Note: Descriptions are shown in the official language in which they were submitted.
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FUEL INJECTOR FOR GAS TURBINE ENGINE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gas turbine engines
and, more particularly, to a fuel injector for such
engines.
2. Description of the Prior Art
Many small gas turbine engines utilize fuel pressure
to atomize fuel at the fuel nozzle of an injector to
inject fuel into the combustion chamber. At low fuel
flows, such as starting conditions, the fuel flow rate is
too low to pressurize the fuel to produce adequate
droplet size for a particular injector. Such fuel
systems are designed for maximum pressure at full engine
power. Thus, the smallest flow number possible for a
given engine design is determined by the maximum pressure
available from the fuel pump at maximum power. At
starting conditions and low power, small quantities of
fuel are required, thereby developing low pressure drop.
This results in inadequate atomization at low power and
leads to poor emissions and combustion instability.
Furthermore, since the fuel injector is immersed in
a very hot environment of the gas turbine engine,
stagnation of the fuel in the delivery passages can be
detrimental to the injector in that the heat transfer
from the walls of the injector is reduced which can lead
to hot spots on the otherwise wetted wall. It has been
found that excessive wall temperatures can lead to fuel
coking and subsequent injector contamination. Low fuel
flows in these regions further aggravate the situation.
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In some cases, lack of adequate heat transfer in the stem may lead to
unacceptable temperature gradients and attendant stresses in the stem which
can
affect its fatigue life.
It has been found that by swirling a substantial quantity of air around a
nozzle
of a fuel injector, an improvement in low power performance can be obtained.
However, swirling the air can lead to flow separation around the face of the
injector,
resulting in carbon growth and overheating of the injector.
Air swirlers have been developed and are described in U.S. Patent
No. 5,579,645, Prociw et al., issued December 3, 1996, and U.S. Patent
No. 6,082,113 issued on July 4, 2000 for a Gas Turbine Injector by Prociw et
al. and
assigned to Pratt & Whitney Canada Inc. These air swirlers reduce flow
separation at
the injector. However, it is considered that other improvements are required
to
improve low power performance of the injector by improving fuel atomization at
the
injector.
The stem of the injector, that is, the elongated stem through which the
various
fuel conduits are contained, extends from the fuel source across the P3 air
envelope
surrounding the combustor wall. The stem is also subjected to high
temperatures
and, therefore, problems of fuel stagnation that can lead to fuel coking is
also
possible within the stem.
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SUMMARY OF THE INVENTION
It is an aim of the present invention to provide an improved injector wherein
low power fuel atomization will be enhanced.
It is a further aim of the present invention to provide an improved simplex
pressure injector with improved low power performance.
It is yet a further aim of the present invention to provide an improved duplex
pressure injector with improved low power performance.
It is an aim of the present invention to provide a fuel flow path within the
stem and the injector tip which follows a circular path. Parts of the stem and
the
injector tip are provided with annuli which allow a circular and/or spiral
path for the
fuel.
It is yet a further aim of the present invention to provide an improved fuel
flow passage in the stem of the injector. It is known that the velocity of the
flow in
the annular channels is controlled by appropriately sizing the inlet orifice
to produce
the correct pressure loss for the heat transfer rate required. According to
the present
invention, much higher velocities than would occur in conventional designs are
attributable to the present method since a large portion of the fuel flow is
in the
tangential direction and not governed by the mass of fuel.
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In the present invention, this control of the flow
velocity to produce the correct pressure loss is
determined not by a single metering or trim orifice at
the inlet to the injector but by providing such metering
orifices throughout the stem prior to the fuel entering
the injector.
A construction in accordance with the present
invention comprises a fuel injector for a combustor in a
gas turbine engine, wherein the combustor includes a
combustor wall defining a combustion chamber surrounded
by pressurized air, the injector comprising an injector
tip adapted to protrude, when in use, through the
combustor wall into the chamber, the injector tip having
an injector body extending along an injector tip axis, a
primary fuel nozzle formed in the injector tip
concentrically of the injector tip axis and communicating
with a primary fuel chamber formed as a cone upstream of
the fuel nozzle and coaxial therewith, at least a first
annular fuel channel defined in the injector body
upstream of the primary fuel chamber concentric with the
injector tip axis and communicating with the primary fuel
chamber, and means for providing a flow of pressurized
fuel to the first annular channel tangentially thereof in
order to provide a swirl to the fuel flow in the first
annular fuel channel, the primary fuel chamber and thus
to the injector tip, thereby atomizing the fuel as it
exits the primary fuel nozzle.
