Information
-
Patent Grant
-
6351948
-
Patent Number
6,351,948
-
Date Filed
Thursday, December 2, 199924 years ago
-
Date Issued
Tuesday, March 5, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Freay; Charles G.
- Rodriguez; William
-
CPC
-
US Classifications
Field of Search
US
- 060 740
- 060 742
- 060 746
- 060 39463
- 123 198 D
- 123 468
- 123 469
-
International Classifications
-
Abstract
A fuel injector for a gas turbine engine includes an elongated primary fuel tube residing within an elongated secondary fuel tube. The primary fuel tube is brazed or otherwise metallurgically joined to the injector housing proximate opposite end regions of the primary fuel tube. Between the end regions, the primary fuel tube includes a spiral configuration or profile that engages the inner wall of the secondary fuel tube in line-to-line interference contact along a sufficient portion of the lengths of the primary and secondary fuel tubes effective to reduce thermal and vibration stresses on the primary fuel tube and essentially eliminate fatigue failure at the brazed end regions and to increase its axial compliance, thereby lowering internal stresses imparted by a given thermal strain caused by rigid attachment of the relatively cool primary tube to the relatively hot support housing.
Description
FIELD OF THE INVENTION
The present invention relates to gas turbine engine fuel injectors and, in particular, fuel injectors for the combustor of a gas turbine engine.
BACKGROUND OF THE INVENTION
Pressure atomizing fuel injectors for supplying primary fuel and secondary fuel to the combustor of a gas turbine engine are in use. These pressure atomizing injectors typically include a primary fuel tube to provide a relatively low fuel flow rate to a primary fuel discharge orifice of the injector during all regimes of engine operation. The primary fuel tube usually is disposed within a secondary fuel tube that provides a variable, metered secondary fuel flow to a secondary fuel discharge orifice as needed during high power engine operation regimes. During high power engine operation, the secondary fuel flows through the secondary fuel tube about the primary fuel tube to maintain the latter relatively cooler compared to the former.
A particular pressure atomizing fuel injector assembles the primary fuel tube and secondary fuel tube in the injector housing by metallurgical braze or weld joints near opposite ends thereof. During high power engine operation, the fuel injector undergoes thermal expansion and vibration resonance which generate internal stresses, especially on the relatively cooler primary fuel tube, found to cause premature fatigue failure (cracking) of one or more of the brazed joints proximate the opposite ends of the primary fuel tube. Fatigue failure of the braze joints of the primary fuel tube can lead to primary fuel internal leakage and requires costly repair or overhaul of the affected fuel injector.
An object of the present invention is to provide a fuel injector for a gas turbine engine having a fuel tube configured and assembled in an injector housing in a manner to reduce fatigue failure at metallurgical joints positioning the fuel tube in the injector housing and along the length of the fuel tube.
SUMMARY OF THE INVENTION
The present invention provides in one embodiment a fuel injector for a gas turbine engine wherein an elongated fuel tube is positioned in an internal passage in a fuel injector housing using metallurgical joints and is provided with a spiral configuration along at least a portion of its length between the joints for engaging an adjacent surface in the housing in line-to-line interference engagement at one or more locations in a manner that reduces fatigue failure (cracking) of the metallurgical joints during service in a gas turbine engine.
In a particular illustrative embodiment of the present invention, a fuel injector includes an elongated primary fuel tube residing within a an elongated secondary fuel tube. The primary fuel tube is positioned by brazed or other metallurgical joints proximate opposite end regions of the primary fuel tube. Between the brazed end regions, the primary fuel tube includes a generally helical spiral configuration or profile that engages the inner wall of the secondary fuel tube in line-to-line interference contact along a sufficient portion of the lengths of the primary and secondary fuel tubes effective to substantially reduce fatigue failure at the brazed joints during engine service. In another illustrative embodiment, the outer secondary fuel tube can include the generally helical spiral configuration, while the primary fuel tube is straight. The spiral of the secondary fuel tube can engage the outer surface of the primary fuel tube and/or the inner surface of a passage in the strut portion of the fuel injector.
