle relative to the direction parallel to the mixing chamber.

[0014] Another aspect of the present disclosure includes any of the above aspects and further includes a plurality of baffles between the inner and outer walls adjacent the outlet of the HP air injection loop.

[0015] Another aspect of the present disclosure includes any of the above aspects, wherein the mixing element includes a filter element upstream of the one or more rows of HP air-fuel injectors.

[0016] Another aspect of the present disclosure includes any of the above aspects, wherein the mixing element and the HP air-fuel injection element each include one or more mounting elements configured to receive fasteners that couple the mixing element and the HP air-fuel injection element to a combustion liner that defines the combustion chamber.

[0017] Another aspect of the present disclosure includes any of the above aspects, wherein the HP air source is in direct fluid communication with the compressor discharge of the GT system.

[0018] Another aspect of the present disclosure encompasses a combustor for a gas turbine system, the combustor comprising: a combustor body including a combustion liner; and a plurality of axially staged fuel (AFS) injectors facing the combustion liner, the one or more AFS injectors including a mixing element defining a mixing chamber therein, the mixing chamber having an inlet and an outlet, the outlet configured to be in fluid communication with a combustion chamber of the combustor; and a high-pressure (HP) air-fuel injection element including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector including an inner wall defining an inner HP air jet, an outer wall concentric with the inner wall, the inner wall and the outer wall defining an outer HP air jet loop therebetween. a spacer member spacing the HP air jets from the outer wall; a plurality of fuel injector passages extending from an outer surface of the outer wall through the spacer member and the inner wall to the inner HP air jets, each fuel injector passage having a first end open to the outer surface of the outer wall and a second end including a fuel injector directed toward the inner HP air jet defined by the inner wall; and a fuel plenum defined in the HP air fuel injection member and in fluid communication with the first end of each fuel injector passage, the fuel plenum configured to deliver fuel from a fuel source to each fuel injector, each inner HP air jet and each HP air jet loop configured to direct a flow of HP air from the HP air source along with fuel to an inlet of the mixing chamber.

[0019] Another aspect of the present disclosure includes any of the above aspects, wherein the HP air-fuel injection member further includes a plurality of HP air inlet openings downstream of the one or more rows of HP air-fuel injectors for directing a separate flow of HP air into the air-fuel mixture and to the inlet of the mixing chamber.

[0020] Another aspect of the present disclosure includes any of the above aspects, wherein the flow of HP air also entrains low pressure (LP) air from an LP air source to direct LP air into the inlet of the mixing chamber along with the HP air and fuel.

[0021] Another aspect of the present disclosure includes any of the above aspects, wherein the inner HP air jet is elongated and includes a first end and a second end separated by an intermediate section, each of the first end and the second end being narrower than the intermediate section.

[0022] Another aspect of the present disclosure includes any of the above-described aspects, wherein the HP air injection loop has opposing sides each having a first longitudinal end and a second longitudinal end separated by an intermediate longitudinal portion, and wherein the first longitudinal end and the second longitudinal end on each of the opposing sides are narrower than the intermediate longitudinal portion.

[0023] Another aspect of the present disclosure encompasses a gas turbine (GT) system comprising a compressor section, a combustion section operatively coupled to the compressor section, and a turbine section operatively coupled to the combustion section, the combustion section including at least one combustor including a combustor body including a combustion liner, a head-end fuel nozzle assembly at a forward end of the combustor body, and a plurality of axially staged fuel (AFS) injectors facing the combustor body downstream from the head-end fuel nozzle assembly, the at least one AFS injector including a mixing element defining a mixing chamber therein, the mixing chamber having an inlet and an outlet, the outlet configured to be in fluid communication with a combustion chamber of the combustor, and a high-pressure (HP) air-fuel injection element including one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber, each HP air-fuel injector defining an inner HP air jet. the inner HP air injection member includes an inner wall having a plurality of HP injectors, a concentric outer wall surrounding the inner wall, the inner wall and the outer wall defining an outer HP air injection loop therebetween, a spacer member spacing the inner wall from the outer wall, a plurality of fuel injector passages extending from an outer surface of the outer wall through the spacer member and the inner wall to the inner HP air jet, each fuel injector passage having a first end open to the outer surface of the outer wall and a second end including a fuel injector directed toward the inner HP air jet defined by the inner wall, and a fuel plenum defined in the HP air fuel injection member and in fluid communication with the first end of each fuel injector passage, the fuel plenum configured to deliver fuel from a fuel source to each fuel injector, each inner HP air jet and each HP air injection loop configured to direct a flow of HP air from the HP air source along with fuel to an inlet of the mixing chamber.

[0024] Two or more aspects described in this disclosure, including those described in the Summary of the Invention, may be combined to form embodiments not specifically described herein, i.e., all embodiments described in this application may be combined with each other.

[0025] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. [Brief explanation of the drawings]

[0026] These and other features of the present disclosure may be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings, which set forth various embodiments of the present disclosure. [Figure 1] FIG. 1 is a functional block diagram of an exemplary gas turbine system that may be used with a combustor that includes axial fuel stage (AFS) injectors according to embodiments of the present disclosure. [Figure 2] FIG. 1 is a cross-sectional side view of a combustor including an AFS injector according to an embodiment of the present disclosure. [Figure 3] FIG. 1 is a perspective, partially cross-sectional view of an AFS injector according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a perspective partial cross-sectional view taken along the line AA in FIG. 3 according to an embodiment of the present disclosure. [Figure 5] 5 is a perspective partial cross-sectional view similar to FIG. 4 according to another embodiment of the present disclosure. [Figure 6] 5 is a perspective partial cross-sectional view similar to FIG. 4 according to an additional embodiment of the present disclosure. [Figure 7] 1 is a schematic perspective cross-sectional view of a high-pressure (HP) air-fuel injector according to an embodiment of the present disclosure; [Figure 8] FIG. 1 is a bottom-up schematic view of an HP air-fuel injector according to an embodiment of the present disclosure. [Figure 9] 1A and 1B are perspective and cross-sectional views of an HP air fuel injector within an HP air fuel injection member according to an embodiment of the present disclosure; [Figure 10] FIG. 10 is a side view of the HP air-fuel injector in FIG. [Figure 11] 11-11 cross-sectional view of FIG. 9. [Figure 12] 12-12 cross-sectional view of FIG. 9. [Figure 13A] FIG. 10 is a diagram of an HP air fuel injector according to another embodiment of the present disclosure. [Figure 13B]FIG. 10 is a diagram of an HP air fuel injector according to another embodiment of the present disclosure. [Figure 13C] FIG. 10 is a diagram of an HP air fuel injector according to another embodiment of the present disclosure. [Figure 13D] FIG. 10 is a diagram of an HP air fuel injector according to another embodiment of the present disclosure. [Figure 14A] 1 is a bottom-up schematic view of an HP air-fuel injector according to various embodiments of the present disclosure; FIG. [Figure 14B] 1 is a bottom-up schematic view of an HP air-fuel injector according to various embodiments of the present disclosure; FIG. [Figure 15] FIG. 2 is a perspective, partially cross-sectional view of an AFS injector according to another embodiment of the present disclosure. [Figure 16] BB arrow cross-sectional view of FIG. 8. [Figure 17] FIG. 1 is a cross-sectional view of multiple parallel sintered metal layers of a mixing element or high-pressure air injection element of an AFS injector according to an embodiment of the present disclosure. [Figure 18] FIG. 1 is a schematic block diagram of an exemplary additive manufacturing system for additive manufacturing mixing elements and / or HP air-fuel injection elements of an AFS injector according to embodiments of the present disclosure.

[0027] The drawings of the present disclosure are not necessarily to scale. The drawings are intended to illustrate exemplary aspects of the present disclosure only and are not intended to limit the scope of the present disclosure. In the drawings, like reference numerals represent like elements between the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0028] First, to clearly explain the present technology, it is necessary to select terminology when referring to and describing relevant machine components in the exemplary application of a turbomachine combustor and axial fuel stage (AFS) injector. Wherever possible, terms common in the art will be used consistent with their ordinary meaning. Unless otherwise noted, such terms should be interpreted broadly within the context of this application and the accompanying claims. It will be apparent to those skilled in the art that a component will often be referred to using several different or overlapping terms. What may be described as a single component in this specification may be described as consisting of multiple components in another context. Alternatively, what may be described as including multiple components in one place in this specification may be described as a single component in another place.

