U.S. patent application number 09/871343 was filed with the patent office on 2002-12-05 for method and apparatus for mixing fuel to decrease combustor emissions.
Invention is credited to Foust, Michael Jermoe, Mongia, Hukam Chand.
Application Number | 20020178732 09/871343 |
Document ID | / |
Family ID | 25357242 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020178732 |
Kind Code |
A1 |
Foust, Michael Jermoe ; et
al. |
December 5, 2002 |
METHOD AND APPARATUS FOR MIXING FUEL TO DECREASE COMBUSTOR
EMISSIONS
Abstract
A combustor for a gas turbine engine operates with high
combustion efficiency and low carbon monoxide, nitrous oxide, and
smoke emissions during low, intermediate, and high engine power
operations is described. The combustor includes a mixer assembly
including a pilot mixer and a main mixer. The pilot mixer includes
a pilot fuel injector, at least one swirler, and an air splitter.
The main mixer extends circumferentially around the pilot mixer and
includes a plurality of fuel injection ports and a conical air
swirler upstream from the fuel injection ports. During idle engine
power operation, the pilot mixer is aerodynamically isolated from
the main mixer, and only air is supplied to the main mixer. During
increased power operations, fuel is also supplied to the main
mixer, and the main mixer conical swirler facilitates radial and
circumferential fuel-air mixing to provide a substantially uniform
fuel and air distribution for combustion.
Inventors: |
Foust, Michael Jermoe; (West
Chester, OH) ; Mongia, Hukam Chand; (West Chester,
OH) |
Correspondence
Address: |
JOHN S. BEULICK
C/O ARMSTRONG TEASDALE LLP
ONE METROPOLITAN SQUARE
SUITE 2600
ST. LOUIS
MO
63102-2740
US
|
Family ID: |
25357242 |
Appl. No.: |
09/871343 |
Filed: |
May 31, 2001 |
Current U.S.
Class: |
60/776 ;
60/737 |
Current CPC
Class: |
F23R 3/343 20130101;
F23R 3/14 20130101; F23R 3/286 20130101 |
Class at
Publication: |
60/776 ;
60/737 |
International
Class: |
F23R 003/30 |
Claims
What is claimed is:
1. A method for operating a gas turbine engine to facilitate
reducing an amount of emissions from a combustor including a mixer
assembly including a pilot mixer and a main mixer, the pilot mixer
including a pilot fuel nozzle and a plurality of axial swirlers,
the main mixer including a main swirler and a plurality of fuel
injection ports, said method comprising the steps of: injecting
fuel into the combustor through the pilot mixer, such that the fuel
discharged downstream from the pilot mixer axial swirlers; and
directing airflow into the combustor through the main mixer such
that the airflow is swirled with at least one of a conical swirler
and a cyclone swirler prior to being discharged from the main
mixer.
2. A method in accordance with claim 1 wherein said step of
directing airflow into the combustor further comprises the step of
injecting fuel radially outward from an annular fuel manifold
positioned between the main mixer and the pilot mixer.
3. A method in accordance with claim 1 wherein said step of
directing airflow into the combustor further comprises the step of
swirling airflow within the main mixer with an axial swirler prior
to swirling the airflow with at least one of a conical swirler and
a cyclone swirler.
4. A method in accordance with claim 1 wherein at least one of the
main mixer conical swirler and the main mixer cyclone swirler
includes a first set of swirling vanes and a second set of swirling
vanes, said step of step of directing airflow into the combustor
further comprises the step of directing airflow through the main
mixer to swirl a portion of the airflow with the first set of
swirling vanes and to swirl a portion of the airflow with the
second set of swirling vanes.
5. A method in accordance with claim 4 wherein said step of
directing airflow through the main mixer to swirl a portion of the
airflow further comprises the step of swirling the airflow in the
direction with the first and second sets of swirling vanes.
6. A method in accordance with claim 4 wherein said step of
directing airflow through the main mixer to swirl a portion of the
airflow further comprises the step of swirling the airflow in a
first direction with the first set of swirling vanes, and in a
second direction that is opposite the first direction with the
second set of swirling vanes.
