Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FUEL NOZZLE ASSEMBLY FOR A GAS TURBINE ENGINE
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a ~uel nozzle assembly
for a ga~ turDine engine, and more specifically, to such a
fuel nozzle assembly ~or a gas turbine engi~e having a fuel
tube and an air tube enclosing the fuel tube to define an
annular air passage therebetween, the air tube being biased
into a sealing engagement with the fuel delivery tube and
where differential axial expansion of the air delivery tube
and fuel delivery tube tightens the sealing engagement
between the tubes. The ~uel nozzle assembly is constructed
such that the air passage i8 readily accessible for
cleaning.
Description of the Pr~or Art:
A typical fuel nozzle assembly capable of
separately delivering both air and fuel to a combustion
chamber generally comprises a fuel delivery tube supported
from one end and having a fuel nozzle tip with a conical
surface secured to the other, and an air delivery tube,
also supported by the same one end, the air delivery tube
enclosing the fuel delivsry tube in a spaced relationship
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to define there~etween an annular air flow channel. A
5wirl cap is threaded onto the free end of the air delivery
tube and tightened so that a conical opening in the swirl
cap sealingly engages the conical surface of the nozzlP
tip. The swirl cap is further provided with a plurality of
small apertures equilangularly spaced around the center of
the swirl cap for directing atomizing air from the air flow
channel in a direction convergent to the fuel which exits
the fuel nozzle tip in an outwardly diverging conical
pattern.
As the air delivered through the assembly is
primarily used only at ignition of the gas turbine engine
to atomize the fuel, it is important to provide an
atomizing air pattern which is predictable and delivers an
atomized fuel-air mixture generally adjacent to either a
flame cross-over tube or a spark ignitor, or both.
The fuel nozzle tip injects fuel in an outwardly
diverging, generally conical, pattern. However, during low
fuel flow, fuel pressure atomization is poor and air is
introduced through the swirl cap to further atomize the
fuel injected by nozzle. In such a manner, the conical
pattern is altered to result in a nodular or 4-spoke spray
pattern. This additional atomizing air is necessary during
light-off ignition to provide greater atomization of the
fuel as it is introduced through the nozzle to reduce
unburned fuel emissions and to obtain better distribution
of the air ~uel mix~ure to insure that it is properly
delivered to th~ turbine to propagate the combustion
process in the turbine. After light-off ignition is
complete, the atomization air is cut of~ and fuel only is
delivered through the nozzle to continue the combustion
process.
To ensure that the air 10w atomizes the fuel
stream to the nodular spray pattern desired during
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atomization, the air ~low is channeled through apertures
having the same geometric orientation as the opening in the
fuel nozzle tip through which the fuel is directed.
Coni~al surfaces are utilized in such prior art
devices as the coni al seal, once established, was thought
to provide the best air-tight seal available. To make the
conical seal a high quality, air-tight seal, however, it
was necessary to apply a fine grinding paste to the conical
nozæle tip prior to engaging the nozzle tip with the swirl
cap. Further, and more seriously, the conical nozzle ~ip
and swirl cap utilized in achieving such a sealing
interface lead to the formation of gaps at the fuei
nozzle/swirl cap interface durin~ axial expansion of the
air delivery tube. This causes severe deterioration in the
ability of the fuel nozzle assembly to provide the desired
atomized fuel spray characteristics. In addition, such
gaps cncourage the formation of contaminants which further
deteriorate the performance of the fuel nozzle assembly.
The prior art devices are also prone to the accumulation of
deposits in the air delivery channel which tends to clog it
and do not provide access to th~ air delivery channel for
removing such deposits. one such prior art ~uel nozzle
having a conical engagement between the swirl cap and the
fuel delivery tube is disclosed in U.S. Patent No.
4,154,056 entitled ~Fuel Nozzle Assembly for a Gas Turbine
Enginen, issued May 15, 1979 and assigned to the assignee
of the present invention.
