Method of reducing NOx emissions in a gas turbine engine

A breech loaded fuel nozzle cartridge assembly is provided for use with a fuel nozzle capable of use with gaseous or distillate fuels. The cartridge assembly includes an elongated water delivery pipe having an interior through passageway extending from a rearward open end to a forward open end. A mounting coupling is fixed to the exterior of the pipe adjacent its rearward end for use in mounting the cartridge assembly within the rearward end of a fuel nozzle body. The forward end of the cartridge pipe is provided with an interior water swirler and an exterior distillate fuel swirler, while the forward end of the fuel nozzle body is provided with an air swirler so that at the fuel nozzle tip, an outer conical air spray, an intermediate distillate or gaseous fuel spray and an inner conical water spray combine to provide a homogenous mixture at the point of combustion.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a fuel nozzle construction for use in gas 
turbine engines and, specifically, to a fuel nozzle utilizing water 
injection and which can be used with both gaseous and distillate fuels. 
It is well known to inject water into the combustion chamber of a gas 
turbine engine. For example, in U.S. Pat. No. 2,847,825, there is 
disclosed a water injection system utilized to augment the thrust of an 
aircraft gas turbine engine for short periods of time, for example during 
take-off and other emergency conditions. 
In U.S. Pat. No. 3,021,673, there is disclosed a water injection system for 
an automotive gas turbine for improving the acceleration characteristics 
of the engine. 
In U.S. Pat. No. 4,044,549, a process is disclosed for providing low 
emission combustion gases wherein water is admixed with the fuel for the 
purpose of forming water vapor containing fuel droplets. 
The utilization of water injection systems for substantially reducing NOx 
emissions is also disclosed in U.S. Pat. Nos. 4,110,973; 4,160,362; 
4,259,837; 4,290,558; 4,337,618; 4,342,198; 4,519,769; and 4,600,151. 
In the known water injection systems, water is typically injected from a 
position radially outwardly of the fuel, i.e., the atomized water is fed 
through the swirl vanes of the gas tip. However, experience has shown that 
this causes extreme thermogradients in the surrounding cap/cowl and 
combustion chamber liner assembly as a result of the direct impingement of 
the water on the hot component parts. The resultant thermal stresses 
create cracks and greatly reduce the useful life of the components, 
necessitating increased inspection frequency, maintenance and repair. 
Previously, a solution to this problem has been attempted by substituting 
metal materials which are less prone to cracking, and by insulating the 
metals with thermal barrier ceramic coatings. While both of the above 
approaches have had limited success to the extent of extending the useful 
lives of the components, cracking still occurs. 
This invention relates to an improvement over the conventional water 
injection techniques in that NOx emissions are reduced and the cracking 
problem associated with water injection is substantially abated. In 
accordance with this invention, the injected water is introduced directly 
into the flame center where it is more efficient at NOx control, and also 
eliminates direct water impingement on hot metals. The fuel nozzle of this 
invention also provides the capability of burning either gaseous or 
distillate fuel, utilizing water injection with both. 
Preliminary tests of this concept have proven favorable. Specifically, 
water has been injected through the oil passage on a dual fuel style 
nozzle while running on gaseous fuel. Results show NOx levels have 
decreased, liner metal temperature gradients are more favorable, and 
dynamic pressure activity has remained acceptable. 
In accordance with one exemplary embodiment of the invention, a fuel nozzle 
cartridge assembly including a water delivery pipe is provided for 
insertion into a central distillate fuel passage of a fuel nozzle body, 
from the rearward end of the body. This arrangement provides two separate 
and concentric passageways allowing pressurized water to be fed through 
the water delivery pipe and injected through the center of the nozzle body 
into the combustor as a finely atomized conical spray. Distillate fuel is 
fed through a side mounted inlet and travels through the annulus formed 
between the internal diameter of the body and the outside diameter of the 
water delivery pipe. The distillate fuel is injected into the combustor as 
a conical spray surrounding the water cone with atomization assisted by 
high pressure air introduced radially outwardly of the distillate fuel 
spray. 
In the event gaseous fuel is to be burned, the distillate fuel passageway 
is shut down upstream of the nozzle body, and gaseous fuel is introduced 
into the combustion zone via a separate gaseous fuel passageway in the 
nozzle body. Water continues to be injected via the water delivery pipe 
within the distillate fuel passageway, and is again injected into the 
center of the flame. 
