Low emissions gas turbine combustor

A gas turbine combustor including: a primary combustion chamber; a secondary combustion chamber downstream of the primary combustion chamber; a venturi having a venturi throat; a transition piece; a cap assembly attached to the primary combustion chamber, and an external turbulator member in operable communication with the cap assembly, wherein the primary combustion chamber includes a mixing hole arrangement for improving homogeneity of an air and fuel mixture in the combustor; the venturi throat is disposed within a predetermined distance upstream from the downstream end of the primary combustion chamber; the transition piece is composed of a duct body, with a plurality of dilution holes formed in the duct body; and the external turbulator member includes a step positioned at the second end of the centerbody, the step defining a radial distance about the second end of the centerbody.

FIELD OF THE INVENTION

The invention described herein relates to a combination of gas turbine combustor components that is capable of reducing NOxemissions to less than 5 ppm.

This disclosure relates to a gas turbine combustor with improved emissions performance and stability.

BACKGROUND OF THE INVENTION

Gas turbines comprise a compressor for compressing air, a combustor for producing a hot gas by mixing fuel and air and burning the resulting mixture, and a turbine to extract work from the expanding hot gas produced by the combustor. Gas turbine compressors pressurize inlet air which is then reverse flowed to the combustor where it is used to provide air to the combustion process. Each combustion chamber assembly comprises a cylindrical combustor liner, a fuel injection system, and a transition piece that guides the flow of the hot air from the combustor liner to the entrance of the turbine section.

Gas turbines are known to emit various undesirable oxides, such as nitrogen oxide (NOx), carbon monoxide (CO), as well as unburned hydrocarbons. It is well known that both oxidation of molecular nitrogen and oxidation of carbon monoxide to carbon dioxide depend on the temperature of the hot gas which is produced inside the turbine combustor and then flows through the transition piece to the turbine section. In addition, the residence time of the reactants in the combustor at these high temperatures is also a factor in producing undesirable emissions. To improve the performance of the combustor with respect to emissions, gas temperatures have to be high enough for an adequate period of time to oxidize carbon monoxide without being so high that excessive amounts of nitrogen oxides are produced.

Existing dry low NOx combustors (DLN combustors) minimize the generation of NOx, CO and other pollutants. These DLN combustors provide a fuel-lean mixture of fuel and air prior to combustion. Dilution air is provided to the combustor liner to absorb heat and reduce the temperature rise to a level where thermal NOx is not formed. Dilution air may also be provided to the transition piece between the combustor and the first stage nozzle. However, in many cases, even combustors with lean premixed fuel and air still achieve sufficiently high temperatures to produce undesirable emissions.

NOx emissions requirements are becoming more stringent Accordingly, there is a need for a lower NOx emission combustor that utilizes various ways to control the influx and movement of air in the combustor as well as to effect independent and variable control of fuel flow to fuel introduction locations of the combustor.

BRIEF DESCRIPTION OF THE INVENTION

The invention described herein relates to a gas turbine combustor comprising: a primary combustion chamber; a secondary combustion chamber downstream of the primary combustion chamber; a venturi connecting the primary and secondary combustion chambers, the venturi having a venturi throat; a transition piece connected to a downstream end of the secondary combustion chamber for confining a flow of combustion products from the combustor to a turbine first stage nozzle; a cap assembly attached to the primary combustion chamber, the cap assembly comprising a centerbody having a first end and a second end, and an external turbulator member in operable communication with the cap assembly and being spaced from a wall of the centerbody to form a gap that defines a passage, wherein the primary combustion chamber includes a mixing hole arrangement for improving homogeneity of an air and fuel mixture in the combustor, the mixing hole arrangement including a plurality of mixing holes in a liner of the primary combustion chamber at least one of which is a mixing hole that is sized and positioned so that to impede a fluid flow penetration into a primary mixing zone located at the upstream end of the combustor; the venturi throat is disposed within a predetermined distance upstream from the downstream end of the primary combustion chamber; the transition piece is composed of a duct body, with a plurality of dilution holes formed in the duct body, the dilution holes located at selected X, Y and Z coordinates measured from a zero reference point at a center of an exit plane of the transition piece, and the external turbulator member including a step positioned at the second end of the centerbody, the step defining a radial distance about the second end of the centerbody, wherein the external turbulator is formed having a step-to-gap ratio relative to the centerbody in a range of about 0.8 to about 1.2.

In another aspect, a method for achieving NOx emissions of less than 5 ppm in a gas turbine combustor, the combustor including a primary combustion chamber, a secondary combustion chamber downstream of the primary combustion chamber, a venturi connecting the primary and secondary combustion chambers, the venturi having a venturi throat, a transition piece connected to a downstream end of the secondary combustion chamber for confining a flow of combustion products from the combustor to a turbine first stage nozzle, and a cap assembly attached to the primary combustion chamber and having a centerbody, the method comprising: impeding a fluid flow penetration from a mixing hole of the primary combustion chamber into at least one of a fuel flow and a primary mixing zone of the combustor; expanding an annular fluid flow and a center fluid flow by disposing the venturi throat a predetermined distance upstream from the downstream end of the primary combustion chamber; forming a plurality of dilution holes in the duct body of the transition piece, the dilution holes located at selected X, Y and Z coordinates measured from a zero reference point at a center of an exit plane of the transition piece; and guiding a cooling airflow through a passage defined by a gap extending between a wall of the centerbody and a turbulator member having a step portion, the turbulator member formed having a step-to-gap ratio relative to the centerbody of between about 0.8 and 1.2, the step-to-gap ratio enhancing air/fuel mixing and reducing an amount of the cooling airflow required by the combustor.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and particularly toFIG. 1, a gas turbine10(partially shown) includes a compressor12(partially shown), a combustor14, and a turbine section represented here by a single blade16. The compressor12pressurizes inlet air and reverse-flows it to the combustor14where it is used to cool the combustor and to provide air for the combustion process. The combustor may be one of several arranged in a “can-annular” array about the turbine rotor, each supplying gas to the first stage turbine nozzle.

