COMBUSTION SYSTEM FOR A GAS TURBINE ENGINE

Abstract

A combustor for a gas turbine engine includes a pilot fuel injector and a plurality of circumferentially located main injectors for injecting fuel and air into a combustion chamber defined by a liner wall of a combustor basket. A combustion zone is located in the combustion chamber where the fuel and air are ignited to produce hot combustion gases. A plurality of vortex generators are located in circumferentially spaced relation on the liner wall and comprise structures extending radially inward into the combustion chamber to create vortices at predetermined circumferential locations downstream from where the fuel and air are ignited to effect a reduction in emissions of the combustion gases.

Description

FIELD OF THE INVENTION

The present invention relates to gas turbine engines and, more particularly, to a combustion system for a gas turbine engine in which the combustion system is configured to produce reduced emissions.

BACKGROUND OF THE INVENTION

Combustion turbines, such as gas turbine engines, generally comprise a compressor section, a combustor section, a turbine section and an exhaust section. In operation, the compressor section can induct and compress ambient air. The combustor section generally may include a plurality of combustors for receiving the compressed air and mixing it with fuel to form a fuel/air mixture. The fuel/air mixture is combusted by each of the combustors to form a hot working gas that may be routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanding gas exiting the turbine section can be exhausted from the engine via the exhaust section.

The combustion process typically produces pollutants of various types and, of particular interest from the standpoint of maintaining a minimum level of pollutants, is production of nitrogen oxides (NOx) and carbon monoxide (CO). For example, elevated levels of NOx can result from elevated combustion temperatures and/or an extended residence time of the combustion products in the combustor, and elevated levels of CO can result from reduced combustion temperatures and/or insufficient residence time in the combustor. During part or low load operation of a gas turbine engine, the production of CO and/or NOx emissions can become more significant.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a combustor for a gas turbine engine is provided and includes a pilot fuel injector and a plurality of circumferentially located main injectors for injecting fuel and air into a combustion chamber defined by a liner wall of a combustor basket. A combustion zone is located in the combustion chamber where the fuel and air are ignited to produce hot combustion gases. A plurality of vortex generators are located in circumferentially spaced relation on the liner wall and comprise structures extending radially inward into the combustion chamber to create vortices at predetermined circumferential locations downstream from where the fuel and air are ignited to effect a reduction in emissions of the combustion gases.

The vortex generators may be located on the combustion chamber to mix cooler and hotter portions of the combustion gases to effect the reduction in emissions of the combustion gases.

The predetermined circumferential locations of the vortex generators may correspond to an axial location downstream of formation of a stabilized flame in the combustion chamber.

The predetermined circumferential locations of the vortex generators may be axially aligned with an area of fuel and air combustion in the combustion chamber.

The combustor may include a plurality of through holes formed in the liner wall and resonator structures located over at least some of the through holes on a radially outward facing side of the liner wall, and the vortex generators may be located over at least some of the through holes at substantially the same axial location as the resonator structures. Additionally, the vortex generators may include surfaces having apertures for passage of cooling air out of the vortex generator into the combustion chamber.

The main injectors may be are equally spaced from each other in a circular pattern upstream from the combustion zone, and the vortex generators may be generally equally spaced in a circular pattern at an axial location of the combustion zone.

The vortex generators may comprise tetrahedral shaped protrusions extending from the liner wall. Additionally, the vortex generators may include two triangular shaped side walls converging in a downstream direction, and a ramp surface extending between converging edges of the side walls. The ramp surface may angle radially inward in the downstream direction.

In accordance with another aspect of the invention, a method is provided for reducing emissions in a combustor having a pilot fuel injector and a plurality of circumferentially located main injectors for injecting fuel and air into a combustion chamber defined by a liner wall of a combustor basket. The method comprises igniting the fuel and air in a combustion zone located in the combustion chamber to produce hot combustion gases; and creating vortices at predetermined circumferential locations downstream from where the fuel and air are ignited by providing a plurality of vortex generators comprising structures extending radially inward into the combustion chamber and located in circumferential locations downstream from where the fuel and air are ignited to effect a reduction in emissions of the combustion gases.

