FIELD OF THE INVENTION
[0001] The present invention generally involves a gas turbine engine that combusts a hydrocarbon
fuel mixed with air to generate a high temperature gas stream that drives turbine
blades to rotate a shaft attached to the blades and more particularly to the engine's
fuel nozzle having a pilot nozzle that premixes fuel and air while achieving lower
nitrogen oxides.
BACKGROUND OF THE INVENTION
[0002] Gas turbine engines are widely used to generate power for numerous applications.
A conventional gas turbine engine includes a compressor, a combustor, and a turbine.
In a typical gas turbine engine, the compressor provides compressed air to the combustor.
The air entering the combustor is mixed with fuel and combusted. Hot gases of combustion
are exhausted from the combustor and flow into the blades of the turbine so as to
rotate the shaft of the turbine connected to the blades. Some of that mechanical energy
of the rotating shaft drives the compressor and/or other mechanical systems.
[0003] As government regulations disfavor the release of nitrogen oxides into the atmosphere,
their production as byproducts of the operation of gas turbine engines is sought to
be maintained below permissible levels. One approach to meeting such regulations is
to move from diffusion flame combustors to combustors that employ lean fuel and air
mixtures using a fully premixed operations mode to reduce emissions of, for example,
nitrogen oxides (commonly denoted NOx) and carbon monoxide (CO). These combustors
are variously known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean
Pre Mixed (LPM) combustion systems.
[0004] Fuel-air mixing affects both the levels of nitrogen oxides generated in the hot gases
of combustion of a gas turbine engine and the engine's performance. A gas turbine
engine may employ one or more fuel nozzles to intake air and fuel to facilitate fuel/air
mixing in the combustor. The fuel nozzles may be located in a head end portion of
the combustor, and may be configured to intake an air flow to be mixed with a fuel
input. Typically, each fuel nozzle may be internally supported by a center body located
inside of the fuel nozzle, and a pilot can be mounted at the downstream end of the
center body. As described for example in
US Patent No. 6,438,961, which is incorporated in its entirety herein by this reference for all purposes,
a so-called swozzle can be mounted to the exterior of the center body and located
upstream from the pilot. The swozzle has curved vanes that extend radially from the
center body across an annular flow passage and from which fuel is introduced into
the annular flow passage to be entrained into a flow of air that is swirled by the
vanes of the swozzle.
[0005] Various parameters describing the combustion process in the gas turbine engine correlate
with the generation of nitrogen oxides. For example, higher gas temperatures in the
combustion reaction zone are responsible for generating higher amounts of nitrogen
oxides. One way of lowering these temperatures is by premixing the fuel air mixture
and reducing the ratio of fuel to air that is combusted. As the ratio of fuel to air
that is combusted is lowered, so too the amount of nitrogen oxides is lowered. However,
there is a trade-off in performance of the gas turbine engine. For as the ratio of
fuel to air that is combusted is lowered, there is an increased tendency of the flame
of the fuel nozzle to blow out and thus render unstable the operation of the gas turbine
engine. A pilot of a diffusion flame type has been used for better flame stabilization
in a combustor, but doing so increases NOx.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Aspects and advantages of the invention are set forth below in the following description,
or may be obvious from the description, or may be learned through practice of the
invention.
[0007] In theory, the closer one comes to having at every point in the combustion chamber,
a stoichiometric relationship between the fuel and air that undergoes combustion at
a given temperature of combustion, the closer one comes to minimizing the generation
of nitrogen oxides as byproducts of the combustion. With a fuel nozzle configured
as described below, it becomes possible to achieve a more uniform equivalence ratio
across the plane of the center body tip of the outer nozzle and thus more closely
approximate achieving in the combustion chamber of the gas turbine engine such theoretical
conditions of the desired stoichiometric relationship between the fuel and air that
undergoes combustion at a given temperature of combustion. Moreover, to overcome one
of the drawbacks of a diffusion flame type of pilot, a premix pilot also can be used
as a pilot to stabilize the pilot flame, even in low fuel to air ratio to prevent
an increase in NOx.
[0008] In one aspect of the invention, a fuel nozzle includes premix conduits that are configured
with concentric axes that are parallel to the burner tube axis to direct the fuel/air
mixture axially from the premixed pilot nozzle, there is at least one air jet beside
each of the premix conduits wherein each of the air jets is directed radially outwardly
from the premix conduits so that each of the air jets can entrain some portion of
fuel/air mixture to direct the mixture radially outward from the premix conduits to
form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into
the combustion chamber of a gas turbine. The air jets desirably are disposed at the
downstream end of an annular channel that is disposed radially outwardly of the premix
conduits.
[0009] In another aspect of the present invention, each of the premix conduits is itself
configured concentrically about a central longitudinal axis disposed at an acute angle
with respect to the axis of burner tube to direct the fuel/air mixture radially outwardly
about the axis of burner tube to form a more uniform fuel/air mixture in the burn
exit plane of the nozzle and into the combustion chamber of a gas turbine.
[0010] In another aspect of the present invention, each of the premix conduits is itself
configured concentrically about a bi-directed central longitudinal axis that has a
first leg disposed parallel to the axis of burner tube and a second leg disposed at
an acute angle with respect to the axis of burner tube to direct the fuel/air mixture
radially outwardly about the axis of burner tube to form a more uniform fuel/air mixture
in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine.
[0011] In a further aspect, the fuel nozzle is itself configured concentrically about a
central longitudinal axis disposed at an acute angle with respect to the axis of burner
tube to direct the fuel/air mixture radially outwardly about the axis of burner tube,
there is at least one air jet beside each of the premix conduits so that each of the
air jets can entrain some portion of fuel/air mixture to further direct the mixture
radially outwardly from the premix conduits to form a more uniform fuel/air mixture
in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine.
Moreover, one or more of the air jets desirably is directed radially outwardly from
the premix conduits to entrain some portion of fuel/air mixture to further direct
the mixture radially outwardly from the premix conduits to form a more uniform fuel/air
mixture in the burn exit plane of the nozzle and into the combustion chamber of a
gas turbine.