7. A combustor for a gas turbine comprising: a pilot mixer
comprising an air splitter, a pilot fuel nozzle, and a plurality of
axial air swirlers upstream from said pilot fuel nozzle, said air
splitter downstream from said pilot fuel nozzle, said air swirlers
radially outward from and concentrically mounted with respect to
said pilot fuel nozzle; and a main mixer radially outward from and
concentrically aligned with respect to said pilot mixer, said main
mixer comprising a plurality of fuel injection ports and a swirler
comprising at least one of a conical air swirler and a cyclone air
swirler, said main mixer swirler upstream from said main mixer fuel
injection ports.
8. A combustor in accordance with claim 7 further comprising an
annular fuel manifold between said pilot mixer and main mixer, said
fuel manifold comprising a radially inner surface and a radially
outer surface, said main mixer fuel injection ports configured to
inject fuel radially outward from said fuel manifold radially outer
surface.
9. A combustor in accordance with claim 7 wherein said main mixer
further comprises an axial swirler.
10. A combustor in accordance with claim 9 wherein said main mixer
axial swirler upstream from at least one of said conical air
swirler and said cyclone air swirler.
11. A combustor in accordance with claim 7 wherein said at least
one of a conical air swirler and a cyclone air swirler comprises
first swirling vanes and second swirling vanes, said first swirling
vanes configured to swirl air in a first direction, said second
swirling vanes configured to swirl air in a second direction.
12. A combustor in accordance with claim 11 wherein said first
swirling vanes first direction opposite said second swirling vanes
second direction.
13. A combustor in accordance with claim 11 wherein said first
swirling vanes first direction is identical said second swirling
vanes second direction.
14. A mixer assembly for a gas turbine engine combustor, said mixer
assembly configured to control emissions from the combustor and
comprising a pilot mixer and a main mixer, said pilot mixer
comprising a pilot fuel nozzle, and a plurality of axial swirlers
upstream and radially outward from said pilot fuel nozzle, said
main mixer radially outward from and concentric with respect to
said pilot mixer, said main mixer comprising a plurality of fuel
injection ports and a swirler upstream from said fuel injection
ports, said main mixer swirler comprising at least one of a conical
main swirler and a cyclone swirler.
15. A mixer assembly in accordance with claim 14 further comprising
an annular fuel manifold between said pilot mixer and said main
mixer, said main mixer fuel injection ports configured to inject
fuel radially outward from said annular fuel manifold.
16. A mixer assembly in accordance with claim 15 wherein said mixer
assembly main mixer further comprises an axial swirler.
17. A mixer assembly in accordance with claim 16 wherein said mixer
assembly main mixer axial swirler upstream from said at least one
of a conical main swirler and a cyclone swirler.
18. A mixer assembly in accordance with claim 15 wherein said main
mixer at least one of a conical main swirler and a cyclone air
swirler comprises a plurality of swirling vanes.
19. A mixer assembly in accordance with claim 18 wherein said main
mixer plurality of swirling vanes comprise first swirling vanes
configured to swirl air in a first direction, and second swirling
vanes configured to swirl air in a second direction opposite said
first swirling vanes first direction.
20. A mixer assembly in accordance with claim 18 wherein said main
mixer plurality of swirling vanes comprise first swirling vanes
configured to swirl air in a first direction, and second swirling
vanes configured to swirl air in a second direction identical said
first swirling vanes first direction.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates generally to combustors and, more
particularly, to gas turbine combustors.
[0002] Air pollution concerns worldwide have led to stricter
emissions standards both domestically and internationally. Aircraft
are governed by both Environmental Protection Agency (EPA) and
International Civil Aviation Organization (ICAO) standards. These
standards regulate the emission of oxides of nitrogen (NOx),
unburned hydrocarbons (HC), and carbon monoxide (CO) from aircraft
in the vicinity of airports, where they contribute to urban
photochemical smog problems. In general, engine emissions fall into
two classes: those formed because of high flame temperatures (NOx),
and those formed because of low flame temperatures which do not
allow the fuel-air reaction to proceed to completion (HC &
CO).
