DUAL FUEL INJECTION METHOD AND APPARATUS

Abstract: A dual fuel premix injector (22, 222) for injecting liquid and/or gaseous fuel into a gas turbine engine (20) is designed to minimize emissions and contamination. The dual fuel premix injector (22, 222) includes a fuel-air mixing chamber (90, 290) bounded by an injector outer wall (83, 283). A plurality of inwardly-directed fuel atomizers (82, 126, 282) are mounted to the inner surface of the outer wall (83, 283) for introducing liquid fuel into the fuel-air mixing chamber (90, 290). The fuel atomizers (82, 126, 282) may be either air-blast atomizers (82, 282) or tubular atomizers (126).

Description: Description DUAL FUEL INJECTION METHOD AND APPARATUS Technical Field The present invention relates to fuel injectors for gas turbine engines. More particularly, the invention relates to a dual fuel injector that can operate using liquid and/or gaseous fuel. Background Art The use of fossil fuel as the combustible fuel in gas turbine engines results in the combustion products of carbon monoxide, carbon dioxide, water vapor, smoke, particulates, unburned hydrocarbons, nitrogen oxides, and sulfur oxides. Of these above products, carbon dioxide and water vapor are considered normal and unobjectionable. Governmental imposed regulations, however, further restrict the amount of other combustion products being emitted in the exhaust gases. In the past, the majority of the products of combustion have been controlled by design modifications. For example, smoke has normally been controlled by design modifications in the combustor, particulates are normally controlled by traps and filters, and sulfur oxides are normally controlled by the selection of low sulfur fuels. This leaves carbon monoxide, unburned hydrocarbons, and nitrogen oxides as the emissions of primary concern in the exhaust gases being emitted from the gas turbine engine. Oxides of nitrogen are produced in two ways in conventional combustion systems. For example, oxides of nitrogen are formed at high temperatures within the combustion zone by the direct combination of atmospheric nitrogen and oxygen, and by the presence of organic nitrogen in the fuel. The rates with which nitrogen oxides form depend upon the flame temperature and, consequently, a small reduction in flame temperature can result in a large reduction in the nitrogen oxides. Past and some present systems use water injection in order to reduce the maximum temperature in the combustion zone of a gas turbine combustor. An injector nozzle used with a water injection system is disclosed in U.S. Patent No. 4,600,151 issued on 15 July 1986, to Jerome R. Bradley. The disclosed injector nozzle includes an annular shroud operatively associated with a plurality of sleeves, one inside the other in spaced apart relation. The sleeves form a liquid fuel-receiving chamber and a water or auxiliary fuel-receiving chamber positioned inside the liquid fuel-receiving chamber. The fuel-receiving chamber is used to discharge water or auxiliary fuel in addition or alternatively to the liquid fuel. The sleeves further form an inner air-receiving chamber for receiving and directing compressor discharged air into the fuel spray cone and/or water or auxiliary fuel to mix therewith. Another fuel injector is disclosed in U.S. Patent No. 4,327,547 issued 4 May 1982, to Eric Hughes et al. This fuel injector employs water injection to reduce emissions of oxides of nitrogen, and an outer annular gas fuel duct with a venturi section having air purge holes to prevent liquid fuel from entering the gas fuel duct. Further included is an inner annular liquid fuel duct having inlets for water and liquid fuel. The inner annular duct terminates in a nozzle, and a central flow passage through which compressed air also flows terminates in a main diffuser having an inner secondary diffuser. The surfaces of both diffusers are arranged so that they are washed by the compressed air in order to reduce or prevent the accretion of carbon to the injector. The diffusers in effect form a hollow pintle. The above systems, and the nozzles used therewith, are examples of attempts to reduce the emissions of oxides of nitrogen. However, the nozzles described above fail to efficiently mix the gaseous fluids and/or the liquid fluids in order to control the emissions of oxides of nitrogen emitted from the combustor. An improved dual fuel injector nozzle for reducing the emission of oxides of nitrogen, carbon monoxide, and unburned hydrocarbons within the combustion zone of a gas turbine engine is disclosed in U.S. Patent No. 5,404,711 issued 11 April 1995, to Amjad P. Rajput. The injector provides a series of premixing chambers that are serially aligned with respect to one another. Despite the improvements that have been developed, there is still a need for a dual fuel injection method and apparatus that will minimize harmful emissions and that will be capable of being efficiently packaged for use in a turbine engine. Accordingly, it is an object of the present invention to solve one or more of the above-noted problems. Disclosure of the Invention In accordance with one aspect of the present invention, a fuel injector comprises a fuel-air mixing chamber having one or more fuel atomizers disposed on the outer surface thereof. Each fuel atomizer includes an air passage and a fuel passage. Each fuel atomizer may comprise a cylindrical tube and a fuel metering orifice intersecting with the cylindrical tube substantially tangentially. Preferably, each cylindrical tube fuel atomizer is canted at an angle of about 70E with respect to a central axis of the fuel injector. Also preferably, each cylindrical tube fuel atomizer is canted at a radial cant angle of about 37E with respect to an outer surface of the fuel-air mixing chamber. In accordance with another aspect of the present invention, a fuel injector comprises: an injector centerbody; an injector outer wall disposed radially outwardly of the injector centerbody; an annular fuel-air mixing chamber disposed between the injector centerbody and the injector outer wall; and one or more fuel atomizers. Each fuel atomizer is on