The pro~lems identified in the prior art devices
may be traced to the fact that the temperature of the fuel
flowing through the fuel delivery tube is generally about
100 Fahrenheit. The temperature o~ the air in the space
between the tubes, however, may reach 600 Fahrenheit.
Such a temperature difference between the fuel tube and the
air tube often causes varied axial expansion of the fuel
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tube and air tube, resulting in a disengagement of the
conical seal between the fuel nozzle tip and the air
delivery tube, thus creating the above-mentioned gap at the
sealing interface between the two. This gap provides an
area where contaminantq from the air flowing therethrough
or carbon deposits caused by occasional reverse flow from
the combustor, can accumulate to prevent the gap from
resealing. The air tube itself may also become clogged
with contaminanks. During shutdowns, the conical seal
interface may be contaminated by fuel oil from the nozzle
tip.
As such, any gap between the air tube and the
fuel nozzle tip provides an air leakage path that
deleteriously affects the atomizing air distribution such
that an unpredictable fuel-air pattern can exist which
produces erratic and unpredictable light-o~f
characteristics. If contamination of the air passage is
severe enough, the flow of atomizing air may be completely
cut off, preventing light-offs.
Further, once the fuel nozzle assembly of the
known prior art is assembled and mounted in a combustion
chamber of a gas turbine engine, it becomes extremely
difficult to mechanically clean the air delivery channel
and remove the contaminants which may be causing either
leakage at the sealing interface or blockage of the air
delivery pipe.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a
fuel nozzl~ assembly ~or a gas turbine engine which
maintains a constant sealing interface without gapping
between the fuel delivery tube and the air delivery tube
during axial expansion of the air delivery tube.
Another object of this invention is to provide an
integral fuel nozzle tip/end cap for a fuel nozzle assembly
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where the sealing interface between the air delivery tube
and fuel delivery tube i5 remote from the fuel atomization
point such that the effect of air leakage at the sealing
interfac~ on fuel atomization is minimized.
Yet another object of thi~ invention is to
provide a fuel nozzle assembly where the air delivery
tube/fuel delivery tube sealing interface is improved by
becoming even more air-tight during axial expansion of the
air delivery tube.
Still yet another object of this invention is to
provide a fuel nozzle assembly wher~ the seal between the
air delivery tube and the support flange sealing is
tightened during axial expansion of the air delivery tube.
Another object o~ this invention is to provide a
fuel nozzle assembly where at least part of the axial
expansion of the air delivery tube is absorbed by the fuel
nozzle assembly without detrimental effect on the operation
o~ the fuel nozzle.
Yet another object o~ this invention is to
provide a fuel nozzle assembly wherein the fuel delivery
tube/air delivery tube interface is unlikely to accumulate
carbon deposits during axial expansion of the air delivery
tube.
Still yet another object of this invention is to
provide a fuel nozzle assembly ~or a gas turbine engine or
the like, wherein contamination of the air delivery tube is
minimized.
Another object of this invention is to provide an
air-tight sealing interface between the fuel delivery tube
and the air delivery tube without applying grinding pastes
to the nozzle tip.
Yet another object o~ this invention is to
provide a fuel nozzle assembly in which thP air delivery
tube is readily detachable from the assembly so that the
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air channel is accessible for cleaning.
These and other objects and adv~ntages are
achieved by the present invention which provides a fuel
nozzle assembly for a gas turbine engine. The nozzle
assembly is comprised of a fuel delivery tube substantially
enclosed by an air delivery tube. The fuel deli~ery tube
has an integral fuel nozzle/end cap attached to its
discharge end. The air delivery tube substantially
encloses the fuel delivery tube to define an air passage
between the fuel delivery tube and the air delivery tube.
The integral ~uel nozzle/end cap includes a central opening
through which the fuel delivery tube discharges fuel, small
apertures ~or the passage of atomizing air which are
aligned with the annular air passage of the nozzle assembly
such that air flowing through the air delivery tube will
flow through the apertures and atomize the fuel exiting the
fuel delivery tube and a lip for proper alignment of the
end cap with the air delivery tube.
