Reverse-flow annular combustor for reduced emissions

A combustor for a gas turbine engine is provided. The combustor includes an inner liner; an outer liner circumscribing the inner liner; and a combustor dome having a first edge coupled to the inner liner and a second edge coupled to the outer liner. The combustor dome forms a combustion chamber with the inner liner and the outer liner. The combustion chamber receives air flow through the inner and outer liners, and the combustor dome is configured to bifurcate the air flow at the combustor dome into a first stream directed to the inner liner and a second stream directed to the outer liner.

TECHNICAL FIELD

The present invention generally relates to gas turbine engines, and more particularly relates to rich burn, quick quench, lean burn (RQL) reverse-flow annular combustors for gas turbine engines that provide reduced emissions.

BACKGROUND

A gas turbine engine may be used to power aircraft or various other types of vehicles and systems. Such engines typically include a compressor that receives and compresses incoming gas such as air; a combustor in which the compressed gas is mixed with fuel and burned to produce high-pressure, high-velocity exhaust gas; and one or more turbines that extract energy from the exhaust gas exiting the combustor.

There is an increasing desire to reduce gaseous pollutant emissions, particularly oxides of nitrogen (NOx), that form during the combustion process. One approach to reduce NOx emissions is the implementation of a rich burn, quick quench, lean burn (RQL) combustion concept. A combustor configured for RQL combustion includes three serially arranged combustion zones: a rich burn zone at the forward end of the combustor, a quench zone downstream of the rich burn zone, and a lean burn zone downstream of the quench zone. By precisely controlling the stoichiometry between the air and fuel in each of these zones, NOx emissions can be minimized. In addition to reducing emissions, combustor designers further attempt to manage the temperature characteristics of the combustion process, which is particularly difficult in an RQL combustor. High temperatures may cause thermal stresses and other problems. While increased cooling flows may improve cooling, such additional air flow may interfere with the stoichiometries of the RQL combustion process.

Accordingly, it is desirable to provide improved RQL combustors in gas turbine engines with improved NOx emission and temperature characteristics. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.

BRIEF SUMMARY

In accordance with an exemplary embodiment, a combustor for a gas turbine engine is provided. The combustor includes an inner liner; an outer liner circumscribing the inner liner; and a combustor dome having a first edge coupled to the inner liner and a second edge coupled to the outer liner. The combustor dome forms a combustion chamber with the inner liner and the outer liner. The combustion chamber receives air flow through the inner and outer liners, and the combustor dome is configured to bifurcate the air flow at the combustor dome into a first stream directed to the inner liner and a second stream directed to the outer liner.

In accordance with another exemplary embodiment, a combustor for a gas turbine engine with an engine centerline is provided. The combustor includes an inner liner; an outer liner circumscribing the inner liner; and a combustor dome having a first edge coupled to the inner liner and a second edge coupled to the outer liner. The combustor dome forms a combustion chamber with the inner liner and the outer liner, and the combustion chamber defines a rich burn zone, a quench zone, and a lean burn zone to support combustion of air flow through to inner liner and the outer liner. The combustor further includes a first row of air admission holes in the inner liner configured to admit a first set of quench jets into the quench zone; a second row of air admission holes in the outer liner configured to admit a second set of quench jets into the quench zone, the first row of air admission holes being circumferentially offset relative to the second row of air admission holes; a third row of air admission holes in the inner liner configured to admit a first set of dilution jets into the dilution zone; and a fourth row of air admission holes in the outer liner configured to admit a second set of dilution jets into the dilution zone. A fuel injector is coupled to the outer liner and configured to inject a stream of fuel into the combustion chamber in a tangential direction relative to the engine centerline.

DETAILED DESCRIPTION

Broadly, the exemplary embodiments discussed herein provide a gas turbine engine with a rich burn, quick quench, lean burn (RQL) combustor having improved NOx emissions and temperature characteristics. Particularly, in one exemplary embodiment, the combustor includes a combustor dome configured to bifurcate the combustion gases into a first combustion stream towards the inner liner and a second combustion stream toward the outer liner. The combustor may further include a fuel injector that injects a substantially tangential stream of fuel into the combustion chamber; quench air admission holes that admit a set of interleaved, over-penetrating quench jets; and a row of dilution air admission holes that admit a set of dilution jets. Embodiments discussed herein may find beneficial use in many industries and applications, including aerospace, automotive, and electricity generation.