[0029] Additionally, several descriptive terms are used repeatedly in this specification, and it may be helpful to define these terms at the beginning of this section. These terms and their definitions are as follows, unless otherwise specified: As used herein, the terms "downstream" and "upstream" refer to directions with respect to fluid flow (e.g., the flow of working fluid through a turbomachine, or the flow of air through a combustor or AFS injector, or the flow of coolant through one of the turbomachine's subsystems). The term "downstream" corresponds to the direction in which the fluid is flowing, and the term "upstream" refers to the direction opposite to the flow (i.e., the direction from which it is flowing). The terms "forward" and "aft" refer to directions not further specified, with "forward" referring to the forward or compressor end of a turbomachine or combustor and "aft" referring to the aft or turbine end of a turbomachine or combustor.

[0030] The term "axial" refers to movement or position parallel to an axis (e.g., the axis of a combustor, an AFS injector mixing chamber, or a turbomachine). The term "radial" refers to movement or position perpendicular to an axis (e.g., the axis of a combustor or turbomachine). If a first component is closer to the axis than a second component, the first component is described herein as "radially inward" or "proximal to the axis" of the second component. Conversely, if a first component is located farther from the axis than the second component, the first component is described herein as "radially outward" or "distal to the axis" of the second component. Finally, the term "circumferential" refers to movement or position about an axis. As noted above, depending on the context, such terms may be applied relative to the axis of a combustor or the axis of a turbomachine.

[0031] Furthermore, certain descriptive terms are used repeatedly in this specification, as described below: The terms "first," "second," and "third" are used interchangeably to distinguish one component from another, and do not denote the location or importance of the individual components.

[0032] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the disclosure. As used herein, the singular "a," "an," or "an" refers to the plural unless the context clearly dictates otherwise. As used herein, the terms "comprises" and / or "includes" refer to the presence of stated features, integers, steps, operations, components, and / or parts, and do not exclude the presence or addition of one or more other features, integers, steps, operations, components, parts, and / or groups thereof. The terms "optional" or "optionally" mean that the event described following the term may or may not occur, or the feature described following the term may or may not be present, and such descriptions encompass both the occurrence of the event or the presence of the feature and the absence of the event or the absence of the feature.

[0033] When a component or layer is referred to as being "on," "engaged with," "connected to," "coupled to," or "attached to" another component or layer, it may be directly on, directly engaged with, connected to, coupled to, or attached to that other component or layer, or there may be intervening components or layers. In contrast, when a component is referred to as being "directly on," "directly engaged with," "directly connected to," or "directly coupled to" another component or layer, there are no intervening components or layers. Other terms used to describe relationships between components (e.g., "between" and "directly between," "adjacent" and "directly adjacent," etc.) are to be interpreted similarly. As used herein, the term "and / or" encompasses any and all combinations of one or more of the listed items. The terms "coupled" and "attached" may be used interchangeably herein.

[0034] An embodiment of the present disclosure provides an axial fuel stage (AFS) injector for a combustor, as well as a combustor and gas turbine (GT) system including such an AFS injector. The AFS injector includes a mixing element having a mixing chamber defined therein. The mixing chamber includes an inlet and an outlet, the outlet configured to be in fluid communication with a combustion chamber of the combustor. The high-pressure (HP) air-fuel injection element includes one or more rows of HP air-fuel injectors for directing an air-fuel mixture into the mixing chamber. Each HP air-fuel injector includes an inner wall defining an inner HP air jet and a concentric outer wall surrounding the inner wall. The inner and outer walls define an outer HP air jet loop therebetween, and a spacer member spaces the inner wall from the outer wall. A plurality of fuel injector passages extend from an outer surface of the outer wall through the spacer member and the inner wall to the inner HP air jet. Each fuel injector passage has a first end opening to the outer surface of the outer wall and a second end including a fuel injector directed toward an inner HP air jet defined by the inner wall. A fuel plenum is defined in the HP air fuel injection member and is in fluid communication with the first end of each fuel injector passage. The fuel plenum is configured to deliver fuel from a fuel source to each fuel injector. Each inner HP air jet and each HP air jet loop is configured to direct a flow of HP air from the HP air source along with fuel to an inlet of the mixing chamber.

[0035] The HP air injection loop creates an air curtain that concentrates HP high-velocity air in the wake behind where the fuel exits the fuel injector to prevent flame adhesion to the hardware. The inner HP air injection port and HP air injection loop can be tailored to generate a specific velocity profile. A mixing chamber directs the air-fuel mixture into the combustion liner for combustion in the secondary combustion zone. To reduce overall system pressure loss and improve air utilization efficiency in the combustor, AFS injectors may optionally mix up to three air sources, two of which may be high-pressure air (e.g., compressor discharge air) and the remaining air may be low-pressure air (e.g., post-impingement cooling air). In either case, AFS injectors can rapidly premix one or more air sources with highly reactive fuels, such as hydrogen, to achieve reduced emissions such as nitrogen oxides (NOx) and adequate flame-holding capability. AFS injectors also achieve high fuel-air mixing, minimize flow pressure loss, and prevent fuel from entering the low-velocity air flow region. Additionally, the AFS injector can be packaged in a relatively small form factor and attached to the combustion liner of the combustor body, which can then be attached to the GT system through a relatively small opening in the compressor discharge casing. The AFS injector can be additively manufactured to include multiple parallel sintered metal layers.

[0036] 1 illustrates a functional block diagram of an exemplary gas turbine (GT) system 90 that may incorporate various embodiments of a combustor 100 and axial fuel stage (AFS) injector 150 (FIG. 2) of the present disclosure. As shown, the GT system 90 generally includes an inlet section 102, which may include a series of filters, cooling coils, moisture separators, and / or other devices for cleaning or conditioning a working fluid (e.g., air) 104 entering the GT system 90. A working fluid 106 (air) flows to a compressor 108 in a compressor section 110, where kinetic energy is progressively added to the working fluid 106 to produce compressed, high-pressure (HP) air 112 (hereinafter referred to as "HP air 112" or "compressed air 112"). The HP air 112 is typically mixed with fuel 114A and / or 114B from a fuel source 116 to produce a combustible mixture in one or more combustors 100 of a combustion section 120 operatively coupled to the compressor section 110. The combustible mixture is combusted to produce high temperature and pressure combustion gases 122.

[0037] The combustion gases 122 flow through a turbine 128 (i.e., expansion turbine) of a turbine section 130 operatively coupled to the combustion section 120 to produce work. For example, the turbine 128 may be connected to a shaft 132 such that rotation of the turbine 128 drives the compressor 108 to produce the HP air 112. Alternatively or additionally, the shaft 132 may connect the turbine 128 to another load, such as a generator 134 for generating electricity. Exhaust gases 136 from the turbine 128 flow through an exhaust section 138 that connects the turbine 128 to a downstream exhaust stack 140. The exhaust section 138 may include, for example, a heat recovery steam generator (not shown) to clean the exhaust gases 136 and extract additional heat before they are released to the environment. When two or more combustors 100 are used, they may be spaced circumferentially about a turbine inlet 142 of the turbine 128.

[0038] In one embodiment, the GT system 90 includes an engine model commercially available from GE Vernoa (Cambridge, Massachusetts, USA). The present disclosure is not limited to any particular GT system and may be implemented with other engines, including, for example, GE Vernoa's HA, F, B, LM, GT, TM, and E-class engine models, as well as engine models from other manufacturers. The present disclosure is not limited to implementation with any particular turbomachine and may be applicable to steam turbines, jet engines, compressors, turbofans, etc.

[0039] The following describes a combustor 100 that may be used in the GT system 90. Figure 2 illustrates a cross-sectional side view of the combustor 100 disposed within the GT system 90. As described further herein, the combustor 100 may include one or more axial fuel stage (AFS) injectors 150 according to embodiments of the present disclosure.

[0040] 2, the combustor 100 is at least partially surrounded by an outer casing 152, such as a compressor discharge casing and / or a turbine casing. The interior of the outer casing 152 is in fluid communication with the compressor discharge 109 of the compressor 108 and provides the HP air source 154. That is, the HP air source 154 includes HP air 112 from the compressor discharge 109 of the compressor 108. The HP source 154 is in direct fluid communication with the compressor discharge 109 of the GT system 90. However, the HP air source 154 may be any source of HP air 112 that can be channeled to various openings or flow passages of the combustor 100 (i.e., within the AFS injectors 150) for component cooling and / or combustion.

[0041] As shown in FIG. 2 , the combustor 100 for the GT system 90 includes a combustor body 160. The combustor body 160 may be manufactured using any now known or later developed technology. For example, the combustor body 160 may be manufactured using additive manufacturing. The combustor body 160 may include a combustion liner 164, which may include, for example, a cylindrical portion 166 and a tapered transition portion 168. The combustion liner 164 may have an axis A, the direction of which may vary slightly depending on the axial position of the curved combustion liner 164. The tapered transition portion 168 is at the aft end (to the right in FIG. 2 ) of the cylindrical portion 166. As will be apparent to one skilled in the art, the tapered transition portion 168 transitions the hot gas path (HGP) from a circular cross-section of the cylindrical portion 166 of the liner to an arcuate cross-section that mates with the turbine inlet 142 of the turbine 128. The combustor 100 may further include an aft frame 170 at the aft end (to the right in FIG. 2) of the tapered transition section 168 .