the injector outer wall and is adapted to carry a flow of fuel for mixing with a flow of air. Each fuel atomizer also includes an inner air passage, an outer air passage, and a fuel passage disposed between the inner air passage and the outer air passage. In accordance with a further aspect of the present invention, a fuel injector comprises: an injector centerbody; an injector outer wall disposed radially outwardly of the injector centerbody; an annular fuel-air mixing chamber disposed between the injector centerbody and the injector outer wall; and one or more fuel atomizers, each disposed on the injector outer wall. Each fuel atomizer includes an air passage and a fuel passage. In accordance with yet another aspect of the present invention, a fuel injector comprises: an injector centerbody; an injector outer wall disposed radially outwardly of the injector centerbody; an annular fuel-air mixing chamber disposed between the injector centerbody and the injector outer wall; and one or more fuel atomizers. Each fuel atomizer is disposed on the injector outer wall and is adapted to carry a flow of fuel for mixing with a flow of air. Each fuel atomizer includes an inner air passage, an outer air passage, and a fuel passage disposed between the inner air passage and the outer air passage. In accordance with a still further aspect of the present invention, a method of mixing main liquid fuel with air in a fuel injector is provided, where the fuel injector includes a main liquid fuel feed line and fuel-air mixing chamber having an outer surface. The method comprises the steps of introducing fuel from the outer surface, introducing air from the outer surface, and mixing the fuel and air with additional air passing through the fuel-air mixing chamber. Preferably, the method includes a step of forming a film of fuel having an inside fuel film surface and an outside film fuel surface, and the step of introducing air includes a step of supplying a flow of air along the inside fuel film surface and a step of supplying a flow of air across the outside fuel film surface, so as to apply shearing forces to the film of fuel in order to break the fuel up into droplets . The method and apparatus of the present invention provides improved fuel-air mixing and minimizes contact of liquid fuel droplets with the walls of the fuel air mixing chamber and contamination of the injector. As a result, emissions of NOx and CO are minimized. Brief Description of the Drawings Other features and advantages are inherent in the apparatus and method claimed and disclosed or will become apparent to those skilled in the art from the following detailed description in conjunction with the accompanying drawings in which: FIG. 1 is a partially sectioned side view of a gas turbine engine having a dual fuel injector according to a first embodiment of the present invention; FIG. 2 is an enlarged rear perspective view of the dual fuel injector shown in FIG. 1; FIG. 3 is a front elevational view of the dual fuel injector shown in FIG. 2; FIG. 4 is an enlarged partial cross- sectional view of the dual fuel injector shown in FIG. 2, taken along lines 4-4 of FIG. 3; FIG. 4A is an enlarged fragmentary cross- sectional view of one of the air-blast atomizers shown in FIG. 4; FIG. 5 is an enlarged partial cross- sectional view of the dual fuel injector shown in FIG. 2, taken along lines 5-5 of FIG. 3; FIG. 6 is a cross sectional view, similar to that of FIG. 5, of a fuel-air mixing chamber in accordance with a second embodiment of the present invention; FIG. 7 is a cross-sectional view of the fuel-air mixing chamber of FIG. 6, taken along lines 7-7 of FIG. 6; FIG. 8 is a plan view of a dual fuel injector according to a third embodiment of the present invention; FIG. 9 is an enlarged partial cross- sectional view of the dual fuel injector shown in FIG. 8, taken along lines 9-9 of FIG. 8; and FIG. 9A is an enlarged fragmentary cross- sectional view of one of the air-blast atomizers shown in FIG. 9. Best Mode for Carrying Out the Invention As seen in FIG. l, a gas turbine engine 20 has a dual fuel (gaseous/liquid) premix injector 22. The gas turbine engine 20 includes an outer housing 24 having a plurality of openings 26 therein, each having a pre-established position in relationship to one another. The openings 26 are distributed about a central axis 28 of the outer housing 24. A dual fuel premix injector 22 extends through each of the openings 26. For convenience, however, only one dual fuel premix injector 22 and one opening 26 are shown. Accordingly, the dual fuel premix injector 22 is positioned in one of the openings 26 and is supported by the outer housing 24 in a conventional manner. The outer housing 24 is positioned about a compressor section 30 centered about the central axis 28. A turbine section 32 is centered about the central axis 28, and a combustor section 34 is centered about the central axis 28 and is interposed between the compressor section 30 and the turbine section 32. The gas turbine engine 20 has an annular inner case 36 axially aligned about the central axis 28 and disposed radially inwardly of the combustor section 34. The turbine section 32 includes a power turbine 38 having an output shaft (not shown) connected thereto for driving an accessory component (not shown) such as a generator or a pump. Another portion of the turbine section 32 includes a gas producer turbine 40 connected in driving relationship to the compressor section 30. When the gas turbine engine 20 is operating, a flow of compressed air exits the compressor section 30 and is used for (i) cooling, (ii) for atomizing liquid fuel, such as number 2 diesel fuel, and (iii) for mixing with a combustible fuel for pilot and main combustion in the combustor section 34, as described in further detail below. The combustor section 34 includes an annular combustor 42 that is radially spaced inwardly by a pre-established distance from the outer housing 24 and is supported from the outer housing 24 in a conventional manner. The annular combustor 42 has an annular outer shell 44 that is coaxially positioned about the central axis 28, an annular inner