FIG. 1is a cross-sectional view of an engine100in accordance with an exemplary embodiment. In one embodiment, the engine100is a multi-spool gas turbine main propulsion engine. The engine100includes an intake section110, a compressor section120, a combustion section130, a turbine section140, and an exhaust section150.

The intake section110receives air drawn into the engine100and directs the air into the compressor section120. The compressor section120may include one or more compressors that raise the pressure of the air, and directs the compressed air into the combustion section130. In the depicted embodiment, a two-stage compressor is shown, although it will be appreciated that one or more additional compressors could be used.

The combustion section130, which is discussed in greater detail below, includes a combustor160that mixes the compressed air with fuel and ignites the resulting mixture to generate high energy combustion gases that are then directed into the turbine section140. In one embodiment, the combustor160is implemented as a reverse flow combustor unit, although other embodiments may include a different type of combustor. The turbine section140includes one or more turbines in which the combustion gases from the combustion section130expand and rotate the turbines. The combustion gases are then exhausted through the exhaust section150.

FIG. 2is a more detailed cross-sectional view of a portion of the engine100ofFIG. 1, and particularly illustrates the combustion section130ofFIG. 1. InFIG. 2, only half the cross-sectional view is shown; the other half being substantially rotationally symmetric about a centerline and axis of rotation200. In certain embodiments, the combustor160may be an annular rich burn, quick quench, lean burn (RQL) reverse-flow gas turbine engine combustor, as will now be described in more detail. In other embodiments, the combustor160may be another type of combustor.

The combustor160includes a radially inner case202and a radially outer case204concentrically arranged with respect to the inner case202. The inner and outer cases202and204circumscribe the centerline200to define an annular pressure vessel206. The combustor160is arranged within the annular pressure vessel206. Particularly, the combustor160includes an inner liner210and an outer liner212circumscribing the inner liner210. The liners210and212and cases202and204define respective inner and outer air plenums216and218.

As described in further detail below, the combustor160further includes a combustor dome220respectively coupled to inner and outer liners210and212at a first (or inner) edge224and a second (or outer) edge226. The inner liner210, the outer liner212, and the combustor dome220cooperate to form a combustion chamber214therebetween. The combustor160further includes a series of fuel injectors230(one of which is shown) coupled to the outer liner212; quench air admission holes240and250respectively formed in the inner and outer liners210and212; and dilution air admission holes260and270also respectively formed in the inner and outer liners210and212. As noted above, the combustor160is an RQL combustor, and the various components of the combustor160cooperate to reduce NOx emissions.

During operation, a portion of the pressurized air from the compressor section120(FIG. 1) enters a rich burn zone RB of the combustion chamber214in the inner and outer liners210and212. The pressurized air entering the rich burn zone RB is schematically shown inFIG. 2as air flow282and286. As described in further detail below, the fuel injectors230are arranged to supply fuel to the rich burn zone RB in a compound angular direction, which includes a radially inward direction toward the centerline200, an axial direction toward the combustor dome220, and a tangential direction about the circumference of the combustion chamber214to result in improved mixing of the fuel with the primary air jets282and286. The air flow282and286intermixes with a stoichiometrically excessive quantity of fuel introduced through the fuel injectors230to support initial combustion in the rich burn zone RB. Although not shown, primary air admission holes and corresponding primary air jets may be provided.

FIG. 2illustrates the main path of the combustion gases290flowing through the combustion chamber214. The rich stoichiometry of the fuel-air mixture in the rich burn zone RB produces a relatively cool, oxygen-deprived flame, thus preventing excessive NOx formation and guarding against blowout of the combustion flame during any abrupt reduction in engine power.

As described in more detail below, the combustor dome230includes a number of effusion holes222to permit compressed air to pass therethrough as a cooling flow on the interior surface of the combustor dome220. In particular, the effusion holes222allow a buffering layer of cooling air to pass from the exterior surface to the interior surface of the combustor dome220, and then in a generally downstream direction with the hot combustion gases290. This layer of cooling air reduces the direct contact of the hot combustion gases290with interior surface of the combustor dome220as well as convectively cools the wall of the combustor dome220as the air passes through the effusion holes222. The durability of the combustor dome220may be extended by a reduction in temperature gradients along the surface.

