Abstract:
A gas turbine engine fuel nozzle includes an axis of symmetry extending therethrough, the nozzle body including a first passage extending coaxially therethrough, a second passage, and a third passage, the second passage circumscribing the first passage, the third passage formed radially outward of the second passage, and a nozzle tip coupled to the nozzle body, the nozzle tip including at least one primary discharge opening in flow communication with the first passage, at least one secondary discharge opening in flow communication with the second passage, and at least one tertiary discharge opening in flow communication with the third passage.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and, more particularly, to a fuel nozzle for a gas turbine engine. 
   Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards that regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC &amp; CO). 
   Accordingly, at least one known industrial gas turbine application includes a steam injection system that is configured to inject steam into the combustor to facilitate reducing nitrous oxide emissions from the gas turbine engine. However, when the steam injection system is not in use, i.e. during dry operation, at least one known gas turbine engine utilizes at least one of an air or fuel purge to reduce the potential for cross-talk between adjacent fuel nozzles and/or to reduce backflow into the fuel nozzle caused by off-board steam system leakage. Cross-talk as used herein is defined as the inflow through a first fuel nozzle and outflow through a second fuel nozzle caused by a circumferential pressure distribution within the combustor. More specifically, at least one known gas turbine engine includes a relatively large steam circuit flow area, such that compressor discharge bleed air supply is insufficient to purge the fuel nozzles. Similarly, utilizing gas to purge the fuel nozzle results in a relatively small purge flow, which is insufficient to provide protection against the aforementioned situations. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect, a method for delivering fuel in a gas turbine engine is provided. The method includes channeling fuel through the first passage such that fuel is discharged through the nozzle tip at least one primary discharge opening, channeling fuel through the second passage such that fuel is discharged through the nozzle tip at least one secondary discharge opening, and channeling steam through the third passage such that steam is discharged through the nozzle tip at least one tertiary discharge opening in a first operational mode. 
   In another aspect, a gas turbine engine fuel nozzle is provided. The gas turbine engine fuel nozzle includes an axis of symmetry extending therethrough, the nozzle body including a first passage extending coaxially therethrough, a second passage, and a third passage, the second passage circumscribing the first passage, the third passage formed radially outward of the second passage, and a nozzle tip coupled to the nozzle body, the nozzle tip including at least one primary discharge opening in flow communication with the first passage, at least one secondary discharge opening in flow communication with the second passage, and at least one tertiary discharge opening in flow communication with the third passage. 
   In a further aspect, a gas turbine engine assembly is provided. The gas turbine engine assembly includes a gas turbine engine, at least two manifolds coupled to the gas turbine engine, the at least two manifolds including a first manifold and a second manifold, the first manifold configured to deliver to the gas turbine engine a first gas, the second manifold configured to deliver to the gas turbine engine a first fuel; and at least one fuel nozzle. The fuel nozzle includes an axis of symmetry extending therethrough, the nozzle body including a first passage extending coaxially therethrough, a second passage, and a third passage, the second passage circumscribing the first passage, the third passage formed radially outward of the second passage, and a nozzle tip coupled to the nozzle body, the nozzle tip including at least one primary discharge opening in flow communication with the first passage, at least one secondary discharge opening in flow communication with the second passage, and at least one tertiary discharge opening in flow communication with the third passage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine; 
       FIG. 2  is a cross-sectional view of an exemplary combustor used with the gas turbine engine shown in  FIG. 1 ; 
       FIG. 3  is a schematic illustration of an exemplary fuel delivery system for the gas turbine engine shown in  FIG. 1 ; 
       FIG. 4  is a cross-sectional view of an exemplary fuel nozzle that can be used with the gas turbine engine shown in  FIG. 1 ; 
       FIG. 5  is an end view of a portion of the fuel nozzle shown in  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of the fuel nozzle shown in  FIG. 4  during a first operational mode; 
       FIG. 7  is a cross-sectional view of the fuel nozzle shown in  FIG. 4  during a second operational mode. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of an exemplary gas turbine engine  10  including a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18 , and a low pressure turbine  20  arranged in a serial, axial flow relationship. Compressor  12  and turbine  20  are coupled by a first shaft  24 , and compressor  14  and turbine  18  are coupled by a second shaft  26 . In one embodiment, gas turbine engine  10  is an LMS100 engine commercially available from General Electric Company, Cincinnati, Ohio. 
   In operation, air flows through low pressure compressor  12  from an upstream side  28  of engine  10 . Compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . Highly compressed air is then delivered to combustor assembly  16  where it is mixed with fuel and ignited. Combustion gases are channeled from combustor assembly  16  to drive turbines  18  and  20 . 
     FIG. 2  is a cross-sectional view of a combustor, such as combustor  16 , that may be used with gas turbine engine  10 . Combustor  16  includes an inner liner  30  and an outer liner  32 . Inner and outer liners  30  and  32  are joined at an upstream end  36  by a dome assembly  40 . The cross section shown in  FIG. 2  is taken through one of a plurality of swirler assemblies  42  that are mounted on dome assembly  40 . A fuel line  44  delivers fuel to a fuel nozzle  46  that supplies fuel to an inlet  48  of swirler assembly  42 . Fuel is mixed with air in swirler assembly  42  and the fuel/air mixture is introduced into combustor  16  from an outlet  50  of swirler assembly  42 . 