shell 46 that is positioned radially inwardly of the annular outer shell 44 and coaxially positioned about the central axis 28, an inlet end portion 48 having a plurality of generally evenly spaced openings 50 therein, and an outlet end portion 52. Each of the openings 50 has one of the dual fuel premix injectors 22, having an injector central axis 54, generally positioned therein in fluid communication with the inlet end portion 48 of the annular combustor 42. As an alternative to the annular combustor 42, a plurality of can-type combustors or a side can annular combustor could be incorporated without changing the essence of the invention. As further shown in FIGS. 2 through 4, each of the dual fuel premix injectors 22 includes a pilot liquid fuel supply tube 56, a gaseous pilot fuel supply tube 58, a main liquid fuel supply tube 60, and a main gaseous fuel supply tube 62. Each dual fuel premix injector 22 also includes an inner air inlet fitting 64. Air enters each dual fuel premix injector 22 through openings 66 in the inner air inlet fitting 64 and through an annular opening 68. The annular opening 68 is centered about the injector central axis 54, and is surrounded by an air flow restrictor 70. Air entering the dual fuel premix injector 22 through the annular opening 68 is swirled by a plurality of main air swirler blades 72 (that generate vorticity in the flow of air) before being mixed with fuel, as described in further detail below. The pilot liquid fuel supply tube 56 is in fluid communication with a pilot liquid fuel feed line 74 for introducing pilot liquid fuel generally along the injector central axis 54. The pilot liquid fuel feed line 74 includes a tapered outlet end 75. The gaseous pilot fuel supply tube 58 is in fluid communication with an annular pilot gaseous fuel feed passage 76, centered about the injector central axis 54. A first cylindrical wall 77, also centered about the injector central axis 54, surrounds the annular pilot gaseous fuel feed passage 76. The main liquid fuel supply tube 60 is in fluid communication with an annular main liquid fuel manifold cavity 78, which is centered about the injector central axis 54, and which is in turn in fluid communication with a main liquid fuel feed passage 80 associated with each of ten air-blast atomizers 82 mounted to an injector outer wall 83. The air-blast atomizers 82 are equally spaced radially about the injector central axis 54, as best seen in FIG. 3. The main gaseous fuel supply tube 62 is in fluid communication with an annular main gaseous fuel manifold cavity 84, which is centered about the injector central axis 54. The annular main gaseous fuel manifold cavity 84 is in fluid communication with twenty hollow spoke members 86 through a wall 87, which is centered about the injector central axis 54. The wall 87 is disposed radially outwardly of the annular main gaseous fuel manifold cavity 84. The twenty hollow spoke members 86 are equally spaced radially about the injector central axis 54, as best seen in FIG. 3. Each hollow spoke member 86 has a plurality of passages 88 therein for introducing gaseous fuel, such as methane gas, from the annular main gaseous fuel manifold cavity 84 into an annular fuel-air mixing chamber 90, the outer surface of which is defined by the injector outer wall 83. The annular fuel-air mixing chamber 90 is centered about the injector central axis 54. An annular cooling/pilot air passage 92, which is centered about the injector central axis 54, is disposed radially outwardly of the first cylindrical wall 77 and radially inwardly of a second cylindrical wall 93, that is also centered about the injector central axis 54. The second cylindrical wall 93 includes an impingement jet generator 96, having perforations 98 therein, radially inward of the annular fuel-air mixing chamber 90. The wall 87, along with a centerbody tip 100 comprises the injector centerbody, generally indicated at 102. The centerbody tip 100 and the impingement jet generator 96, define a cooling duct 104 therebetween. The centerbody tip 100 includes a plurality of equally spaced radial swirler blades 106. As best seen in FIGS. 4, each air-blast atomizer 82 is generally centered about a corresponding air-blast atomizer centerline 108 that is canted with respect to the injector central axis 54 by an axial cant angle, " , equal to about 45N. However, the axial cant angle of a given dual fuel premix injector 22 will depend upon the application and working conditions in which the dual fuel premix injector 22 is to operate. As best seen in FIG. 4A, each air-blast atomizer 82 includes an air-blast atomizer central air passage 110, an air-blast atomizer annular liquid fuel passage 112, and an air-blast atomizer annular outer air passage 114, each centered about the air-blast atomizer centerline 108. Each air-blast atomizer central air passage 110 places the exterior of the injector outer wall 83 in fluid communication with the annular fuel-air mixing chamber 90. Similarly, a pair of outer air orifices 116, best seen in FIG. 2, associated with each air-blast atomizer 82 place the exterior of the injector outer wall 83 in fluid communication with the associated air-blast atomizer annular outer air passage 114 that is in turn in fluid communication with the annular fuel-air mixing chamber 90. Swirler blades 118 are disposed within the air- blast atomizer annular liquid fuel passage 112, to generate vorticity in a flow of fuel within the air- blast atomizer annular liquid fuel passage 112, and swirler blades 120 are disposed within the air-blast atomizer annular outer air passage 114, to generate vorticity in a flow of air within the air-blast atomizer outer air passage 114. A conically-shaped pilot fuel pintle swirler 122, that includes a plurality of pilot fuel pintle fuel swirler blades 123, for generating vorticity in a flow of pilot fuel, is disposed within a pilot fuel exit passage 124 that is in fluid communication with the inlet end portion 48 of the annular combustor 42 (FIG. 1) . The conically-shaped pilot fuel pintle swirler 122, is supported and centered within the pilot fuel exit passage 124 by the pilot