As described in further detail below, the cooling air from the effusion holes222also functions to bifurcate combustor flow in the vicinity of the combustor dome220into an inner combustion stream292and an outer combustion stream294. The combustor streams292and294are generally air flow, although fuel and/or combustion products (e.g., a portion of the combustion gases290) may be included in the air flow streams292and294. Generally, the inner combustor stream292flows towards the inner liner210(e.g., toward the engine centerline200), and the outer combustion stream294flows towards the outer liner212(e.g., away from the engine centerline200). Particularly, the arrangement of the effusion holes222may be used to influence the size and direction of the combustion streams292and294, and thus, the combustion characteristics as desired. As an example, control of the cooling flows and the combustion streams292and294enable a more even and predictable combustion process. As shown, the split between the inner combustion stream292and the outer combustion stream294may be about even, e.g., 50% to 50%. However, in other embodiments, the split between the inner combustion stream292and the outer combustion stream294may be uneven, such as 60% to 40% or 70% to 30% in favor of either of the inner combustion stream292or the outer combustion stream294. The effusion cooling produced by the effusion holes222becomes entrained with the inner and outer combustor streams292and294in the designated proportion such that the cooling air interaction with the combustion process in the rich-burn zone RB is minimized. As such, the combustor streams292and294may subsequently function as a coolant or an oxidizer in the combustion process.

The combustion gases290from the rich burn zone RB, which include unburned fuel, enter a quench zone Q. Quench jets242and252flow from the plenums216and218and into the quench zone Q through the quench air admission holes240and250in the inner and outer liners210and212, respectively. The quench jets242and252are referred to as quench air because they rapidly mix the combustion gases290from a stoichiometrically rich state at the forward edge of the quench zone Q to a stoichiometrically lean state at, or just downstream of, the aft edge of the quench zone Q. This supports further combustion and releases additional energy from the fuel. Since thermal NOx formation is a strong time-at-temperature phenomenon, it is important that the fuel-rich mixture passing through the quench zone Q be mixed rapidly and thoroughly to a fuel-lean state in order to avoid excessive NOx generation. Thus, the design of the quench air jet arrangement in an RQL combustor is important to the successful reduction of NOx levels. As described below, the quench air admission holes240and250are arranged to produce interleaved and over-penetrating quench jets242and252for rapid mixing within the quench zone Q.

Finally, the combustion products from the quench zone Q enter a lean burn zone LB where the combustion process concludes. As the combustion gases290flow into the lean burn zone LB, the quench jets242and252are swept downstream and also continue to penetrate radially and spread out laterally to intermix thoroughly with the combustion gases290. Additionally, dilution jets262and272flow from the plenums216and218through dilution air admission holes260and270respectively formed in the inner and outer liners210and212to result in a stoichiometrically lean quantity of fuel in the lean burn zone LB. The dilution air admission holes260and270additionally function to provide a desired temperature distribution and to complete the combustion process such that smoke and NOx emissions are reduced. In other exemplary embodiments, the dilution air admission holes260and270may be omitted. From the lean burn zone LB, the combustion gases290flow into the transition liner234, which diverts the combustion gases290into the turbine section140.

FIG. 3is a partial isometric view of a combustor dome220of the combustor160ofFIG. 2in accordance with an exemplary embodiment. Characteristics of the combustor dome220(and the combustor160ofFIG. 2) can be considered in three dimensions, as indicted by the legend300and discussed further inFIGS. 4-9. A radial direction302extends between the first edge224and the second edge226, generally perpendicular to the engine centerline200. As an example, the bifurcated combustion streams292and294are depicted in the radial direction, particularly radially inward and outward within the annular configuration of the combustor dome220. An axial direction304extends outwardly from the surface of the transition liner210, generally parallel to the engine centerline200. A tangential direction306extends around the surface of the combustion dome220and around the engine centerline200. In this context, “tangential” refers to a vector flowing around the annular combustor dome220or the combustor160(FIG. 2).