A transition piece18connects the downstream end of the combustor with the inlet end of the turbine to deliver the hot products of combustion to the turbine.

The combustor14may comprise an upstream combustion chamber24and a downstream combustion chamber26connected with each other via a venturi throat region28. The combustor14is surrounded by a combustor flow sleeve30which channels compressor discharge air flow to the combustor14. An outer casing32which is bolted to a turbine casing34surrounds the combustor14.

Fuel is provided to the combustor14via primary nozzles36arranged in an annular array around a secondary nozzle38. The primary nozzles36provide fuel to the upstream combustor24and the secondary nozzle38provides fuel to the downstream combustion chamber26. A sparkplug20is used to provide ignition to the various combustors14in conjunction with crossfire tubes22(one shown).

In an exemplary embodiment, shown inFIG. 2, the secondary nozzle may be a nozzle as disclosed in U.S. 2007/0130955 A1. This nozzle comprises two fuel introduction locations, e.g., secondary nozzle pegs40and a secondary nozzle pilot tip42. The secondary nozzle pegs40provide fuel to a pre-mix reaction zone of the combustor14, while the secondary nozzle pilot tip42provides fuel to the downstream combustion chamber26where it is immediately burned (diffusion combustion).

With the above arrangement, the secondary nozzle38comprises a combustion system fuel delivery section having separate and individually controlled fuel circuits. This allows for the ability to individually vary fuel flow rates delivered to the two fuel introduction locations of the secondary nozzle. For example, the fuel flow rate through the secondary nozzle pilot tip42may be varied independently from the fuel flow rate through the secondary nozzle pegs40. Furthermore, the secondary nozzle pegs40and the secondary nozzle pilot tip42each have their own independent fuel piping circuit, each having independent and exclusive fuel sources.

In an exemplary embodiment, the fuel flow rate delivered through the secondary nozzle pilot tip42is less than about 2% of the total gas turbine fuel flow, and is in the range of about 0.002 pps (pounds per second) to about 0.020 pps.

The ability to control the amount of fuel flow to different regions of the combustor allows for the minimizing of NOx and Co emissions for a given set of operating conditions. In particular, the independent control of the two fuel introduction locations may achieve sub-5 ppm (parts per million) NOx emissions across the full ambient and load range.

The secondary nozzle pegs40are shown inFIG. 3along with the independent fuel circuits and passages. The secondary fuel nozzle38comprises a plurality of concentric tubes. The two radially outermost concentric tubes44and48provide a tertiary gas passage46. providing tertiary gas to the secondary nozzle pilot tip42.

A secondary gas fuel passage50, formed between concentric tubes48and52supplies secondary gas fuel to the secondary pegs40. In addition, a sub-pilot gas fuel passage54formed between concentric tubes52and56supplies fuel to the secondary nozzle pilot tip42.

A water purge passage58defined between concentric tubes56and60provides water to the secondary nozzle pilot tip42to effect NOx and CO emission reductions. Moreover, a liquid fuel passage62comprising the innermost of the plurality of concentric passages forming the secondary nozzle38and defined by tube60, provides liquid fuel to the secondary nozzle pilot tip42.

Even though four independent fuel circuits are shown inFIG. 2, the number of fuel circuits may be varied according to specific operational and design considerations.

The secondary nozzle pilot tip42is shown inFIG. 4. In one embodiment, it may comprise a three-piece assembly, having a sub-pilot portion64(containing the sub-pilot gas fuel at the secondary nozzle pilot tip42and abutting tube52), a water purge portion66(containing the water at the secondary nozzle pilot tip42and abutting tube56), and a tip portion68(forming an outlet end to the secondary nozzle38). The three pieces may be fixedly joined, for example, by an electron beam welding process.

FIG. 5shows a lip seal70between tube56and a secondary nozzle base72. The lip seal70prevents fuel leakage within the secondary nozzle38by forming a controlled interference fit between the tube56and the secondary nozzle base.

In the exemplary embodiment described above, the emission of undesirable oxide pollutants is reduced by independently controlling the delivery of fuel to the various portions of the combustor chamber. Controlling the air fuel mixture in the combustor also allows for a decrease in undesirable emissions.

A mixing hole arrangement incorporated with the upstream combustor chamber is shown inFIG. 6. The combustor liner120includes a head end130of a dry low NOx combustor140. The combustor140includes a primary nozzle end150and a venturi throat170, between which the head end130is disposed. The liner120included in this head end130of the combustor140defines a plurality of mixing holes180disposed circumferentially around the liner120. Hole spacing is measured in angles (i.e. 24 degrees between two holes180) relative to a longitudinal central axis190of the combustor14. The holes180allow air flowing through a flow sleeve160to penetrate into a primary mixing zone200, through which the longitudinal central axis190runs. Once in the primary mixing zone200, the air mixes with fuel to facilitate combustion. As shown inFIG. 7, the primary mixing zone200is disposed within the combustor140, radially between the liner120and a center-body tube220and axially between the primary nozzle end150and the venturi throat170.

The liner120referred to above can be found in combustors producing varying amounts of power. Referring toFIG. 8, the liner120for the combustor140of a 35 megawatt combustion turbine is illustrated (the illustration is flat, though in application the mixing holes180are disposed radially about the liner120, which is in a cylindrical construction), and includes an arrangement260of mixing holes180sized and positioned for allowing airflow into the primary mixing zone200. These mixing holes180are disposed in two rows (a first row280aand a second row280b) of ten mixing holes180each. The first row280ais typically located 4.9 inches from the primary nozzle end150shown inFIG. 6, and includes mixing holes180that are 0.77 inches in diameter and alternatively positioned at distances of 24 and 48 degrees from each other around the cylindrical liner120(i.e. the mixing holes180are positioned in a pattern of 24-48-24-48 degrees from each other around the liner12). The second row280bis located 6.15 inches from the primary nozzle end150, and includes mixing holes180that are 1.04 inches in diameter and positioned at distances of 36 degrees from each other around the liner120. Two cross-fire tubes290a-bare also illustrated between the first row280aand the primary nozzle end150.