A support flange i5 provided for mounting the
fuel delivery tube on a gas turbine engine. The support
flange has an opening which receives a biasing spring. The
biasing force of the spring forces the air delivery tube in
a tight fit against the integral fuel nozzle/end cap of the
fuel delivery tube. During thermal expansion of the air
delivery tube, the air delivery tube expands along its axis
partly against the end cap to further tighten the fit
between the two and partly against the biasing spring which
absorbs the expansion force. Expansion of the air delivery
tube also tightens the fit between the air delivery tube
and the support flange. As varied axial expansion of the
air tube and fuel tube caused by an extreme temperature
difference between air flowing through the air tube and
fuel flowing through the fuel tube is either absorbed by
the spring or utilized to tighten the seal between the air
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tube and the fuel tube, the tight seal between the ~ir tube
and the ~uel tube is maintained and the phenomena of
gapping at the fuel tube/air tube interface observed in the
prior art does not occ~r.
To provide a nozzle assembly in which the
atomizing air passage iæ readily accessible for cleaning
and in which the fuel tube and air tube are secured
togPther; the air delivery tube is biased by spring force
into a secure, aligned fit with the integral fuel
nozzle~end cap of the air delivery tube. The integral fuel
nozzle/end cap, which is screwed onto the fuel delivery
tube, may be easily detached from the fuel delivery tube to
release the air deliv~ry tube and permit ready access to
the annular air passage for cleaning.
BRIEF ~ESC~IPTXON OF_TH~_DRAWINGS
The invention may be better understood and
further advantages and uses thereof are readily apparent,
when considered ln view of the following detailed
description of exemplary embodiments, taken with the
accompanying drawing in which:
Figure la i9 an axial cross-sectional view of the
delivery end of a typical prior art fuel nozzle assembly
under normal operating conditions;
Figure lb is an axial cross-sectional view
similar to Figure.la of ~he delivery end of the prior art
fuel nozzle assembly which has undergone axial expansion
caused by severe high temperature operating conditions;
Figure 2 is an axial cross-sectional view of the
fuel nozzle assembly of the present invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring ~irst to FIG5. la and lb, the end of
the nozzle assembly 10 of a typical prior art fuel nozzle
assembly is shown. The nozzle assembly 10 includes an
inner fuel delivery tube 12 and a surrounding outer air
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delivery tube 14. The air delivery tube 1~ is concentric
and substantially coextensive with the fuel delivery tube
12. The fuel delivery tube 12 has a delivery end 13 which
includes an axial opening in which a fuel nozzle tip 15 is
threaded onto the fuel delivery tube 12. The fuel nozzle
tip 15 inaludes a conical face 16 for engaging the air
delivery tube 14. Th~ air delivery tube 14 extends axially
with, and concentric to, the fuel delivery tube 12 to
de~ine an annular air passage 18 between the outer wall of
fuel delivery tube 12 and th~ inner wall of air delivery
tube 14 throughout their common axial extent. The end 20
o~ air delivery tube 14 has a reduced outer diameter
threaded ~or receipt of a swirl cap 22.
The swirl cap 22 includes a centrally located
opening 24. The central opening 24 is shaped to define a
tapered conical surface 26. The swirl cap further includes
small apertures 28 equilangularly spaced around the swirl
cap 22 for directing atomizing air in a predetermined
convergent direction to intercept and atomize the fuel
exiting fuel no~zle tip lS. The tapered conical surface 26
is sized to conform to the taper of the conical face 16 of
fuel nozzle tip 15 so that as swirl cap 22 is tightened
onto air delivery tube 14, the nozzle tip 15 projects into
the opening 24 and, when properly tightened, provides a
sealed engagement between the conical face 16 and surface
26. Figure la shows the nozzle assembly 10 of the prior
art when subjected to normal temperature conditions, i.e.
when there is no extreme temperature differential between
the fuel flowing in the fuel delivery tube 12 and the air
flowing in the air delivery tube 14. As clearly shown in
Figure la, when there is no temperature differential
between the tubes, the fuel and ~ir delivery tubes are
sealed at the nozzle tip 15/conical surface 26 interface.