[0042] Combustion liner 164 contains and channels combustion gases 122 to turbine section 130 ( FIG. 1 ). More specifically, combustion liner 164 defines a combustion chamber 172 in the hot gas path (HGP) within which combustion occurs. Combustion liner 164 may have a tapered transition section 168 that is separate from cylindrical section 166, as in many conventional combustion systems. Alternatively, as shown in FIG. 2 , combustion liner 164 may have a one-piece (or “unibody”) construction, in which cylindrical section 166 and tapered transition section 168 are integrated with one another as part of a single, additively manufactured part. Thus, all references herein to combustion liner 164 encompass both conventional combustion systems having separate cylindrical sections and tapered transition sections, as well as combustion systems having unibody liners.

[0043] The combustor body 160 also includes an air flow passage 174 defined at least in part by the cylindrical portion 166 of the combustion liner 164. As described herein, the air flow passage 174 is configured to deliver air (e.g., HP air 112A from the HP air source 154) to a head-end fuel nozzle assembly 176 (hereinafter simply referred to as the “head-end assembly 176”) of the combustor 100 at the forward end (left end in FIG. 2 ) of the combustion liner 164. That is, the air flow passage 174 is sized, shaped, and / or configured to deliver air (e.g., HP air 112A from the HP air source 154) to the head-end assembly 176 of the combustor 100. The air flow passage 174 may be defined entirely by the cylindrical portion 166, or the air flow passage 174 may be provided between the cylindrical portion 166 and a flow sleeve 177 spaced along at least a portion of the outer surface of the cylindrical portion 166. The air flow passage 174 has an open end 178 or one or more air flow openings near the head end assembly 176 through which HP air 112A from the HP air source 154 enters. The HP air 112A from the HP air source 154 may be taken directly from the compressor discharge 109, i.e., without using any air other than for simultaneous convective cooling of the combustor body 160.

[0044] An annular partition 179, located between the cylindrical portion 166 and the flow sleeve 177, separates a forward portion of the air flow passage 174 from an aft portion of the air flow passage 174. The axial position of the annular partition 179 is generally aligned with the cap assembly 198, described below, such that the forward portion of the air flow passage 174 is radially outward of the head end assembly 176 (rather than the combustion chamber 172) and does not require significant cooling. Aft of the annular partition 179, the flow sleeve 177 may include a plurality of impingement holes 192 (shown in the outer sleeve 190) to allow the HP air 112B to enter the air flow passage 174. After passing through the impingement holes 192, the HP air 112B undergoes a pressure drop, becoming LP air 182 and flowing through the air flow passage 174 to and / or into one or more AFS injectors 150, as described further herein.

[0045] The head end assembly 176 generally includes one or more axially extending fuel nozzles 194 extending downstream from the end cover 196 and a cap assembly 198 extending radially and axially within the outer casing 152 downstream from the end cover 196 and defining a forward boundary of the combustion chamber 172. The head end assembly 176 may include any now known or later developed axially extending fuel nozzles 194 for channeling the first fuel 114A from the axially extending fuel nozzles 194 to the primary combustion zone 202. In certain embodiments, the axially extending fuel nozzles 194 of the head end assembly 176 extend at least partially through the cap assembly 198 and deliver a combustible mixture of the fuel 114A and HP air 112A to the primary combustion zone 202.

[0046] The combustor body 160 also includes axial fuel stage (AFS) injector openings or seats 180 facing the combustion liner 164 downstream of the head-end assembly 176. The openings or seats 180 extend through the wall of the combustion liner 164. One or more AFS injector openings or seats 180 (hereinafter referred to as “openings 180”) may be provided, in which AFS injectors 150 are mounted and configured to receive HP air 112B from the HP air source 154 (although other air flows are possible as described herein). Each AFS injector opening 180 may include any necessary structure (e.g., threaded fasteners, bolt holes, welded areas, etc.) to which the AFS injector 150 may be mounted. As shown, the combustor 100 and combustor body 160 may include multiple circumferentially spaced AFS injector openings 180 and corresponding AFS injectors 150. Any number of AFS injectors 150 may be used.

[0047] As described below, in some embodiments, the AFS injector 150 may be configured to receive low-pressure (LP) air 182 from a low-pressure (LP) air source 184, such as a cooling passage, and direct the LP air 182 along with fuel 114B to the combustion liner 164. The fuel 114B may be supplied from a fuel source 116 using any form of fuel line 188. The fuels 114A, 114B may be any currently known or future developed combustor 100 fuel, such as, but not limited to, fuel oil, natural gas, hydrogen, and / or blends thereof. The fuels 114A, 114B may be the same or different.

[0048] In several embodiments, LP air 182 can be supplied to AFS injectors 150 from LP air source 184 in a variety of ways. In certain embodiments, LP air 182 originates from HP air source 154 but is used for cooling before being used by AFS injectors 150. In one example, combustor body 160 further includes cooling passages 186 defined at least in part by tapered transition section 168. In this configuration, one or more cooling passages 186 constitute LP air source 184. One or more cooling passages 186 may be in fluid communication with other cooling passages (not shown) in combustor 100 (e.g., in aft frame 170). In any event, LP air 182 from LP air source 184 may be used to cool one or more high-temperature components of combustor 100. More specifically, LP air 182 from LP air source 184 is removed from compressor discharge 109 and then passes through cooling passage 186 (which may be defined at least in part by tapered transition 168).

[0049] In one example, the cooling passage 186 may be defined by a flow sleeve 190 surrounding the tapered transition section 168. If desired, impingement cooling holes 192 may be provided in the flow sleeve 190 or the tapered transition section 168 so that the HP air 112 from the HP air source 154 enters and becomes the LP air 182. In this regard, the LP air source 184 includes one or more cooling passages 186 defined along at least a portion of the combustion liner 164 (e.g., the tapered transition section 168) as well as cooling passages upstream of other high temperature components of the combustor 100. Furthermore, the one or more cooling passages 186 may be downstream of an impingement cooling member (e.g., the outer sleeve portion 168 with the impingement cooling holes 192 or the sleeve 190 around the portion 190 with the holes 192) that is in direct fluid communication with the compressor discharge 109 (i.e., the HP air source 154) of the GT system 90. The high-temperature components may include any components of the combustor 100 that require cooling, and the LP air 182 may be directed into the cooling passages 186 as desired. That is, one or more cooling passages 186 may be defined in or along (another) high-temperature component of the combustor 100 other than the tapered transition 168 (e.g., the aft frame 170). The LP air source 184 may also be considered to be in fluid communication with the cooling passages 186 defined along at least a portion of the combustion liner 164 of the combustor 100. In either case, the one or more cooling passages 186 are between the AFS injectors 150 and the HP air source 154, and in some embodiments, the cooling passages 186 are configured to deliver the LP air 182 from the LP air source 184 to the AFS injectors 150. Because the LP air 182 from the LP air source 184 is used to cool components of the combustor 100, it is also referred to herein as “post-cooling” or “post-impingement air.”

[0050] As described above, the combustor 100 includes one or more axially staged fuel (AFS) injectors 150 facing the combustor body 160 (i.e., the combustion liner 164). As described above, the AFS injectors 150 may include multiple AFS injectors 150 spaced circumferentially around the combustor body 160. Each AFS injector 150 extends radially toward an opening 180 in the combustion liner 164 downstream of the head-end assembly 176 (i.e., downstream of the axially extending fuel nozzles 194). As described below, the AFS injectors 150 are configured to receive HP air 112B and second fuel 114B from the HP air source 154 for combustion in the secondary combustion zone 204 downstream of the primary combustion zone 202. In certain embodiments, the AFS injectors 150 may optionally draw LP air 182 from the LP air source 184. In this case, LP air 182 from LP air source 184 may be routed to AFS injector 150, for example, via cooling passage 186, and combined with HP air 112B and second fuel 114B for combustion in a secondary combustion zone 204 downstream of the primary combustion zone 202.