Referring toFIG. 9, the liner120for the combustor140of an 80 megawatt combustion turbine is illustrated (the illustration is flat, though in application the mixing holes180are disposed circumferentially about the liner120, which is in a cylindrical construction) and includes an arrangement320of mixing holes180sized and positioned for allowing airflow into the primary mixing zone200. These mixing holes180are disposed in two rows (a first row340aand a second row340b) of twelve (340a) and six (340b) mixing holes180, respectively. The first row340ais located 6.39 inches from the primary nozzle end150shown inFIG. 6, and includes mixing holes180of that are 1.125 inches in diameter and alternatively positioned at distances of 20 and 40 degrees from each other around the cylindrical liner120(i.e. the mixing holes180are positioned in a pattern of 20-40-20-40 degrees from each other around the liner120). The second row340bis located 7.64 inches from the primary nozzle end150, and also includes mixing holes180that are 1.125 inches in diameter. However, the mixing holes180in the second row340bare positioned consistently at distances of 60 degrees from each other around the liner12. Two cross-fire tubes290a-blike those mentioned above are additionally illustrated at the left of the first row340a.

Mixing hole180arrangements like arrangements260and320typically result in a fluid flow240(which may be air) from the flow sleeve160, through the mixing holes180, and radially into the primary mixing zone200, as shown inFIG. 10. The fluid flow240enters the primary mixing zone200roughly orthogonally to a direction of a fuel flow300introduced into the mixing zone200. Because of a velocity of fluid flow240, that flow240penetrates the fuel flow300to a depth sufficient to impact the center-body tube220. Due to the impact of the fluid flow240against the center-body220, this fluid flow240“splashes” off of the center-body tube220, resulting in a pocketed, heterogeneous air and fuel mixture380like that which is shown inFIG. 11. InFIG. 11, the darker regions represent pockets of fuel4000a-bthat have been pushed away from the center-body tube220by the splashing fluid flow240.

Referring now toFIG. 12, a less heterogeneous air and fuel mixture420is illustrated. InFIG. 12, fuel pocketing has been reduced as compared with the fuel pocketing ofFIG. 11. This less heterogeneous mixture420achieves improved NOx emissions in combustors such as dry low NOx combustors, like the one partially illustrated in ofFIGS. 6 and 7. This homogeneity can be achieved by impeding penetration of the fluid flow240into the primary mixing zone200during combustor operation, as shown inFIG. 13. InFIG. 13, penetration of the fluid flow240into the fuel flow300is reduced (impeded) compared with the mixing ofFIG. 10(which results from hole arrangements260and320) reducing splash of the fluid flow240off the center-body tube220. Penetration of the fluid flow240into the primary mixing zone300can be represented as a percentage of the distance between the liner120and the centerbody220. Anything over 100% would be a condition where the fluid flow splashes off the centerbody with 200% representing a much stronger splash than, for example 125%. The penetration is calculated using standard correlations for a jet (fluid flow240) penetrating into crossflow, a standard correlation being Ymax/Dj=sqrt(Momentum of Jet/Momentum of crossflow)*C1(where Ymax=Max jet penetration, Dj=Jet diameter, Momentum of Jet=0.5*ρj*Vj2, Momentum of Cross-flow=0.5*ρcf*Vcf2, C1=1.15 for these calculations, ρj=Density of jet fluid, ρcf=Density of cross-flow fluid, Vj=Jet Velocity, and Vcf=Cross flow velocity). Fluid flow240penetrating than about 195% or more into the primary mixing zone200can lead to a heterogeneous air-fuel mixture that creates undesirably high emissions. InFIG. 13, the fluid flow240penetrates less than or equal to about 165% into the primary mixing zone20, with an exemplary range of between about 100% and 165%. The exemplary range optimizes a balance between decreasing emissions and maintaining stability.

Referring toFIG. 14, an exemplary embodiment of a mixing hole arrangement100that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated. This arrangement100impedes penetration of the fluid flow240into the fuel flow300and primary mixing zone200, allowing for the homogeneous mixture240. Impeding the fluid flow240, as shown inFIG. 13, via this arrangement100causes the fluid flow240to penetrate less than or equal to about 165% into the primary mixing zone200, with an exemplary range of between about 150% and 165%, as was mentioned above. The arrangement100comprises a plurality of mixing holes102defined by a liner104(the illustration is flat, though in application the mixing holes102are disposed radially about the liner104, which is cylindrical in construction) of the head end106. At least one of this plurality of mixing holes102is at least one of sized (diameter) and positioned to impede penetration of the fluid flow240into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for a 35 megawatt variety turbine. The mixing holes102are arranged in three rows, illustrated as a first row110a, a second row110b, and a third row110c. The mixing holes102in at least one of the three rows are sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In the exemplary embodiment, the mixing holes102in the first row110aare positioned to include alternating distances of 24 and 36 degrees between each mixing hole102around the liner104(i.e. the mixing holes102are at 24 degrees, 60 degrees, 84 degrees, 120 degrees, and so on around the liner104), at a distance of 3.65 inches from the primary nozzle end150(illustrated inFIG. 6). These mixing holes102also have a diameter112aof 0.59 inches. The mixing holes102in the second row110b(in the exemplary embodiment) are positioned at102at 12, 60, 90, 126, 168, 192, 234, 270, 312, and 348 degrees around the liner104, at a distance of 4.9 inches from the primary nozzle end15. These mixing holes102have a diameter112bof 0.71 inches. The mixing holes102in the third row110c(also in the exemplary embodiment) are positioned 36 degrees from each other around the liner104, at a distance of 6.15 inches from the primary nozzle end15. These mixing holes102have a diameter112cof 0.98 inches.

Three rows, the overall decrease in diameter112a-cof the mixing holes102, and the positioning of the mixing holes102are all elements of the arrangement100that may impede fluid flow240penetration as shown inFIG. 13, and result in the less heterogeneous mixture420shown inFIG. 12. It should be appreciated that though these three rows110a-ceach include the same number of mixing holes102(ten), each individual row may include more or less mixing holes102. It should also be appreciated that the arrangement100is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement100decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes102might be sized and positioned to impede fluid flow24penetration into the primary mixing zone20.