The present invention can be practiced with pressure atomizing fuel injectors, airblast fuel injectors, and hybrid airblast-pressure atomizing fuel injectors to this end to reduce fatigue failure of a fuel tube therein.
DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross-sectional view of a pressure atomizing fuel injector pursuant to an illustrative embodiment of the present invention.
FIG. 1A
is an enlarged cross-sectional view of the metering valve region of the fuel injector of
FIG. 1
, while
FIG. 1B
is an enlarged cross-sectional view of the injector tip.
FIG. 2
is a sectional view of a straight secondary fuel tube having a spiraled primary fuel tube disposed therein prior to assembly in the fuel injector housing.
FIG. 3
is a schematic view of the apparatus for imparting a helical spiral to the primary fuel tube.
FIG. 4
is a sectional view of a primary fuel tube received in spiraled secondary fuel tube, both tubes in partially broken away strut of the fuel injector housing prior to bending of the strut.
DESCRIPTION OF THE INVENTION
Referring to
FIGS. 1-2
, a pressure atomizing fuel injector
5
in accordance an embodiment of the present invention is shown. The fuel injector includes a tubular injector housing
10
having a flange
10
a
fastened thereto and adapted to be fastened (e.g. bolted) to an engine housing
11
(shown schematically) in conventional manner and an injector tip T fastened to the injector housing
10
and disposed in an opening in a gas turbine engine combustor wall
12
a
(partially shown) in conventional manner. The fuel injector
5
shown employs pressure of the fuel to effect atomization of the fuel into the combustor
12
as is known, although the present invention can be practiced with airblast fuel injectors and hybrid airblast-pressure atomizing fuel injectors which are well known for gas turbine engine combustor fuel injection systems.
The fuel injector is shown in
FIGS. 1
,
1
A and
1
B including the injector housing
10
having an inlet fitting
22
that is supplied with pressurized fuel from a fuel manifold
25
and fuel pump (not shown) in conventional manner. A plurality of fuel injectors identical to injector
5
can be arranged about the combustor
12
and can be supplied with pressurized fuel from the manifold
25
in similar manner.
The inlet fitting
22
is communicated to an injector housing chamber
30
by passage
32
. Disposed in the chamber
30
are a fuel check valve
33
and fuel metering valve
34
for controlling secondary fuel flow. The check valve
33
is biased by coil spring
35
such that head
33
a
of the check valve
33
is opened against spring bias relative to check valve seat
37
at a predetermined fuel pressure to supply pressurized fuel to primary fuel chamber
31
via one or more passages
31
a
. Passage
31
a
is provided in a valve support member
36
defining a secondary fuel chamber therein, FIG.
1
A. The fuel chamber
31
communicates via passages
31
b
,
31
c
to open end
90
a
of an elongated primary fuel tube
90
to supply fuel thereto whenever the check valve
33
is open. A fuel tight plug P is disposed in passage
31
c
. The primary fuel tube
90
supplies the primary fuel flow from the open check valve
33
to central nozzle passage
70
and oblique nozzle passages
71
(one shown) to a central primary fuel discharge orifice
72
of the nozzle tip T for discharge as an atomized primary fuel spray cone into the combustor
12
, FIG.
1
B.
The metering valve
34
is disposed in the tubular valve support member
36
. The valve support member
36
includes an end that is biased against check valve seat
37
and an opposite end held against support cup
38
by a coil spring
42
. The support cup
38
is positioned in chamber
31
by braze joint JT. The coil spring
42
engages a flange of a perforated fuel filter screen or sleeve
44
against the check valve seat
37
. In effect, the spring
42
holds the check valve seat
37
, valve support member
36
, support cup
38
, and filter screen
44
in position in the chamber
31
. Fuel-tight O-ring seals
39
a
,
39
b
are provided about the check valve seat
37
and secondary metering valve seat
40
. Valve support member
36
is positioned in chamber
31
by braze joint JT.