[0051] Figure 3 shows a perspective, partial cross-sectional view of an AFS injector 150, and Figure 4 shows a perspective, partial cross-sectional view taken along line AA in Figure 3 according to an embodiment of the present disclosure. Figure 5 shows a perspective, partial cross-sectional view similar to Figure 4 according to another embodiment, and Figure 6 shows a perspective, partial cross-sectional view similar to Figure 4 according to another embodiment. The AFS injector 150 includes a mixing element 210 and a high-pressure (HP) air-fuel injection element 212. The mixing element 210 and the HP air-fuel injection element 212 are coupled together to form the AFS injector 150. More specifically, as shown in FIG. 3 , the mixing element 210 and the HP air-fuel injection element 212 may each include one or more mounting elements 213 configured to receive fasteners 215 (e.g., bolts, welds, or other fasteners) that couple the mixing element 210 and the HP air-fuel injection element 212 to the combustion liner 164 (e.g., the flow sleeve 190) that defines the combustion chamber 172 ( FIG. 2 ), such as AFS injector mounts 275 on the combustion liner 164. Alternatively, the mixing element 210 and the HP air-fuel injection element 212 may be formed as a single, integral member, for example, by additive manufacturing. Each AFS injector 150 is aligned with a respective opening 180 in the combustion liner 164. The HP air-fuel injection element 212 may hereinafter be referred to simply as the “injection element 212.”

[0052] As shown in FIGS. 3-4 , the mixing element 210 includes a mixing chamber 214 defined therein. The mixing chamber 214 includes an inlet 216 and an outlet 218. The inlet 216 is radially inward of the HP air-fuel injection element 212 and the outlet 218. The outlet 218 is configured to be in fluid communication with the combustion liner 164 of the combustor 100 ( FIG. 2 ). The outlet 218 may be defined by the mixing element 210 and may have any cross-sectional shape. In one example, the outlet 218 has an axially elongated slot cross-sectional shape, but may have a different shape. In either case, the mixing element 210 has its outlet 218 positioned and secured within the opening 180 of the combustion liner 164. The outlet 218 may be flush with the inner surface of the combustion liner 164 or may be located inside the combustion liner 164.

[0053] The mixing chamber 214 may take a variety of forms. More specifically, as shown in FIGS. 3-4 , the mixing chamber 214 may be axially elongated or may comprise a generally elongated chamber having elongated opposing walls 220, 222 and opposing ends 226. The mixing chamber 214 is referred to as “axially elongated” because its longitudinal length is generally aligned with the axis A of the combustion liner 164 and its longitudinal length may generally be greater than its circumferential width. As shown in FIG. 3 , the opposing ends 226 may be rounded as they transition to the respective opposing walls 220, 222. That is, the two opposing side walls 220, 222 and the opposing ends 226 join at their longitudinal ends and collectively define an oval or elliptical cross-sectional shape. While not shown, the mixing chamber 214 may have some curvature and / or narrowing from the inlet 216 to the outlet 218, if desired. The mixing chamber 214 may extend radially relative to the circumference C of the combustion liner 164. The mixing chamber 214 extends radially (i.e., along a particular radial direction R) relative to the axis A of the combustion liner 164. The dimensions of the mixing chamber 214 are user-determined based on the characteristics of the fuel 114B, HP air 112, LP air 182 (if used), and / or the combustion liner 164, among many other considerations. As shown in FIG. 4, the length LM of the mixing chamber 214 from the inlet 216 to the outlet 218 is user-determined. The dimensions of all components of the mixing element 210 (and HP air-fuel injection element 212) of the AFS injector 150 may be customized to produce a desired (final) air-fuel mixture 296 (FIG. 3). Additionally, the radial height RH from the radially outermost (top) surface of the injection member 212 to the radially inner surface of the combustion liner 164 may be optimized to facilitate fitting of the combustion liner 164 (with the AFS injector 150 attached) through an opening in the combustor casing.

[0054] With continued reference to FIGS. 3-6, the HP air-fuel injection member 212 will now be described. The HP air-fuel injection member 212 may also be referred to as a "top hat." The HP air-fuel injection member 212 includes one or more rows 230 of HP air-fuel injectors 232 for directing an (initial) air-fuel mixture 236 into the mixing chamber 214. FIGS. 3 and 4 show one row 230 of HP air-fuel injectors 232. FIG. 5 shows a perspective, partial cross-sectional view of an AFS injector 150 having two rows 230A-B of HP air-fuel injectors 232. That is, the one or more rows 230 of HP air-fuel injectors 232 include a first row 230A of HP air-fuel injectors 232 and a second row 230B of HP air-fuel injectors 232. FIG. 6 shows a perspective, partial cross-sectional view of an AFS injector 150 having three rows 230A-C of HP air-fuel injectors 232. More specifically, the HP air-fuel injectors 232 in one or more rows 230 include an HP air-fuel injector 232 in a first row 230A, an HP air-fuel injector 232 in a second row 230B, and an HP air-fuel injector 232C in a third row 230C between the HP air-fuel injector 232A in the first row 230A and the HP air-fuel injector 232B in the second row 230B.

[0055] The HP air-fuel injectors 232 in one or more rows 230 may be angled to promote mixing of the fuel 114B with the HP air 112B (and optionally the LP air 182) to form the air-fuel mixture 236. For example, as shown in FIG. 5 , the HP air-fuel injectors 232A, 232B in the first and second rows 230A, 230B may be angled at acute angles α1 and α2, respectively, relative to the radial direction R to direct the air-fuel mixture 236 into the mixing chamber 214. Note that the angles α1 and α2 of the rows 230A, 230B may be the same or different. Similarly, as shown in FIGURE 6, the HP air-fuel injectors 232C in the third row 230C may direct the air-fuel mixture 236 in a direction parallel to the mixing chamber 214 (i.e., the radial direction R), and the HP air-fuel injectors 232A, 232B in the first and second rows 230A, 230B may direct the air-fuel mixture 236 at acute angles α3, α4, respectively, relative to the direction parallel to the mixing chamber 214 (i.e., the radial direction R). Note that the angles α3, α4 of the rows 230A, 230B may be the same or different. FIGURE 15 shows a perspective, partial cross-sectional view of an AFS injector 150, similar to FIGURE 3, but according to another embodiment of the present disclosure, using LP air 182. As shown in FIG. 15, when supplying LP air 182, one or more rows 230 of HP air-fuel injectors 232 are intended to direct the air-fuel mixture 236 so that the LP air 182 is entrained in the air-fuel mixture 236 exiting therefrom.

[0056] FIG. 7 shows a schematic perspective cross-sectional view, and FIG. 8 shows a bottom-up schematic view of an HP air-fuel injector 232 according to an embodiment of the present disclosure. Note that the schematic views of the HP air-fuel injector 232 in FIGS. 7 and 8 are referred to as "schematic" because the injector is typically fabricated with the rest of the injection member 212, for example, using additive manufacturing, and is not a separate entity as shown. Additionally, FIG. 9 shows a perspective cross-sectional view of the HP air-fuel injector 232 within the injection member 212, FIG. 10 shows a side view of the HP air-fuel injector 232 of FIG. 9, FIG. 11 shows a cross-sectional view of the HP air-fuel injector 232 and a portion of the injection member 212 taken along line 11-11 of FIG. 9, and FIG. 12 shows a cross-sectional view of the HP air-fuel injector 232 and a portion of the injection member 212 taken along line 12-12 of FIG. 9 through a fuel injector according to an embodiment of the present disclosure.

[0057] 3 and 9, the HP air-fuel injection member 212 may optionally include a filter element 238 upstream (i.e., radially outward) of the set of HP air-fuel injectors 232. The filter element 238 may include any now known or later developed filter structure capable of preventing unwanted contaminants from entering the AFS injectors 150 from the HP air source 154.

[0058] 7 and 8 , each HP air fuel injector 232 includes an inner wall 240 defining an inner high-pressure (HP) air jet 242 and a concentric outer wall 244 surrounding the inner wall 240. The inner wall 240 and the outer wall 244 define an outer HP air jet loop 246 therebetween. That is, as shown in FIGS. 7 and 11 , an outer surface 250 of the inner wall 240 and an inner surface 252 of the outer wall 244 define the HP air jet loop 246 therebetween. The inner wall 240 may define the inner HP air jets 242 with various cross-sectional shapes. In one non-limiting example, each inner HP air jet 242 has an elongated cross-sectional shape, such as a rounded slot, an oval, or an ellipse. In this example, the length of the inner HP air jets 242 is greater than their width, and they are typically relatively narrow openings. However, the inner HP air jets 242 may have other cross-sectional shapes. For example, FIGS. 13A1-13A4 illustrate a circular cross-sectional shape for an inner HP air jet 242 according to one embodiment. FIGS. 13B1-13B4 illustrate a circular cross-sectional shape for an inner HP air jet 242 according to another embodiment. FIGS. 13C1-13C4 illustrate an elliptical or oval cross-sectional shape for an inner HP air jet 242 according to another embodiment. FIGS. 13D1-13D4 illustrate a racetrack (elongated ellipse) cross-sectional shape for an inner HP air jet 242 according to another embodiment. FIGS. 13A1-13A4 illustrate an embodiment with two spacer members 270 and two fuel injectors 278, while FIGS. 13B1-13B4 illustrate an embodiment with four spacer members 270 and four fuel injectors 278.