More particularly, swirl slots communicate the first
annular channel to the primary fuel chamber.
In a more specific embodiment of the present
invention, there is provided a secondary fuel delivery
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arrangement whereby a secondary annular fuel channel is
provided concentrically and outwardly of the primary
fuel channel, a secondary annular conical fuel swirl
chamber.is provided concentrically and outwardly.of the
primary swirl fuel chamber, and a secondary fuel nozzle
is provided concentrically and outwardly of the primary
fuel nozzle and the injector tip axis, means for
providing a flow of pressurized fuel to the secondary
annular channel tangential thereof in order to provide a
swirl to the fuel flow in the secondary annular fuel
channel, the secondary annular fuel channel communicating
with the secondary fuel swirl chamber so as to provide a
swirl to the fuel whereby the secondary fuel will exit
the secondary fuel nozzle in an atomized fashion.
It has been found that when the tangential velocity
of the swirling fuel increases as it progresses in the
conical primary fuel chamber, external air is entrained
back into the primary fuel chamber along the tip axis,
resulting in the formation of a thin hollow spinning film
of fuel in the primary fuel chamber. As the fuel exits
from the nozzle, it forms a thin conical unstable film
that breaks down into droplets.
It is a further feature of the present invention to
provide the injector with an air swirl member defining
first air passages forming an annular array communicating
the pressurized air from outside the wall into the
combustion chamber, the first air passage being
concentric with the primary fuel nozzle and the tip axis
whereby the first air passages are arranged to further
atomize the fuel emanating from the primary fuel nozzle,
and a set of second air passages arranged in annular
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array in the injector tip spaced radially outwardly from
the first air passages whereby the second passages are
arranged to shape the spray of thiE~ mixture of atomized
fuel and air and to add supplemental air to the mixture.
In a further embodiment of an injector in accordance
with the present invention including an injector tip that
has annular fuel flow passages, there is a stem
containing at least one fuel flow passage extending from
a stem fuel inlet to a fuel delivery outlet, a first
annular fuel flow cavity provided in the stem near the
fuel stem inlet, an inlet conduit extending from the fuel
stem inlet to the annular cavity, the inlet conduit being
angled to provide a tangential flow direction to the fuel
passing through the conduit to the annular cavity, an
outlet conduit extending at an acute angle from the first
annular cavity to receive the fuel therefrom in a
tangential direction, a first linear fuel conduit
extending from the outlet conduit and extending axially
of the stem and communicating with an injector inlet
conduit at the fuel delivery outlet, the injector inlet
conduit being angled to direct the fuel flow to a first
annular passage in the injector tip in a tangential
direction to provide a swirl to the fuel flow entering
the annular passage in the injector tip.
In a more specific embodiment of the present
invention, there is provided a metering of the fuel flow
in the various conduits in the stem where alternating
fuel flow conduits have differing cross-sectional areas
arranged to provide the proper velocity to the fuel flow
and result in the pressure loss to enhance the heat
transfer rate.
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As can be seen, throughout the injector tip and the
stem, care has been taken to ensure tangential injection
into the annular passages, thus maximizing the angular
momentum of the fuel flow into the annular channels. The
kinetic energy in the flow is dissipated at the stem and
injector walls enhancing the heat transfer of the
passages.
The passage metering and the fuel swirl slots in the
injector tip are designed to control injector temperature
and to eliminate fuel stagnation wherever possible.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the
invention, reference will now be made to the accompanying
drawings, showing by way of illustration, a preferred
embodiment thereof, and in which:
Fig. 1 is a fragmentary vertical cross-section of an
injector in accordance with an embodiment of the present
invention;
Fig. 2 is a front elevation of the injector in
accordance with Fig. 1;
Fig. 3 is a fragmentary axial cross-section in
accordance with another embodiment of the injector in
accordance with the present invention;
Fig. 4 is a perspective schematic view showing the
flow passages of the injector in accordance with the
present invention, including both the injector tip and
the stem;
Fig. 5 is a schematic view showing the fuel passages
within the injector tip of the embodiment shown somewhat
in Fig. 1; and
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Fig. 6 is a perspective schematic view showing the
flow passages based on the embodiment shown in Fig. 3 of
the injector tip but showing only the secondary fuel flow
passages.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present specification describes two embodiments
of the present invention. The first embodiment shown in
Figs. 1 and 2 is a simplex injector while the second
embodiment shown in Fig. 3 is a duplex injector.