The secondary metering valve
34
is biased relative to valve seat
40
by a coil spring
50
held in position on the stem of the secondary metering valve by spring retainer cap
51
. Fuel in the valve support member
36
flows to the secondary valve head
34
a
via passages (e.g. 6 passages-not shown) in valve seat
40
. The secondary valve
34
is held closed by spring
50
until fuel pressure reaches a preselected valve opening pressure. Then, the secondary fuel flow is metered to a chamber
52
by opening of the secondary valve
34
relative to the valve seat
40
.
The chamber
52
communicates to open end
10
a
of elongated secondary fuel tube
100
to supply metered secondary fuel flow to an annular secondary fuel passage
101
defined between the primary fuel tube
90
and the secondary fuel tube
100
. The secondary fuel passage
101
supplies metered secondary fuel to the annular passage
74
that communicates to oblique passages
76
and annular passage
78
of the nozzle tip T to supply the secondary fuel to annular secondary fuel discharge orifice
80
for discharge as an atomized secondary fuel spray cone into the combustor
12
, FIG.
1
B. As shown in
FIGS. 1 and 2
, the intermediate length
90
L of the primary fuel tube
90
resides within the secondary fuel tube
100
in a strut portion
10
s
of the injector housing
10
such that secondary fuel flowing through the secondary fuel passage
101
during high power engine operation regimes exerts a cooling effect on the primary fuel tube
90
. The secondary fuel tube
100
is spaced from the inner wall of the injector housing strut
10
s
by a Type
300
series austenitic stainless steel coil spacer spring
110
to provide a thermally insulating space between the housing strut portion
10
s
and the secondary fuel tube
100
.
The end
90
a
of the primary fuel tube
90
extends beyond the secondary fuel tube
100
and is metallurgically joined to the injector housing
10
. In particular, a region of the primary fuel tube
90
proximate the end
90
a
is brazed to the housing
10
to provide an annular braze joint J
1
therebetween. The other opposite end
90
b
of the primary fuel tube
90
also extends beyond the secondary fuel tube
100
and is metallurgically joined to an injector nozzle tip adapter
10
c
to provide an annular braze joint J
2
therebetween. The nozzle tip adapter
10
c
is welded to the end of the strut portion
10
s
at weld joint JS.
The primary fuel tube
90
typically comprises Hastelloy X alloy brazed at end
90
a
to the injector housing
10
also comprising Hastelloy X alloy using a gold/nickel (AM
4787
) braze material. The end
90
b
of the primary fuel tube
90
is brazed to the injector nozzle tip adapter
10
c
using the same braze material as described above. The end
100
a
of the secondary fuel tube
100
is metallurgically joined to the support cup
38
. In particular, a region of the secondary fuel tube
100
proximate the end
100
a
is brazed to the support cup
38
to provide an annular braze joint J
3
therebetween. The other opposite end
100
b
of the secondary fuel tube
100
is metallurgically joined to annular end sleeve
112
to provide tack welded joint
34
therebetween. The sleeve
112
is free to slide relative to the housing strut portion
10
s.
FIG. 2
illustrates the primary fuel tube
90
disposed within the secondary fuel tube
100
before assembly in the injector housing
10
. The primary fuel tube
90
is shown including a generally helical spiral
90
c
along its intermediate length between the ends
90
a
,
90
b
thereof with the spiral outer surface or wall engaging the inner surface or wall
100
c
of the secondary fuel tube in line-to-line interference contact at one or more locations L therebetween. The line-to-line interference engagement between the primary and secondary fuel tubes
90
,
100
is effected by selecting the outer diameter OD of the spiral
90
c
of the primary tube (outer diameter relative to centerline of the secondary tube
100
in
FIG. 2
) and the inner diameter of the secondary fuel tube accordingly. For example only, the outer diameter OD of the spiral
90
c
primary fuel tube
90
can be 0.155 inch, while the inner diameter of the secondary fuel tube
100
can be 0.155 inch to this end. The non-secondary outer diameter of the primary fuel tube
90
can be 0.100 inch for the outer diameter OD of spiral
90
c
set forth.