[0059] In another embodiment, as shown in FIG. 8 , the inner HP air jet 242 is elongated and includes a first end 254 and a second end 256 separated by a middle portion 258. FIGS. 14A and 14B show bottom-up schematic views of an HP air-fuel injector 232 similar to that of FIG. 8 according to various embodiments of the present disclosure. As shown in FIGS. 8 and 14A , the first end 254 and the second end 256 may be narrower than the middle portion 258, allowing more HP air 112B to flow through the middle portion 258 of the inner HP air jet 242. That is, W2 > W1, as shown in FIG. 14A . In this example, the width W3 of the HP air jet loop 246 is constant.

[0060] The HP air injection loop 246 can have any cross-sectional shape surrounding the inner wall 240 and is typically concentric with the inner wall 240. In FIG. 7, the HP air injection loop 246 has an oval or racetrack shape that reflects the shape of the outer surface 250 of the inner wall 240. As shown in FIGS. 7 and 8, the HP air injection loop 246 can also have opposing side surfaces 260, 262. Each side surface 260, 262 can include opposing leading edges 263, 265 (so named because they first encounter the airflow), a first longitudinal end 264, and a second longitudinal end 266 separated by an intermediate longitudinal portion 268. The portions labeled "longitudinal" are so named because they are elongated, straight portions of the HP air injection loop 246, rather than the curved leading edges 263, 265. In some embodiments, as shown in Figure 14B, the first leading edge 263 and the second leading edge 265 can have a width W4 that is greater than the widths (e.g., W5, W6) of the other portions 264, 266, 268 of the HP air injection loop 246, thereby allowing more HP air 112B to flow therethrough to promote mixing, i.e., W4 > W5 > W6, as shown in Figure 14B.

[0061] Similar to the inner HP air jets 242 shown in FIGS. 8 and 14B , the first and second longitudinal ends 264, 266 on each of the opposing sides 260, 262 of the HP air jet loop 246 may be narrower than the intermediate longitudinal portion 268, allowing more HP air 112B to flow through the intermediate portion 268. That is, W5 > W6, as shown in FIG. 14B . Here, the HP air jet loop 246 has opposing sides 260, 262, each having a first longitudinal portion 264 and a second longitudinal portion 266 separated by the intermediate longitudinal portion 268, and the first and second longitudinal portions 264, 266 on each of the opposing sides are narrower than the intermediate longitudinal portion 268. The dimensions of the inner HP air jets 242 and the HP air jet loop 246 can be determined by the user to generate the desired air-fuel mixture 236. Additionally, the axial spacing of the inner HP air jets 242 (and HP air-fuel injectors 232) can be determined by the user, for example, in a given row 230 and relative to the axis A of the combustion liner 164, to produce a desired air-fuel mixture 236.

[0062] 7 and 12, each HP air fuel injector 232 may include a spacer member 270 that spaces the inner wall 240 from the outer wall 244. The spacer member 270 may define the widths of the HP air injection loop 246 and the supporting inner and outer walls 240, 244 relative to one another.

[0063] 7 and 9-12, HP air-fuel injector 212, and more specifically HP air-fuel injector 232, also includes a plurality of fuel injector passages 272 that extend from an outer surface 274 of outer wall 244 through spacer member 270 and inner wall 240 to inner HP air jets 242. Each fuel injector passage 272 has a first end 276 that opens to outer surface 274 of outer wall 244 and a second end 277 (FIGS. 7, 11) that includes a fuel injector 278 (FIGS. 7, 11) that is directed toward inner HP air jets 242 defined by inner wall 240. Each fuel injector 278 is directed toward inner HP air jets 242, and HP air 112B passing through inner HP air jets 242 draws fuel 114B from fuel injector 278 to produce air-fuel mixture 236.

[0064] The HP air fuel injection member 212 also includes a fuel plenum 280 defined therein and in fluid communication with the first end 276 of each fuel injector passage 272. The fuel plenum 280 is thus configured to supply fuel 114B from the fuel source 116 (FIGS. 1-2) to each fuel injector 278. The fuel plenum 280 may extend within the HP air fuel injection member 212 in any manner necessary to supply fuel 114B to the fuel injectors 278. More specifically, the fuel plenum 280 may be defined to extend around the adjacent HP air fuel injectors 232. The AFS injector 150, and more specifically, the HP air fuel injection member 212, may include an inlet port 282 (FIG. 3) in fluid communication with the fuel plenum 280 and is configured to receive fuel 114B from the fuel source 116 (FIGS. 1-2). The inlet port 282 of each AFS injector 150 may be fluidly coupled to the fuel source 116, for example, by a fuel line 188 ( FIG. 2 ) and, optionally, a distribution plenum (not shown) around the combustion liner 164. In either case, the fuel plenum 280 is configured to supply fuel 114B from the fuel source 116 to the fuel injectors 278. As discussed above, the fuel 114B may be any currently known or future developed combustor 100 fuel, such as, but not limited to, fuel oil or natural gas. As a technical advantage of the AFS injectors 150, the fuel 114B may also include highly reactive fuels, such as hydrogen. The fuel 114B may also include a blend of fuels, such as natural gas and hydrogen.

[0065] The fuel injectors 278 may take a variety of shapes. In one embodiment, as shown in FIGS. 7, 11, and 12, one or more fuel injectors 278 directed toward the inner HP air jets 242 in the inner wall 240 may each include an elongated slot, facilitating their printing using additive manufacturing. In any case, the fuel injectors 278 may introduce the fuel 114B into the inner HP air jets 242 in any desired direction. Furthermore, the type, number, orientation, spacing, and dimensions of the fuel injectors 278 may be selected depending on, for example, a variety of characteristics of the combustor 100, the HP air 112B, the LP air 182 (if used), and / or the fuel 114B. For example, with respect to the fuel 114B, these characteristics may include, but are not limited to, the type of liquid or gas, the level of reactivity, the viscosity, the desired flow rate or volume, the pressure, the temperature, etc. Similar characteristics of the air 112B and / or 182 may also be considered. In any event, other configurations of fuel injector 278 are possible.

[0066] In some embodiments, as shown in FIGS. 3 and 9-12, the HP air-fuel injection member 212 may further include multiple HP air inlet openings 284 downstream of one or more rows of HP air-fuel injectors 232 to direct a separate flow of HP air 112C (from the HP air source 154) into the air-fuel mixture 236 and the inlet 216 of the mixing chamber 214. The inlet openings 284 may have any desired number, cross-sectional shape, size, etc. to provide the desired HP air 112C to the air-fuel mixture 236. In some embodiments, the inlet openings 284 may be elongated slots that can be easily printed using additive manufacturing. Any number of rows of inlet openings 284 may be used. FIGS. 9-11 show two rows of inlet openings, while FIGS. 3 and 12 show only one row of inlet openings 284. FIG. 4 shows the HP air-fuel injection member 212 without any inlet openings.

[0067] As mentioned above, FIG. 15 illustrates a perspective, partial cross-sectional view of an AFS injector 150 according to another embodiment. In this embodiment, the mixing element 210 and / or the HP air-fuel injection element 212 are configured with openings 286 to allow LP air 182 from the LP air source 184 described herein to be introduced into the air-fuel mixture 236. More specifically, the HP air 112B as part of the air-fuel mixture 236 incorporates the LP air 182 from the LP air source 184 and directs the LP air 182, along with the HP air 112B and fuel 114B, into the inlet 216 of the mixing chamber 214. While not required, FIG. 15 illustrates an embodiment in which the HP air-fuel injection element 212 includes multiple HP air inlet openings 284 downstream of one or more rows of HP air-fuel injectors 232 to direct a separate flow of HP air 112C into the air-fuel mixture 236 and the inlet 216 of the mixing chamber 214. HP air flow 112B draws LP air 182 from LP air source 184 and draws the LP air 182 along with HP air 112B and fuel 114B into inlet 216 of mixing chamber 214. However, it is not necessary to use both HP air inlet opening 284 and LP air 182.