Referring to the embodiment shown in Figs. 1 and 2,
the simplex injector is designated by the reference
numeral 30. The injector 30 is shown mounted in an
opening in the combustor wall 31. The injector 30
includes an injector body 32, an injector face 33, as
shown in Fig. 2, and an injector tip 34.
A tip axis X extends through the tip 34 and the
body 32, as shown in Fig. 1. A stem 40 is connected to
the body 32, and at least.a fuel passage 36 is formed in
the stem 40 which is also covered by protective
sleeve 38. The body 32 defines cavities, such as annular
channels 41, 42, and 44, that are concentric to the tip
axis X. The fuel line 36 communicates with the
channel 41 in a somewhat tangential manner in order that
the fuel under pressure will be provided a swirl in the
annular channel 41. The annular channels 42 and 44
communicate with each other by means of slots 46 which
are defined helically so as to provide a swirl or spin to
the fuel as it passes from the annular channel 42 and to
channel 44.
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A conical fuel swirl chamber 48 is defined
downstream of the channel 44, and slots 49 communicate
the channel 44 to the chamber 48. As the diameter in the
conical chamber 48 decreases, the velocity of the
spinning fuel increases until it reaches the cylindrical
nozzle 50. It is believed that the spinning fuel flow
will create a film on the conical walls of the chamber 48
by centrifugal force, and external air may be drawn into
the chamber to flow back along the tip axis X into the
chamber 48. This separation effect results in a thin,
hollow, spinning film which develops at the nozzle 50.
As the fuel leaves the nozzle, it forms a thin conical
sheet which stabilizes into droplets.
An annular air swirl member 52 is connected to the
injector tip 34, as shown in Figs. 1 and 2. The air
swirl member 52 comprises a series of annular spaced-
apart passages 54 distributed around the nozzle 50. As
described in U. S. Patent Application 09/083,199, the air
flow from P3 air into the combustor passes through the
holes or passages 54 in such a way as to avoid flow
separation and to develop a conical fuel spray pattern
within the combustor.
A second set of annularly spaced-apart passages 56
may be provided to shape the fuel air cone and to augment
the combustion air into the combustor. Both sets of
passages 54 and 56 are specifically sized to admit a
predetermined quantity of air at the engine design point.
Referring now to the embodiment of Fig. 3, the
duplex injector 60 is described which includes an
injector body 62 and an injector tip 64. The tip axis X2
passes through the injector tip 64 as shown.
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The injector body 62 fits in a stem cavity 74. In
this embodiment, the air swirl member 66 includes a
cylindrical portion which has a greater diameter than the
injector body 62.
The injector body 62 defines, with the cavity 74 of
the stem 72, a primary fuel channel 68. The fuel
channel 68 is annular because of the valve device 73
within the cavity so formed. The fuel annular channel 68
communicates with the primary fuel line 86 which is
arranged to deliver the pressurized fuel tangentially of
the channel 68 so as to create a fuel swirl within the
primary fuel channel 68.
A primary fuel swirl chamber 70 is defined as a
conical chamber downstream of the channel 68 and
communicates with the nozzle 71. Slots 75 are defined
between the valve 73 and the conical wall of the
chamber 70. These slots are designed to enhance the
spinning effect of the primary fuel from the primary fuel
channel to the primary fuel chamber 70 and ultimately
through the nozzle 71.
A secondary fuel channel 76 is formed between the
injector body 62 and the cylindrical portion 67 of the
air swirl member 66. Passages are provided in the
cylindrical member 67 to communicate with the secondary
fuel line 88 in the stem 72. The fuel line and the
passages will provide a swirl to the secondary fuel as it
enters the secondary annular channels 76. The annular
channel 76 communicates with the downstream annular
secondary fuel channel 78 by means of slots 80 which are
designed to enhance the swirl of the secondary fuel. A
conical secondary fuel chamber 82 is also provided which
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is annular to the axis X2 and the primary fuel chamber 70.
The secondary fuel chamber 82 has the same effect on the
secondary swirling fuel as has the primary chamber 70.