No gapping is present at the interface, and contamination
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of the air passage 18 is unlikely. The air atomization of
the fuel spray generally xesults in the desired atomized
nodular spray pattern.
Turning to Figure lb, the fuel nozzle assembly 10
is shown when subjeot to axial expansion of the air
delivery tube cause by the extr~me thermal conditions
during operation. During normal engine operation,
combu~tion air from the compressor surrounds the air
delivery tube 14 and has a temperature of approximately
~00 to 700F. The ~uel, however, generally has a
temperature o~ about 100F., holding the ~uel delivery tube
12 to a much lower temperature than that of the air
delivery tube 14. This causes the air delivery tube to
axially expand to a gr2ater extent than the axial expansion
of the fuel tube, and results in a gap 29 between the
conical tip 16 and the inner surface 26. Typically, the
gap 29 hetween the conical tip 16 and the inner surfac~ 26
may extend as muah as 0.030 inches. Because of
contaminants in the air flow or the occasional reverse flow
of combustion products into this gap, particles build up or
become lodged in gap 29, which buildup prevents the gap
from closing when the extreme temperature differential of
the tubes is removed following completion of the turbine
ignition. Thus, prior to a subsequent ignition of the
turbine, the gap would already be present even without a
temperature dif~erential between the tubes. The air
leakage through ~his gap deleteriously alters the discharge
of the atomizing air flow, changing the atomization spray
pattern of the fuel nozzle assembly and thereby altering
the light-off response of the combustor.
Turning next to FIG. 2, the fuel nozzle assembly
30 of the present invention may be seen. The fuel nozzle
assembly 30 includes an inner fuel delivery tube 32 and an
outer air delivery tube 34 extending axially from a support
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~lange 36 at one end. The air delivery tube 34 is
concentric and subætant~ally coextensive with the fuel
delivery tuba 32.
The fuel delivery tube 32 has an axial opening which
i internally threaded at each end thereof. A fuel line (not
`j ~hown) i8 normally recei~ed in the fuel inlet end 40. The
delivery end 48 of the fuel delivery ~ube 32 ~erminates in
engaging mea~ such as an integral fuel nozzle/end cap 49
threaded onto the fuel delivery tube 32. The integral fuel
nozzle/end cap 49 includes a threaded ~kirt portion 50 for
attaching the integral fuel nozzle/end cap 49 to the
delivery end 48, a flange 51 and an end cap portion 53 ~or
engaging the end 60 of a~r delivery tube 34. A sealing
_ washer 52 i8 interposed between the flange Sl and the
thre~ded skirt portion 50 to prevent oil leaking from ~he
fuel delivery tube. Ths end cap port~on 53 is gurther
provided with a central opening 54 in communication with
the central opening of delivery end 48 for delivery of fuel
from the fuel delivery tube 32. End cap por~ion 53 is
further provided with ~mall aperture~ 56 ~quilangularly
spaced around cQntral opening 54 in communication with
annular air pas~age 58 for delivery o~ air ~rom passage 58
through apertures 56 for direct~ng atomizing air in a
pr~determined conver~ent direction to intercept and atomize
the fuel exiting ~he central op~ning 54 o~ the integral
fuel nozzle/end cap 49.
The air deliv~ry tube 34 extends axially with,
and concentric to, the ~uel delivery ~ube 32 to de~ine the
annular air passag~ 58 between the outer wall of fuel
delivery tube 34 and ~he inner wall of air delivery tube 34
throughout their common axial extent. The e~d 60 o air
delivery ~ube 34 mates with end cap por~ion 53 of the
integral fuel nozzle/end cap 49 in a mann~r ~o be described
more fully later to provide the seal between air delivery
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tube 34 and fuel delivery tube 32.