The vortex generators may comprise hollow structures having an interior area and cooling air may be provided to the interior area of the vortex generators.

The vortex generators may comprise resonators providing acoustic damping.

The vortex generators may mix cooler and hotter portions of the combustion gases to effect the reduction in emissions of the combustion gases.

The predetermined circumferential locations of the vortex generators may be axially aligned with an area of fuel and air combustion in the combustion chamber.

The main injectors may be equally spaced from each other in a circular pattern upstream from the combustion zone, and the vortex generators may be generally equally spaced in a circular pattern at an axial location of the combustion zone.

The vortex generators may comprise tetrahedral shaped protrusions extending from the liner wall.

The vortex generators may include two triangular shaped side walls converging in a downstream direction, and a ramp surface may extend between converging edges of the side walls.

The ramp surface may angle radially inward in the downstream direction.

The vortices may mix the combustion gases to effect a reduction in the flame length downstream of the vortex generators.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 is a partial cross-sectional view of a gas turbine engine incorporating a combustor configured in accordance with aspects of the present invention;

FIG. 2 is a perspective view of selected planes in a combustor, illustrating a thermal analysis at the selected planes;

FIG. 3 is a cross-sectional view of a combustor incorporating aspects of the invention;

FIG. 4 is a perspective view of a vortex generator in accordance with aspects of the invention;

FIG. 5 is a perspective view of a portion of an outer side of a combustor liner wall illustrating aspects of the invention; and

FIG. 6 is a cross-sectional view illustrating an alternative configuration for the vortex generator.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

In accordance with an aspect of the invention, a configuration for a combustor in a gas turbine engine is provided that reduces low temperature areas of a combustion zone with a resulting reduction in carbon monoxide (CO) and/or NOx in the working gas provided to a turbine section of the engine. In particular embodiments, mixing structure is provided for inducing increased mixing of gases at specific predetermined locations within a combustion chamber of the combustor to maintain combustion zone regions associated with the predetermined locations at an elevated temperature sufficient to minimize CO and/or NOx formation. In particular, the mixing structure is provided for implementing a method of minimizing CO and/or NOx formation in a part load operation of the engine, when gas flow conditions have a reduced tendency to mix the reactant mixture within the combustor. Further aspects of the invention include thermally protecting the mixing structure by providing a flow of cooling air to the mixing structure without substantially altering a flow of cooling air into the combustion zone relative to a combustor configured without the mixing structure. Further, the mixing structure may be configured as a resonator structure to provide acoustic damping specific to known frequencies within the combustor. For example, the resonator structure may be provided in place of or in addition to resonator structure of a combustor modified to include the mixing structure, as is discussed in further detail below.

Referring to FIG. 1, a combustor 12 in a gas turbine engine 10 is illustrated. The combustor 12 receives compressed air from a compressor 14 and mixes the compressed air with a fuel to provide a reactant mixture that is combusted in a combustion zone 16 within the combustor 12, creating a hot working gas comprising combustion products of the reactant mixture. The hot working gas is conducted from the combustor 12 through a transition duct 18 to a turbine section 20 where work is extracted through expansion of the hot working gas, and the hot working gas subsequently passes out of the engine as exhaust gas through an exhaust duct 22.

Referring to FIG. 2, in accordance with an aspect of the invention, a thermal analysis of the combustion zone of a prior combustor is provided and comprises a plot that can be based on a CFD (Computational Fluid Dynamics) model facilitating identification of lower temperature regions that can increase CO and/or NOx formation, such as during part load operating conditions. The thermal analysis is based on a combustion zone in a prior combustor that is similar to the combustor 12 of the present invention, but constructed without a mixing structure that is described below for the present invention. The prior combustor is hereinafter referred to as a baseline combustor and represents a baseline combustor for comparison with the combustor 12 incorporating aspects of the present invention. Elements of the baseline combustor corresponding to the present combustor 12 are labeled with the same reference numerals primed.