In this exemplary embodiment of the invention, the water delivery pipe has 
an interior through passageway extending from a rearward open end to a 
forward open end. A mounting coupling is fixed to the exterior of the pipe 
adjacent its rearward end for use in mounting the cartridge assembly 
within the rearward end of the fuel nozzle body. A pipe fitting is also 
secured to the rearward end of the pipe for attachment to a water supply 
source. 
The forward end of the cartridge pipe is provided with an interior water 
swirler and an exterior distillate fuel swirler, and the forward end of 
the fuel nozzle body is provided with an air swirler so that at the fuel 
nozzle tip, an outer conical air spray, an intermediate distillate fuel 
spray and an inner conical water spray combine to provide a homogenous 
mixture at the point of combustion. 
In a broad aspect of the invention, therefore, a cartridge for supplying 
water under pressure to a fuel nozzle is provided which comprises an 
elongated tubular member having a discharge orifice at a forward end 
thereof, a coupling at a rearward end thereof, and a mounting element for 
securing the cartridge within a fuel nozzle body adjacent the rearward 
end. 
In another broad but related aspect of the invention, a fuel nozzle for a 
gas turbine is provided which comprises a fuel nozzle body having gaseous 
fuel and distillate fuel discharge orifices at a forward end thereof, a 
tubular water feed cartridge assembly having a water discharge orifice at 
a forward end thereof; the elongated tubular water feed being 
concentrically mounted within a distillate fuel passageway of the nozzle 
body such that the water discharge orifice lies radially within the 
gaseous fuel and distillate fuel discharge orifices. 
In still another related broad aspect of the invention, a method for 
reducing NOx emissions and for eliminating stress cracking in the 
combustion components of a gas turbine includes the steps of (a) injecting 
fuel into the combustion chamber of a gas turbine as a first conical 
spray; and (b) injecting water into the combustion chamber as a second, 
finely atomized conical spray located radially inwardly of the first 
conical spray so as to avoid direct water impingement on hot metal 
surfaces within said combustion chamber. 
Additional objects and advantages of the present invention will become 
apparent from the detailed description of the invention which follows.

DETAILED DESCRIPTION OF THE DRAWINGS 
With reference to FIG. 1, a cast fuel nozzle body 10 in accordance with 
this invention is provided with an integral mounting flange 12 for 
attachment to an outer case assembly 12A of a gas turbine combustor 
(partially shown in phantom). The fuel nozzle body 10 is designed for use 
in burning either gas or distillate fuel. To this end, the fuel nozzle 
body 10 is provided with a first interior passageway 14 including an inlet 
end 16 and an outlet end 18 for supplying gaseous fuel to the combustion 
zone 20 of the combustor. 
A second passageway 22 is provided in the fuel nozzle body 10 including an 
inlet end 24 and an outlet end 26 for supplying air to the combustion zone 
20 of the combustor. 
A third passageway 28 is centrally located within the fuel nozzle body 10 
and extends from a rearward inlet end 30 to a forward outlet end 32 for 
supplying distillate fuel, i.e., oil, to the combustion zone 20. 
Mounted on the forward end of the fuel nozzle body 10 is a nozzle assembly 
34 which includes an outer gas tip 36, an intermediate air cone 38 and an 
inner air swirler 40. The nozzle assembly 34 is threadably secured to the 
nozzle body 10 as will be described in more detail below. 
With reference now particularly to FIGS. 1 and 4, the gas tip 36 includes a 
conical portion 42, a rearward mounting portion 44, and a forward end 46 
provided with a plurality of angled apertures 48 arranged about a central 
opening 46' at the forward end 46. An outer ring 50 is fixed to the 
conical portion 42 by a plurality of angled vanes or ribs 52 to thereby 
establish passageways 54 for directing and swirling additional air from 
the compressor into the combustion zone 20 as will be explained in greater 
detail below. 
The rearward mounting portion 44 of the gas tip 36 is formed with exterior 
threads for engagement with interior threads formed on a radially 
outermost portion 56 of the nozzle body 10. 
The intermediate air tip 38 is provided with a forward end 58 provided with 
a central aperture 58', a conical portion 60, a cylindrical portion 62 
just behind the conical portion 60, and a rearward mounting portion 64. 
The rearward mounting portion 64 is provided with exterior threads for 
engagement with interior threads formed on a radially intermediate portion 
66 of the nozzle body 10. 