[0012] Those of ordinary skill in the art will better appreciate the features and aspects
of such embodiments, and others, upon review of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Embodiments of the present invention will now be described, by way of example only,
with reference to the accompanying drawings in which:
FIG. 1 is a block diagram of a turbine system having a fuel nozzle coupled to a combustor
in accordance with an embodiment of the present technique;
FIG. 2 is a cross-sectional view of several portions of a combustor in a gas turbine
system of the present disclosure;
FIG. 3 depicts an exemplary embodiment of components of the present invention in a
view that is partially in perspective and partially in cross section;
FIG. 4 depicts another exemplary embodiment of components of the present invention
in a cross sectional view;
FIG. 5 is a cross sectional view taken along the sight lines designated 5 - - 5 in
FIG. 4;
FIG. 6 depicts a further exemplary embodiment of components of the present invention
in a cross sectional view;
FIG. 7 depicts yet another exemplary embodiment of components of the present invention
in a cross sectional view;
FIG. 8 depicts in cross section an alternative exemplary embodiment of the section
circumscribed by the dashed outline designated by the numeral 8 in FIG. 6;
FIG. 9 depicts another exemplary embodiment of components of the present invention
in a cross sectional view similar to the view shown in FIG. 4;
FIG. 10 schematically represents embodiments of the methods of the present invention
for operating a fuel/air nozzle for a gas turbine engine; and
FIG. 11 schematically represents alternative embodiments of the methods of the present
invention for operating a fuel/air nozzle for a gas turbine engine.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Reference will now be made in detail to present embodiments of the invention, one
or more examples of which are illustrated in the accompanying drawings. The detailed
description uses numerical and letter designations to refer to features in the drawings.
Like or similar designations in the drawings and description have been used to refer
to like or similar parts of embodiments of the invention.
[0015] Each example is provided by way of explanation of the invention, not limitation of
the invention. In fact, it will be apparent to those skilled in the art that modifications
and variations can be made in the present invention without departing from the scope
or spirit thereof. For instance, features illustrated or described as part of one
embodiment may be used on another embodiment to yield a still further embodiment.
Thus, it is intended that the present invention covers such modifications and variations
as come within the scope of the appended claims and their equivalents.
[0016] It is to be understood that the ranges and limits mentioned herein include all sub-ranges
located within the prescribed limits, inclusive of the limits themselves unless otherwise
stated. For instance, a range from 100 to 200 also includes all possible sub-ranges,
examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and
187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3,
and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to
5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes
7.
[0017] Referring to FIG. 1, a simplified drawing of several portions of a gas turbine system
10 is illustrated. The turbine system 10 may use liquid or gas fuel, such as natural
gas and/or a hydrogen rich synthetic gas, to run the turbine system 10. As depicted,
a plurality of fuel nozzles 12 of the type described more fully below intakes a fuel
supply 14, mixes the fuel with air, and distributes the air-fuel mixture into a combustor
16. The air-fuel mixture combusts in a chamber within the combustor 16, thereby creating
hot pressurized exhaust gases. The combustor 16 directs the exhaust gases through
a turbine 18 toward an exhaust outlet 20. As the exhaust gases pass through the turbine
18, the gases force one or more turbine blades to rotate a shaft 22 along an axis
of the system 10. As illustrated, the shaft 22 may be connected to various components
of the turbine system 10, including a compressor 24. The compressor 24 also includes
blades that may be coupled to the shaft 22. As the shaft 22 rotates, the blades within
the compressor 24 also rotate, thereby compressing air from an air intake 26 through
the compressor 24 and into the fuel nozzles 12 and/or combustor 16. The shaft 22 also
may be connected to a load 28, which may be a vehicle or a stationary load, such as
an electrical generator in a power plant or a propeller on an aircraft, for example.
As will be understood, the load 28 may include any suitable device capable of being
powered by the rotational output of turbine system 10.
[0018] FIG. 2 is a simplified drawing of cross sectional views of several portions of the
gas turbine system 10 schematically depicted in FIG. 1. As schematically shown in
FIG. 2, the turbine system 10 includes one or more fuel/air nozzles 12 located in
a head end portion 27 of one or more combustors 16 in the gas turbine engine. Each
illustrated fuel nozzle 12 may include multiple fuel nozzles integrated together in
a group and/or a standalone fuel nozzle, wherein each illustrated fuel nozzle 12 relies
at least substantially or entirely on internal structural support (e.g., load bearing
fluid passages). Referring to FIG. 2, the system 10 comprises a compressor section
24 for pressurizing a gas, such as air, flowing into the system 10 via air intake
26. In operation, air enters the turbine system 10 through the air intake 26 and may
be pressurized in the compressor 24. It should be understood that while the gas may
be referred to herein as air, the gas may be any gas suitable for use in a gas turbine
system 10. Pressurized air discharged from the compressor section 24 flows into a
combustor section 16, which is generally characterized by a plurality of combustors
16 (only one of which is illustrated in FIGs. 1 and 2) disposed in an annular array
about an axis of the system 10. The air entering the combustor section 16 is mixed
with fuel and combusted within the combustion chamber 32 of the combustor 16. For
example, the fuel nozzles 12 may inject a fuel/air mixture into the combustor 16 in
a suitable fuel-air ratio for optimal combustion, emissions, fuel consumption, and
power output. The combustion generates hot pressurized exhaust gases, which then flow
from each combustor 16 to a turbine section 18 (FIG. 1) to drive the system 10 and
generate power. The hot gases drive one or more blades (not shown) within the turbine
18 to rotate the shaft 22 and, thus, the compressor 24 and the load 28. The rotation
of the shaft 22 causes blades 30 within the compressor 24 to rotate and draw in and
pressurize the air received by the intake 26. It readily should be appreciated, however,
that a combustor 16 need not be configured as described above and illustrated herein
and in general may have any configuration that permits pressurized air to be mixed
with fuel, combusted and transferred to a turbine section 18 of the system 10.
[0019] FIGs. 3 - 9 schematically illustrate various embodiments of fuel/air nozzles 12 in
accordance with exemplary embodiments of the present invention. In each of FIGs. 4,
8 and 9 for example, at least each upstream end of each premix conduit 41 defines
a central axis 41d configured and disposed so that the flow of fluid that enters the
entrance opening 66a of each premix conduit 41 is directed parallel to the central
axis 36 of the centerbody 52. In each of FIGs. 6 and 7 for example, at least each
upstream end of each premix conduit 41 defines a central axis 41d configured and disposed
so that the flow of fluid that enters the entrance opening 66a of each premix conduit
41 is directed at an acute angle away from the central axis 36 of the centerbody 52
in the range of 0.1 degrees to twenty degrees. As schematically shown in FIG. 3 for
example, one embodiment of the fuel/air nozzle 12 includes premix conduits 41 that
are configured with concentric axes that are parallel to the burner tube axis 36 to
direct the fuel/air mixture axially from the premixed pilot nozzle 40. In the embodiments
that are schematically shown in FIGs. 4, 5 and 9, there is at least one air jet 42
beside each of the premix conduits 41 wherein each of the air jets 42 can entrain
some portion of fuel/air mixture to direct the mixture radially outwardly from the
premix conduits 41 to form a more uniform fuel/air mixture in the burn exit plane
44 of the nozzle 12 and into the combustion chamber 32 of the combustor 16 (FIGs.