As is depicted by double cross-hatching in FIG. 2, specific combustion zone regions 24′, can be formed in the baseline combustor 12′ where lower temperature reactant mixture and combustion products can result in elevated emission levels in the working gas provided to the turbine section of the gas turbine engine. The lower temperature combustion zone regions 24′ are located generally radially outward from a central region 26′ of hotter reactant mixture and combustion products.

As noted above, lower residence times and cooler fluid temperatures of the reactant mixture and combustion products can result in higher levels of emissions remaining in the combustion products provided to the turbine section. For example, the lower temperature regions 24′ of the baseline combustor 12′ may comprise fluid temperatures that are too low to completely combust or “burn-out” the fuel in the reactant mixture, resulting in an elevated level of CO in the combustion products produced in these regions, whereas increased or complete burn-out may occur in the central higher temperature region 26′, and can extend in between the lower temperature regions 24. In accordance with aspects of the invention, characteristics of the fluid flow in the specific lower temperature regions 24′ are altered to increase exposure of the combustion products in the lower temperature regions 24′ to the higher temperature combustion products of the higher temperature region 26′, as is described below.

Referring to FIG. 3, the combustor 12 described herein comprises a combustor basket 30 having a combustion chamber 32 defined by a liner wall 34 of the combustor basket 30. The combustion zone 16 is located within the combustion chamber 32, and receives a reactant mixture comprising fuel and air from a plurality of main nozzles or fuel injectors 36 that are equally spaced from each other in a circular pattern upstream of the combustion zone 16. The main injectors 36 surround a pilot fuel nozzle or injector 38 that can also supply a mixture of fuel and air to the combustion zone 16.

In accordance with a further aspect of the combustor 12, a mixing structure is provided, generally designated by 40 and specifically comprising a plurality of vortex generators 42. The vortex generators 42 are formed as separate elements extending around an inner surface 44 of the liner wall 34 surrounding the combustion zone 16. Specifically, the vortex generators 42 are located in circumferentially spaced relation to each other extending radially inward from the inner surface 44 of the liner wall 34 into the combustion zone 16. The vortex generators 42 are configured to create vortices 46 at predetermined circumferential locations downstream from where the fuel and air are ignited in the combustion chamber 32 in order to effect a reduction in CO and/or NOx emissions of the combustion gases, as will be discussed further below.

Referring to FIG. 4, a vortex generator 42 is illustrated and is preferably in the form of a tetrahedral shaped protrusion extending from the liner wall 34. The vortex generator 42 includes a two triangular shaped side walls 48a, 48b that converge toward each other in the downstream direction, as defined by an opening angle α. The two side walls 48a, 48b meet at an apex edge 49 that defines a radially inward extending height H. Further, a generally planar ramp surface 50 extends between converging edges 52a, 52b of the side walls 48a, 48b, and angles radially inward in the downstream direction, as defined by an attack angle β. The ramp surface 50 of the vortex generator 42 is configured to direct a localized portion of the flow of reactant mixture and combustion products radially inward, and the side walls 48a, 48b form an area of low static pressure where the flow leaves the ramp surface 50 of each vortex generator 42 at the edges 52a, 52b to create two counter-rotating vortices 46, located downstream of the side walls 48a, 48b of the vortex generators 42. It may be noted that the vortex generators could alternatively be formed with the side walls converging in the upstream direction, which would result in a direction of rotation for the vortices that is opposite from that shown in FIG. 4.

The vortices 46 formed by the vortex generators 42 are provided to induce a predetermined amount of mixing between lower temperature regions of reactant mixture and combustion products, e.g., as described for the radially outer regions in FIG. 2, and the higher temperature regions within the combustor, e.g., as described for the radially inner region 26. That is, the dimensions of the opening angle α, attack angle β and height H are selected to optimize or provide vortices for a predetermined mixing for a given axial location of the vortex generators 42 at a downstream location from formation of a stabilized flame in the combustion chamber 16. In particular, the vortex generators 42 can be configured with dimensions to optimize mixing of the radially outer cooler and hotter regions in the combustor 12 during a reduced or part load operation, such as during a conventional turn down operation when the engine may be operated at 60% load. In accordance with specific aspects associated with vortex generators 42 positioned at the axial location in the combustor 12 illustrated herein, the opening angle α may be about two and a half times as great as the attack angle β.