     FIG. 3  is a schematic illustration of an exemplary fuel delivery system  60  that can be used with a gas turbine engine, such as gas turbine engine  10  (shown in  FIG. 1 ). In the exemplary embodiment, fuel delivery system  60  includes a steam circuit  62  and a gas circuit  64  which respectively deliver a first gas, i.e. steam, and a first fuel, i.e. gas, to gas turbine engine  10 . Steam circuit  62  and gas circuit  64  are both metered and sized to achieve a pressure ratio within fuel delivery system  60  appropriate for the gas being delivered to gas turbine engine  10 . Steam circuit  62  delivers a metered steam flow to gas turbine engine  10  and gas circuit  64  delivers a metered first gas flow to gas turbine engine  10 . 
   Steam circuit  62  includes a connecting line  66  which extends from a metering valve (not shown) to a first manifold  70 . The metering valve is positioned between a steam supply source (not shown) and connecting line  66 . In one embodiment, the first gas supply source is a steam supply source. First manifold  70  is connected to a connecting line  72  which extends from manifold  70  to a plurality of fuel nozzles, such as fuel nozzle  46 , shown in  FIG. 2 . Fuel nozzles  46  are coupled to gas turbine engine  10  and deliver the secondary steam and secondary gas flows to gas turbine engine  10  once gas turbine engine  10  has been operating for a predetermined length of time and is being accelerated from the initial idle speed. 
   Gas circuit  64  includes a connecting line  80  which extends from a metering valve (not shown) to a second manifold  82 . The metering valve is positioned between a gas supply source (not shown) and connecting line  80 . In one embodiment, the gas supply source is a natural gas supply source. In an alternative embodiment, gas supply source is a liquid fuel source. Second manifold  82  is coupled to fuel line  44  which extends from manifold  82  to fuel nozzle  46 . Fuel nozzles  46  are coupled to gas turbine engine  10  to deliver the first fuel to gas turbine engine  10  during initial operation of gas turbine engine  10  and while gas turbine engine  10  is operating during all operational conditions. In operation, fuel delivery system  60  is capable of delivering the steam and gas such that gas turbine engine  10  is capable of operating during all operational conditions. 
     FIG. 4  is a cross-sectional view of an exemplary fuel nozzle  100  that can be used with gas turbine engine  10  and system  60  (shown in  FIG. 3 ).  FIG. 5  is an end view of a portion of fuel nozzle  100  (shown in  FIG. 4 ). Nozzle  100  includes a first fuel inlet  102 , a second fuel inlet  104 , and a steam inlet  106 . In the exemplary embodiment, first and second fuel inlets  102  and  104  are coupled to gas circuit  64 , and steam inlet  106  is coupled to steam circuit  62 . Fuel nozzle  100  also includes a nozzle body  110 , and a nozzle tip  112 . Nozzle body  110  has a first end  120  and a second end  122 . First fuel inlet  102 , second fuel inlet  104 , and steam inlet  106  are each positioned adjacent first end  120  and nozzle tip  112  is positioned adjacent second end  122 . 
   In the exemplary embodiment, first fuel inlet  102  extends from nozzle body  110  and includes a coupling  130 , and second fuel inlet  104  extends from nozzle body  110  and includes a coupling  132  which permits each of first and second fuel inlets  102  and  104  to be coupled to fuel line  44  (shown in  FIGS. 2 and 3 ). Additionally, steam inlet  106  includes a coupling  134  which permits steam inlet  106  to be coupled to steam  72  (shown in  FIG. 3 ). 
   More specifically, nozzle body  110  includes a first wall  140  that defines a first passage  142  that is positioned approximately along a centerline axis  143  of nozzle body  110 . In the exemplary embodiment, first passage  142  extends from coupling  130  to nozzle tip  112  and is configured to channel fuel from coupling  130  to nozzle tip  112 . Nozzle body  110  also includes a second wall  150 . In the exemplary embodiment, second wall  150  is coupled radially outwardly from first wall  140 , and substantially circumscribes first wall  140  such that a second passage  152  is defined between first wall  140  and second wall  150 . Accordingly, second passage  152  has a diameter  154  that is greater than a diameter  144  of first passage  142 . Nozzle body  110  also includes a third wall  160 . In the exemplary embodiment, third wall  160  is coupled radially outwardly from second wall  150 , and substantially circumscribes second wall  150  such that a third passage  162  is defined between second wall  150  and third wall  160 . Accordingly, third passage  162  has a diameter  164  that is greater than second passage diameter  154 . In the exemplary embodiment, third wall  160  forms an exterior surface  166  of nozzle body  110 . 