An annular nozzle 84 is also provided in order to allow
the secondary fuel to form a conical spray with the
primary fuel in the combustion chamber defined by
combustor wall 94.
The air swirl member 66 is provided with air swirl
passages 90 so as to focus the air flow from the P3 air
into the combustion chamber just outside the fuel
injector face. Auxiliary air passages 92 are also
provided in the swirl component 66 and have a similar
effect to those described with the simplex injector 30.
It is noted that another difference between the
duplex injector 60 and the prior art is the absence of
core air passages and the primary injector heat shield.
The elimination of these elements reduces the
manufacturing complexity as well as its cost. A duplex
injector 60 is more compact for a given fuel flow rate.
This injector does not have to be concerned with the heat
transfer problems arising from the presence of core air
in the interior passage of the injector. The integration
of the air swirler component 66 with the fuel nozzles 71
and 84 helps reduce the overall size of the injector
tip 64. The swirl component 66 design with the duplex
injector 60 aids atomization particularly at low power
when the fuel pressure in the secondary annular channel
is too low to generate the thin film required for
adequate atomization.
Referring now to Fig. 4, the stem 172 is shown
generally in dotted lines. However, primary passage 174
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and second passage 176 are illustrated in this drawing.
The injector 160 is a duplex injector similar to that
described in relation to Fig. 3. Thus, the injector
tip 160 includes a primary fuel channel 168 and a
secondary fuel channel 176.
The remote end of the stem is provided with a
primary fuel inlet 140 which communicates with a circular
cylindrical primary fuel chamber 142 by means of the
inlet conduit 144. As noted in the drawings, the
conduit 144 is angled so that it delivers the fuel in a
tangential direction within the cylindrical chamber 142.
The primary fuel chamber 142 is shaped to allow the
primary fuel flow to swirl therein and exit through an
outlet conduit 146 which is of somewhat smaller diameter
than the chamber in order to provide a first metering
passage. The conduit 146 communicates with a linear
conduit 148 which has a larger cross-sectional area than
the conduit 146.
The linear conduit 148 communicates with a delivery
conduit 186 which is angled to deliver the primary fuel
into the annular channel 168 tangentially. The delivery
conduit 186 is also of a smaller cross-sectional area
than the conduit 148 in order to meter the fuel flow into
the channel 168.
The secondary fuel passage 175 of the stem 172 has a
secondary fuel inlet conduit 150 which is angled to
deliver the fuel to the annular channel 152 at the entry
end of the stem 172. An outlet conduit 154 delivers the
fuel flow from the annular channel 152 at a somewhat
tangential angle to deliver the fuel to the linear
conduit 156 which is of a larger cross-sectional area
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than the conduit 154. At the injector end of the stem,
an angled two-part delivery conduit 188 is provided for
delivering the fuel to the annular channel 176 in a
tangential direction so as to provide a swirl to.the fuel
flow within the annular channel 176.
Figs. 5 and 6 correspond generally with the injector
tip of Fig. 1, and although there are some constructional
differences, they do resemble each other in principle.
Thus, the reference numerals used in Fig. 5 will
correspond to the reference numerals used in Fig. 1 but
have been raised by 200.
Thus, the fuel is delivered by means of the delivery
conduit 236 into the annular channel 241. The slots 246
are all angled to deliver the fuel from the channels 241
and 242 into the annular channel 244. Angled slots 249
deliver the fuel tangentially to the chamber 248.
The schematic depiction of the fuel flow passages
shown in Fig. 6 resembles the duplex injector shown in
Fig. 3. The drawing represents the secondary fuel
distribution in the injector tip (the primary flow is not
shown) and that will now be described with similar
reference numerals to those used in Fig. 3 but raised
by 300.
Thus, the delivery conduit 388 is shown here with
its two components 388a and 388b. As noted, the cross-
sectional diameter of the conduit portion 388a is larger
than the cross-sectional diameter of the portion 388b,
thereby providing the metering effect mentioned
previously in order to provide the proper pressure drop.
The delivery conduits 388a and 388b are so arranged
in the stem that the portion 388b is directed
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tangentially to the annular channel 375 or 376. The so-
called angular slots 380 are, in fact, as shown in
Fig. 6, in two parts, one being a first outlet
portion 380a delivering the fuel from the channel 376,-
and the second part 380b is of a smaller diameter and is
angled to provide the fuel flow tangentially to the
conical fuel swirl chamber 382.