The support flange 36, which mounts the fuel
delivery tube on the gas turbine engine, extends radially
outwardly from the fuel deliv0ry tube 32. Th~ support
flange 36 has a threaded, radlally extending atomizing air
inlet 39 for receipt of an air line (not shown).The support
flange also includes a spring receiving opening 42 for
receipt of a bia~ing spring 44.
When mounting the air delivery tube 34 onto fuel
delivery tube 32, biasing ~pring 44 compresses, exerting
axial force onto beveled washer 46. In turn, beveled
washer 46, acting through split piston ring 47, exerts
axial pressure on air delivery tube 34. Integral fuel
nozzle/end cap 49 is attached to fuel delivery tube 34 by
screwing threaded skirt portion 50 of integral fuel
nozzle/end cap 49 into the delivery end 48 of fuel delivery
tube 34 until tight. Once the integral fuel nozzle/end cap
is secured to the fuel delivery tube 32, the air delivery
tube 34, under the influence of axial pressure from biasing
spring 44, engages the end cap portion 53 of the integral
fuel nozzle/end cap 49 in a tight fit. Thus, the fuel
delivery tube 32 and air delivery tube 34 are sealed
together such that leakage of atomizing air which adversely
affects the atomization of fuel is unlikely.
Further~ split piston ring 47, acting under
pressure exerted by beveled washer 46, exerts radial
pressure along its common circumference with support flanga
36 to eliminate any gap between the support flange 36 and
the air delivery tube 34. Thus, additional air leakage
which would otherwise occur at the support flange 36/air
delivery tube 34 in~erface is eliminated by the air-tight
seal between support flange 36 and split piston ring 47.
Alignment of annular air passage 58 and apertures
56 is provided by a lip 62 of end cap portion 53. As the
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threaded portion 50 of integral fuel nozzle/end cap 49 is
tightened onto fuel delivery tube 32, the protruding lip 62
of integral fuel nozzle/end cap 49 engage~ the protruding
tip portion 61 of end 600 The engagement of protruding tip
61 and protruding lip 62 aligns the air delivery tube 34
and the integral fuel nozzle/end cap 49 in a desired
orientation which simultaneously aligns annular air passage
58 and aperture 56 such that air flowing through air
passage 58 is communicated to aperture 56.
When the fuel nozzle assembly 30 of the present
invention is subjected to normal temperature conditi~ns,
i.e. when there i8 no extreme temperature differential
between the fuel flowing in the fuel delivery tube 32 and
air delivery tube 34, the ~uel and air delivery tubes are
sealed at the interface of the end portion 53 of the
integral fuel nozzle/end cap 49 and end 60 of air delivery
tube 34 interface. No gapping i5 present at ~he interface,
and contamination of the air passage 58 i= unlikely. The
air atomization o~ the fuel spray generally results in the
desired atomiæed nodular spray pattern.
When the fuel nozzle assembly of the present
invention is subject to axial expansion of the air delivery
tube caused by the extreme thermal conditions which arise
during operation of the gas turbine engine, the air
delivery tube 34 expands axially to a greater extent than
the fuel delivery tube 32. As the air delivery tube 34
expands, the end 60 o~ air delivery tube 34 expands axially
with respect to ~nd cap portion 53. The sealing interface
between end 60 and end cap portion 53 is tightened, thus
improving the seal between the two to prevent the leakage
of atomizing air. Continued axial expansion of the air
delivery tube 34 will compress biasing spring 44 and will
not cause separation of the seal between fuel delivery tube
32 and air delivery tube 34 as biasing spring 44 will
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accommodate axial expansion of the air delivery tube 34.
The increased axial force due to compression of biasing
spring 44 will also increase radial pressure of split
piston ring 47 on support flange 36 to further decrease air
leakage at the support flange 36/air delivery tube 34
interface by strengthening the air-tight seal between
support flange 36 and split piston ring 47.