Referring toFIG. 15, an exemplary embodiment of a mixing hole arrangement2001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 15illustrates a table201that represents positioning of the mixing hole arrangement2001in a liner like liner104ofFIG. 14. This arrangement2001impedes penetration of the fluid flow240into the fuel flow300and primary mixing zone200, allowing for the homogeneous mixture420. The arrangement2001comprises a plurality of mixing holes represented in the table201by a measure of diameter disposed in an appropriate row and column. At least one of this plurality of mixing holes in arrangement2001is at least one of sized (diameter) and positioned to impede fluid flow240penetration into the primary mixing zone20shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for a 35 megawatt turbine. The mixing holes of arrangement2001are arranged in three rows, illustrated in table201as a first column, a second column, and a third column. The mixing holes in at least one of the three rows are sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In this embodiment, mixing hole diameter decreases as the rows move away from the primary nozzle end150(FIG. 6), as opposed to increasing as shown inFIG. 14. The mixing holes of the arrangement2001that are disposed in the third row (represented in the third column of the table201) are positioned to include alternating distances of 24, 36, and 48 degrees between each mixing hole around the circular liner (i.e. the mixing holes102are at 24 degrees, 48 degrees, 84 degrees, 132 degrees, 156 degrees and so on around the liner104), at a distance of 6.15 inches from the primary nozzle end150(which is shown inFIG. 6). These mixing holes also have a diameter of 0.59 inches. The mixing holes of the arrangement2001in the second row (represented in the second column of the table201) are positioned at 12, 60, 90, 126, 168, 192, 234, 270, 312, and 348 degrees around the liner, at a distance of 4.9 inches from the primary nozzle end150. These mixing holes have a diameter of 0.71 inches. The mixing holes of the arrangement2001in the first row (represented in the third column of the table201) are positioned 36 degrees from each other around the liner, at a distance of 3.65 inches from the primary nozzle end150(as shown inFIG. 1). These mixing holes have a diameter of 0.98 inches.

Three rows, the overall decrease in diameter of the mixing holes, and the positioning of the mixing holes are all elements of the arrangement2001that may impede fluid flow240penetration to various levels in the primary mixing zone200, and result in the less heterogeneous mixture420shown inFIG. 12. Impeding the fluid flow240via this arrangement2001causes the fluid flow240to penetrate variously depending on whether the flow is from the holes in the first row second row or third row. Fluid flow240from the first row has maximum penetration and penetrates more than or equal to about 250% into the primary mixing zone200with an exemplary range between about 250% and 280%. Fluid flow from the second row penetrates less than or equal to about 175% into the primary mixing zone200, with an exemplary range of between about 130% and 175%, whereas the third row penetrates less than or equal to about 100% into the primary mixing zone200, with an exemplary range of between about 80% and 100%. It should be appreciated that though the three rows of the arrangement2001each include the same number of mixing holes (ten), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement2001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement2001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIG. 16, an exemplary embodiment of a mixing hole arrangement3001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 16illustrates a table301that represents positioning of the mixing hole arrangement3001in a liner like liner104of FIG.14. The arrangement3001comprises a plurality of mixing holes represented in the table301by a measure of diameter disposed in an appropriate row and column. At least one of the plurality of mixing holes of the arrangement3001is at least one of sized (diameter) and positioned to impede fluid flow240penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for a 35 megawatt turbine. The mixing holes are arranged in three rows, illustrated in table301as a first column, a second column, and a third column. The mixing holes in the three rows are sized to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200, with the first column and the second column illustrating rows that are positioned to impede airflow penetration and allow for a less heterogeneous air and fuel mixture420(FIG. 12). In this embodiment, mixing hole diameter remains constant throughout all three rows, with each of the mixing holes of the arrangement3001having a diameter of 0.777 inches. The mixing holes in the first row (represented in the first column of the table301) are positioned at 24, 48, 84, 132, 156, 204, 228, 276, 300, and 336 degrees, at a distance of 3.65 inches from the primary nozzle end150(as shown inFIG. 6). The mixing holes in the second row (represented in the second column of the table301) are positioned at 12, 60, 90, 126, 168, 192, 234, 270, 312, and 348 degrees around the circular liner, at a distance of 4.9 inches from the primary nozzle end150. The mixing holes in the third row (represented in the third column of the table301) are positioned 36 degrees from each other around the liner, at a distance of 6.15 inches from the primary nozzle end150.

Three rows, the overall decrease in diameter of the mixing holes in the arrangement3001, and the positioning of the mixing holes are all elements of the arrangement3001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. Impeding the fluid flow240via this arrangement3001causes the fluid flow240from the first row to penetrate more than or equal to about 200% into the primary mixing zone200with an exemplary range of between about 200% and 220%, fluid flow240from the second row to penetrate less than or equal to about 165% into primary mixing zone200with an exemplary range of between about 150% and 165% and fluid flow240from the third row to penetrate less than or equal to about 130% into the primary mixing zone200, with an exemplary range of between about 115% and 130% It should be appreciated that though these three rows each include the same number of mixing holes (ten), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement3001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement3001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIG. 17, an exemplary embodiment of a mixing hole arrangement4001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 17illustrates a table401that represents positioning of the mixing hole arrangement4001in a liner like liner104ofFIG. 14. The arrangement4001comprises a plurality of mixing holes represented in the table401by a measure of diameter disposed in an appropriate row and column. At least one of the plurality of mixing holes of the arrangement4001is at least one of sized (diameter) and positioned to impede airflow penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for a 35 megawatt turbine. The mixing holes are arranged in three rows, illustrated in table401as a first column, a second column, and a third column. The mixing holes of the arrangement4001that are in the first row and second row (represented in the first column and second column respectively of the table401) of this embodiment4001are sized to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200, while only some of the mixing holes in the third row (represented in the third column of the table401) are necessarily sized to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. This is the case because in this embodiment, the mixing holes within the third row are themselves of varying sizes, and some may not be of a size that will impede penetration. As to positioning in this embodiment, the first row and the second row are positioned to impede airflow penetration and allow for a less heterogeneous air and fuel mixture420(FIG. 12). The mixing holes in the first row are positioned at 24, 48, 84, 132, 156, 204, 228, 276, 300, and 336 degrees around the liner, at a distance of 3.65 inches from the primary nozzle end150(as shown inFIG. 6). These mixing holes have a diameter of 0.59 inches. The mixing holes in the second row are positioned at 12, 60, 90, 126, 168, 192, 234, 270, 312, and 348 degrees around the liner, at a distance of 4.9 inches from the primary nozzle end150. These mixing holes have a diameter412bof 0.71 inches. The mixing holes in the third row are 36 degrees from each other around the liner, at a distance of 3.65 inches from the primary nozzle end150. These mixing holes alternate between having a diameter of 0.71 inches and a diameter of 1.39 inches in this embodiment.