[0003] At least some known gas turbine combustors include between
10 and 30 mixers, which mix high velocity air with a fine fuel
spray. These mixers usually consist of a single fuel injector
located at a center of a swirler for swirling the incoming air to
enhance flame stabilization and mixing. Both the fuel injector and
mixer are located on a combustor dome.
[0004] In general, the fuel to air ratio in the mixer is rich.
Since the overall combustor fuel-air ratio of gas turbine
combustors is lean, additional air is added through discrete
dilution holes prior to exiting the combustor. Poor mixing and hot
spots can occur both at the dome, where the injected fuel must
vaporize and mix prior to burning, and in the vicinity of the
dilution holes, where air is added to the rich dome mixture.
[0005] One state-of-the-art lean dome combustor is referred to as a
dual annular combustor (DAC) because it includes two radially
stacked mixers on each fuel nozzle which appear as two annular
rings when viewed from the front of a combustor. The additional row
of mixers allows tuning for operation at different conditions. At
idle, the outer mixer is fueled, which is designed to operate
efficiently at idle conditions. At high power operation, both
mixers are fueled with the majority of fuel and air supplied to the
inner annulus, which is designed to operate most efficiently and
with few emissions at high power operation. While the mixers have
been tuned for optimal operation with each dome, the boundary
between the domes quenches the CO reaction over a large region,
which makes the CO of these designs higher than similar rich dome
single annular combustors (SACs). Such a combustor is a compromise
between low power emissions and high power NOx.
[0006] Other known combustors operate as a lean dome combustor.
Instead of separating the pilot and main stages in separate domes
and creating a significant CO quench zone at the interface, the
mixer incorporates concentric, but distinct pilot and main air
streams within the device. However, the simultaneous control of low
power CO/HC and smoke emission is difficult with such designs
because increasing the fuel-air mixing often results in high CO/HC
emissions. The swirling main air naturally tends to entrain the
pilot flame and quench it. To prevent the fuel spray from getting
entrained into the main air, the pilot establishes a narrow angle
spray. This may result in a long jet flames characteristic of a low
swirl number flow. Such pilot flames produce high smoke, carbon
monoxide, and hydrocarbon emissions and have poor stability.
BRIEF SUMMARY OF THE INVENTION
[0007] In an exemplary embodiment, a combustor for a gas turbine
engine operates with high combustion efficiency and low carbon
monoxide, nitrous oxide, and smoke emissions during low,
intermediate, and high engine power operations. The combustor
includes a mixer assembly including a pilot mixer and a main mixer.
The pilot mixer includes a pilot fuel injector, at least one
swirler, and an air splitter. The main mixer extends
circumferentially around the pilot mixer and includes a plurality
of fuel injection ports and a conical air swirler that is upstream
from the fuel injection ports.
[0008] During idle engine power operation, the pilot mixer is
aerodynamically isolated from the main mixer, and only air is
supplied to the main mixer. During increased power operations, fuel
is also supplied to the main mixer, and the main mixer conical
swirler facilitates radial and circumferential fuel-air mixing to
provide a substantially uniform fuel and air distribution for
combustion. More specifically, airflow exiting the main mixer
swirler forces fuel injected from the fuel injection ports radially
outward into the main mixer to mix with the airflow. As a result,
the fuel-air mixture is uniformly distributed within the combustor
which facilitates complete combustion within the combustor, thus
reducing high power operation nitrous oxide emissions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is schematic illustration of a gas turbine engine
including a combustor;
[0010] FIG. 2 is a cross-sectional view of a combustor that may be
used with the gas turbine engine shown in FIG. 1;
[0011] FIG. 3 is an enlarged view of a portion of the combustor
shown in FIG. 2 taken along area 3; and
[0012] FIG. 4 is a cross-sectional view of an alternative
embodiment of a combustor that may be used with the gas turbine
engine shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0013] FIG. 1 is a schematic illustration of a gas turbine engine
10 including a low pressure compressor 12, a high pressure
compressor 14, and a combustor 16. Engine 10 also includes a high
pressure turbine 18 and a low pressure turbine 20.