An example of an alternative vortex generator 42 may comprise a shorter vortex generator 42 having a larger opening angle α and attack angle β. For example, in an alternative vortex generator 42, the opening angle α may be about two times as great as the attack angle β. It has been observed that such a vortex generator 42 can have a stronger effect on mixing to increase the reduction of emissions closer to the vortex generators 42, such as at an upstream location of the transition duct 18, but may have reduced effects, as compared to the previously described vortex generator 42, in downstream portions of the transition duct 18. However, the alternative vortex generator 42 may have an increased static pressure at the ramp surface 50, which may result in passage of hot gases into the vortex generator 42 in the event cooling air passages are provided in surfaces of the vortex generator 42, as is discussed further below.

In accordance with a further aspect of the invention, the circumferential placement of the individual vortex generators 42 is selected with reference to the previously described lower temperature regions 24 as identified and described herein. The vortex generators 42 are preferably equally spaced around the circumference of the liner wall 34, and are placed with reference to the locations of the main injectors 36. Hence, the number of vortex generators 42 located circumferentially around an axial location of the combustion zone 16 may equal the number of main injectors 36, although this is not necessarily required. The circumferential placement of the vortex generators 42 is selected such that they effectively interact with low temperature streaks or flows of reactant mixture flowing from the main injectors 36 toward the transition duct 18.

In accordance with another aspect of the invention, the vortex generators 42 are positioned axially along the liner wall 34 at a location selected to have a significant mixing effect on the reactant mixture to reduce emissions. The positioning of the vortex generators 42 is also selected so as to ensure that cooling may be provided to the vortex generators 42, extending the lifetime of the vortex generators in the hot environment of the combustion zone 16.

In the baseline combustor described above with reference to FIG. 2, the liner wall 34 is provided with a plurality of resonator structures (see resonators 58 in FIGS. 3 and 5) at a downstream location of the combustion chamber 32, such as a plurality of Helmholtz resonators mounted around an exterior surface of the liner wall 34. A plurality of holes 60 are formed through the liner wall 34 to place the interior of the resonators 58 in fluid communication with the gases passing through the combustion chamber 32 in order to provide damping of predetermined frequencies produced in the combustion zone 16. The resonators 58 are each configured as a housing having an outer wall that is in fluid communication with an air plenum 62 surrounding the combustor 12, and providing air to the interior of each resonator 58 to prevent ingress of hot combustion gases from the combustion chamber 32 into the resonator 58 and to provide cooling. The resonators 58 may comprise resonators such as are disclosed in U.S. Pat. No. 6,530,221, which patent is incorporated herein in its entirety.

Referring to FIG. 3, in order to provide cooling to the vortex generators 42, the vortex generators 42 are configured as hollow housings that are positioned on the liner wall 34 at locations of the holes 60, i.e., at the same axial location as the resonators 58, and include apertures or fluid passages 64 formed in the side walls 48a, 48b and the ramp surface 50 to provide a flow of cooling air from the plenum 62. Further, the vortex generators 42 can be formed as resonators extending into the combustion chamber 32 for acoustic damping of frequencies produced in the combustion zone 16. The damping frequency f of the vortex generators 42 generally may be described by the relationship:

f=(c/2π)(A/(VI))^1/2  (1)

where:

• • c=speed of sound of the fluid in the resonator (vortex generator 42);
  • A=area of the neck, i.e., total area of the passages 64;
  • V=volume of the resonator (vortex generator 42); and
  • l=length of the neck, i.e., thickness of the material forming the side walls 48a, 48b and ramp surface 50, defining the length of the passages 64.