1 and 2). In the embodiment depicted in FIGs. 4 and 5, each of the air jets 42 desirably
is directed radially outwardly from the premix conduits 41 so that each of the air
jets 42 more readily can entrain more of the fuel/air mixture to direct more of the
mixture radially outwardly from the premix conduits 41 to form a more uniform fuel/air
mixture in the burn exit plane 44 of the nozzle 12 and into the combustion chamber
32 of the combustor 16 (FIGs. 1 and 2).
[0020] As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine
engine desirably includes an axially elongating peripheral wall 50 defining an outer
envelope of the nozzle 12. The peripheral wall 50 of fuel/air nozzle 12 has an outer
surface 50a and an inner surface 50b facing opposite the outer surface 50a and defining
an axially elongating inner cavity 50c.
[0021] As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine
engine desirably includes a hollow, axially elongating centerbody 52 disposed within
the inner cavity 50c of the fuel/air nozzle 12 and defining a central axis 36, which
is the same as the central axis of the burner tube. The centerbody 52 is defined by
a centerbody wall 52a that defines an upstream end 52b and a downstream end 52c disposed
axially opposite the upstream end 52b. The centerbody wall 52a is defined by an exterior
surface 52d and an interior surface 52e facing opposite the exterior surface 52d.
The interior surface 52d of the centerbody wall 52a defines an axially elongating
interior passage 53 that is disposed concentrically about the central axis 36 of the
centerbody 52. A primary air flow channel 51 is defined in the annular space between
the inner surface 50b of the peripheral wall 50 and the exterior surface 52d of the
centerbody wall 52a.
[0022] As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine
engine desirably includes an axially elongated, hollow fuel supply line 54 extending
axially through the interior passage 53 of the centerbody 52. The fuel supply line
54 has an upstream end 54a that is disposed at the upstream end 52b of the centerbody
52 and that is configured for connection to a source of fuel (not shown). The fuel
supply line 54 has a downstream end 54b that is disposed at the downstream end 52c
of the centerbody 52. A secondary air flow channel is defined by an annular space
between the interior surface 52e of the centerbody 52 and the exterior surface of
the fuel supply line 54, and that annular space defines the axially elongating interior
passage 53 schematically shown in FIG. 3.
[0023] As schematically shown in FIG. 3, the primary fuel may be supplied to the combustion
chamber 32 of the combustor 16 (FIG. 2) through a plurality of air swirler vanes 56
that are fixed and extend across the flow path of the primary air flow channel 51.
These air swirler vanes 56 define a so-called swozzle that extends radially from the
exterior surface of centerbody wall 52a. As schematically shown in FIG. 3, each of
the air swirler vanes 56 of the swozzle desirably is provided with internal fuel conduits
57 that terminate in fuel injection ports or holes 58 from which primary fuel (indicated
by the arrows designated by the numeral 57a) flowing from the conduits 57 can be injected
into the primary air (indicated by the arrows designated by the numeral 51a) that
flows past the fuel injection ports 58 in the air swirler vanes 56. As primary air
flow 51a is directed against the air swirler vanes 56, a swirling pattern is imparted
to the primary air flow 51a that facilitates the mixing of the primary air flow 51a
with the primary fuel that is ejected from the holes 58 of the air swirler vanes 56
into the passing primary air flow 51a. The primary air flow 51a mixed with the primary
fuel then may flow into the pre-mixing annulus 51 that is defined between the peripheral
wall 50 and the inner centerbody 52, wherein the primary air flow 51a and the primary
fuel continue to mix together prior to entering the combustion chamber 32.
[0024] As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine
engine desirably includes a premixed pilot nozzle 40 that has an upstream end 40a
connected to the downstream end 52c of the centerbody 52. In the embodiment depicted
in FIG. 3, the downstream end 52c of the centerbody 52 and the upstream end 40a of
the premixed pilot nozzle 40 are defined in part by different sections of the metal
cylinder that forms the centerbody 52 and the outermost wall that defines the premixed
pilot nozzle 40. The premixed pilot nozzle 40 has a downstream end 40b disposed axially
opposite the upstream end 40a of the premixed pilot nozzle 40.
[0025] As schematically shown in FIGs. 3, 4 and 9 for example, the premixed pilot nozzle
40 defines a pilot fuel nozzle 60, which defines an upstream end 60a and a downstream
end 60b. As schematically shown in FIGs. 4 and 9 for example, the upstream end 60a
of the pilot fuel nozzle 60 is connected in fluid communication with the downstream
end 54b of the fuel supply line 54. The downstream end 60b of the pilot fuel nozzle
60 defines at least one fuel jet 61 configured in fluid communication with the upstream
end 60a of the pilot fuel nozzle 60. As schematically shown by the arrows designated
62 in FIGs. 4 and 9 for example, fuel 62 entering the pilot fuel nozzle 60 via the
downstream end 54b of the fuel supply line 54 exits the pilot fuel nozzle 60 via a
plurality of fuel jets 61 (shown in dashed line in FIG. 5).
[0026] As schematically shown in FIGs. 3, 4 and 9 for example, the premixed pilot nozzle
40 further defines an annular-shaped fuel plenum wall 63 disposed radially outwardly
from the pilot fuel nozzle 60 and desirably concentrically with respect to the burner
tube axis 36 shown in FIG. 3. As schematically shown in FIGs. 3, 4 and 9 for example,
the fuel plenum wall 63 defines a fuel plenum 64 between the pilot fuel nozzle 60
and the fuel plenum wall 63. As schematically shown in FIGs. 4 and 9 for example,
the fuel plenum wall 63 further defines a plurality of fuel holes 63a through which
fuel is discharged from the fuel plenum 64. As schematically shown in FIGs. 4 and
9 for example, at least one of the fuel holes 63a is connected in fluid communication
with at least one of the fuel jets 61 via the fuel plenum 64. Desirably, each of the
fuel holes 63a is connected in fluid communication with each of the fuel jets 61 via
the fuel plenum 64.