   In the exemplary embodiment, nozzle tip  112 , an end portion  167  and a body portion  168  that is coupled to and substantially circumscribes end portion  167  such that nozzle tip  112  has a substantially cylindrical cross-sectional profile. In the exemplary embodiment, nozzle tip  112  includes at least one first opening  170  that is formed through end portion  167  and is positioned along centerline axis  143 . More specifically, first opening  170  is configured to discharge fuel that is channeled through first passage  142 , through nozzle tip end portion  167 , and into combustor  16 . Nozzle tip  112  also includes a second plurality of openings  172  that are formed through nozzle tip end portion  167 , and are positioned radially outwardly from first opening  170 . In the exemplary embodiment, second plurality of openings  172  are configured to discharge fuel that is channeled through second passage  152 , through nozzle tip end portion  167 , and into combustor  16 . Nozzle tip  112  also includes a third plurality of openings  174  that are formed through nozzle tip end portion  167 , and are positioned radially outwardly from second plurality of openings  172 . In the exemplary embodiment, third plurality of openings  174  are configured to discharge steam that is channeled through third passage  162 , through nozzle tip end portion  167 , and into combustor  16 . In the exemplary embodiment, first, second, and third plurality of openings  170 ,  172 , and  174  are each configured to discharge either fuel or steam, respectively, through nozzle tip  112  in a flow path that is substantially parallel with centerline axis  143 . 
   Nozzle tip  112  also includes a fourth plurality of openings  176  that are formed through nozzle tip body portion  168 , and are positioned upstream from third plurality of openings  174 . In the exemplary embodiment, fourth plurality of openings  176  are configured to discharge steam that is channeled through third passage  162 , through fourth plurality of openings  176 , and into combustor  16 . In the exemplary embodiment, fourth plurality of openings  176  are configured to discharge steam through nozzle tip body portion  168  in a flow path that is positioned at a predefined angle with respect to centerline axis  143 . Moreover, and in the exemplary embodiment, fourth plurality of openings  176  a diameter  180  that is less than a diameter  182  of third plurality of openings  174  that during operation a first quantity of steam is channeled through fourth plurality of openings  176  that is less than a second quantity of steam that is channeled through third plurality of openings  174 . 
     FIG. 6  is an enlarged cross-sectional view of fuel nozzle  100  (shown in  FIG. 4 ) during a first operational mode.  FIG. 7  is an enlarged cross-sectional view of fuel nozzle  100  (shown in  FIG. 4 ) during a second operational mode. During operation, gas turbine  10 , and thus fuel nozzle  46  can be operated in either a first mode or a second mode. In the exemplary embodiment, the first mode is referred to herein as an active mode, i.e. steam is channeled through fuel nozzle  100  and into combustor  16 . Whereas, during the second mode, referred to herein as the inactive or dry mode, steam is not channeled through fuel nozzle  100  and into combustor  16 . 
   Accordingly, when nozzle  100  is operated in the active mode (shown in  FIG. 6 ), steam is channeled from steam circuit  62  to nozzle  100  via coupling  134 . More specifically, steam is channeled from steam circuit  62  into third passage  162 . The steam is then channeled from nozzle body first end  120  to nozzle body second end  122 , and thus nozzle tip  112 . In the exemplary embodiment, during the active mode, steam is channeled through openings  174  and openings  176  in combustor  16 . More specifically, a first quantity of steam is channeled through openings  174  and a second quantity of steam, that is less than the first quantity of steam, is channeled through openings  176 . For example, since openings  174  have a larger diameter than openings  176  a majority of the steam is channeled through openings  174  in the active mode. Accordingly, channeling steam through openings  174  and  176  during the active mode facilitates increasing the fuel efficiency of gas turbine engine  10 . 
   Alternatively, when nozzle  100  is operated in the dry mode, steam is not channeled through nozzle  100 . More specifically, when nozzle  100  is operated in the dry mode, the air pressure drop across swirler  42  generates a pressure differential between openings  174  and openings  176  such that an airflow  190  is forced through openings  176  into third passage  162  and then through openings  174 . Thus, during the inactive mode, openings  176  facilitate purging fuel nozzle  100 . More specifically, during dry operation, the air pressure drop across swirler  42  facilitates providing the driving pressure for a purge flow across nozzle tip  112 . Moreover, through appropriate selection of the design variables, protection against circumferential pressure gradients and steam system leaks will be maintained without significantly impacting gas/steam emissions performance. 
   The above described fuel nozzle for a gas turbine engine is cost-effective and reliable. The fuel nozzle includes a separate steam injection circuit that is positioned on the outermost annulus of the fuel nozzle. Moreover, the nozzle stem forms the outer boundary of the steam circuit. Specifically, the above described fuel nozzle includes a series of orifices formed through the nozzle stem immediately upstream of the swirler/nozzle interface such that during active operation a fraction of the steam exits these “upstream holes,” while the remainder is injected at the tip. Whereas, during dry operation, the air pressure drop across the swirler provide the driving pressure for a purge flow across the nozzle tip. Through appropriate selection of the design variables, protection against circumferential pressure gradients and steam system leaks will be maintained without significantly impacting gas/steam emissions performance. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.