fuel pintle fuel swirler blades 123. In accordance with a second embodiment of the present invention, all aspects of the structure and operation of the dual fuel premix injector 22 are essentially identical to that described above and shown in FIGS 1-5, with the exception that the air- blast atomizers 82, best shown in FIGS. 4, 4A, and 5, are each replaced in the second embodiment with tubular atomizers 126, shown in FIGS. 6 and 7. In FIGS 6 and 7, the injector outer wall 83, having an inner diameter of about 3.500 inches (8.890 cm), and an outer diameter of about 3.749 inches (9.523 cm), and having an inlet end 127 and an outlet end 128, is shown with ten tubular atomizers 126 mounted thereto. Each tubular atomizer 126 includes a substantially cylindrical atomizer tube 129 to which liquid fuel is supplied via an atomizer metering orifice 130 having a diameter of about 0.040 inches (0.102 cm) . Each atomizer tube 129 has an inner diameter of about 0.194 inches (0.493 cm). As seen in FIG. 7, each atomizer tube 129 is flush with the outer surface of the injector outer wall 83. Each atomizer tube 129 extends into the fuel-air mixing chamber 90 to an extent such that the ends of the atomizer tubes 129 nearest to the injector central axis 54 define a circle (designated as 131) , centered about the injector central axis 54 and having a diameter of about 2.787 inches (7.079 cm). As seen in FIG. 6, each atomizer tube 129 is substantially centered about an atomizer tube axis 132 that is canted at an atomizer tube axial cant angle, $, equal to about 7ON. As seen in FIG. 7, each atomizer tube axis 132 is canted at an atomizer tube radial cant angle, : , equal to about 37N, with respect to a radius extending orthogonally from the injector central axis 54 to the atomizer tube axis 132 at the outer diameter of the injector outer wall 83. Each metering orifice 130 is positioned and oriented such that it intersects with the corresponding atomizer tube 129 substantially tangentially to the inner surface of the atomizer tube 129 and is canted at a metering orifice angle, N, equal to about 3ON with respect to the injector central axis 54. The above noted characteristics of each tubular atomizer 126 have been found to yield optimal performance with regard to minimizing emissions over a wide range of operating conditions. With regard to the tubular atomizers 126, an air to liquid mass flow ratio of 2.5 or greater has been found to provide the best performance. A dual fuel premix injector 222, in accordance with a third embodiment of the present invention, is shown in FIGS. 8, 9, and 9A. The dual fuel premix injector 222 is similar to the dual fuel premix injector 22 in accordance with the first embodiment of the present invention. Accordingly, similar parts of the first and third embodiments have generally been assigned reference numerals ending with two identical digits. The dual fuel premix injector 222 has an injector central axis 254 and includes a pilot liquid fuel supply tube 256, a gaseous pilot fuel supply tube 258, a main liquid fuel supply tube 260, and a main gaseous fuel supply tube 262. Air enters each dual fuel premix injector 222 through an inner annular opening 266 and through an outer annular opening 268. The outer annular opening 268 is centered about the injector central axis 254, and is surrounded by an air flow restrictor 270. Air entering the dual fuel premix injector 222 through the outer annular opening 268 is swirled by a plurality of main air swirler blades 272 (that generate vorticity in the flow of air) before being mixed with fuel, as described in further detail below. The pilot liquid fuel supply tube 256 is in fluid communication with a pilot liquid fuel feed line 274 for introducing pilot liquid fuel generally along the injector central axis 254. The pilot liquid fuel feed line 274 includes a tapered outlet end 275. The gaseous pilot fuel supply tube 258 is in fluid communication with an annular pilot gaseous fuel feed passage 276, centered about the injector central axis 254, that contains pilot gaseous fuel swirler blades 277 (that generate vorticity in the flow of pilot gaseous fuel) . A first cylindrical wall 278, also centered about the injector central axis 254, surrounds the annular pilot gaseous fuel feed passage 276. The main liquid fuel supply tube 260 is in fluid communication with an annular main liquid fuel manifold cavity 279, which is centered about the injector central axis 254, and which is in turn in fluid communication with a main liquid fuel feed passage 280 associated with each of ten air-blast atomizers 282 mounted to an injector outer wall 283. The air-blast atomizers 282 are equally spaced radially about the injector central axis 254. The main gaseous fuel supply tube 262 is in fluid communication with an annular main gaseous fuel manifold cavity 284, which is in fluid communication with twenty hollow spoke members 286 through a second cylindrical wall 287. The twenty hollow spoke members 286 are equally spaced radially about the injector central axis 254. Each hollow spoke member 286 has a plurality of passages 288 therein for introducing gaseous fuel, such as methane gas, from the annular main gaseous fuel manifold cavity 284 into an annular fuel-air mixing chamber 290, the outer surface of which is defined by the injector outer wall 283. The annular fuel-air mixing chamber 290 is centered about the injector central axis 254. A tapered cylindrical pilot passage casing 289 is radially spaced outwardly from the first cylindrical wall 278, and an annular pilot air passage 291 is disposed between the tapered cylindrical pilot passage casing 289 and the first cylindrical wall 278. Pilot air swirler blades 292 are disposed within the annular pilot air passage 291, to generate vorticity in a flow of air therein. An annular cooling/pilot air passage 293, which is centered about the injector central axis 254, is disposed radially outwardly of the tapered cylindrical pilot passage casing 289 and radially inwardly of the second cylindrical wall 287. The tapered cylindrical pilot passage casing 289 includes a plurality of canted radial passages 295 