[0027] As schematically shown in FIGs. 3, 4 and 9 for example, the premixed pilot nozzle
40 further defines a plurality of axially elongated, hollow premix conduits 41 disposed
radially outwardly from the fuel plenum wall 63. As schematically shown in the embodiment
depicted in FIGs. 4 and 9 for example, each of the premix conduits 41 desirably is
defined in part by the plenum wall 63. As schematically shown in FIG. 3 for example,
each premix conduit 41 has an upstream end 41a that is disposed near the downstream
end 52c of the centerbody 52. As schematically shown in FIGs. 4 and 9 for example,
each premix conduit 41 defines at its upstream end 41a an entrance opening 66a that
communicates fluidly with the interior passage 53 of the centerbody 52. The arrows
designated 53a in FIGs. 4 and 9 schematically indicate the flow of air 53a that enters
the entrance opening 66a of each premix conduit 41 from the interior passage 53 of
the centerbody 52.
[0028] As schematically shown in FIGs. 4 and 9 for example, each premix conduit 41 is connected
in fluid communication with at least one of the fuel holes 63a that is defined in
the fuel plenum wall 63 of the fuel plenum 64. The arrows designated 62a in FIGs.
4 and 9 schematically indicate the flow of fuel 62a that exits from the fuel plenum
64 through the fuel holes 63a defined in the fuel plenum wall 63 and passes into each
premix conduit 41. The arrows designated 62b in FIGs. 4 and 9 schematically indicate
the flow of the fuel-air mix 62b that travels downstream in the premix conduits 41
of the premixed pilot nozzle 40.
[0029] As schematically shown in FIGs. 4 and 9 for example, each premix conduit 41 has a
downstream end 41b that is disposed axially opposite the upstream end 41a of the premix
conduit 41 and that is disposed near the downstream end 40b of the premixed pilot
nozzle 40. As schematically shown in FIGs. 4 and 9 for example, each downstream end
41b of each premix conduit 41 defines an exit opening 66b that allows fluid, i.e.,
the fuel-air mix 62b, to discharge from the hollow premix conduit 41. As schematically
shown in FIGs. 4 and 9 for example, each downstream end 41b of each premix conduit
41 defines a central axis 41c, and the walls that define each premix conduit 41 are
disposed concentrically about this central axis 41c. Moreover, as schematically shown
for the embodiment of the premixed pilot nozzle 40 depicted in FIGs. 4 and 9 for example,
each central axis 41c is a straight line that is disposed so that the flow of the
fluid that is the mix of fuel and air that discharges from the exit opening 66b of
each premix conduit 41 is directed parallel to the central axis 36 of the centerbody
52.
[0030] While the fuel-air mix 62b tends to spread radially from each central axis 41c once
the fuel-air mix 62b leaves the exit opening 66b of each premix conduit 41, applicants
have shown that the radial spread is not very significant. Indeed, applicants' studies
have shown that the equivalence ratio at the section of the burn exit plane 44 (FIGs.
4 and 9) that is located immediately downstream of the exit opening 66b of each premix
conduit 41 can be almost twice the equivalence ratio that exists at the section of
the burn exit plane 44 (FIGs. 4 and 9) that is located immediately downstream of the
central axis 36 of the centerbody 52. High equivalence ratio at a location that is
immediately downstream of the exit opening 66b of each premix conduit 41 can continuously
and effectively light the fuel/air mixture through the axially elongating inner cavity
50c (FIG. 3) and can make the flame stable even if the flame is at lean-blow-out (LBO)
condition. This is one of the important roles of a premix pilot, and the premix pilot
60 fulfills this role without an increase of NOx.
[0031] Various embodiments of the present invention include features that counteract this
much higher equivalence ratio that exists at the section of the burn exit plane 44
(FIGs. 4 and 9) that is located immediately downstream of the exit opening 66b of
each premix conduit 41. As schematically shown for the embodiments of the premixed
pilot nozzle 40 that are depicted in FIGs. 3, 4, 5 and 9 for example, the premixed
pilot nozzle 40 further defines an annular channel 70 that is disposed radially outwardly
from the premix conduits 41. In the embodiments that are depicted in FIGs. 3, 4, 5
and 9 for example, the inner wall 43 of the annular channel 70 also serves to define
the outer wall 43 of the premix conduits 41. In the embodiments that are depicted
in FIGs. 3, 4, 5 and 9 for example, the centerbody wall 52a also serves to define
the outer wall 52a of the annular channel 70.
[0032] As schematically shown for the embodiments of the premixed pilot nozzle 40 that are
depicted in FIGs. 3, 4 and 9 for example, the upstream end of the annular channel
70 is configured to communicate fluidly with the interior passage 53 of the centerbody
52 and thus receives a flow of air from the interior passage 53 of the centerbody
52. At the downstream end of the annular channel 70, a plurality of air jets 42 is
defined. At least one of the air jets 42 is disposed nearby at least one of the exit
openings 66b of at least one of the premix conduits 41. Desirably, as shown in FIGs.
4, 5 and 9 for example, at least one of the air jets 42 is disposed nearby each of
the exit openings 66b of each one of the premix conduits 41.
[0033] As schematically shown in FIG. 9 for example, each of the passages that defines one
of the air jets 42 is defined concentrically around a central axis 42a that is disposed
parallel to the central axis 41c of the downstream end 41b of the nearby premix conduit
41. In so doing, the higher velocity air leaving each air jets 42 entrains some of
the fuel/air mixture leaving the premix conduits 41 and serves to direct the fuel/air
mixture that exists at the section of the burn exit plane 44 (FIG. 9) that is located
immediately downstream of the exit opening 66b of each premix conduit 41. The overall
result is a more uniform equivalence ratio at the burn exit plane 44 (FIG. 9) of the
fuel-air nozzle 12, and this also can be used by lighting source as a pilot.