FIG. 4is a cross-sectional view of the combustor160ofFIG. 2through line4-4. Particularly,FIG. 4illustrates the fuel injectors230mounted on the outer liner212in the radial-tangential plane. The fuel injectors230may be equally angularly spaced about the annular combustion chamber214(FIG. 2). As noted above, the fuel injectors230may inject a portion of the fuel232at a compound angle, e.g., inFIG. 2, the fuel injectors230inject the fuel232in a radially inward direction toward the centerline200and in an axial direction toward the combustor dome220. As further shown inFIG. 4, the fuel injectors230inject the fuel in tangential direction within the annular combustion chamber214. The tangential component of the fuel232may promote blending and burn uniformity within rich burn zone RB of the combustion chamber214(FIG. 2), which may enhance the cooling characteristics of the liners210and212and combustor dome220, the NOx emissions characteristics, and the temperature distributions of the combustion gases290entering the turbine section140(FIG. 1). The fuel injectors230may be pressure-swirl or air blast injectors (or a combination thereof) and provided with airflow as necessary or desired to control smoke or other combustor characteristics. Although two fuel injectors230are shown inFIG. 3, any number may be provided.

FIG. 5is a cross-sectional view of the combustor160ofFIG. 2through line5-5in accordance with a first exemplary embodiment. As noted above, the combustor dome220is configured as ring with a concave inner surface that faces the combustion chamber214(FIG. 2).FIG. 5particularly illustrates a plan view of the combustor dome220in the radial-tangential plane and more clearly shows the effusion holes222that permit compressed air to pass through to the interior surface of the combustor dome220. As discussed above, the effusion holes222are generally relatively small, closely spaced holes serving to direct a flow of cooling air onto the walls of combustor dome220. The effusion holes222are generally 0.01 to 0.04 inches in diameter, although the diameter may vary with application and may depend on factors such as the dimensions of the combustor dome220, the temperature of the combustion gases290(FIG. 2), and the velocity of the cooling flow. Individual hole shape is generally cylindrical or oval, with minor deviations due to manufacturing method, e.g., edge rounding, tapers, out-of-round, oblong, or the like. In other embodiments, the effusion holes may be non-cylindrical. For some applications, the effusion holes222may be uniformly spaced. Alternatively, the effusion holes222may be unevenly spaced to provide more tailored cooling flows.

As introduced above, the effusion holes222may be patterned to improve combustion characteristics, particularly the bifurcated combustion streams292and294(FIG. 2). In the embodiment ofFIG. 4, the effusion holes222are generally arranged in groups402,404, and406. A first group402of effusion holes222is adjacent the first edge224of the combustor dome220and the effusion holes222of the first group402have an orientation that is approximately completely radial. In other words, the first group402includes effusion holes222with angles of approximately 0° relative to a radial direction and can direct cooling air toward the inner edge224, as indicated by arrow412. As such, the arrow412corresponds to the direction of the cooling air from the first group402of effusion holes222and further corresponds to the inner combustion stream292ofFIG. 2, which is encouraged in the depicted direction by the cooling air flowing through the first group402of effusion holes222.

A second group406is adjacent the second edge226of the combustor dome220, and the effusion holes222of the second group406have an orientation that is approximately completely radial. In other words, the second group406includes effusion holes222with angles of approximately 0° relative to a radial direction and can direct cooling air toward the outer edge226, as indicated by arrow416. As such, the arrow416corresponds to the direction of the cooling air from the second group406of effusion holes222and further corresponds to the outer combustion stream294ofFIG. 2, which is encouraged in the depicted direction by the cooling air flowing through the second group406of effusion holes222. In some embodiments, the effusion holes222in groups402and406may not be completely radial. As an example, the effusion holes222in groups402and406may be between about 0° to 45° in the radial direction, such that the bifurcated streams292and294develop appropriately, as discussed above.