for feeding air from the annular cooling air passage 293 to the annular pilot air passage 291. Air may also optionally be fed to the annular pilot air passage 291 through an air assist passage 296 that is in turn supplied with compressed air through an air assist supply tube 297 that is connected to an external source of compressed air, such as a "shop air" system or a dedicated compressor. A third cylindrical wall 298, which is centered about the injector central axis 254, is disposed radially outwardly of the outer annular opening 268. An impingement jet generator 299, having perforations 299' therein, is disposed radially inward of the annular fuel-air mixing chamber 290 and is secured within the third cylindrical wall 298. The third cylindrical wall 298, along with a centerbody tip 300, that includes an inner cylindrical wall 301, comprises the injector centerbody, generally indicated at 302. The centerbody tip 300 and the impingement jet generator 299, define a labyrinth- shaped cooling duct 304 therebetween. Each air-blast atomizer 282 is generally centered about a corresponding air-blast atomizer centerline 308 that is canted with respect to the injector central axis 254 by an axial cant angle equal to about 45N. However, the axial cant angle of a given dual fuel premix injector 222 will depend upon the application and working conditions in which the dual fuel premix injector 222 is to operate. As best seen in FIG. 9A, each air-blast atomizer 282 includes an air-blast atomizer central air passage 310, an air-blast atomizer annular liquid fuel passage 312, and an air-blast atomizer annular outer air passage 314, each centered about the air- blast atomizer centerline 308. Each air-blast atomizer central air passage 310 places the exterior of the injector outer wall 283 in fluid communication with the annular fuel-air mixing chamber 290. Similarly, an outer air opening 316, best seen in FIG. 8, associated with each air-blast atomizer 282 places the exterior of the injector outer wall 283 in fluid communication with the associated air-blast atomizer annular outer air passage 314 that is in turn in fluid communication with the annular fuel-air mixing chamber 290. Swirler blades 318 are disposed within the air- blast atomizer annular liquid fuel passage 312, to generate vorticity in a flow of fuel through the air- blast atomizer annular liquid fuel passage 312, and swirler blades 320 are disposed within the air-blast atomizer annular outer air passage 314, to generate vorticity in a flow of air within the air-blast atomizer outer air passage 314. A conically-shaped pilot fuel pintle swirler 322, for generating vorticity (or augmenting the level of vorticity, in the case of gaseous pilot fuel, that also flows past the pilot gaseous fuel swirler blades 277) in a flow of pilot fuel, is disposed within a pilot fuel exit passage 324 that is in fluid communication with the inlet end portion 48 of the annular combustor 42 (FIG. 1) . Industrial Applicability The dual fuel premix injector 22 of FIGS. 2- 5 operates as follows. Compressed air from the compressor section 30 enters the openings 66 in the inner air inlet fitting 64 and the annular opening 68 from the left hand side of the dual fuel premix injector 22, as seen in FIGS. 1, 2, 4, and 5. The compressed air that enters the dual fuel premix injector 22 through the annular opening 68 is swirled by the main air swirler blades 72. The compressed air that enters the dual fuel premix injector 22 through the openings 66 passes through the annular cooling/pilot air passage 92 and is used for cooling the injector centerbody 102 in the vicinity of the annular combustor 42 and for cooling the centerbody tip 100 as the air passes through the perforations 98 (thereby creating impingement jets) , the cooling duct 104, and the radial swirler blades 106 into the annular combustor 42. This air is also used, during pilot operation, for mixing with pilot fuel, as discussed in further detail below. When the gas turbine engine 20 is operating using main gaseous fuel, the compressed air that enters the dual fuel premix injector 22 through the annular opening 68 mixes with gaseous fuel which is introduced from the main gaseous fuel supply tube 62 to the annular main gaseous fuel manifold cavity 84 and then to the annular fuel-air mixing chamber 90 through the hollow spoke members 86 and the passages 88 therein. After exiting the annular fuel-air mixing chamber 90, the gaseous fuel-air mixture is burned in the annular combustor 42. If pilot gaseous fuel is to be used, for example, for starting (lightoff) of the gas turbine engine 20, air is introduced from the compressor section 30 into the openings 66, through the annular cooling/pilot air passage 92, the perforations 98 (thereby creating impingement jets) , the cooling duct 104, and the radial swirler blades 106. This air mixes with gaseous fuel that flows from the pilot gaseous fuel supply tube 58, through the annular pilot gaseous fuel passage 76, and past the conically-shaped pilot fuel pintle swirler 122 and the pilot fuel pintle fuel swirler blades 123 in the pilot fuel exit passage 124. When the gas turbine engine 20 is operating using main liquid fuel, compressed air from the compressor section 30 flows into the openings 66 in the inner air inlet fitting 64 and the annular opening 68 from the left hand side of the dual fuel premix injector 22, as seen in FIGS. 1, 2, 4, and 5. The compressed air that enters the dual fuel premix injector 22 through the annular opening 68 is swirled by the main air swirler blades 72 and mixes with a fuel-air mixture introduced into the annular fuel-air mixing chamber 90 by the air-blast atomizers 82. Each air-blast atomizer 82 operates as follows. Compressed air passes from the exterior of the dual fuel premix injector 22 into the air-blast atomizer central air passage 110, due to a pressure differential between the exterior (at a higher pressure) and interior (at a lower pressure) of the dual fuel premix injector 22 during operation of the gas turbine engine 20. In a similar fashion, compressed air is also fed from the exterior of the dual fuel premix injector 