[0034] As schematically shown in FIG. 4 for example, each of the passages that defines one
of the air jets 42 is defined concentrically around a central axis 42a that is disposed
at an acute angle with respect to the central axis 41c of the downstream end 41b of
the nearby premix conduit 41. The magnitude of this acute angle desirably is in the
range of 0.1 degrees to twenty degrees. Moreover, the air jet 42 in the FIG. 4 embodiment
desirably is configured and disposed so that the respective air jet 42 directs the
flow of air exiting the air jet 42 in a direction away from the nearby one of the
exit openings 66b of the premix conduits 41. Thus, in the embodiment schematically
shown in FIG. 4 for example, each air jet 42 is pointed so that the air leaving that
air jet 42 moves in a direction that is both downstream and radially away from the
central axis 36 of the centerbody 52 as well as radially away from the central axis
41c of downstream end 41b of the respective nearby premix conduit 41. In so doing,
the air leaving each air jets 42 entrains some of the fuel/air mixture leaving the
premix conduits 41 and serves to direct the fuel/air mixture that exists at the section
of the burn exit plane 44 (FIG. 4) that is located immediately downstream of the exit
opening 66b of each premix conduit 41 radially outwardly toward the peripheral wall
50 (FIG. 3). The overall result is a more uniform equivalence ratio at the burn exit
plane 44 (FIG. 4) of the fuel-air nozzle 12, and this also can be used by lighting
source as a pilot.
[0035] In another embodiment of the present invention depicted schematically in FIG. 6 for
example, with the exception of the embodiment of the premixed pilot nozzle 40 that
is depicted schematically in FIG. 6, the embodiment of FIG. 6 is like the embodiment
of FIGs. 3, 4, 5 and 9. As schematically in FIG. 6, each of the premix conduits 41
is itself configured concentrically about a central longitudinal axis 41c that is
disposed at an acute angle with respect to the central axis 36 of the centerbody 52.
The magnitude of this acute angle desirably is in the range of 0.1 degrees to twenty
degrees. Thus, in the premixed pilot nozzle 40 that is depicted schematically in FIG.
6, each of the premix conduits 41 is configured and disposed so as to direct the fuel/air
mixture exiting from the exit opening 66b of each premix conduit 41 radially outwardly
away from the central axis 36 of the centerbody 52 so as to form a more uniform fuel/air
mixture in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion
chamber of a gas turbine 10 and so as to continuously and effectively light the fuel/air
mixture that is supplied through an axially elongating inner cavity 50c (FIG. 3) of
the fuel-air nozzle 12. Though not specifically illustrated in FIG. 6 for example,
the axial length of one or more of the premix conduits 41 can extend beyond the downstream
end 40b of the premixed pilot nozzle 40 in a manner concentrically around the central
axis 41c of the downstream end 41b of premix conduit 41.
[0036] In another embodiment of the present invention depicted schematically in FIG. 8 for
example, with the exception of the embodiment of the premix conduits 41 of the premixed
pilot nozzle 40 that is depicted schematically in FIG. 6, the embodiment of FIG. 8
is like the embodiment of FIGs. 3, 4, 5, 6 and 9. In the embodiment depicted schematically
in FIG. 8, each of the premix conduits 41 is itself configured concentrically about
a bi-directed central longitudinal axis having a first leg 41d and a second leg 41c.
As schematically in FIG. 8, the first leg 41d of the bi-directed central longitudinal
axis is disposed parallel to the central axis 36 of the centerbody 52 and extends
between the upstream end 41a and the downstream end 41b of each premix conduit 41.
A second leg 41c of the bi-directed central longitudinal axis is disposed at an acute
angle with respect to the central axis 36 of the centerbody 52 and extends through
the downstream end 41b of each premix conduit 41. The magnitude of this acute angle
desirably is in the range of 0.1 degrees to twenty degrees. Thus, the premix conduit
41 that is depicted schematically in FIG. 8 is configured and disposed so as to direct
the fuel/air mixture exiting from the exit opening 66b radially outwardly away from
the central axis 36 of the centerbody 52 so as to form a more uniform fuel/air mixture
in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber
of a gas turbine 12 and so as to continuously and effectively light the fuel/air mixture
that is supplied through an axially elongating inner cavity 50c (FIG. 3) of the fuel-air
nozzle 12.
[0037] In another embodiment of the present invention depicted schematically in FIG. 7 for
example, with the exception of the embodiment of the premix conduits 41 and annular
channel 70 of the premixed pilot nozzle 40 that is depicted schematically in FIGs.
3, 4, 5 and 9, the embodiment of FIG. 7 is like the embodiments of FIGs. 3, 4, 5 and
9. As schematically in FIG. 7, each of the premix conduits 41 is itself configured
concentrically about a central longitudinal axis 41c that is disposed at an acute
angle with respect to the central axis 36 of the centerbody 52. The magnitude of this
acute angle desirably is in the range of 0.1 degrees to twenty degrees. Thus, in the
premixed pilot nozzle 40 that is depicted schematically in FIG. 7, each of the premix
conduits 41 is configured and disposed so as to direct the fuel/air mixture exiting
from the exit opening 66b of each premix conduit 41 radially outwardly away from the
central axis 36 of the centerbody 52 so as to form a more uniform fuel/air mixture
in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber
of a gas turbine 10 and so as to continuously and effectively light the fuel/air mixture
that is supplied through an axially elongating inner cavity 50c (FIG. 3) of the fuel-air
nozzle 12.
[0038] As schematically shown for the embodiment of the premixed pilot nozzle 40 that is
depicted in FIG. 7 for example, the upstream end of the annular channel 70 is configured
to taper as it proceeds in the downstream direction toward the air jets 42 that are
disposed beside each of the exit openings of premix conduits 41. As described above
with regard to the embodiment of FIGs. 3, 4 and 5, each of the air jets 42 is directed
radially outwardly from the premix conduits 41 so that each of the air jets 42 can
entrain some portion of fuel/air mixture to further direct the mixture radially outwardly
from the premix conduits 41 to form a more uniform fuel/air mixture in the burn exit
plane 44 of the fuel-air nozzle 12 and into the combustion chamber 32 of a combustor
16 (FIGs. 1 and 2) and to continuously and effectively light the fuel/air mixture
that is supplied through an axially elongating inner cavity 50c (FIG. 3) of the fuel-air
nozzle 12.
[0039] Each embodiment of the premixed pilot nozzle 40 provides a small well anchored premixed
flame near the base of the fuel-air nozzle 12, thus anchoring the swirling fuel air
mixture exiting the fuel-air nozzle 12. The improved flame stability enables lower
fuel/air operations, thus extending LBO and the emissions operability window.
