Abstract:
A method enables a gas turbine engine to be assembled. The method comprises coupling a fuel nozzle within the engine to inject fuel into the engine, wherein the fuel nozzle includes three independent injection circuits arranged such that the second injection circuit is between the first and third injection circuits, coupling a liquid fuel source to a first injection circuit defined within the nozzle and including an annular discharge opening, and coupling a water source to one of the second injection circuit and the third injection circuits such that the water source is coupled in flow communication to an annular discharge opening.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines, more particularly to combustors used with gas turbine engines. 
   Known turbine engines include a compressor for compressing air which is suitably mixed with a fuel and channeled to a combustor wherein the mixture is ignited within a combustion chamber for generating hot combustion gases. More specifically, at least some known combustors include a dome assembly, a cowling, and liners to channel the combustion gases to a turbine, which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator. Moreover, at least some known combustors include ignition devices, such as ignitors, primer nozzles, and/or pilot fuel nozzles, which are used during pre-selected engine operations to facilitate igniting the mixture within the combustion gases. 
   At least some known fuel injectors are dual fuel injectors capable of supplying a liquid fuel, a gaseous fuel, or a mixture of liquid and gaseous fuels to the combustor. To facilitate reducing emissions within such combustors, at least some known combustors include water injection systems to facilitate nitrous oxide emission abatement. Within such systems, the water is premixed with the fuel during liquid fuel operation and is injected into the combustor through the fuel injector. Combining the water with liquid fuel in a single fuel circuit provides a design compromise, as the fuel/water mixture is optimized for flow and atomization, rather than requiring the liquid fuel and water to be individually optimized. However, within known fuel injectors, the water injection may provide only limited benefits, as the combined fuel/water mixture may become unmanageable at higher fuel flows. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method for assembling a gas turbine engine is provided. The method comprises coupling a fuel nozzle within the engine to inject fuel into the engine, wherein the fuel nozzle includes three independent injection circuits arranged such that the second injection circuit is between the first and third injection circuits, coupling a liquid fuel source to a first injection circuit defined within the nozzle and including an annular discharge opening, and coupling a water source to one of the second injection circuit and the third injection circuits such that the water is coupled in flow communication to an annular discharge opening. 
   In another aspect, a fuel nozzle for a gas turbine engine is provided. The fuel nozzle includes three injection circuits. A first injection circuit includes an annular discharge opening and is for injecting liquid fuel downstream from the nozzle into the gas turbine engine. The second injection circuit is aligned substantially concentrically with respect to the first injection circuit. The third injection circuit is aligned substantially concentrically with respect to the first injection circuit, such that the second injection circuit is between the first and third injection circuits. One of the second and third injection circuits is for injecting water downstream from the nozzle into the gas turbine engine. One of the second injection circuit and the third injection circuit includes an annular discharge opening. 
   In a further aspect a gas turbine engine includes a combustor including a combustion chamber and at least one fuel nozzle. The at least one fuel nozzle includes three injection circuits. The first injection circuit includes an annular discharge opening and is for injecting only liquid fuel into the combustion chamber. The second injection circuit is aligned substantially concentrically with respect to the first and third injection circuits, such that the second injection circuit extends between the first and third injection circuits. One of the second and third injection circuits includes an annular discharge. One of the second and third injection circuits is for only injecting water into the combustion chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of an exemplary gas turbine engine; 
       FIG. 2  is a cross-sectional illustration of an exemplary combustor that may be used with the gas turbine engine shown in  FIG. 1 ; 
       FIG. 3  is an enlarged cross-sectional view of a portion of the fuel nozzle shown in  FIG. 2 ; and 
       FIG. 4  is an end view of the fuel nozzle shown in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of a 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 . Compressor  12  and turbine  20  are coupled by a first shaft  22 , and compressor  14  and turbine  18  are coupled by a second shaft  21 . 
   In operation, air flows through low pressure compressor  12  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow from combustor  16  exits combustor  16  and drives turbines  18  and  20 , and then exits gas turbine engine  10 . 
     FIG. 2  is a cross-sectional illustration of a portion of an exemplary combustor  16  that may be used with gas turbine engine  10 . Combustor  16  includes an annular outer liner  40 , an annular inner liner  42 , and a domed end  44  that extends between outer and inner liners  40  and  42 , respectively. Outer liner  40  and inner liner  42  are spaced radially inward from a combustor casing  46  and define a combustion chamber  48  therebetween. Combustor casing  46  is generally annular and extends around combustor  16 . Combustion chamber  48  is generally annular in shape and is defined between from liners  40  and  42 . 