[0068] FIG. 16 shows a cross-sectional view taken along the line B-B of FIG. 8. Referring to FIGS. 8 and 16, the AFS injector 150 may include a plurality of baffles 288 between the inner wall 240 and the outer wall 244 adjacent the outlet 290 of the HP air injection loop 246. The baffles 288 shape the HP air flow 112B in the HP air injection loop 246 to form an HP air curtain adjacent the outlet 290 (FIG. 7) of the inner HP air injection port 242 from which the air-fuel mixture 236 exits. In either case, the baffles 288 act to direct and shape the HP air curtain 292 around the air-fuel mixture 236 exiting the inner HP air injection port 242 (i.e., downstream of the fuel injector 278) to minimize low-velocity regions where fuel can become entrained and cause flame retention. The baffles 288 promote mixing of the HP air 112B with the LP air 182 to reduce NOx emissions. The baffle members 288 may take any shape that creates the desired air flow shape of the air curtain 292 .

[0069] As noted above, Figure 15 illustrates an embodiment of the AFS injector 150 that utilizes LP air 182. However, the use of LP air 182 is optional and can be omitted by not providing fluid communication between the AFS injector 150 and the LP air source 184. In this configuration, the mixing element 210 and / or injection element 212 may include a wall 294 that prevents the LP air 182 from entering the mixing chamber 214, as shown in Figure 3.

[0070] In operation, as shown in FIGS. 3, 4, 7, and 12, HP air 112B is supplied to each inner HP air jet 242, possibly via a filter 238. Fuel 114B is supplied from a fuel plenum 280 to each fuel injector 278 via fuel injector passages 272. The flow of HP air 112B at the inner HP air jets 242 entrains fuel 114B (possibly also under pressure from a fuel source 116 (FIGS. 1-2)) to produce an air-fuel mixture 236. If LP air 182 is supplied, it is also entrained in the air-fuel mixture 236, as shown in FIG. 15. If HP air inlet openings 284 are provided downstream of the HP air-fuel injectors 232 in one or more rows 230, they may direct a separate flow of HP air 112C into the air-fuel mixture 236. HP air jet loop 246 positions HP air 112B on either side of the trailing edge of inner HP air jet 242 (i.e., inner wall 240) by forming an HP air curtain 292 to minimize the trailing edge wake of fuel injector 278. This configuration improves mixing due to shear between HP air 112B and fuel 114B and other supplied air streams (e.g., LP air 182 and / or HP air 112C from HP air inlet opening 284). In one non-limiting example, this configuration results in a 90% mixture of fuel and air.

[0071] In either case, the air-fuel mixture 236 is directed to the inlet 216 of the mixing chamber 214 and ultimately to the combustion liner 164 as an air-fuel mixture 296 for combustion in the secondary combustion zone 204. Thus, the air-fuel mixture 236 entering the mixing chamber 214 (and the air-fuel mixture 296 exiting the mixing chamber 214) may include HP air 112B and fuel 114B, and may also include LP air 182 and additional HP air 112C (if these two air streams are provided). The air-fuel mixtures 236, 296, even when mixed with LP air 182, still maintain a relatively high pressure, although not as high as the HP air 112B, 112C taken directly from the HP air source 154 (e.g., compressor discharge 109 (FIG. 2)), and thus can be referred to as high pressure. Each HP air-fuel injector 232 is configured to direct the air-fuel mixture 236 toward the inlet 216 of the mixing chamber 214. Additional mixing of the air 112B, 112C, and / or 182 with the fuel 114B occurs within the mixing chamber 214 before the air-fuel mixture 296 exits the AFS injector 150 and enters the combustion liner 164 for combustion in the secondary combustion zone 204. Low velocity and / or fuel-rich enriched regions that could support a flame are eliminated. The HP air-fuel injector 232 mixes the fuel 114B with the HP air 112B without the problems previously described.

[0072] The AFS injector 150 (i.e., the mixing element 210 and the injection element 212) can be made of any combustion- and oxidation-resistant material now known or later developed. The material can be a metal, either a pure metal or an alloy. The AFS injector 150 can include metals commonly used in turbine components, such as turbine blades or nozzles, that have higher temperature and oxidation resistance than materials commonly used in combustion hardware. In this case, the material may comprise a non-reactive metal powder, such as, but not limited to, a non-explosive or non-conductive powder, such as a cobalt-chromium-molybdenum (CoCrMo) alloy, stainless steel, an austenitic nickel-chromium-based alloy, such as nickel-chromium-molybdenum-niobium (NiCrMoNb) alloy (e.g., Inconel 625 or Inconel 718), nickel-chromium-iron-molybdenum (NiCrFeMo) alloy (e.g., Hastelloy® X available from Haynes International), nickel-chromium-cobalt-molybdenum (NiCrCoMo) alloy (e.g., Haynes 233 or Haynes 282 available from Haynes International), or nickel-chromium-cobalt-titanium (NiCrCoTi) alloy (e.g., GTD262 developed by General Electric). Other possibilities include, for example, Rene 108, CM247, MarM247, and other precipitation-hardened (PH) nickel-based alloys.

[0073] In some embodiments, the AFS injector 150 (i.e., the mixing element 210 and / or the injection element 212) may be additively manufactured using any now known or later developed technology capable of forming a unitary body. As a result, as shown in FIG. 17 , the mixing element 210 and / or the injection element 212 includes multiple parallel sintered metal layers 298. FIG. 18 shows a schematic / block diagram of an exemplary computerized metal powder additive manufacturing system 310 (hereinafter “AM system 310”) for producing the AFS injector 150 (i.e., the mixing element 210 and / or the injection element 212) (only one layer of which is shown). While this disclosure describes building the mixing element 210 and / or the injection element 212 using multiple melt beam sources 312, 314, 316, 318, it will be apparent that the teachings of this disclosure are equally applicable to building the mixing element 210 and / or the injection element 212 using any number of melt beam sources. In this example, the AM system 310 is configured for direct metal laser melting (DMLM). The general teachings of this disclosure are equally applicable to other forms of metal powder additive manufacturing, such as selective laser melting (SLM), and possibly other forms of additive manufacturing (i.e., other than metal powder applications). While the layers of mixing element 210 and / or injection element 212 on the build platform 320 are shown as circular elements in FIG. 18, the additive manufacturing process can be readily adapted to produce any shape on the build platform 320.

[0074] The AM system 310 generally includes an additive manufacturing control system 330 ("control system") and an AM printer 332. As described below, the control system 330 executes a set of computer-executable instructions or code 334 for building the mixing element 210 and / or the jet element 212 using multiple melt beam sources 312, 314, 316, and 318. In the illustrated example, the four melt beam sources include four lasers. However, the teachings of this disclosure are applicable to any melt beam source, such as an electron beam, laser, etc. The control system 330 is shown implemented as computer program code on a computer 336. In this regard, the computer 336 includes a memory 338 and / or storage system 340, a processor unit (PU) 344, an input / output (I / O) interface 346, and a bus 348. Additionally, the illustrated computer 336 communicates with external I / O devices / resources 350.

[0075] Generally, processor unit (PU) 344 executes computer program code 334 stored in memory 338 and / or storage system 340. During execution of computer program code 334, processor unit (PU) 344 can read and / or write data to memory 338, storage system 340, I / O devices 350, and / or AM printer 332. Bus 348 provides a communication link between each component within computer 336, and I / O devices 350 may include any device (e.g., keyboard, pointing device, display, etc.) that allows a user to interact with computer 336. Computer 336 is merely representative of various possible combinations of hardware and software. For example, processor unit (PU) 344 may comprise a single processing unit or may be distributed across one or more processing units on one or more locations, e.g., a client and a server. Similarly, memory 338 and / or storage system 340 may reside in one or more physical locations. Memory 338 and / or storage system 340 may comprise any combination of various types of non-transitory computer-readable storage media, including magnetic media, optical media, random access memory (RAM), read-only memory (ROM), etc. Computer 336 may comprise any type of computing device, such as an industrial controller, a network server, a desktop computer, a laptop, a handheld device, etc.

[0076] As described above, the AM system 310, and particularly the control system 330, executes code 334 to create the mixed element 210 and / or the jet element 212. The code 334 may include, among other things, a set of computer-executable instructions 334S (also referred to herein as “code 334S”) for operating the AM printer 332 and a set of computer-executable instructions 334O (also referred to herein as “code 334O”) that define the mixed element 210 and / or the jet element 212 that are physically created by the AM printer 332. As described herein, the additive manufacturing process begins with a non-transitory computer-readable storage medium (e.g., memory 338, storage system 340, etc.) that stores the code 334. The set of computer-executable instructions 334S for operating the AM printer 332 may include any now known or later developed software code capable of operating the AM printer 332.