[0040] With fuel/air nozzles 12 such as the embodiments described above, it becomes feasible
to implement advantageous methods of operating a fuel/air nozzle 12 for a gas turbine
engine 10. One embodiment of such a method of operating a fuel/air nozzle 12 for a
gas turbine engine 10 desirably includes the following steps schematically shown in
FIG. 10: the step 81 of delivering a primary flow of air 51a (e.g., FIG. 3) downstream
past the swozzle to swirl the primary flow of air; the step 82 of delivering a primary
flow of fuel 57a (e.g., FIG. 3) through the swozzle to mix with the swirled primary
flow of air 51a downstream of the swozzle; the step 83 of delivering a flow of pilot
fuel 62 (e.g., FIG. 4) through a hollow fuel supply line 54 to the premix pilot nozzle
40; the step 84 of delivering a secondary flow of air 53a (e.g., FIG. 4) downstream
through the centerbody 52 (e.g., FIG. 3) to the premix pilot nozzle 40; the step 85
of mixing the pilot fuel 62 with the secondary flow of air 53a in a plurality of axially
elongated, hollow premix conduits 41 (e.g., FIG. 4) that discharge the fuel/air mixture
62b (e.g., FIGs. 4 and 9) from the downstream end 41b of the premix pilot nozzle 40;
and the step 86 of expelling the fuel/air mixture 62b from the premix conduits 41
of the premixed pilot nozzle 40 away from the central axis 36 of the centerbody 52
(e.g., FIGs. 3, 4 and 6 - 9).
[0041] Another embodiment of such a method of operating a fuel/air nozzle 12 for a gas turbine
engine 10 desirably includes the following steps schematically shown in FIG. 11: the
step 81 of delivering a primary flow of air 51a (e.g., FIG. 3) downstream past the
swozzle to swirl the primary flow of air; the step 82 of delivering a primary flow
of fuel 57a (e.g., FIG. 3) through the swozzle to mix with the swirled primary flow
of air 51a downstream of the swozzle; the step 83 of delivering a flow of pilot fuel
62 (e.g., FIG. 4) through a hollow fuel supply line 54 to the premix pilot nozzle
40; the step 84 of delivering a secondary flow of air 53a (e.g., FIG. 4) downstream
through the centerbody 52 (e.g., FIG. 3) to the premix pilot nozzle 40; the step 85
of mixing the pilot fuel 62 with the secondary flow of air 53a in a plurality of axially
elongated, hollow premix conduits 41 (e.g., FIG. 4) that discharge the fuel/air mixture
62b (e.g., FIGs. 4 and 9) from the downstream end 41b of the premix pilot nozzle 40;
the step 87 of diverting some of the secondary flow of air 53a (e.g., FIGs. 4, 7 and
9) to an annular channel 70 that is disposed radially outwardly from the premix conduits
41 of the premixed pilot nozzle 40; and the step 88 of expelling air from the annular
channel 70 away from the premixed pilot nozzle 40 (e.g., FIGs. 4, 7 and 9). Desirably,
the pressure of the air expelled from the annular channel 70 exceeds the pressure
of the air entering the annular channel 70. Desirably, as schematically shown in FIG.
7 for example, the annular channel 70 includes an upstream end that is configured
to taper as it proceeds in the downstream direction. Desirably, as schematically shown
in FIG. 7 for example, a further embodiment of the method comprises the step of expelling
the fuel/air mixture from the premix conduits 41 of the premixed pilot nozzle 40 away
from the central axis 36 of the centerbody 52. Desirably, as schematically shown in
FIG. 4 for example, a further embodiment of the method comprises the step of expelling
the fuel/air mixture 62b from the premix conduits 41 of the premixed pilot nozzle
40 in a direction that is parallel to the central axis 36 of the centerbody 52. Desirably,
as schematically shown in FIGs. 4 and 7 for example, a further embodiment of the method
comprises the step of expelling the fuel/air mixture 62b from the annular channel
70 in a direction that is radially away from the central axis 36 of the centerbody
52.
[0042] This written description uses examples to disclose the invention, including the best
mode, and also to enable any person skilled in the art to practice the invention,
including making and using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the claims, and may include
other examples that occur to those skilled in the art. Such other and examples are
intended to be within the scope of the claims if they include structural elements
that do not differ from the literal language of the claims, or if they include equivalent
structural elements with insubstantial differences from the literal languages of the
claims.
[0043] Various aspects and embodiments of the present invention are defined by the following
numbered clauses:
- 1. A fuel/air nozzle for a gas turbine engine, the fuel/air nozzle comprising:
an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle,
the peripheral wall having an outer surface and an inner surface facing opposite the
outer surface and defining an axially elongating inner cavity;
a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air
nozzle and defining a central axis, the centerbody being defined by a centerbody wall
defining an upstream end and a downstream end disposed axially opposite the upstream
end, the centerbody wall being defined by an exterior surface and an interior surface
facing opposite the exterior surface, the interior surface of the centerbody wall
defining an axially elongating interior passage disposed concentrically about the
central axis of the centerbody;
an elongated, hollow fuel supply line extending axially through the interior passage
of the centerbody, the fuel supply line having an upstream end disposed at the upstream
end of the centerbody and configured for connection to a source of fuel, the fuel
supply line having a downstream end disposed at the downstream end of the centerbody;
a primary air flow channel being defined by an annular space between the exterior
surface of the centerbody and the inner surface of the peripheral wall;
a premixed pilot nozzle having an upstream end connected to the downstream end of
the centerbody, the premixed pilot nozzle having a downstream end disposed axially
opposite the upstream end of the premixed pilot nozzle;
the premixed pilot nozzle further defining a plurality of axially elongated, hollow
premix conduits, each premix conduit having an upstream end disposed near the downstream
end of the centerbody and defining an entrance opening that communicates fluidly with
the interior passage of the centerbody, each premix conduit defining at least one
fuel hole connected in fluid communication with the downstream end of the fuel supply
line, each premix conduit having a downstream end defining an exit opening that allows
fluid to discharge from the hollow premix conduit, at least each upstream end of each
premix conduit defining a central axis configured and disposed so that the flow of
fluid that enters the entrance opening of each premix conduit is directed parallel
to the central axis of the centerbody; and
an annular channel disposed radially outwardly from the premix conduits, the annular
channel being configured to communicate fluidly with the interior passage of the centerbody.
- 2. The fuel/air nozzle as in clause 1, wherein the upstream end of at least one premix
conduit defines a central axis that is not parallel to the central axis of the downstream
end of that at least one premix conduit.
- 3. The fuel/air nozzle as in clause 1 or 2, wherein the annular channel defines a
plurality of air jets at a downstream end thereof.