[0014] In operation, air flows through low pressure compressor 12
and compressed air is supplied from low pressure compressor 12 to
high pressure compressor 14. The highly compressed air is delivered
to combustor 16. Airflow (not shown in FIG. 1) from combustor 16
drives turbines 18 and 20.
[0015] FIG. 2 is a cross-sectional view of combustor 16 for use
with a gas turbine engine, similar to engine 10 shown in FIG. 1,
and FIG. 3 is an enlarged view of combustor 16 taken along area 3.
In one embodiment, the gas turbine engine is a CFM engine available
from CFM International. In another embodiment, the gas turbine
engine is a GE90 engine available from General Electric Company,
Cincinnati, Ohio.
[0016] Each combustor 16 includes a combustion zone or chamber 30
defined by annular, radially outer and radially inner liners 32 and
34. More specifically, outer liner 32 defines an outer boundary of
combustion chamber 30, and inner liner 34 defines an inner boundary
of combustion chamber 30. Liners 32 and 34 are radially inward from
an annular combustor casing 36 which extends circumferentially
around liners 32 and 34.
[0017] Combustor 16 also includes an annular dome 40 mounted
upstream from outer and inner liners 32 and 34, respectively. Dome
40 defines an upstream end of combustion chamber 30 and mixer
assemblies 41 are spaced circumferentially around dome 40 to
deliver a mixture of fuel and air to combustion chamber 30.
[0018] Each mixer assembly 41 includes a pilot mixer 42 and a main
mixer 44. Pilot mixer 42 includes an annular pilot housing 46 that
defines a chamber 50. Chamber 50 has an axis of symmetry 52, and is
generally cylindrical-shaped. A pilot fuel nozzle 54 extends into
chamber 50 and is mounted symmetrically with respect to axis of
symmetry 52. Nozzle 54 includes a fuel injector 58 for dispensing
droplets of fuel into pilot chamber 50. In one embodiment, pilot
fuel injector 58 supplies fuel through injection jets (not shown).
In an alternative embodiment, pilot fuel injector 58 supplies fuel
through injection simplex sprays (not shown).
[0019] Pilot mixer 42 also includes a pair of concentrically
mounted swirlers 60. More specifically, swirlers 60 are axial
swirlers and include a pilot inner swirler 62 and a pilot outer
swirler 64. Pilot inner swirler 62 is annular and is
circumferentially disposed around pilot fuel injector 58. Each
swirler 62 and 64 includes a plurality of vanes 66 and 68,
respectively, positioned upstream from pilot fuel injector 58.
Vanes 66 and 68 are selected to provide desired ignition
characteristics, lean stability, and low carbon monoxide (CO) and
hydrocarbon (HC) emissions during low engine power operations.
[0020] A pilot splitter 70 is radially between pilot inner swirler
62 and pilot outer swirler 64, and extends downstream from pilot
inner swirler 62 and pilot outer swirler 64. More specifically,
pilot splitter 70 is annular and extends circumferentially around
pilot inner swirler 62 to separate airflow traveling through inner
swirler 62 from that flowing through outer swirler 64. Splitter 70
has a converging-diverging inner surface 74 which provides a
fuel-filming surface during engine low power operations. Splitter
70 also reduces axial velocities of air flowing through pilot mixer
42 to allow recirculation of hot gases.
[0021] Pilot outer swirler 64 is radially outward from pilot inner
swirler 62, and radially inward from an inner surface 78 of pilot
housing 46. More specifically, pilot outer swirler 64 extends
circumferentially around pilot inner swirler 62 and is radially
between pilot splitter 70 and pilot housing 46. In one embodiment,
pilot inner swirler vanes 66 swirl air flowing therethrough in the
same direction as air flowing through pilot outer swirler vanes 68.