A transition (or third) group404of effusion holes222is arranged radially between the first group402and the second group406. The effusion holes222of the third group404have orientations that function to transition cooling air (and combustion gases) into the radial directions of the first and second groups402and406, as indicated by the arrows414. In some embodiments, the third group204of effusion holes222may have a tangential component to even out the temperature distribution along the circumference of the combustion chamber214(FIG. 2) and/or to increase residence time on the combustor dome220. In other embodiments, the third group204of effusion holes222may be omitted.

In general and additionally referring toFIG. 2, the first, second, and third groups402,404, and406may have any number of rows and densities that achieve the desired bifurcation of the combustion streams292and294. For example, if the combustion streams292and294are to be equal in flow rate, volume and/or velocity, the first and second groups402and406may have an equal number of effusion holes222, whereas a greater number of effusion holes222in the one of the groups402or406may lead to a larger combustion stream292or294. As such, the cooling air from the effusion holes222tends to encourage the combustion streams292and294in the desired direction while cooling the combustor dome220and minimizing interaction with the combustion process. As such, the combustion streams292and294may have an equal flow split at the radial midline of the combustor dome220. However, the combustion streams292and294may have different predetermined ratios at positions other than the radial midline. For example, the combustion streams292and294may have a flow rate split of 75/25.

FIG. 5depicts a first embodiment of the combustor dome220that functions to bifurcate the combustion streams292and294(FIG. 2) with the arrangement of the effusion holes222, although any mechanism for accomplishing this function may be provided. In general, any combination of structure that results in appropriate amount of air flow, direction of air flow, and gradients may be provided to bifurcate the combustion streams292and294. As another example,FIG. 6is a partial cross-sectional view of the combustor160ofFIG. 2through line5-5in accordance with an alternate exemplary embodiment. In the embodiment ofFIG. 6, the combustor dome220is provided with four groups502,504,506, and508of effusion holes222. The first group502of effusion holes222is adjacent the first edge224and includes effusion holes222generally arranged in a circumferential or tangential row. Similarly, the second group508of effusion holes222is adjacent the second edge226and includes effusion holes222generally arranged in a circumferential or tangential row.

The third and fourth groups504and506are each arranged in radial rows, and each of the rows is associated with a louver (or baffle)514and516. The louvers514and516are mounted or otherwise formed on the combustor dome220and extend into the combustion chamber214(FIG. 2) in an axial direction. The arrangement of the third group504and associated louvers514are circumferentially offset or clocked relative to the arrangement of the fourth group506and associated louvers516in an alternating pattern.

The louvers514and516may extend to any desired length, such as about 50% or 60% of the radial span of the combustor dome220, and in one exemplary embodiment, are about the same length as the respective groups504and506of effusion holes222. The length and arrangement of the louvers514and516influence the direction of the cooling flow from the effusion holes222. Particularly, the arrangement of the third groups504and louvers514tend to direct cooling air in a radial direction toward the first edge224, as indicated by the arrows524, and the arrangement of the fourth groups506and louvers516tend to direct cooling air in a radial direction toward the second edge226, as indicated by the arrows526. The cooling air flows524and526resulting from arrangement of the third and fourth groups504and506, as well as the associated louvers514and516, function to bifurcate the combustion streams292and294(FIG. 2), as described above. Given the equal spacing of the louvers514and516and the third and fourth groups504and506, the cooling air flows524and526(and thus the combustion streams292and294ofFIG. 2) are generally equal, although any other proportion may be provided.

The louvers514and516may be a single radial leg, as shown, or in other embodiments may be U-shaped opening in the direction of the intended direction of air flow. Generally, the number, geometry, and arrangement of the louvers514and516may be optimized to increase the effectiveness of the bifrucation and/or cooling of the combustor dome220. The arrangement of louvers514and516particularly reduces the amount of cross-flow and/or flow in a circumferential direction that may reduce cooling and bifrucaton efficiency. Generally, the dimensions of the louvers514and516may vary depending on the dimensions of the combustor dome220, the cooling requirements, the desired bifucation characteristics, and manufacturing or maintenance limitations.

In the depicted embodiment, the effusion holes222ofFIG. 5are oriented to direct the cooling air at an angle perpendicular to the surface of the combustor dome220. However, in other embodiments, the direction of the effusion holes222ofFIG. 6may be oriented to direct cooling air in any desired direction, such as discussed above in reference toFIG. 5.