Three rows, the overall decrease in diameter of the mixing holes of the arrangement4001, and the positioning of the mixing holes are all elements of the arrangement4001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. Impeding the fluid flow240via this arrangement4001causes the fluid flow240to penetrate less than or equal to about 165% into the primary mixing zone200, with an exemplary range of between about 150% and 165% for the first and second rows. Fluid flow240from the holes of the third row with a diameter of 0.71 penetrate less than or equal to about 120% into the primary mixing zone200, with an exemplary range of between about 100% and 120%, while fluid flow240from holes of the third row with diameter of 1.39 inches penetrate more than or equal to about 200% into the primary mixing zone20with an exemplary range of between about 200% and 220%. It should be appreciated that though the three rows of the arrangement4001each include the same number of mixing holes (ten), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement4001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement4001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200. In this particular embodiment, the mixing holes in the third row having the diameters of 0.71 and 1.39 are differently sized to specifically cause local heterogeneity to maintain the balance between stability and emissions.

Referring toFIG. 18, an exemplary embodiment of a mixing hole arrangement5001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 18illustrates a table501that represents positioning of the mixing hole arrangement5001in a liner like liner104ofFIG. 14. Impeding the fluid flow240via this arrangement5001causes the fluid flow240to penetrate less than or equal to about 165% into the primary mixing zone200, with an exemplary range of between about 150% and 165%, as was mentioned above and is illustrated inFIG. 13. The arrangement5001comprises a plurality of mixing holes represented in the table501by a measure of diameter disposed in an appropriate row and column. At least one of the plurality of mixing holes in the arrangement5001is at least one of sized (diameter) and positioned to impede airflow penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for an 80 megawatt turbine. The mixing holes of the arrangement5001are arranged in three rows, illustrated in table501as a first column, a second column, and a third column. The mixing holes in at least one of the three rows are sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. The mixing holes in the first row (represented in the first column of the table501) are positioned 30 degrees from each other around the liner, at a distance of 5.14 inches from the primary nozzle end150(as shown inFIG. 6). These mixing holes have a diameter of 0.784 inches. The mixing holes in the second row (represented in the second column of the table501) are positioned 30 degrees from each other around the liner, at a distance of 6.39 inches from the primary nozzle end150. These mixing holes have a diameter of 0.85 inches. The mixing holes in the third row (represented in the third column of the table501) are positioned 30 degrees from each other around the liner, at a distance of 7.64 inches from the primary nozzle end15. These mixing holes have a diameter of 0.912 inches.

Three rows, the overall decrease in diameter of the mixing holes of the arrangement5001, and the positioning of the mixing holes are all elements of the arrangement5001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. It should be appreciated that though these three rows each include the same number of mixing holes (twelve), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement5001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement5001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIG. 19, an exemplary embodiment of a mixing hole arrangement6001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 19illustrates a table601that represents positioning of the mixing hole arrangement6001in a liner like liner104ofFIG. 14. The arrangement6001comprises a plurality of mixing holes represented in the table601by a measure of diameter disposed in an appropriate row and column.

At least one of the plurality of mixing holes of the arrangement6001is at least one of sized (diameter) and positioned to impede fluid flow240penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for an 80 megawatt turbine. The mixing holes are arranged in three rows, illustrated in table601as a first column, a second column, and a third column. The mixing holes in at least one of the three rows are sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In this embodiment mixing hole diameter decreases as the rows move away from the primary nozzle end150(FIG. 6), as opposed to increasing as shown inFIG. 18. The mixing holes in the first row (represented in the first column of the table601) are positioned 30 degrees from each other around the liner, at a distance of 5.14 inches from the primary nozzle end150. These mixing holes have a diameter of 0.912 inches. The mixing holes in the second row (represented in the second column of the table601) are positioned 30 degrees from each other around the liner, at a distance of 6.39 inches from the primary nozzle end150. These mixing holes have a diameter of 0.85 inches. The mixing holes in the third row (represented in the third column of the table601) are positioned 30 degrees from each other around the liner, at a distance of 7.64 inches from the primary nozzle end150. These mixing holes have a diameter of 0.784 inches.

Three rows, the overall decrease in diameter of the mixing holes in the arrangement6001, and the positioning of the mixing holes are all elements of the arrangement6001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. Impeding the fluid flow240via this arrangement6001causes the fluid flow240to penetrate variously depending on whether the flow is from the holes in the first row second row or third row. Fluid flow240from the first row has maximum penetration and penetrates more than or equal to about 250% into the primary mixing zone200with and exemplary range between about 250% and 280%. Fluid flow from the second row penetrates less than or equal to about 175% into the primary mixing zone200, with an exemplary range of between about 130% and 175%, whereas the third row penetrates less than or equal to about 100% into the primary mixing zone200, with an exemplary range of between about 80% and 100%. It should be appreciated that though these three rows each include the same number of mixing holes (twelve), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement6001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement6001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIG. 20, an exemplary embodiment of a mixing hole arrangement7001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIG. 20illustrates a table701that represents positioning of the mixing hole arrangement7001in a liner like liner104ofFIG. 14. Impeding the fluid flow240via this arrangement7001causes the fluid flow240to penetrate less than or equal to about 138% into the primary mixing zone200, with an exemplary range of between about 110% and 138%, as was mentioned above and is illustrated inFIG. 13. The arrangement7001comprises a plurality of mixing holes represented in the table701by a measure of diameter disposed in an appropriate row and column. At least one of this plurality of mixing holes in the arrangement7001is at least one of sized (diameter) and positioned to impede fluid flow240penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for an 80 megawatt turbine. The mixing holes are arranged in three rows, illustrated in table701as a first column, a second column, and a third column. The mixing holes in at least one of the three rows are sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In this arrangement7001, size of the mixing holes remains constant throughout all three rows (respectfully represented in the first column, second column, and third column of the table701), with each mixing hole having a diameter of 0.85 inches. The mixing holes in the first row (represented in the first column of the table701) are positioned 30 degrees from each other around the liner, at a distance of 5.14 inches from the primary nozzle end150(as shown inFIG. 6). The mixing holes in the second row (represented in the second column of the table701) are positioned 30 degrees from each other around the liner, at a distance of 6.39 inches from the primary nozzle end150. The mixing holes in the third row (represented in the third column of the table701) are positioned 30 degrees from each other around the liner, at a distance of 7.64 inches from the primary nozzle end150.