It may be understood the above equation (1) for damping frequency f is based on assumptions regarding the temperature and other characteristics affecting the speed of sound c of the fluid in the resonator (vortex generator 42), and that more complex modeling may be implemented to provide an accurate resonator design for damping at a desired frequency.

The passages 64 are preferably located along areas or surfaces of lower static pressure on the vortex generator 42, with a greater number of the passages 64 provided at the lowest static pressure areas. In particular, a greater number of passages 64 can be provided to the side walls 48a, 48b, where there is a lower static pressure, while a fewer number of passages 64 are provided to the ramp surface 50 and are preferably located adjacent to the downstream tip of the ramp surface 50, defining a lower static pressure location of the ramp surface 50. Locating the passages 64 at locations of lower static pressure reduces the likelihood of hot gas injection into the vortex generators 42.

Further, it may be understood that in addition to the sides of the vortex generator 42 forming the resonator, as defined by the side walls 48a, 48b and ramp surface 50, an outer wall of the resonator is defined by a portion of the liner wall 34 including a plurality of the holes 60 placing the interior of the vortex generator 42 in fluid communication with the air in the plenum 62, as may be seen in FIG. 5. Also, it can be seen in FIG. 5 that the illustrated vortex generator 42 is positioned circumferentially between the locations of two resonators 58. In a configuration of the present combustor 12, the previous baseline combustor 12 can be modified to include the vortex generators 42 by removing or leaving off every other resonator 58 on the outer side of the liner wall 34 at alternating circumferential locations, and instead providing a vortex generator 42 at each of these alternating locations, extending radially inward from the liner wall 34.

Referring to FIG. 6, an alternative configuration for the vortex generator 42 configured as a resonator is illustrated. In this configuration, an outer wall extension 66 is provided extending radially outward from the liner wall 34, and forming a continuous volume with the volume formed by the side walls 48a, 48b and ramp surface 50. The outer wall extension 66 may comprise a shape resembling that of a resonator 58, but typically extending outwardly from the liner wall less than a resonator 58, and can include an outer wall 66a having passages 68 that provide fluid communication between the air plenum 62 and the interior of the vortex generator 42. The present configuration for the vortex generator 42 may be implemented in the event that a volume defined by an outer wall at the liner wall 34 is not sufficiently large to obtain the damping frequency f required for the resonator function of the vortex generator 42. Hence, the outer wall extension 66 extending through and past the liner wall 34 can provide an additional volume for tuning the resonator to a desired damping frequency f.

It should be understood that the axial location of the vortex generators 42 corresponding to the location of the resonators 58 is selected to enable the vortex generators 42 to utilize the air supply of the plenum 62, such as is provided through the holes 60, as a cooling air supply for the vortex generators 42. Further, in order to avoid injecting additional cool air into the combustion chamber 32, beyond a designed amount of air injected via the resonators 58, the vortex generators 42 are configured to be used as replacements at previous resonator locations. Hence, the vortex generators 42 are configured such that they can act as resonators, maintaining a desired vibration damping function in the combustor 12, while generating vortices to facilitate mixing for a reduction of CO and/or NOx production.

By providing the vortex generators 42 configured and located as described above, operation of the combustor 12 results in the vortex generators 42 effecting a reduction in flame length downstream of the vortex generators 42, as compared to a flame length at a similar location in the previous baseline combustor 12. As a result of providing the vortex generators 42 to generate vortices for mixing the cooler reactant mixture and combustion products with the hotter gases in the combustion zone 16, a more complete burn-out can be obtained further upstream with a resulting shorter flame length.