The inner air swirler 40, shown in detail in FIGS. 5 and 6, is formed with 
a forward conical portion 68 provided with a central flared aperture 68' 
and a generally cylindrical stepped portion 70 extending rearwardly of the 
conical portion, terminating in a rearward mounting portion 72. The latter 
is provided with exterior threads for engagement with interior threads 
formed on a radially innermost portion 74 of the nozzle body 10. 
It will be appreciated from the above description, and particularly from 
FIGS. 1 and 4, that the gas tip 36 and intermediate air tip 38 combine to 
form a gas passageway 76 communicating directly with the gas passageway 
14. When the gas turbine is in a gaseous fuel burning mode, gas flowing 
through passageway 14 flows into passageway 76 and exits the apertures 48, 
and is directed by the ring 50 into the combustion zone 20. 
At the same time, the intermediate air tip 38 combines with the inner air 
swirler 40 to form a passageway 78 communicating directly with the air 
passageway 22 in the nozzle body 10. Air flowing through passageway 22 
flows into passageway 78 and exits an orifice 80 created by the opening 
58' of the air tip 38 and the forward conical portion 68 of the distillate 
tip 40. 
As best seen in FIG. 6, the air swirler 40 is provided on its exterior 
peripheral surface with a plurality of angled grooves 82 which cause the 
air flowing through passageway 78 to swirl prior to exiting the orifice 
80. 
The air swirler 40 is also provided with an interior bore 84 which extends 
from an open rearward end 86 to the forward smaller diameter opening 68'. 
Bore 84 forms an extension of the third passageway 28 for distillate fuel, 
so that when the gas turbine is in a distillate fuel burning mode, the 
distillate fuel flowing through passageway 28 from a distillate fuel inlet 
28', enters bore 84 at end 86 and exits at the opening 68'. 
It will be further appreciated from the above description that in attaching 
the nozzle assembly 34 to the nozzle body 10, the air swirler 40 is 
threaded first, followed by the intermediate air tip 38 and then the gas 
tip 36. Upon attachment of the gas tip 36, a forward, radially inwardly 
directed lip 88 thereof engages an annular shoulder 90 provided in the air 
tip 38 to lock the latter in place. At the same time, a lock plate 92 is 
staked between the gas tip 36 and the radially outermost portion 60 of the 
nozzle body 10 to lock the gas tip in place. 
In further accord with an exemplary embodiment of this invention, a breech 
load cartridge assembly 94 is inserted within the distillate passageway 28 
from the rear of the nozzle body 10. 
With reference particularly to FIGS. 1, 2 and 4, the cartridge assembly 94 
includes an elongated tubular member or water delivery pipe 96 having an 
interior through passageway 98 extending from a rearward open end 100 to a 
forward open end 102. A mounting coupling 104 is fixed to the exterior of 
the pipe 96 adjacent its rearward end 100 by any suitable means, 
preferably welding. The coupling 104 is formed with a forward threaded 
portion 106, an intermediate sealing flange 108 (adapted to cooperate with 
a sealing gasket 108') and a rearward end 110. A pipe fitting 112 is 
secured to the rearward end 100 of the pipe 96 for attachment to a water 
supply conduit (not shown). 
The forward end 102 of pipe 96 is threaded on its exterior surface at 114 
to receive a distillate fuel swirler 116, which may be welded in place 
about its rearward edge as shown at 117. The distillate swirler 116, best 
seen in FIGS. 2, 4, 7 and 8, is a generally tubular member provided with 
interior threads extending from an open rearward end 118 along a major 
portion of the length of the swirler (see FIGS. 2 and 4). The forward end 
120 of the swirler is tapered at 122, terminating at a water discharge 
orifice 124. The distillate swirler 116 is provided on its exterior 
surface, adjacent the forwardmost portion of the interior threads, with an 
enlarged annular flange or ring 130 provided with a plurality of angular 
grooves or slots 132 for swirling the distillate fuel as will be described 
in more detail below. Just ahead of the ring or flange 130, a generally 
cylindrical portion 134 of the swirler 116 is formed with a plurality of 
circumferentially arranged flats 136 which create additional space for the 
swirling distillate fuel. 
The exterior surface of the tapered portion 122 of the distillate swirler 
116 combined with an interior tapered surface of the inner distillate tip 
40 to form an annular discharge orifice 138 for the distillate fuel. 