22 through each outer air orifice 116, into the air-blast atomizer annular outer air passage 114, where it is swirled by the swirler blades 120. (Although not shown in the drawings, it is contemplated that a supply of compressed air could be fed to the air blast atomizer central air passage 110 and/or to the air-blast atomizer annular outer air passage 114 by other means, such as from a "shop-air" source of compressed air.) Meanwhile, liquid fuel is introduced into each air-blast atomizer annular liquid fuel passage 112 from the main liquid fuel supply tube 60, through the annular main liquid fuel feed manifold cavity 78, through each main liquid fuel feed passage 80. The liquid fuel is swirled by the swirler blades 118 within each air-blast atomizer annular liquid fuel passage 112. The swirling of the liquid fuel causes it to form a film on the interior surface of the outer wall of the atomizer fuel passage 112 as it exits the atomizer fuel passage 112. The film of fuel is simultaneously broken up into droplets (atomized) and mixed with air upon exiting the air-blast atomizer 82. This atomizing and mixing action is due to the shearing forces applied to the film of fuel as it is caught between the compressed air exiting from the air-blast atomizer central air passage 110 (i.e., along an inside fuel film surface) , flowing at a first air-blast atomizer air mass flow rate, and the swirling compressed air exiting from the air-blast atomizer outer annular air passage 114 (i.e., along an outside fuel film surface) , flowing at a second air- blast atomizer air mass flow rate different from the first air-blast atomizer air mass flow rate. This liquid fuel-air mixture is further mixed with swirling air in the annular fuel-air mixing chamber 90 before being ignited in the annular combustor 42. If liquid pilot fuel is to be used, for example, for starting (lightoff) of the gas turbine engine 20, the liquid pilot fuel is introduced into the pilot liquid fuel feed line 74 from the pilot liquid fuel supply tube 56. The liquid pilot fuel passes through the tapered outlet end 75 of the pilot liquid fuel feed line 74 and past the conically-shaped pintle swirler 122 and the pilot fuel pintle fuel swirler blades 123, causing the liquid pilot fuel to form a uniform film on the interior of the pilot fuel exit passage 124. As the film of liquid pilot fuel exits the pilot fuel exit passage 124, it is simultaneously atomized and mixed with air introduced from the compressor section 30 into the openings 66, through the annular cooling/pilot air passage 92, the perforations 98, the cooling duct 104, and the radial swirler blades 106. This atomizing and mixing action is due to the shearing forces exerted on the film of liquid pilot fuel, exiting from the pilot fuel exit passage 124, by the compressed air exiting from the radial swirler blades 106. Preferably, the radial swirler blades 106 cause the compressed air passing therethrough to rotate in a direction opposite to the direction in which the liquid pilot fuel is rotating due to the influence thereon by the conically-shaped pilot fuel pintle swirler 122 and the pilot fuel pintle fuel swirler blades 123. The liquid pilot fuel-air mixture is then ignited in the annular combustor 42. For liquid main fuel operation using the tubular atomizers 126 shown in FIGS. 6 and 7, in accordance with the second embodiment of the present invention, the dual fuel premix injector 22 operates in the following manner. Liquid fuel is supplied from the annular main liquid fuel feed manifold cavity 78 to the inner surface of each atomizer tube 126 through the corresponding metering orifice 130. Simultaneously, due to the pressure differential between the exterior and interior of the dual fuel premix injector 22, compressed air is drawn in from the outside of the injector outer wall 83 into each atomizer tube 126. Although not shown in the drawings, it is contemplated that a supply of compressed air could be fed to each atomizer tube 126 by other means, such as from a "shop-air" source of compressed air. In each atomizer tube 126, the liquid fuel forms a film of fuel on the inner surface of the atomizer tube 126. Due to the tangential orientation of each metering orifice 130 with respect to the inner surface of the corresponding atomizer tube 126, the film of fuel rotates about the atomizer tube axis 132. As the rotating film of fuel exits from the atomizer tube 126 into the annular fuel-air mixing chamber 90, the film of fuel is atomized into droplets by the shearing action of swirling air passing through the fuel-air mixing chamber 90 from the annular opening 68. To enhance atomization, each atomizer tube 126 is oriented so that the film of fuel exiting therefrom is rotating in a direction about the injector central axis 54 in a direction opposite to the direction of the rotation (caused by the main air swirler blades 72) of the air passing through the fuel-air mixing chamber 90 from the annular opening 68. The resulting fuel-air mixture then exits the dual fuel premix injector 22 and is ignited in the annular combustor 42. The dual fuel premix injector 222, in accordance with the third embodiment of the present invention, shown in FIGS. 8, 9, and 9A, operates as follows. Compressed air from the compressor section 30 enters the inner annular opening 266 and the outer annular opening 268 from the left hand side of the dual fuel premix injector 22, as seen in FIGS. 8 and 9. The compressed air that enters the dual fuel premix injector 222 through the outer annular opening 268 is swirled by the main air swirler blades 272. The compressed air that enters the dual fuel premix injector 222 through the inner annular opening 266 passes through the annular cooling air passage 293 and is used for cooling the injector centerbody 302 in the vicinity of the annular combustor 42 and for cooling the centerbody tip 300 as the air passes through the perforations 299 • (thereby creating impingement jets) and the labyrinth-shaped cooling duct 304 into the annular combustor 42. This air is also used, during pilot operation, for mixing with pilot fuel, as discussed in further detail