Three rows, the overall decrease in diameter of the mixing holes in the arrangement, and the positioning of the mixing holes are all elements of the arrangement7001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. It should be appreciated that though these three rows each include the same number of mixing holes (twelve), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement7001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement7001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIG. 21, an exemplary embodiment of a mixing hole arrangement8001that will allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated. This arrangement8001impedes penetration of the fluid flow240into the fuel flow300and primary mixing zone200, allowing for the homogeneous mixture420. Impeding the fluid flow240via this arrangement8001causes the fluid flow240to penetrate less than or equal to about 110% into the primary mixing zone200, with an exemplary range of between about 90% and 110%, as was mentioned above and is illustrated inFIG. 13. The arrangement8001comprises a plurality of mixing holes802defined by a liner804(the illustration is flat, though in application the mixing holes802are disposed circumferentially about the liner804, which is cylindrical in construction) of the head end806. At least one of this plurality of mixing holes802is at least one of sized (diameter) and positioned to impede fluid flow penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for an 80 megawatt turbine. The mixing holes802are arranged in four rows, illustrated as a first row810a, a second row810b, a third row810c, and a fourth row810d. The mixing holes802in at least one of the four rows810a-dare sized (diameter) and positioned to impede penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In this embodiment, mixing hole802size remains constant throughout all four rows810a-d, with each mixing hole802having a diameter812of 0.655 inches. The mixing holes802in the first row810aare positioned 24 degrees from each other around the liner804, at a distance of 5.14 inches from the primary nozzle end150(as shown inFIG. 6). The mixing holes802in the second row810bare positioned 24 degrees from each other around the liner804, at a distance of 6.39 inches from the primary nozzle end150. The mixing holes802in the third row810care positioned 24 degrees from each other around the liner804, at a distance of 7.64 inches from the primary nozzle end150. The mixing holes802in the fourth row810dare positioned 24 degrees from each other around the liner804, at a distance of 8.89 inches from the primary nozzle end150.

Four rows, the overall decrease in diameter812of the mixing holes802, the positioning of the mixing holes802, and the number (fifteen) of mixing holes in each row810a-dare all elements of the arrangement8001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. It should be appreciated that though these four rows810a-deach include the same number of mixing holes802(fifteen), each individual row may include more or less mixing holes802. It should also be appreciated that the arrangement8001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement8001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes802might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

Referring toFIGS. 22 and 23, two embodiments of a mixing hole arrangement8001and9001that will each allow for the improved less heterogeneous air and fuel mixture420shown inFIG. 12is illustrated.FIGS. 22 and 23illustrate tables801and901that represent positioning of the two embodiments of the mixing hole arrangement8001and9001, respectively, each in a liner like liner104ofFIG. 14. The arrangement8001and9001comprise a plurality of mixing holes represented in the tables801and901by a measure of diameter disposed in an appropriate row and column. At least one of this plurality of mixing holes of the arrangement8001and9001is at least one of sized (diameter) and positioned to impede fluid flow240penetration into the primary mixing zone200shown inFIG. 13.

The combustor140in this embodiment is a dry low NOx combustor (like that which is shown inFIG. 6), which may be for an 80 megawatt turbine. The mixing holes of the arrangement9001in at least one of the three rows are sized (diameter) and positioned to impede airflow penetration of the fluid flow240into the fuel flow300and primary mixing zone200. In this arrangement9001, mixing hole diameter varies in the first row and third row (represented in the first column and third column respectively of the tables801and901). The mixing holes in the first row of both embodiments are positioned 20 degrees from each other around the liner, at a distance of between about 4.75 and 5.14 inches from the primary nozzle end150(as shown inFIG. 6). These mixing holes alternate between having a diameter of 0.784 inches and a diameter of 0.912 inches. The mixing holes in the second row (represented in the second column of the tables801and901) of both embodiments are positioned 20 degrees from each other around the liner, at a distance of 6.39 inches from the primary nozzle end15. These mixing holes have a diameter of 0.85 inches. The mixing holes in the third row of both embodiments are positioned 20 degrees from each other around the liner, at a distance of from 7.64 to 8.15 inches from the primary nozzle end150. These mixing holes alternate between having a diameter of 0.784 inches and a diameter of 0.912 inches.

Three rows, the overall decrease in diameter of the mixing holes in the arrangement9001, and the positioning of the mixing holes are all elements of the arrangement9001that may impede fluid flow240penetration, and result in the less heterogeneous mixture420shown inFIG. 12. Impeding the fluid flow240via this arrangement9001causes the fluid flow240in the second row to penetrate less than or equal to about 165% into the primary mixing zone200, with an exemplary range of between about 150% and 165%, fluid flow240from holes in the first and third rows of the diameter of 0.74 inches to penetrate less than or equal to about 155% into the primary mixing zone200, with an exemplary range of between about 140% and 155%, fluid flow240from holes in the first and third rows of the diameter of 0.912 inches to penetrate more than or equal to about 175% with an exemplary range of between about 175% and 185%. It should be appreciated that though these three rows each include the same number of mixing holes (twelve), each individual row may include more or less mixing holes. It should also be appreciated that the arrangement9001is intended to increase homogeneity, but may not be intended to maximize homogeneity of a fluid and fuel mixture. A mixture that is too homogeneous will decrease stability along with decreasing NOx emissions. The arrangement9001decreases emissions while maintaining a balance between emissions and stability. Striking this balance (i.e. to making a mixture too homogeneous) is one reason why only some of the plurality of mixing holes might be sized and positioned to impede fluid flow240penetration into the primary mixing zone200.