A water swirler 140 is threadably received within the distillate fuel 
swirler 116. The water swirler 140, best seen in FIGS. 2, 4 and 9-12 
includes a generally cylindrical, solid main body portion 142, a tapered 
forward surface 144, and a radially enlarged mounting portion 146 provided 
with exterior threads 148. 
The forward tapered surface 144, which extends axially beyond the solid 
body portion, is formed with a plurality of angularly oriented swirl slots 
150 (only one of which is shown in FIGS. 9 and 10 but all of which are 
shown in FIG. 12) for swirling water flowing through the pipe 94, as 
described in more detail below. An axially oriented screw driver slot 152 
is provided in the water swirler, enabling the swirler to be threadably 
secured within the forward end of the distillate fuel swirler 116. 
In place, and as best seen in FIG. 4, the forward tapered surface 144 of 
the water swirler engages the interior tapered surface of the tapered 
portion 122 of the distillate fuel swirler 116, so that the swirl slots 
150 combine with the interior surface of tapered portion 122 to form a 
plurality of circumferentially closed passageways. At the same time, an 
annular space 154 is created between the tapered surface 144 and the 
radially enlarged mounting portion 148. As a result, water flowing through 
pipe 112 must flow through the slot 152, annular space 154 and swirl slots 
152 in order to exit the orifice 124. 
The water swirler 140 is threadably secured within the distillate fuel 
swirler 116, and the latter is then threadably secured to the forward end 
102 of the pipe 94, so that the forward end 102 of the pipe abuts the 
rearward end of the water swirler 140. 
To assemble the water feed cartridge 94 to the fuel nozzle body 10, the 
pipe 94 is inserted into the nozzle body from its rearward end, with the 
forward threaded portion 106 of the mounting coupling 104 engaging the 
interior threads 156 formed in a counter bore portion of the passageway 
28. At the forward end of the cartridge assembly, the enlarged radial ring 
130 of the distillate fuel swirler 116 engages the interior surface of the 
distillate tip 40 to thereby provide support for the cartridge assembly at 
the forward end of the nozzle body 10. 
In use, and as already stated above, the nozzle body 10 and cartridge 
assembly 94 may be used in either a gaseous fuel burning mode or a 
distillate fuel burning mode. 
When burning gaseous fuel, the distillate fuel supply is shut off upstream 
of the inlet 28' and gaseous fuel is introduced into the nozzle body 10 
via inlet 16 and passageway 14. The gaseous fuel flows through the conical 
gas passageway 76 and is swirled as it is discharged through the angled 
apertures 48 as a conical spray. At the same time, air under pressure is 
introduced into the nozzle body via inlet 24 and passageway 22. The air 
then flows through the passageway 78 and is swirled as it flows through 
the angled grooves 82 prior to discharge through the orifice 80, also in 
conical form. At the same time, additional air from the compressor flows 
through the passageway 54 defined by ring 50 and the conical portion 42 of 
the outer gas tip 38, swirled by vanes or ribs 52. 
Simultaneously, water under pressure is introduced into the pipe 96 via 
inlet 100 and passageway 28. The water flows into the water swirler 140 
via slot 152, into the annular space 154, through the angled grooves or 
slots 150 where it is swirled. The water is discharged through the orifice 
124 where it is atomized by the air discharged through the orifice 80, and 
introduced into the flame center where it mixes with the fuel and air to 
form a homogeneous fuel/air/water mixture in the combustion zone 20. 
In the event distillate fuel is burned in the gas turbine, the gaseous fuel 
supply is shut off upstream of the inlet 16, and distillate fuel is 
introduced into the nozzle body 10 via inlet 28' and passageway 28. The 
distillate fuel is swirled as it passes through the angled slots 132 prior 
to discharge through orifice 138 where it mixes with the air and water (as 
described above) at the combustion zone 20. 
It will also be appreciated that the above described breech loaded 
cartridge assembly for a fuel nozzle body, capable of burning either 
gaseous or distillate fuel, will decrease NOx emissions by injecting water 
directly into the flame center. At the same time, this arrangement 
eliminates direct water impingement on hot metal components of the gas 
turbine combustor so that the potential for stress cracking of various 
combustion components is minimized or eliminated. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment, it is to be 
understood that the invention is not to be limited to the disclosed 
embodiment, but on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.