below. When the gas turbine engine 20 is operating using main gaseous fuel, the compressed air that enters the dual fuel premix injector 222 through the outer annular opening 268 mixes with gaseous fuel which is introduced from the main gaseous fuel supply tube 262 to the annular main gaseous fuel manifold cavity 284 and then to the annular fuel-air mixing chamber 290 through the hollow spoke members 286 and the passages 288 therein. After exiting the annular fuel-air mixing chamber 290, the gaseous fuel-air mixture is burned in the annular combustor 42. If pilot gaseous fuel is to be used, for example, for starting (lightoff) of the gas turbine engine 20, air is introduced from the compressor section 30 into the inner annular opening 266, through the annular cooling air passage 293, the perforations 299* (thereby creating impingement jets), and the labyrinth-shaped cooling duct 304. This air mixes with gaseous fuel that flows from the pilot gaseous fuel supply tube 258, through the annular pilot gaseous fuel passage 276 and past the pilot gaseous fuel swirler blades 277 therein, and past the conically-shaped pilot fuel pintle swirler 322 in the pilot fuel exit passage 324. When the gas turbine engine 20 is operating using main liquid fuel, compressed air from the compressor section 30 flows into the inner annular opening 266 and the outer annular opening 268 from the left hand side of the dual fuel premix injector 222, as seen in FIGS. 8 and 9. The compressed air that enters the dual fuel premix injector 222 through the outer annular opening 268 is swirled by the main air swirler blades 272 and mixes with a fuel-air mixture introduced into the annular fuel-air mixing chamber 290 by the air-blast atomizers 282. Each air-blast atomizer 282 operates as follows. Compressed air passes from the exterior of the dual fuel premix injector 222 into the air-blast atomizer central air passage 310, due to a pressure differential between the exterior (at a higher pressure) and interior (at a lower pressure) of the dual fuel premix injector 222 during operation of the gas turbine engine 20. In a similar fashion, compressed air is also fed from the exterior of the dual fuel premix injector 222 through each outer air opening 316, into the air-blast atomizer annular outer air passage 314, where it is swirled by the swirler blades 320. (Although not shown in the drawings, it is contemplated that a supply of compressed air could be fed to the air blast atomizer central air passage 310 and/or to the air-blast atomizer annular outer air passage 314 by other means, such as from a "shop-air" source of compressed air.) Meanwhile, liquid fuel is introduced into each air-blast atomizer annular liquid fuel passage 312 from the main liquid fuel supply tube 260, through the annular main liquid fuel feed manifold cavity 279, through each main liquid fuel feed passage 280. The liquid fuel is swirled by the swirler blades 318 within each air-blast atomizer annular liquid fuel passage 312. The swirling of the liquid fuel causes it to form a film on the interior surface of the outer wall of the atomizer fuel passage 312 as it exits the atomizer fuel passage 312. The film of fuel is simultaneously broken up into droplets (atomized) and mixed with air upon exiting the air-blast atomizer 282. In a manner similar to that of the air-blast atomizers 82, used in the dual fuel premix injector 22 in accordance with the first embodiment of the present invention, this atomizing and mixing action is due to the shearing forces applied to the film of fuel as it is caught between the compressed air exiting from the air-blast atomizer central air passage 310 (i.e., along an inside fuel film surface) , flowing at a first air-blast atomizer air mass flow rate, and the swirling compressed air exiting from the air-blast atomizer outer annular air passage 314 (i.e., along an outside fuel film surface) , flowing at a second air- blast atomizer air mass flow rate different from the first air-blast atomizer air mass flow rate. This liquid fuel-air mixture is further mixed with swirling air in the annular fuel-air mixing chamber 290 before being ignited in the annular combustor 42. If liquid pilot fuel is to be used, for example, for starting (lightoff) of the gas turbine engine 20, the liquid pilot fuel is introduced into the pilot liquid fuel feed line 274 from the pilot liquid fuel feed supply tube 256. The liquid pilot fuel passes through the tapered outlet end 275 of the pilot liquid fuel feed line 274 and past the conically-shaped pintle swirler 322, causing the liquid pilot fuel to form a uniform film on the interior of the pilot fuel exit passage 324. As the film of liquid pilot fuel exits the pilot fuel exit passage 324, it is simultaneously atomized and mixed with air introduced from the compressor section 30 into the inner annular opening 266, through both the annular pilot air passage 291 and the annular cooling air passage 293, via the perforations 299', and the labyrinth-shaped cooling duct 304. This atomizing and mixing action is due to the shearing forces exerted on the film of liquid pilot fuel, exiting from the pilot fuel exit passage 324, by the compressed air exiting from the labyrinth-shaped cooling duct 304. The liquid pilot fuel-air mixture is then ignited in the annular combustor 42. The configurations of the dual fuel premix injectors 22 and 222 in accordance with the present invention provide numerous performance advantages, such as, for example, minimizing fuel contamination, enhancing durability, and lowering emissions. The dual fuel premix injectors 22 and 222 are nominally intended to operate on either natural gas or diesel fuel, with the capability of starting the gas turbine engine 20 on either fuel and transferring between fuels while the gas turbine engine 20 is operating. The use of either of the dual fuel premix injectors 22 and 222 allows the gas turbine engine 20 to achieve low emissions of oxides of nitrogen while operating on either natural gas or liquid fuel through lean-premixed combustion, without other dilutents such as water or steam. Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.