- 4. The fuel/air nozzle as in clause 3, wherein at least one of the air jets being
disposed nearby one of the exit openings of at least one of the premix conduits and
having a central axis that forms an acute angle with the central axis of the centerbody.
- 5. The fuel/air nozzle as in clause 4, wherein the central axis of at least one of
the air jets directs a flow of air exiting the air jet in a direction away from the
central axis of the centerbody.
- 6. The fuel/air nozzle as in any of clauses 1 to 5, wherein the annular channel is
configured to taper as it proceeds in the downstream direction toward the air jets.
- 7. A combustor for a gas turbine engine, the combustor comprising:
a head end portion;
at least one fuel/air nozzle carried by the head portion, each fuel/air nozzle further
comprising:
an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle,
the peripheral wall having an outer surface and an inner surface facing opposite the
outer surface and defining an axially elongating inner cavity;
a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air
nozzle and defining a central axis, the centerbody being defined by a centerbody wall
defining an upstream end and a downstream end disposed axially opposite the upstream
end, the centerbody wall being defined by an exterior surface and an interior surface
facing opposite the exterior surface, the interior surface of the centerbody wall
defining an axially elongating interior passage disposed concentrically about the
central axis of the centerbody;
an elongated, hollow fuel supply line extending axially through the interior passage
of the centerbody, the fuel supply line having an upstream end disposed at the upstream
end of the centerbody and configured for connection to a source of fuel, the fuel
supply line having a downstream end disposed at the downstream end of the centerbody;
a primary air flow channel being defined by an annular space between the exterior
surface of the centerbody and the inner surface of the peripheral wall;
a premixed pilot nozzle having an upstream end connected to the downstream end of
the centerbody, the premixed pilot nozzle having a downstream end disposed axially
opposite the upstream end of the premixed pilot nozzle; and
the premixed pilot nozzle further defining a plurality of axially elongated, hollow
premix conduits, each premix conduit having an upstream end disposed near the downstream
end of the centerbody and defining an entrance opening that communicates fluidly with
the interior passage of the centerbody, each premix conduit being connected in fluid
communication with the downstream end of the fuel supply line, each premix conduit
having a downstream end defining an exit opening that allows fluid to discharge from
the hollow premix conduit, each downstream end of each premix conduit defining a central
axis configured and disposed so that the flow of fluid that discharges from exit opening
is directed parallel to the central axis of each premix conduit; and
an annular channel disposed radially outwardly from the premix conduits, the annular
channel being configured to communicate fluidly with the interior passage of the centerbody.
- 8. The combustor as in clause 7, wherein the annular channel defines a plurality of
air jets at a downstream end thereof.
- 9. The combustor as in clause 8, wherein at least one of the air jets being disposed
nearby one of the exit openings of at least one of the premix conduits and having
a central axis that forms an acute angle with the central axis of the centerbody.
- 10. The combustor as in clause 9, wherein the central axis of at least one of the
air jets directs a flow of air exiting the air jet in a direction away from the central
axis of the centerbody.
- 11. The combustor as in any of clauses 7 to 10, wherein the annular channel is configured
to taper as it proceeds in the downstream direction toward the air jets.
- 12. A method of operating a fuel/air nozzle for a gas turbine engine, the fuel/air
nozzle being defined by a peripheral wall, a hollow centerbody disposed within the
peripheral wall and defining a central axis, a swozzle extending from the exterior
of the upstream end of the centerbody and radially toward the peripheral wall, and
at the downstream end of centerbody a premix pilot nozzle including a plurality of
premix conduits having exit openings, the method comprising the steps of:
delivering a primary flow of air downstream past the swozzle to swirl the primary
flow of air;
delivering a primary flow of fuel through the swozzle to mix with the swirled primary
flow of air downstream of the swozzle;
delivering a flow of pilot fuel through a hollow fuel supply line to the premix pilot
nozzle;
delivering a secondary flow of air downstream through the centerbody to the premix
pilot nozzle;
mixing the pilot fuel with the secondary flow of air in a plurality of axially elongated,
hollow premix conduits that discharge the fuel/air mixture from the downstream end
of the premix pilot nozzle;
diverting some of the secondary flow of air to an annular channel that is disposed
radially outwardly from the premix conduits of the premixed pilot nozzle; and
expelling the fuel/air mixture from the exit openings of the premix conduits of the
premixed pilot nozzle.
- 13. The method as in clause 12, further comprising the step of expelling the fuel/air
mixture from the premix conduits of the premixed pilot nozzle in a direction that
is parallel to the central axis of the centerbody.
- 14. The method as in clause 12 or 13, further comprising the step of expelling the
fuel/air mixture from the premix conduits of the premixed pilot nozzle in a direction
that is radially away from the central axis of the centerbody.
- 15. The method as in any of clauses 12 to 14, wherein the pressure of the air expelled
from the annular channel exceeds the pressure of the air entering the annular channel.
- 16. The method as in any of clauses 12 to 15, wherein the annular channel tapers as
it proceeds in the downstream direction.
- 17. The method as in any of clauses 12 to 16, further comprising the step of expelling
air from the annular channel of the premixed pilot nozzle in a direction that is away
from the exit openings of the premix conduits.
1. A fuel/air nozzle (12) for a gas turbine engine (10), the fuel/air nozzle comprising:
an axially elongating peripheral wall (50) defining an outer envelope of the fuel/air
nozzle (12), the peripheral wall (50) having an outer surface (50a) and an inner surface
(50b) facing opposite the outer surface (50a) and defining an axially elongating inner
cavity (50c);
a hollow, axially elongating centerbody (52) disposed within the inner cavity (50c)
of the fuel/air nozzle (12) and defining a central axis, the centerbody being defined
by a centerbody wall (52a) defining an upstream end (52b) and a downstream end (52c)
disposed axially opposite the upstream end (52b), the centerbody wall (52a) being
defined by an exterior surface (52a) and an interior surface (52e) facing opposite
the exterior surface (52d), the interior surface (52e) of the centerbody wall (52a)
defining an axially elongating interior passage (53) disposed concentrically about
the central axis of the centerbody (52);
an elongated, hollow fuel supply line (54) extending axially through the interior
passage (53) of the centerbody (52), the fuel supply line (54) having an upstream
end (54a) disposed at the upstream end (52b) of the centerbody (52) and configured
for connection to a source of fuel (14), the fuel supply line (54) having a downstream
end (54b) disposed at the downstream end (52c) of the centerbody (52);
a primary air flow channel (51) being defined by an annular space between the exterior
surface (52a) of the centerbody (52) and the inner surface (50b) of the peripheral
wall (50);
a premixed pilot nozzle (40) having an upstream end (40a) connected to the downstream
end (52c) of the centerbody (52), the premixed pilot nozzle (40) having a downstream
end (40b) disposed axially opposite the upstream end (40a) of the premixed pilot nozzle
(40); and
the premixed pilot nozzle (40) further defining a plurality of axially elongated,
hollow premix conduits (41), each premix conduit (41) having an upstream end (41a)
disposed near the downstream end (52c) of the centerbody (52) and defining an entrance
opening that communicates fluidly with the interior passage (53) of the centerbody
(52), each premix conduit (41) having at least one fuel hole (63a) being connected
in fluid communication with the downstream end (54b) of the fuel supply line (54),
each premix conduit (41) having a downstream end (41b) defining an exit opening (66b)
that allows fluid to discharge from the hollow premix conduit (41), each downstream
end (41b) of each premix conduit (41) defining a central axis (41c) that is not parallel
to the central axis of the centerbody (52).