[0077] The set of computer-executable instructions 334O defining the mixing element 210 and / or the injection element 212 may include a precisely defined 3D model of the mixing element 210 and / or the injection element 212 and may be generated from any of a wide variety of well-known computer-aided design (CAD) software systems, such as AutoCAD™, TurboCAD™, DesignCAD3DMax, etc. In this regard, the code 334O may include any file format now known or later developed. Furthermore, the code 334O representing the mixing element 210 and / or the injection element 212 may be converted between different formats. For example, the code 334O may include a Standard Tessellation Language (STL) file created for 3D Systems' stereolithography CAD program, or an additive manufacturing file (AMF), an American Society of Mechanical Engineers (ASME) standard that is an XML-based format designed to allow any CAD software to describe the shape and configuration of any three-dimensional object to be manufactured by any AM printer. Code 334O representing the mixing element 210 and / or injection element 212 may also be converted to a set of data signals and transmitted, received as a set of data signals, converted to code as needed, stored, etc. In either case, code 334O is input to the AM system 310 and may originate from a part designer, an intellectual property (IP) provider, a design firm, the operator or owner of the AM system 310, or other source. In either case, control system 330 executes code 334S and code 334O to divide the mixing element 210 and / or injection element 212 into a series of thin slices that are sequentially deposited as layers of material in the AM printer 332.

[0078] The AM printer 332 may include an enclosed processing chamber 360 to provide a controlled atmosphere for printing the mixed element 210 and / or the ejection element 212. A build platform 320 on which the mixed element 210 and / or the ejection element 212 are built is disposed within the processing chamber 360. Multiple melt beam sources 312, 314, 316, 318 are configured to melt a layer of metal powder on the build platform 320 to produce the mixed element 210 and / or the ejection element 212. While four melt beam sources 312, 314, 316, 318 are illustrated, the teachings of the present disclosure are applicable to systems using any number of beam sources (e.g., 1, 2, 3, or 4 or more). As will be apparent to one skilled in the art, each melting beam source 312, 314, 316, and 318 may have a field that includes a non-overlapping field region capable of exclusively melting the metal powder, or may include one or more overlapping field regions capable of melting the metal powder with two or more beam sources. In this regard, each melting beam source 312, 314, 316, and 318 may generate a melting beam that fuses particles for each slice defined by code 3340. For example, FIG. 18 shows melting beam source 312 creating a layer of mixed element 210 and / or injection element 212 in one region using melting beam 362, and melting beam source 314 creating a layer of mixed element 210 and / or injection element 212 in another region using melting beam 362′.

[0079] Each melt beam source 312, 314, 316, 318 is calibrated by any now known or later developed method, i.e., each melt beam source 312, 314, 316, 318 provides individual positional corrections (not shown) to ensure its individual accuracy, thereby correlating the expected position of the laser or electron beam with its actual position relative to the build platform 320. In one embodiment, each of the multiple melt beam sources 312, 314, 316, 318 can produce a melt beam (e.g., 362, 362′) having the same cross-sectional dimensions (e.g., operational shape and dimensions), power, and scan speed.

[0080] 18 , an applicator (or recoater blade) 370 can create a thin layer of feedstock 372 spread as a blank canvas upon which each successive slice of the final metal mixed element 210 and / or jet element 212 is created. Various parts of the AM printer 332 can be moved to accommodate each new layer being added, for example, the build platform 320 can be lowered and / or the chamber 360 and / or applicator 370 can be raised after each layer. The process can use various feedstocks in the form of fine metal powders, and stocks of feedstock can be held in a powder reservoir 368 accessible to the applicator 370.

[0081] The process chamber 360 is filled with an inert gas, such as argon or nitrogen, and is controlled to minimize or completely eliminate oxygen. The control system 330 is configured to control the flow of a gas mixture 374 within the process chamber 360 from a source of inert gas 376. In this case, the control system 330 may control a pump 380 and / or a flow valve system 382 for the inert gas to control the content of the gas mixture 374. The flow valve system 382 may include one or more computer-controllable valves, flow sensors, temperature sensors, pressure sensors, etc., that can precisely control the flow of specific gases. The pump 380 can be provided with or without the valve system 382. If the pump 380 is omitted, the inert gas can simply enter a conduit or manifold prior to introduction into the process chamber 360. The source of the inert gas 376 can take the form of any conventional source for the materials contained therein, such as a tank, reservoir, or other source. Any sensors (not shown) necessary to measure the gas mixture 374 may be provided. The gas mixture 374 may be filtered using a filter 386 in a conventional manner.

[0082] During operation, a build platform 320 loaded with metal powder is provided within the process chamber 360, and a control system 330 controls the flow of a gas mixture 374 within the process chamber 360 from a source of inert gas 376. The control system 330 also controls the AM printer 332, particularly the applicator 370 and melt beam sources 312, 314, 316, and 318, to sequentially melt layers of metal powder on the build platform 320 to produce the mixed element 210 and / or jet element 212 according to embodiments of the present disclosure. Although a particular AM system 310 has been described herein, the teachings of the present disclosure are not limited to any particular additive manufacturing system or method.

[0083] Once the mixing element 210 and the injection element 212 are formed, they can be assembled with other portions of the combustor 100 to form the AFS injector 150, as shown in Figure 2. For example, as shown in Figure 3, the mixing element 210 and / or the injection element 212 may be bolted to an AFS injector mount 275 (Figures 3 and 15) on the combustion liner 164. More specifically, as described above, the mixing element 210 and the HP air-fuel injection element 212 may each include one or more attachment elements 213 (e.g., bolts or welds) configured to receive fasteners 215 to couple the mixing element 210 and the HP air-fuel injection element 212 to the combustion liner 164 (i.e., the AFS injector mount 275 on the combustion liner 164) that defines the combustion chamber 172.

[0084] Embodiments of the present disclosure may also include a combustor 100 for the GT system 90. The combustor 100 includes a combustor body 160 that includes a combustion liner 164. The combustor 100 may include a plurality of AFS injectors 150 facing the combustion liner 164, as described herein. Returning to FIG. 2 , the combustor 100 generally terminates adjacent a stationary nozzle 297 of a first stage 295 of the turbine 128. The stationary nozzle 297 of the first stage 295 at least partially defines the turbine inlet 142 to the turbine 128. The combustor body 160 (i.e., the combustion liner 164) at least partially defines a hot gas path (HGP) for channeling combustion gases 122 from the primary combustion zone 202 and the secondary combustion zone 204 to the turbine inlet 142 of the turbine 128 during operation of the GT system 90. Because the dimensions of the AFS injector 150 (i.e., the radial height RH between the radially outermost surface of the injection member 212 and the inner surface of the combustion liner 164, as shown in FIG. 4) are small, the AFS injector 150 can be mounted to the combustion liner 164 of the combustor body 160 (FIG. 2), and the combustor body 160 with the AFS injector 150 mounted thereto can be installed in the GT system 90 in a generally axial direction through a relatively small opening (not shown) in the compressor discharge casing (casing 152).

[0085] 1 , the GT system 90 may include a compressor section 110, a combustion section 120 operably coupled to the compressor section 110, and a turbine section 130 operably coupled to the combustion section 120. As described herein, the combustion section 120 includes one or more combustors 100 including a combustor body 160 including a combustion liner 164, and a head-end fuel nozzle assembly 176 at a forward end of the combustor body 160. The combustor 100 may include multiple AFS injectors 150 facing the combustor body 160 (i.e., the combustion liner 164 downstream of the head-end assembly 176), as described herein.

[0086] The present disclosure provides various technical and commercial advantages, examples of which are described below. As described herein, AFS injectors can accept high-pressure air and optionally low-pressure air (e.g., post-impingement cooling air) to reduce overall system pressure loss. The HP air injection loop generates an air curtain to concentrate HP high-velocity air in the wake behind the fuel injector to prevent flame adhesion to hardware. The inner HP air injection port and HP air injection loop can be specifically tailored to generate a desired velocity profile. To reduce overall system pressure loss and improve air utilization efficiency in the combustor, the AFS injectors can optionally mix up to three air sources, two of which can be high-pressure air (e.g., compressor discharge air) and the remaining air can be low-pressure air (e.g., post-impingement cooling air). In either case, the AFS injectors can rapidly premix one or more air sources with a highly reactive fuel, such as hydrogen, to achieve reduced emissions, such as nitrogen oxides (NOx), and adequate flame-holding capability. AFS injectors also achieve high fuel-air mixing, minimize flow pressure loss, and prevent fuel from entering low-velocity airflow regions. Furthermore, AFS injectors are packaged in a relatively small form factor and can be attached to the combustion liner of the combustor body, allowing the combustor body to be attached to the GT system through a relatively small opening in the compressor discharge casing. AFS injectors can be additively manufactured to include multiple parallel sintered metal layers.