Claims: Claims 1. A fuel injector (22, 222) comprising: a fuel-air mixing chamber (90, 290) having an outer surface (83, 283); and one or more fuel atomizers (82, 126, 282), each disposed on the outer surface (83, 283); wherein each fuel atomizer (82, 126, 282) includes an air passage (110, 114, 129, 310, 314) and a fuel passage (112, 130, 312). 2. The fuel injector (22) of claim 1, wherein each air passage (129) is a cylindrical tube (129) having an interior surface. 3. The fuel injector (22) of claim 2, wherein each fuel passage (130) is a fuel metering orifice (130) . 4. The fuel injector (22) of claim 3, wherein each fuel metering orifice (130) includes an outlet portion intersecting with the corresponding cylindrical tube (129) substantially tangentially. 5. The fuel injector (22) of claim 1, wherein the injector (22) has a central axis (54, 254) and each fuel atomizer is canted at an axial cant angle (α, β) with respect to the central axis (54, 254) . 6. The fuel injector (22) of claim 5, wherein the axial cant angle (β) is about 70°. 7. The fuel injector (22, 222) of claim 1, wherein the fuel passage (112, 130, 312) is an annular liquid fuel passage (112, 312) and wherein the fuel injector (22, 222) further includes a plurality of passages (88, 288) in a plurality of hollow spoke members (86, 286) mounted to the fuel injector (22, 222) for introducing gaseous fuel into the fuel-air mixing chamber (90, 290) . 8. The fuel injector (22, 222) of claim 7, wherein the annular liquid fuel passage (112, 312) is in fluid communication with a main liquid fuel supply tube (60, 260) and wherein the fuel injector (22, 222) further includes a main gaseous fuel manifold cavity (84, 284) in fluid communication with the hollow spoke members (86, 286) and wherein the fuel injector (22, 222) further includes a pilot liquid fuel feed line (74, 274) for introducing a flow of liquid pilot fuel. 9. The fuel injector (22, 222) of claim 8, wherein the fuel injector (22, 222) has a central axis (54, 254) and the pilot liquid fuel feed line (74, 274) is disposed generally along the injector central axis (54, 254) . 10. The fuel injector (22, 222) of claim 9, wherein the fuel injector (22, 222) further includes an annular pilot gaseous fuel feed passage (76, 276) for introducing a flow of gaseous pilot fuel. 11. The fuel injector (22, 222) of claim 10, wherein the annular pilot gaseous feed passage (76, 276) is centered about the injector central axis (54, 254). 12. The fuel injector (22, 222) of claim 1, wherein the fuel injector (22, 222) further includes a pilot liquid fuel feed line (74, 274) for introducing a flow of liquid pilot fuel. 13. The fuel injector (22, 222) of claim 12, wherein the fuel injector (22, 222) has a central axis (54, 254) and the pilot liquid fuel feed line (74, 274) is disposed generally along the injector central axis (54, 254). 14. The fuel injector (22, 222) of claim 1, wherein the fuel injector (22, 222) further includes an annular pilot gaseous fuel feed passage (76, 276) for introducing a flow of gaseous pilot fuel. 15. The fuel injector (22, 222) of claim 14, wherein the fuel injector (22, 222) has a central axis (54, 254) and the annular pilot gaseous feed passage (76, 276) is centered about the injector central axis (54, 254). 16. A fuel injector (22, 222) comprising: an injector centerbody (102, 302); an injector outer wall (83, 283) disposed radially outwardly of the injector centerbody (102, 302); an annular fuel-air mixing chamber (90, 290) disposed between the injector centerbody (102, 302) and the injector outer wall (83, 283); and one or more fuel atomizers (82, 126, 282), each disposed on the injector outer wall (83, 283); and wherein each fuel atomizer (82, 126, 282) includes an air passage (110, 114, 129, 310, 314) and a fuel passage (112, 130, 312). 17. The fuel injector (22) of claim 16, wherein each fuel atomizer (126) is canted at a radial cant angle (μ) with respect to a radius extending orthogonally from an injector central axis (54) to an atomizer axis (132) . 18. The fuel injector of claim 17, wherein the radial cant angle (μ) is about 37°. 19. A fuel injector (22, 222) comprising: an injector centerbody (102, 302); an injector outer wall (83, 283) disposed radially outwardly of the injector centerbody (102, 302) ; an annular fuel-air mixing chamber (90, 290) disposed between the injector centerbody (22, 222) and the injector outer wall (83, 283); and one or more fuel atomizers (82, 282), each disposed on the injector outer wall (83, 283) and each adapted to carry a flow of fuel for mixing with a flow of air and each including an inner air passage (110, 310), an outer air passage (114, 314), and a fuel passage (112, 312) disposed between the inner air passage (110, 310) and the outer air passage (114, 314). 20. The fuel injector (22, 222) of claim 19, wherein each fuel passage (112, 312) includes one or more fuel swirler blades (118, 318) for generating vorticity in the flow of fuel. 21. The fuel injector (22, 222) of claim 19, wherein each outer air passage (114, 314) includes one or more swirler blades (120, 320) for generating vorticity in the flow of air. 22. The fuel injector (22, 222) of claim 19, wherein the inner air passage (110, 310) , the outer air passage (114, 314) and the fuel passage (112, 312) are adapted to apply shearing forces to fuel emerging from the fuel passage (112, 312) to break the fuel up into droplets. 23. A method of mixing main liquid fuel with air in a fuel injector (22, 222), the fuel injector (22, 222) including a main liquid fuel feed line (80, 280) and a fuel-air mixing chamber (90, 290) having an outer surface (83, 283), the method comprising the steps of: introducing fuel from the outer surface (83, 283) ; introducing air from the outer surface (83, 283); and mixing the fuel and air with additional air passing through the fuel-air mixing chamber (90, 290) . 24. The method of claim 23, wherein the step of introducing fuel includes a step of forming a film of fuel having an inside fuel film surface and an outside fuel film surface. 25. The method of claim 24, wherein the step of introducing air includes a step of supplying a flow of air along the inside fuel film surface. 26. The method of claim 25, wherein the step of introducing air includes a step of supplying a flow of air across the outside fuel film surface to apply shearing forces to the film of fuel to break the fuel up into droplets. 27. The method of claim 24, wherein the step of forming the film of fuel comprises a step of forming a cylindrically-shaped film of fuel. 28. The method of claim 27, wherein the step of introducing air includes a step of supplying a flow of air along the inside fuel film surface. 29. The method of claim 28, wherein the step of introducing air includes a step of supplying a flow of air across the outside fuel film surface to apply shearing forces to the cylindrically-shaped film of fuel to break the fuel up into droplets.

Inventors: BOONSTRA ANTHONY J, COWELL LUKE H, LOCKYER JOHN F, BOONSTRA, ANTHONY, J., COWELL, LUKE, H., LOCKYER, JOHN, F.
Applicants: SOLAR TURBINES INC, SOLAR TURBINES INCORPORATED
Application year: 1998
Main classification: F23D11
IPC codes: F23D11, F23D17, F23R3