U.S. patent application number 14/102578 was filed with the patent office on 2015-06-11 for combustion system for a gas turbine engine.
The applicant listed for this patent is Stephen A. Ramier, Kai-Uwe Schildmacher, Ulrich Worz, Danning You. Invention is credited to Stephen A. Ramier, Kai-Uwe Schildmacher, Ulrich Worz, Danning You.
Application Number | 20150159878 14/102578 |
Document ID | / |
Family ID | 52014355 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150159878 |
Kind Code |
A1 |
Schildmacher; Kai-Uwe ; et
al. |
June 11, 2015 |
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.
Inventors: |
Schildmacher; Kai-Uwe;
(Mulheim a.d. Ruhr, DE) ; You; Danning; (Shanghai,
CN) ; Worz; Ulrich; (Tega Cay, SC) ; Ramier;
Stephen A.; (Fredericton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schildmacher; Kai-Uwe
You; Danning
Worz; Ulrich
Ramier; Stephen A. |
Mulheim a.d. Ruhr
Shanghai
Tega Cay
Fredericton |
SC |
DE
CN
US
CA |
|
|
Family ID: |
52014355 |
Appl. No.: |
14/102578 |
Filed: |
December 11, 2013 |
Current U.S.
Class: |
60/776 ;
60/735 |
Current CPC
Class: |
F23R 3/16 20130101; F23R
2900/03045 20130101; F23R 3/58 20130101; F23R 3/06 20130101; F23R
2900/00014 20130101 |
International
Class: |
F23R 3/58 20060101
F23R003/58 |
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.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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.
[0003] 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
[0004] 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.
[0005] 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.
[0006] 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.
[0007] The predetermined circumferential locations of the vortex
generators may be axially aligned with an area of fuel and air
combustion in the combustion chamber.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] The vortex generators may comprise resonators providing
acoustic damping.
[0014] The vortex generators may mix cooler and hotter portions of
the combustion gases to effect the reduction in emissions of the
combustion gases.
[0015] The predetermined circumferential locations of the vortex
generators may be axially aligned with an area of fuel and air
combustion in the combustion chamber.
[0016] 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.
[0017] The vortex generators may comprise tetrahedral shaped
protrusions extending from the liner wall.
[0018] 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.
[0019] The ramp surface may angle radially inward in the downstream
direction.
[0020] 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
[0021] 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:
[0022] 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;
[0023] FIG. 2 is a perspective view of selected planes in a
combustor, illustrating a thermal analysis at the selected
planes;
[0024] FIG. 3 is a cross-sectional view of a combustor
incorporating aspects of the invention;
[0025] FIG. 4 is a perspective view of a vortex generator in
accordance with aspects of the invention;
[0026] FIG. 5 is a perspective view of a portion of an outer side
of a combustor liner wall illustrating aspects of the invention;
and
[0027] FIG. 6 is a cross-sectional view illustrating an alternative
configuration for the vortex generator.
DETAILED DESCRIPTION OF THE INVENTION
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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 .alpha.. 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 .beta.. 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.
[0037] 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 .alpha., attack angle .beta. 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 .alpha. may be about two and a half times
as great as the attack angle .beta..
[0038] An example of an alternative vortex generator 42 may
comprise a shorter vortex generator 42 having a larger opening
angle .alpha. and attack angle .beta.. For example, in an
alternative vortex generator 42, the opening angle .alpha. may be
about two times as great as the attack angle .beta.. 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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/2.pi.)(A/(VI)).sup.1/2 (1)
where: [0043] c=speed of sound of the fluid in the resonator
(vortex generator 42); [0044] A=area of the neck, i.e., total area
of the passages 64; [0045] V=volume of the resonator (vortex
generator 42); and [0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
* * * * *