[0087] Approximate expressions used in this specification and claims are used to describe quantitative modifiers that can vary within acceptable limits without causing a change in the basic function to which the quantity relates. Thus, values ​​modified by terms such as "about," "approximately," and "substantially" are not limited to their exact numerical values. In at least some instances, approximate expressions correspond to the precision of the instrument used to measure the value. In some cases, approximate expressions correspond to the precision of the instrument used to measure the value. In this specification and claims, ranges of numerical limitations are combinable and / or interchangeable with each other. Such ranges specify and encompass all subranges within the range, unless otherwise clear from the context. The term "about" used in connection with a particular value in a range applies to both the upper and lower limits and may indicate ±10% of the stated numerical value, except where the precision of the instrument used to measure the value is dependent.

[0088] Corresponding structures, materials, acts, and equivalents of elements identified by functional descriptions in the following claims encompass any structures, materials, or acts that perform the function in combination with other elements specifically recited in the claims. The description of the present disclosure has been provided for purposes of illustration and description and is not intended to be exhaustive or limited to the disclosed form. Numerous modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The embodiments of the present disclosure have been selected and described to best explain the principles and practical applications of the present disclosure and to enable those skilled in the art to understand the disclosure regarding various embodiments and various modifications suitable for particular applications. [Explanation of symbols]

[0089] 90 Gas Turbine System 100 Combustor 108 Compressor 112 Compressed Air 114 Fuel 116 Fuel source 122 Combustion Gas 128 Turbine 150 Axial Fuel Stage Injector 154 High-pressure air source 160 Combustor body 164 Combustion Liner 172 Combustion chamber 176 Head End Fuel Nozzle Assembly 182 Low-pressure air 210 Mixing materials 212 High-pressure air fuel injection member 214 Mixing room 216 Mixing Room Entrance 218 Mixing chamber exit 232 High-Pressure Air Fuel Injector 236 Air-Fuel Mixture 240 Inner Wall 242 Inner high-pressure air outlet 244 Outside wall 246 Outer High-Pressure Air Blowout Loop 270 Spacer member 272 Fuel injector passage 276 first end of fuel injector passage 278 Fuel Injector 280 fuel plenum

Claims

1. An axial fuel stage injector (150) for a combustor (100) of a gas turbine system (90), the axial fuel stage injector (150) comprising: a mixing element (210) having a mixing chamber (214) defined therein, the mixing chamber (214) having an inlet (216) and an outlet (218), the outlet (218) configured to be in fluid communication with a combustion chamber (172) of the combustor (100); a high-pressure air-fuel injection member (212) including one or more rows (230) of high-pressure air-fuel injectors (232) for directing an air-fuel mixture (236) into a mixing chamber (214); each high pressure air fuel injector (232) including: an inner wall (240) defining an inner high pressure air jet (242); a concentric outer wall (244) surrounding the inner wall (240), the inner wall (240) and the outer wall (244) defining an outer high-pressure air jet loop (246) therebetween; a spacer member (270) for spacing the inner wall (240) from the outer wall (244); a plurality of fuel injector passages (272) extending from an outer surface (274) of the outer wall (244) through the spacer member (270) and the inner wall (240) to the inner high-pressure air jet (242), each fuel injector passage (272) having a first end (276) opening to the outer surface (274) of the outer wall (244) and a second end (277) including a fuel injector (278) directed toward the inner high-pressure air jet (242) defined by the inner wall (240); a fuel plenum (280) defined in the high-pressure air fuel injection member (212) and in fluid communication with the first end (276) of each fuel injector passage (272), the fuel plenum (280) configured to deliver fuel (114B) from the fuel source (116) to each fuel injector (278); each inner high-pressure air jet (242) and each high-pressure air jet loop (246) is configured to direct a flow of high-pressure air (112) from a high-pressure air source (154) together with fuel (114B) to an inlet (216) of a mixing chamber (214).

2. 2. The axial fuel stage injector of claim 1, wherein the high-pressure air fuel injection member further comprises a plurality of high-pressure air inlet openings downstream of the one or more rows of high-pressure air fuel injectors for directing a flow of additional high-pressure air into the air-fuel mixture and to the inlet of the mixing chamber.

3. 2. The axial fuel stage injector of claim 1, wherein the flow of high pressure air also entrains low pressure air from a low pressure air source to direct the low pressure air along with the high pressure air and fuel to an inlet of the mixing chamber.

4. 2. The axial fuel stage injector of claim 1, wherein the high-pressure air fuel injection member further includes a plurality of high-pressure air inlet openings downstream of the one or more rows of high-pressure air fuel injectors for directing a separate flow of high-pressure air into the air-fuel mixture and to the inlet of the mixing chamber, the flow of high-pressure air also incorporating low-pressure air from a low-pressure air source for directing the low-pressure air along with the high-pressure air and the fuel to the inlet of the mixing chamber.

5. 2. The axial fuel stage injector of claim 1, wherein the fuel injector directed toward the inner high-pressure air jet in the inner wall of each fuel injector passage includes an elongated slot.

6. 2. The axial fuel stage injector of claim 1, wherein the inner high pressure air jet is elongated and includes a first end and a second end separated by an intermediate portion, each of the first end and the second end being narrower than the intermediate portion.

7. 6. The axial fuel stage injector of claim 5, wherein the high pressure air injection loop has opposing sides each having a first longitudinal end and a second longitudinal end separated by an intermediate longitudinal portion, and wherein the first longitudinal end and the second longitudinal end at each of the opposing sides are narrower than the intermediate longitudinal portion.

8. 2. The axial fuel stage injector of claim 1, wherein the one or more rows of high-pressure air fuel injectors include a first row of high-pressure air fuel injectors and a second row of high-pressure air fuel injectors.

9. 2. The axial fuel stage injector of claim 1, wherein the one or more rows of high-pressure air fuel injectors include a first row of high-pressure air fuel injectors, a second row of high-pressure air fuel injectors, and a third row of high-pressure air fuel injectors between the first row of high-pressure air fuel injectors and the second row of high-pressure air fuel injectors.

10. 10. The axial fuel stage injector of claim 9, wherein the high pressure air-fuel injectors of the third row direct the air-fuel mixture in a direction parallel to the mixing chamber, and the high pressure air-fuel injectors of the first row and the second row direct the air-fuel mixture at an acute angle relative to a direction parallel to the mixing chamber.

11. 10. The axial fuel stage injector of claim 1, further comprising a plurality of baffle members between the inner wall and the outer wall adjacent an outlet of the high pressure air injection loop.

12. The axial fuel stage injector (150) of any preceding claim, wherein the mixing element (210) comprises a filter element (238) upstream of the high pressure air fuel injectors (232) of the one or more rows (230).

13. 2. The axial fuel stage injector of claim 1, wherein the mixing element and the high-pressure air fuel injection element each include one or more mounting elements configured to receive fasteners that couple the mixing element and the high-pressure air fuel injection element to a combustion liner that defines the combustion chamber.

14. The axial fuel stage injector (150) of claim 1, wherein the high pressure air source (154) is in direct fluid communication with a compressor discharge (109) of the gas turbine system (90).

15. A combustor (100) for a gas turbine system (90), the combustor (100) comprising: a combustor body (160) including a combustion liner (164); a plurality of axially staged fuel injectors (150) directed toward a combustion liner (164); and one or more axial fuel stage injectors (150) a mixing element (210) having a mixing chamber (214) defined therein, the mixing chamber (214) having an inlet (216) and an outlet (218), the outlet (218) configured to be in fluid communication with a combustion chamber (172) of the combustor (100); a high-pressure air-fuel injection member (212) including one or more rows (230) of high-pressure air-fuel injectors (232) for directing an air-fuel mixture (236) into a mixing chamber (214); each high pressure air fuel injector (232) including: an inner wall (240) defining an inner high pressure air jet (242); a concentric outer wall (244) surrounding the inner wall (240), the inner wall (240) and the outer wall (244) defining an outer high-pressure air jet loop (246) therebetween; a spacer member (270) for spacing the inner wall (240) from the outer wall (244); a plurality of fuel injector passages (272) extending from an outer surface (274) of the outer wall (244) through the spacer member (270) and the inner wall (240) to the inner high-pressure air jet (242), each fuel injector passage (272) having a first end (276) opening to the outer surface (274) of the outer wall (244) and a second end (277) including a fuel injector (278) directed toward the inner high-pressure air jet (242) defined by the inner wall (240); a fuel plenum (280) defined in the high-pressure air fuel injection member (212) and in fluid communication with the first end (276) of each fuel injector passage (272), the fuel plenum (280) configured to deliver fuel (114B) from the fuel source (116) to each fuel injector (278); each inner high-pressure air jet (242) and each high-pressure air jet loop (246) is configured to direct a flow of high-pressure air (112) from a high-pressure air source (154) together with fuel (114B) to an inlet (216) of a mixing chamber (214).

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