In another embodiment, pilot inner swirler vanes 66 swirl air
flowing therethrough in a first direction that is opposite a second
direction that pilot outer swirler vanes 68 swirl air flowing
therethrough.
[0022] Main mixer 44 includes an annular main housing 90 that
defines an annular cavity 92. Main mixer 44 is concentrically
aligned with respect to pilot mixer 42 and extends
circumferentially around pilot mixer 42. A fuel manifold 94 extends
between pilot mixer 42 and main mixer 44. More specifically, fuel
manifold 94 includes an annular housing 96 that extends
circumferentially around pilot mixer 42 and is between pilot
housing 46 and main housing 90.
[0023] Fuel manifold 94 includes a plurality of injection ports 98
mounted to an exterior surface 100 of fuel manifold for injecting
fuel radially outwardly from fuel manifold 94 into main mixer
cavity 92. Fuel injection ports 98 facilitate circumferential
fuel-air mixing within main mixer 44.
[0024] In one embodiment, manifold 94 includes a first row of
twenty circumferentially-spaced injection ports 98 and a second row
of twenty circumferentially-spaced injection ports 98. In another
embodiment, manifold 94 includes a plurality of injection ports 98
that are not arranged in circumferentially-spaced rows. A location
of injection ports 98 is selected to adjust a degree of fuel-air
mixing to achieve low nitrous oxide (NOx) emissions and to insure
complete combustion under variable engine operating conditions.
Furthermore, the injection port location is also selected to
facilitate reducing or preventing combustion instability.
[0025] Fuel manifold annular housing 96 separates pilot mixer 42
and main mixer 44. Accordingly, pilot mixer 42 is sheltered from
main mixer 44 during pilot operation to facilitate improving pilot
performance stability and efficiency, while also reducing CO and HC
emissions. Furthermore, pilot housing 46 is shaped to facilitate
completing a burnout of pilot fuel injected into combustor 16. More
specifically, an inner wall 101 of pilot housing 46 is a
converging-diverging surface that facilitates controlling diffusion
and mixing of the pilot flame into airflow exiting main mixer 44.
Accordingly, a distance between pilot mixer 42 and main mixer 44 is
selected to facilitate improving ignition characteristics,
combustion stability at high and lower power operations, and
emissions generated at lower power operating conditions.
[0026] Main mixer 44 also includes a first swirler 110 and a second
swirler 112, each located upstream from fuel injection ports 98.
First swirler 110 is a conical swirler and airflow flowing
therethrough is discharged at conical swirler angle (not shown).
The conical swirler angle is selected to provide airflow discharged
from first swirler 110 with a relatively low radial inward
momentum, which facilitates improving radial fuel-air mixing of
fuel injected radially outward from injection ports 98. In an
alternative embodiment, first swirler 110 is split into pairs of
swirling vanes (not shown) that may be co-rotational or
counter-rotational.
[0027] Second swirler 112 is an axial swirler that discharges air
in a direction substantially parallel to center mixer axis of
symmetry 52 to facilitate enhancing main mixer fuel-air mixing. In
one embodiment, main mixer 44 only includes first swirler 110 and
does not include second swirler 112.
[0028] A fuel delivery system 120 supplies fuel to combustor 16 and
includes a pilot fuel circuit 122 and a main fuel circuit 124.
Pilot fuel circuit 122 supplies fuel to pilot fuel injector 58 and
main fuel circuit 124 supplies fuel to main mixer 44 and includes a
plurality of independent fuel stages used to control nitrous oxide
emissions generated within combustor 16.