2. The fuel/air nozzle as in claim 1, wherein each central axis (41c) of at least one
premix conduit (41) is disposed at an acute angle with respect to the central axis
of the centerbody (52).
3. The fuel/air nozzle as in claim 1 or 2, wherein the premixed pilot nozzle (40) further
defines an annular channel (70) disposed radially outwardly from the premix conduits
(41), the annular channel (70) being configured to communicate fluidly with the interior
passage (53) of the centerbody (52), the annular channel (70) defining a plurality
of air jets (61), at least one of the air jets (61) being disposed nearby one of the
exit openings (66b) of at least one of the premix conduits (41) and having a central
axis.
4. The fuel/air nozzle as in claim 3, wherein the central axis (41d) of the upstream
end (41a) of at least one premix conduit (41) is configured and disposed to extend
in a direction parallel to the central axis of the centerbody (52).
5. The fuel/air nozzle as in claim 3 or 4, wherein the central axis (42a) of at least
one of the air jets (42) forms an acute angle with the central axis of the centerbody.
6. The fuel/air nozzle as in any of claims 3 to 5, wherein the annular channel (70) is
configured to taper as it proceeds in the downstream direction toward the air jets
(61).
7. The fuel/air nozzle as in any preceding claim, further comprising a swozzle including
a plurality of swirl blades (56) extending radially across the primary air flow channel
(51), at least one of the swirl blades (56) defining a fuel conduit (57) having an
inlet at one end thereof and an outlet at an opposite end thereof in fluid communication
with the primary air flow channel (51).
8. The fuel/air nozzle as in any preceding claim, wherein the premixed pilot nozzle (40)
defines a pilot fuel nozzle (60), the pilot fuel nozzle (60) defining an upstream
end (60a) and a downstream end (60b), the upstream end (60c) of the pilot fuel nozzle
(60) being connected in fluid communication with the downstream end (54b) of the fuel
supply line (54), the downstream end (60b) of the pilot fuel nozzle (60) defining
at least one fuel jet (61) configured in fluid communication with the upstream end
(60a) of the pilot fuel nozzle (60); and
the premixed pilot nozzle (40) further defining a fuel plenum wall (63) disposed radially
outwardly from the pilot fuel nozzle (60) and defining a fuel plenum (64) between
the pilot fuel nozzle (60) and the fuel plenum wall (63), the fuel plenum wall (63)
further defining a plurality of fuel holes (63a), at least one of the fuel holes (63c)
being connected in fluid communication with at least one of the fuel jets (61) via
the fuel plenum (64), each premix conduit (41) being disposed radially outwardly from
the fuel plenum wall (43) and in fluid communication with at least one of the fuel
holes (63a).
9. A combustor (16) for a gas turbine engine (10), the combustor comprising:
a head end portion (27);
at least one fuel/air nozzle (12) carried by the head portion (27), the at least one
fuel/air nozzle as recited in any of claims 1 to 8.
10. A method of operating a fuel/air nozzle (12) for improved flame stability and NOx
in a gas turbine engine (10), the fuel/air nozzle (12) being defined by a peripheral
wall (50), a hollow centerbody (52) disposed within the peripheral wall (50) and defining
a central axis, a swozzle extending from the exterior (52d) of the upstream end (52b)
of the centerbody (52) and radially toward the peripheral wall (50), and at the downstream
end (52c) of centerbody (52) a premix pilot nozzle (40) including a plurality of premix
conduits (41) having exit openings (66b), the method comprising the steps of:
delivering (81) a primary flow of air (51) downstream past the swozzle to swirl the
primary flow of air (51);
delivering (82) a primary flow of fuel through the swozzle to mix with the swirled
primary flow of air (51) downstream of the swozzle;
delivering (83) a flow of pilot fuel through a hollow fuel supply line (54) to the
premix pilot nozzle (40);
delivering (84) a secondary flow of air downstream through the centerbody (52) to
the premix pilot nozzle (40);
mixing (85) the pilot fuel with the secondary flow of air in a plurality of axially
elongated, hollow premix conduits (41) wherein each premix conduit (41) defines a
central axis at the downstream end (41b) thereof that is not parallel to the central
axis of the centerbody (52) and that discharges the fuel/air mixture from the downstream
end (40b) of the premix pilot nozzle (40); and
expelling the fuel/air mixture from the exit openings (66b) of the premix conduits
(41) of the premixed pilot nozzle (40).
11. The method as in claim 10, further comprising the step of expelling the fuel/air mixture
from the premix conduits (41) of the premixed pilot nozzle (40) in a direction that
is radially away from the central axis of the centerbody (52).
12. The method as in claim 10 or 11, further comprising the step of diverting some of
the secondary flow of air to an annular channel (70) that is disposed radially outwardly
from the premix conduits (41) of the premixed pilot nozzle (40).
13. The method as in claim 12, wherein the pressure of the air expelled from the annular
channel (70) exceeds the pressure of the air entering the annular channel (70).
14. The method as in claim 12 or 13, wherein the annular channel (70) tapers as it proceeds
in the downstream direction.
15. The method as in any of claims 12 to 14, further comprising the step of expelling
air from the annular channel (70) of the premixed pilot nozzle (40) in a direction
that is away from the exit openings (66b) of the premix conduits (41).
16. The method as in claim 15, wherein the air expelled from the annular channel (70)
is directed away from the central axis of the centerbody (52).