In an alternative embodiment of the invention, the secondary fuel tube
100
can include a generally helical spiral, while the primary fuel tube
90
can be straight. In this embodiment, the secondary fuel tube
100
would include a generally helical spiral along its intermediate length between the tube ends with the spiral inner surface or wall engaging the outer surface or wall of the primary fuel tube
90
, FIG.
4
. The spiral outer surface of the secondary fuel tube
100
also can engage the wall of passage
10
p
of the strut portion
10
s
in line-to-line interference contact, whereby the inner surface of the secondary tube spiral engages the primary fuel tube
90
while the outer surface of the secondary tube spiral engages the wall defining the passage
10
p
. The spacer spring
110
thereby can be omitted in this embodiment to simplify construction,
FIG. 4
, which shows tubes
90
,
100
in strut portion
10
s
prior to bending thereof to shape of FIG.
1
.
The spiral
90
c
preferably comprises one complete helical turn having a pitch of 3.27 inches for example only, although 1½ to 2 spiral turns or more and other spiral pitch may be used in practicing the invention depending upon the particular design of the fuel injector and primary and secondary fuel tubes. The length of the spiral
90
c
is selected to provide interference engagement along a sufficient portions or locations of the intermediate lengths of the primary and secondary fuel tubes
90
,
100
effective to reduce or essentially eliminate heretofore observed fatigue failure at the brazed joints J
1
, J
2
during service in a gas turbine engine and to permit increased axial compliance (decreased stress under a given axial deflection) of the primary tube
90
during thermal expansion of the injector support housing to thereby lower thermally induced internal stresses imparted by a given thermal strain caused by rigid attachment of the relatively cool primary tube
90
to the relatively hot support housing
10
and increasing fatigue life.
In practicing the invention, the primary fuel tube
90
can be imparted with the spiral
90
c
in a manner illustrated schematically in FIG.
3
. In particular, the opposite ends
90
a
,
90
b
of the primary fuel tube are clamped in collet chucks or clamps C
1
, C
2
of a conventional lathe (not shown). The primary fuel tube
90
so fixtured in the collet clamps C
1
, C
2
then is bowed to an arcuate profile shown in dashed lines from its original straight tube profile. Bowing is effected by tube buckling to an extent to provide the aforementioned outer diameter OD of the spiral
90
c
. Then, the bowed primary fuel tube
90
is deformed by rotating one of the clamps C
1
, C
2
, or both, a selected angular extent to form the spiral
90
c
with the turn(s) and helical pitch desired. For example, one of the collet clamps C
1
, C
2
is rotated somewhat greater than 360 degrees relative to the other to form a one turn helical spiral in the bowed primary fuel tube
90
. Pitch of the helix is determined by the degree of bowing and the buckled tube length between the collet clamps.
After spiral formation, the primary fuel tube
90
is removed from the lathe, cleaned, and then inserted in the secondary fuel tube
100
as shown in
FIG. 2
to provide the aforementioned line-to-line interference engagement along sufficient portions or locations of the intermediate lengths of the primary and secondary fuel tubes
90
,
100
effective to reduce brazed joint fatigue failure during service in a gas turbine engine. For purposes of illustration only, a primary fuel tube
90
having an as-received straight outer diameter of 0.100 inch can be spiraled in the manner described above and tested for proper spiral outer diameter OD by inserting the spiralled primary fuel tube
90
first in a straight gaging tube (not shown) having an inner diameter of 0.160 inch and then in a second gaging tube (not shown) having an inner diameter of 0.150 inch. The spiraled primary fuel tube
90
must pass through the first gaging tube but not the second gaging tube.