The mixing hole arrangement described above is also applicable to the embodiment incorporating expansion of fluid flow within the combustor described below. In this case, the mixing hole arrangement refers to the upstream portion of the liner shown inFIG. 25.

The combustor of a gas turbine according to an exemplary embodiment presented herein is designed in such a way so that the fluid flow within the combustor chamber is expanded before it passes the downstream end of the centerbody of the upstream portion of the combustor. This helps improve the emissions performance and stability of the combustor flames.

In a prior art combustor shown inFIG. 24, a combustor202defining a liner cavity232and including a venturi222and a centerbody242is illustrated. The centerbody242includes an upstream end302and a downstream end322. The venturi222defines a venturi throat282that is disposed radially outwardly of the centerbody242. The venturi throat282(as shown inFIG. 24) is disposed downstream of the downstream end322of the centerbody242, and an annular cavity352is disposed annularly outwardly about the centerbody242. From this annularly cavity352, an annular fluid flow342flows into and past a recirculation region212of the liner cavity232. Also flowing into the liner cavity232is a center fluid flow362, which flows from the centerbody242.

Because the venturi throat282is disposed downstream of the downstream end322, the annular fluid flow342is directed by the venturi throat282toward the center fluid flow362, after the annular fluid flow362has exited the annular cavity352. In this type of arrangement262, the annular fluid flow342impinges upon the center fluid flow362downstream of the downstream end322, creating a pinching382of the center flow362in a centerline recirculation region392of the liner cavity232. The pinching effect tends to destabilize combustor flames thereby making combustion dynamics or blow-out a greater probability. In addition (when the venturi throat282and the downstream end322are arranged in this manner), it is not until after the annular fluid flow362has passed both the downstream end322of the centerbody242and the venturi throat282that it may expand and create a lower pressure region402that will facilitate expansion of the center fluid flow362. This delays interaction of a flame (not illustrated) associated with the center fluid flow362and a flame (not illustrated) associated with the annular fluid flow342.

Referring now toFIG. 25, the venturi throat282and downstream end322of the centerbody242are illustrated in an exemplary embodiment of an arrangement422that improves expansion of the annular fluid flow342and center fluid flow362in the recirculation region212, thereby simultaneously improving both NOx reduction and flame stability. In this arrangement422, the venturi throat282is disposed less than 0.19 inches downstream of the downstream end322of the centerbody242. The venturi throat282may be disposed less than 0.19 inches downstream of the downstream end322of the centerbody242by moving or extending the centerbody242downstream, or moving the venturi throat282upstream within the venturi222. In an exemplary embodiment, such as that which is shown inFIG. 25, the venturi throat282is disposed 0.5 inches upstream of the downstream end322of the centerbody242. In another exemplary embodiment, the venturi throat282is disposed 0.31 inches upstream of the downstream end322of the centerbody242. The venturi throat282may also be disposed coplanar to (or in a same plane432with) the downstream end322of said centerbody242.

By disposing the venturi throat282upstream of the downstream end322of the centerbody242in these exemplary embodiments, the annular fluid flow342is directed by the venturi throat282toward the centerbody242, with the directing occurring upstream of the downstream end322of the centerbody242. By positioning the venturi throat282in this manner, the annular fluid flow342will begin to expand before moving downstream of the downstream end322of the centerbody242. Since the annular fluid flow342is already expanding as it passes the downstream end322of the centerbody242, it does not restrict the expansion of the center fluid flow362but creates a lower pressure region462to which the center fluid flow362will be exposed upon entry to the liner cavity232. This lower pressure region462facilitates expansion of the center fluid flow362with the annular fluid flow342.

Earlier expansion of the center fluid flow362(in terms of fluid flow direction, and as compared with a component arrangement ofFIG. 24) enhances center fluid flow362recirculation in the recirculation region212, which allows a faster interaction between the flame (not illustrated) associated with the center fluid flow362and the flame (not illustrated) associated with the annular fluid flow342. This faster interaction reduces cold streaks in the combustor202, and improves NOx emissions performance by decreasing CO emissions at a given NOx level, thereby facilitating the combustor202to run at a leaner fuel-air mixture and thus produce less NOx emissions. Earlier expansion also eliminates pinching382(seeFIG. 24), which increases the centerline circulation region392size, and improves the stability of combustor202. It should be appreciated that in an exemplary embodiment, the combustor202is a dry low NOx combustor, which utilizes fuel-lean mixtures and does not use diluents (e.g., water injection) to reduce flame temperature.

In the combustor of the exemplary embodiment presented herein, the amount of undesirable NOx pollutants can be decreased by supplying dilution air in the transition piece of the combustor. This helps reduce the temperature of the reactants in the combustor.

In one prior transition piece, two dilution holes are located adjacent the outlet of the transition piece, close to the first stage nozzle. In commonly owned Publication No. US 2005/0204741 A1, there is provided a transition piece dilution air management system which promotes dilution mixing and emissions reduction. Particularly, the dilution air management system provides dilution air jets in the transition piece at predetermined axial and circumferential locations to optimize reductions in emissions consistent with efficient use of compressor discharge air. However, undesirable emissions remain a problem notwithstanding the various prior proposals.

With further reference toFIGS. 26-28, the exemplary embodiment presented herein relates to a unique arrangement of dilution holes in the transition piece163, the number, size and location of which promote dilution air mixing, allow for longer combustion residence time, (thus also enabling a more stable formation of combustion flame zones), improve flame stability and facilitate complete burning of hydrocarbons. The transition piece163is essentially a duct body or enclosure having a forward end263(towards the outlet end of the combustor chamber) and an aft end283(towards the first stage turbine nozzle), with the cross-sectional shape of the duct body varying from a substantially cylindrical shape at the forward end to a curved rectangular shape at the aft end.