Additionally, it should be noted that although the axial location of the vortex generators 42 is described as generally corresponding to the axial location of the resonators 58, a more complete burn-out and further improved reduction in emissions may be obtained by placement of the vortex generators 42 at a location in the combustion zone 16 axially upstream from the resonators 58. However, in view of the cooling requirements to maintain longevity of the service life for the vortex generators 42, and not increase cooling flow requirements for the combustor 12, it is preferable in the present configuration of the combustor 12 to locate the vortex generators 42 at an axially downstream location corresponding to the resonators 58.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A combustor for a gas turbine engine, the combustor including a pilot fuel injector and a plurality of circumferentially located main injectors for injecting fuel and air into a combustion chamber defined by a liner wall of a combustor basket; a combustion zone located in the combustion chamber where the fuel and air are ignited to produce hot combustion gases; and a plurality of vortex generators located in circumferentially spaced relation on the liner wall and comprising structures extending radially inward into the combustion chamber to create vortices at predetermined circumferential locations downstream from where the fuel and air are ignited to effect a reduction in emissions of the combustion gases.

2. The method of claim 1, wherein the vortex generators are located on the combustion chamber to mix cooler and hotter portions of the combustion gases to effect the reduction in emissions of the combustion gases.

3. The combustor of claim 2, wherein the predetermined circumferential locations of the vortex generators correspond to an axial location downstream of formation of a stabilized flame in the combustion chamber.

4. The combustor of claim 1, wherein the predetermined circumferential locations of the vortex generators are axially aligned with an area of fuel and air combustion in the combustion chamber.

5. The combustor of claim 1, wherein including a plurality of through holes formed in the liner wall and resonator structures located over at least some of the through holes on a radially outward facing side of the liner wall, and the vortex generators located over at least some of the through holes at substantially the same axial location as the resonator structures.

6. The combustor of claim 5, wherein the vortex generators include surfaces having apertures for passage of cooling air out of the vortex generator into the combustion chamber.

7. The combustor of claim 1, wherein the main injectors are equally spaced from each other in a circular pattern upstream from the combustion zone, and the vortex generators are generally equally spaced in a circular pattern at an axial location of the combustion zone.

8. The combustor of claim 1, wherein the vortex generators comprise tetrahedral shaped protrusions extending from the liner wall.

9. The combustor of claim 6, wherein the vortex generators include two triangular shaped side walls converging in a downstream direction, and a ramp surface extending between converging edges of the side walls.

10. The combustor of claim 7, wherein the ramp surface angles radially inward in the downstream direction.

11. A method of reducing emissions in a combustor having a pilot fuel injector and a plurality of circumferentially located main injectors for injecting fuel and air into a combustion chamber defined by a liner wall of a combustor basket, the method comprising:

igniting the fuel and air in a combustion zone located in the combustion chamber to produce hot combustion gases; and

creating vortices at predetermined circumferential locations downstream from where the fuel and air are ignited by providing a plurality of vortex generators comprising structures extending radially inward into the combustion chamber and located in circumferential locations downstream from where the fuel and air are ignited to effect a reduction in emissions of the combustion gases.

12. The method of claim 11, wherein the vortex generators are hollow structures having an interior area and including providing cooling air to the interior area of the vortex generators.

13. The method of claim 12, wherein the vortex generators comprise resonators providing acoustic damping.

14. The method of claim 11, wherein the vortex generators mix cooler and hotter portions of the combustion gases to effect the reduction in emissions of the combustion gases.

15. The combustor of claim 11, wherein the predetermined circumferential locations of the vortex generators are axially aligned with an area of fuel and air combustion in the combustion chamber.

16. The combustor of claim 11, wherein the main injectors are equally spaced from each other in a circular pattern upstream from the combustion zone, and the vortex generators are generally equally spaced in a circular pattern at an axial location of the combustion zone.

17. The combustor of claim 11, wherein the vortex generators comprise tetrahedral shaped protrusions extending from the liner wall.

18. The combustor of claim 17, wherein the vortex generators include two triangular shaped side walls converging in a downstream direction, and a ramp surface extending between converging edges of the side walls.

19. The combustor of claim 18, wherein the ramp surface angles radially inward in the downstream direction.

20. The combustor of claim 11, wherein the vortices mix the combustion gases to effect a reduction in the flame length downstream of the vortex generators.