The subassembly
120
of the spiraled primary fuel tube
90
in the secondary fuel tube
100
is inserted in the injector housing
10
prior to bending (deforming) of the strut portion
10
s
to its compound arcuate configuration shown in FIG.
1
. The coil spring
110
is positioned about the secondary fuel tube
100
. The primary and secondary fuel tubes
90
,
100
and their associated components (e.g. strut end
10
c
, support cup
38
, end sleeve
112
, etc.) then are brazed or welded using conventional brazing/welding procedures. Subsequent bending of the strut portion
10
s
to its compound arcuate shape imparts the arcuate configuration shown in
FIG. 1
to the subassembly
120
of the primary and secondary fuel tubes
90
,
100
. After bending, the primary fuel tube
90
retains its spiral
90
c
that remains in line-to-line interference engagement,
FIG. 1
, along sufficient portions or locations of the intermediate lengths with the inner wall of secondary fuel tube
100
effective to essentially eliminate heretofore observed fatigue failure at the brazed joints J
1
, J
2
.
After the injector housing has been bent and machined to final envelope dimensions, the components of check valve
33
, metering valve
34
and nozzle tip T are assembled to complete the fuel injector
5
.
Tests of the fuel injector
5
described above have been conducted under simulated gas turbine engine conditions of 3×10
7
vibration cycles at greatest tip response resonance frequency with
12
g
forced sinusoidal input at the injector flange
11
in three mutually perpendicular planes (axial, radial and tangential relative to the gas turbine engine axis). Additional separate thermal cycling tests have been conducted using 10,000 thermal shock cycles on the primary fuel tube where a cycle involves maintaining the nozzle strut
10
s
and tip T at a temperature of greater than 950 degrees F, introducing room temperature water through the fuel passages for 0.16 seconds and terminating water flow for one minute, and then repeating the cycle. The fuel injector
5
did not exhibit fatigue failure at brazed joints J
1
, J
2
in any of these simulated engine tests.
While the invention has been described in terms of specific embodiments thereof, it is not intended to be limited thereto but rather only to the extent set forth in the following claims.
Claims
- 1. A fuel injector for a gas turbine engine, comprising:a fuel injector housing, and an elongated fuel tube held in position in said housing by spaced apart joints and including a spiral tube surface along at least a portion of its length between said joints, said spiral tube surface being in contact with another surface disposed in said housing at one or more locations of said spiral tube surface.
- 2. The injector of claim 1 wherein opposite end regions of said fuel tube are held in position by said joints and said spiral tube surface extends from one of said end regions to the other of said end regions.
- 3. The injector of claim 2 wherein opposite end regions of said fuel tube comprise brazed joints.
- 4. The injector of claim 1 wherein said another surface comprises an inner surface of a second fuel tube disposed about said fuel tube in said housing.
- 5. The injector of claim 1 wherein said another surface comprises an outer surface of a second fuel tube disposed inside said fuel tube in said housing.
- 6. The injector of claim 1 wherein said another surface defines a passage in an injector strut.
- 7. A fuel injector for a gas turbine engine, comprising:a fuel injector housing having an internal passage therein, an elongated secondary fuel tube disposed in said internal passage and having an internal wall, and an elongated primary fuel tube disposed in said secondary fuel tube and held in position therein by spaced apart joints, said primary fuel tube including a spiral outer surface along at least a portion of its length between said joints, said spiral outer surface being in contact with said internal wall at one or more locations of said spiral outer surface to reduce fatigue failure at said joints during service in a gas turbine engine.
- 8. Assembly for a fuel injector, comprising an elongated first fuel tube and an elongated second fuel tube disposed in said first fuel tube, one of said first fuel tube and second fuel tube including a spiral surface along at least a portion of its length, said spiral surface being in contact between said first fuel tube and second fuel tube at one or more locations of said spiral surface.
- 9. The assembly of claim 8 wherein said first fuel tube includes said spiral surface.
- 10. The assembly of claim 8 wherein said second fuel tube includes said spiral surface.
US Referenced Citations (9)