In an exemplary embodiment, plural dilution holes323(three are shown inFIG. 27by way of example only) are formed in the transition piece163, located precisely along and about the duct body, as measured in inches along X, Y and Z coordinates, from an origin or zero reference point, at the center303of the transition piece (or duct body) exit plane. The X coordinate extends from the origin303in an upstream direction, i.e., in a direction opposite the flow through the transition piece. In this exemplary embodiment, the transition piece is about twenty inches in length. Twenty eight (28) dilution hole locations have been identified as viable locations for realizing emissions reductions. The X, Y, Z coordinates of the twenty eight dilution hole locations are set out in Table I below.

The number of dilution holes provided in the transition piece or duct body163may vary between five (5) and seventeen (17), with eleven (11) being the optimum number in the exemplary embodiment. The holes323lie along the transition piece or duct body in an envelope within one inch in any direction along the surface of the transition piece from the locations of the holes determined by the X, Y and Z coordinates. In this regard, any combination of the twenty eight hole location sites listed in Table I may be selected for the 5-17 dilution holes. The dilution hole diameter may be in the range of from 0.3 to 1.75 in. and the combined open surface area of the dilution holes should be in the range of from 2 to 7.5 sq. inches. The dilution holes323may have uniform or different diameters within the specified range.

The dilution hole arrangement as described allows for longer combustion residence time (due to lower temperatures) and hence additional CO burnout. This also enables more stable formation of the combustion flame zone, and improves flame stability instead of quenching the combustion process prior to complete burning of hydrocarbons. The end result is a reduction in harmful emissions and improved liner durability.

According to an exemplary embodiment, combustor emissions are reduced and flame stability is increased by providing improved air/fuel mixing and additional airflow to other components/systems of the turbomachine.

Referring toFIG. 29, a turbomachine combustor assembly constructed in accordance with exemplary embodiments of the invention is indicated generally at244. The combustor assembly244includes an outer casing44having a first end portion64that extends to a second end portion74through an intermediate portion84that collectively define an interior portion94. Combustor assembly44is also shown to include an end cover assembly124arranged at first end portion64of outer casing44. End cover assembly124is shown to include a primary nozzle144and a secondary nozzle154. Fuel is introduced through the end cover assembly124, mixed with air and ignited to form high temperature/high pressure gases that are utilized to drive a turbine (not shown). Towards that end, combustor assembly244includes a flow sleeve204that extends within interior portion94and houses a liner assembly234.

As shown, liner assembly234includes a head end section264that extends to a venturi section284to an end liner portion304. The end liner portion304is coupled to a transition piece344via a hula seal assembly374. A cap assembly404extends from end cover assembly124, through head end section264toward venturi section284. Fuel and air are introduced into cap assembly404and head end section264, mixed and delivered into venturi section284where the fuel/air mixture is ignited to form high temperature/high pressure gases that pass to end liner portion304, through transition piece344and toward a first stage of a turbine (not shown).

As best shown inFIGS. 30,31, cap assembly404includes a centerbody544and a cap554. Cap assembly404is mounted to head end section264and protects secondary nozzle assembly154. As will be discussed more fully below, cap assembly404also shrouds cooling air necessary for cooling centerbody544. As shown, centerbody544includes a wall574having an outer surface584that extends from a first end594to a second end604through an intermediate portion614defining an internal passage654. In the exemplary embodiment shown, internal passage654has a diameter of about 3 inches (7.62 cm). However, it should be understood that the diameter of internal passage654can vary in accordance with exemplary embodiments of the invention. An inner swirler or turbulator684is arranged within internal passage654near second end604. Inner turbulator684imparts a swirling effect to the fuel/air mixture to enhance mixing.

In further accordance with the exemplary embodiment shown, cap assembly404includes an external turbulator member754that encapsulates centerbody544extending along wall574from first end594towards second end604. More specifically, external turbulator member754is mounted to, yet spaced from, cap assembly404so as to define a gap or passage784having a width “w”. Cooling air-passes along passage784before exiting cap554. External turbulator member754includes a first end section814extending to a second end section824through an intermediate section834. A step884having a height “s” is arranged at second end section824. That is, step884defines a radial distance “s” between second end section824and intermediate section834. In any event, in accordance with one exemplary aspect of the invention, width “w” and radial distance “s” are sized so that external turbulator754includes a step-to-gap ratio (“s”/“w”) in a range of about 0.8 to about 1.2. Of course, it should be understood that the particular step-gap-ratio range can vary depending on turbomachine size and/or rating. In accordance with another exemplary aspect of the invention, width “w” and radial distance “s” are sized so that external turbulator754includes a step-to-gap ratio in a range of about 0.9 to about 1.1. In accordance with yet another exemplary aspect of the invention, width “w” and radial distance “s” are sized so that external turbulator754includes a has a step-to-gap ratio of about 1.0.

In addition, external turbulator member754includes a plurality of cooling ribs964that extend circumferentially about centerbody544, and a turbulator portion994arranged at second end section834. Cooling ribs964enhance heat transfer from external turbulator member754. Moreover, the step-to-gap ratio, in accordance with the exemplary embodiments of the invention, reduces an amount of cooling airflow required. More specifically, the step enhances external mixing of a fuel air mixture passing over an external surface of the external turbulator while the gap reduces cooling air flow passing over the centerbody. That is by sizing the step-to-gap ratio for a particular desired flow rate, turbomachine emissions are reduced and flame stability is increased. The combined reduction in emissions and increased flame stability enhances combustion efficiency, which results in overall efficiency improvements of the turbomachine. By reducing the amount of cooling air/fuel passing over centerbody544by decreasing gap784and providing improved air/fuel mixing by increasing step864and/or884, additional airflow is available for other components/systems in the turbomachine. This additional airflow enhances operational efficiencies for the turbomachine.