FIGS. 7-9illustrate further details about the quench zone Q of the combustor160and are collectively discussed below.FIG. 7is a partial plan view of an inner surface of the outer liner212of the combustor160ofFIG. 2.FIG. 7schematically shows the position of the fuel injectors230and the quench air admission holes250. In the embodiment ofFIG. 7, the quench air admission holes250include a first tangential or circumferential row254of quench air admission holes250and a second tangential or circumferential row256of quench air admission holes250that are downstream of the first row254. As shown, the quench air admission holes250of the first row254may be relatively larger than the quench air admission holes250of the second row256.

FIG. 8is a partial plan view of an inner surface of the inner liner210of the combustor160ofFIG. 2and schematically shows the position of the quench air admission holes240. In the embodiment ofFIG. 8, the quench air admission holes240include a first tangential or circumferential row244of quench air admission holes240and a second tangential or circumferential row246of quench air admission holes240that are downstream of the first row244. As shown, the quench air admission holes240of the first row244may be relatively larger than the quench air admission holes240of the second row246.

FIG. 9is a cross-sectional view of the combustor160ofFIG. 2through line8-8.FIG. 9particularly shows the quench air admission holes240and250discussed above inFIGS. 7 and 8.FIG. 9further schematically displays the quench jets242and252that respectively flow through the quench air admission holes240and250. In general, the quench jets242flowing through the first row244of quench air admission holes240are circumferentially or tangentially offset relative to the quench jets252flowing through the first row254of quench air admission holes250, and the quench jets242flowing through the second row246are circumferential or tangentially offset with respect to the quench jets252flowing through the second row256. For example, the quench jets252are tangentially adjacent to the quench jets242, and not directly opposite one another. At least some of the quench jets242and252, particularly the quench jets242and252from the major holes of the first rows244and254, may radially penetrate the combustion chamber214more than 50% of the radial depth.

As also shown inFIG. 9, the sizes of the quench jets242and252may be axially aligned or offset with opposing quench jets242and252with respect to both position and size. For example, the quench jets252from the first row254of quench air admission holes250are generally axially aligned with the quench jets242from the second row246of quench air admission holes240. As another example, the two quench jets252from the second row256of quench air admission holes250are centered around each quench jets242from the first row244of quench air admission holes240. As such, in the depicted embodiments, the quench air admission holes240and250may be circumferentially offset between the inner and outer liners210and212and staggered between relatively larger holes and relatively smaller holes. Accordingly, the quench air admission holes240and250produce quench jets242and252in an interleaved and over-penetrating pattern to ensure rapid mixing in the quench zone Q. In other embodiments, the quench air admission holes240and250may be have any suitable sizes and patterns.

This arrangement may result in a more even temperature profile and reduce NOx emissions by providing more desirable stoichiometric conditions. Particularly, this configuration ensures that dilution air spans radially across the entire combustion chamber annulus and that the combustion gases are properly quenched. At least some of the quench air admission holes240and250are “plunged.” In other words, a rim portion of the quench air admission holes240and250extends into the combustion chamber214. The plunged characteristics of the quench air admission holes240and250assist in the quench jets242and252in penetrating to the desired depth, as discussed above. Moreover, in one exemplary embodiment, the outer and inner liners210and212have effusion holes (not shown) that provide a cooling layer of air on the combustor side of the combustion chamber214. In some exemplary embodiments, the plunged quench air admission holes240and250decrease or eliminate any interference with the effusion cooling layer. The quench air admission holes240and250are formed from a single piece, either punched or molded into the liner210and212, or as an insert. Although the air admission holes240and250are depicted as plunged air admission holes240and250, in other embodiments, the air admission holes are not plunged.

Accordingly, exemplary embodiments discussed herein provide improved NOx emission and temperature characteristics by maintaining a desired stoichiometry in the RQL combustor160. This further functions to even out temperature distributions and increase cooling effectiveness, thus resulting in increased durability and operational efficiency. Exemplary embodiments may find beneficial use in many industries, including aerospace, automotive, and plant operations, and in many applications, including electricity generation, naval propulsion, pumping sets for gas and oil transmission, aircraft propulsion, automobile engines, and stationary power plants.