[0029] In operation, as gas turbine engine 10 is started and
operated at idle operating conditions, fuel and air are supplied to
combustor 16. During gas turbine idle operating conditions,
combustor 16 uses only pilot mixer 42 for operating. Pilot fuel
circuit 122 injects fuel to combustor 16 through pilot fuel
injector 58. Simultaneously, airflow enters pilot swirlers 60 and
main mixer swirlers 110 and 112. The pilot airflow flows
substantially parallel to center mixer axis of symmetry 52 and
strikes pilot splitter 70 which directs the pilot airflow in a
swirling motion towards fuel exiting pilot fuel injector 58. The
pilot airflow does not collapse a spray pattern (not shown) of
pilot fuel injector 58, but instead stabilizes and atomizes the
fuel. Airflow discharged through main mixer 44 is channeled into
combustion chamber 30.
[0030] Utilizing only the pilot fuel stage permits combustor 16 to
maintain low power operating efficiency and to control and minimize
emissions exiting combustor 16. Because the pilot airflow is
separated from the main mixer airflow, the pilot fuel is completely
ignited and burned, resulting in lean stability and low power
emissions of carbon monoxide, hydrocarbons, and nitrous oxide.
[0031] As gas turbine engine 10 is accelerated from idle operating
conditions to increased power operating conditions, additional fuel
and air are directed into combustor 16. In addition to the pilot
fuel stage, during increased power operating conditions, main mixer
44 is supplied fuel with main fuel circuit 124 and injected
radially outward with fuel injection ports 98. Main mixer swirlers
110 and 112 facilitate radial and circumferential fuel-air mixing
to provide a substantially uniform fuel and air distribution for
combustion. More specifically, airflow exiting main mixer swirlers
110 and 112 forces the fuel to extend radially outward to penetrate
main mixer cavity 92 to facilitate fuel-air mixing and to enable
main mixer 44 to operate with a lean air-fuel mixture. In addition,
uniformly distributing the fuel-air mixture facilitates obtaining a
complete combustion to reduce high power operation NO.sub.x
emissions.
[0032] FIG. 4 is a cross-sectional view of an alternative
embodiment of a combustor 200 that may be used with gas turbine
engine 10. Combustor 200 is substantially similar to combustor 16
shown in FIGS. 2 and 3, and components in combustor 200 that are
identical to components of combustor 16 are identified in FIG. 4
using the same reference numerals used in FIGS. 2 and 3. More
specifically, combustor includes pilot mixer 42 and fuel manifold
annular housing 96, but does not include main mixer 44. Rather,
combustor 200 includes a main mixer 202 which is substantially
identical with main mixer 44 (shown in FIGS. 2 and 3).
[0033] Main mixer 202 includes an annular main housing 204 that
defines an annular cavity 206. Main mixer 202 is concentrically
aligned with respect to pilot mixer 42 and extends
circumferentially around pilot mixer 42. Fuel manifold 94 extends
between pilot mixer 42 and main mixer 202.
[0034] Main mixer 202 also includes a first swirler 210 and second
swirler 112, each located upstream from fuel injection ports 98.
First swirler 210 is a cyclone swirler and second swirler 112 is an
axial swirler that discharges air in a direction substantially
parallel to center mixer axis of symmetry 52 to facilitate
enhancing main mixer fuel-air mixing. In an alternative embodiment,
first swirler 210 is split into pairs of swirling vanes (not shown)
that may be co-rotational or counter-rotational.
[0035] The above-described combustor is cost-effective and highly
reliable. The combustor includes a mixer assembly that includes a
pilot mixer and a main mixer. The pilot mixer is used during lower
power operations and the main mixer is used during mid and high
power operations. During idle power operating conditions, the
combustor operates with low emissions and has only air supplied to
the main mixer. During increased power operating conditions, the
combustor also supplies fuel to the main mixer which includes a
conical swirler to improve main mixer fuel-air mixing. The conical
swirler facilitates uniformly distributing the fuel-air mixture to
improve combustion and lower an overall flame temperature within
the combustor. The lower operating temperatures and improved
combustion facilitate increased operating efficiencies and
decreased combustor emissions at high power operations. As a
result, the combustor operates with a high combustion efficiency
and low carbon monoxide, nitrous oxide, and smoke emissions.
[0036] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the claims.
* * * * *