   A fuel nozzle  50  extends through domed end  44  for discharging fuel into combustion chamber  48 , as described in more detail below. In one embodiment, fuel nozzle  50  is aligned substantially concentrically with respect to combustor  16 . In the exemplary embodiment, fuel nozzle  50  includes an inlet  54 , an injection or discharge tip  56 , and a body  58  extending therebetween. 
     FIG. 3  is an enlarged side view of a portion of fuel nozzle  50 , and  FIG. 4  is an end view of fuel nozzle  50 . Fuel nozzle  50  is a quad-annular fuel nozzle that includes a plurality of injection circuits  80  and a center axis of symmetry  81  extending therethrough. Specifically, injection circuits  80  are each routed independently through fuel nozzle  50  such that none of the injection circuits  80  are in flow communication with each other within nozzle  50 . 
   Fuel nozzle  50  includes a liquid fuel injection circuit  82 , a gaseous fuel injection circuit  84 , and a water injection circuit  86 . Liquid fuel injection circuit  82  includes a primary fuel injection circuit  88  and a secondary fuel injection circuit  90  that are each coupled in flow communication to a liquid fuel source for injecting only liquid fuel downstream therefrom into combustion chamber  48 . Primary fuel injection circuit  88  includes an annular fuel passageway  92  that extends substantially concentrically through nozzle  50  to an annular discharge opening  94 . In the exemplary embodiment, fuel passageway  92  and discharge opening  94  are each toroidal. 
   In the exemplary embodiment, fuel passageway  92  extends substantially co-axially through nozzle  50  with respect to axis of symmetry  81  such that passageway  92  is a radial distance D pf  from axis of symmetry  81  such that fuel flowing therein flows substantially parallel to axis of symmetry  81  until flowing through an elbow  100 . Elbow  100  is positioned upstream from, and in close proximity to, discharge opening  94  and directs liquid fuel into a convergent portion  102  of passageway  92  such that liquid fuel is discharged inwardly from passageway  92  towards axis of symmetry  81 . 
   Secondary fuel injection circuit  90  includes an annular fuel passageway  110  that extends substantially concentrically through nozzle  50  to annular discharge opening  94 . In the exemplary embodiment, fuel passageway  110  is toroidal and is radially outward from fuel passageway  92 . More specifically, in the exemplary embodiment, fuel passageway  110  is substantially concentrically aligned with respect to fuel passageway  92 , and with respect to axis of symmetry  81 . Accordingly, liquid fuel flowing within passageway  110  flows substantially parallel to axis of symmetry  81  until flowing through an elbow  114 . Elbow  114  is positioned upstream from, and in close proximity to, discharge opening  94  and directs liquid fuel into a convergent portion  116  of passageway  110  such that liquid fuel is discharged inwardly from passageway  110  towards axis of symmetry  81 . 
   Nozzle discharge tip  56  includes a nozzle portion  120  that extends divergently downstream from, and in flow communication with, opening  94 . Accordingly, the combination of passageway convergent portions  102  and  116 , opening  94 , and divergent nozzle portion  120  creates a venturi that facilitates enhancing control of flow discharged from nozzle discharge tip  56 . More specifically, the relative location of opening  94  within discharge tip  56  and with respect to nozzle portion  120  facilitates reducing dwell time for fuel within nozzle discharge tip  56 , such that coking potential within nozzle discharge tip  56  is also facilitated to be reduced. 
   Water injection circuit  86  is used to supply only water to combustion chamber  48  and includes an annular water injection passageway  130  that extends substantially concentrically through nozzle  50  to an annular discharge opening  132 . In the exemplary embodiment, fuel passageway  130  is toroidal and is positioned radially outward from fuel passageway  110 . More specifically, in the exemplary embodiment, water injection passageway  130  is coupled to a water source and is substantially concentrically aligned with respect to fuel passageways  92  and  110 , and with respect to axis of symmetry  81 . Accordingly, water flowing within passageway  130  flows substantially parallel to axis of symmetry  81  until being discharged through annular discharge opening  132 . In the exemplary embodiment, opening  132  is a distance downstream from opening  94 . Accordingly, the orientation of discharge opening  132  with respect to opening  94 , ensures that water is discharged from opening  132  at a wider spray angle than that of the liquid fuel discharged from opening  94 , thus facilitating nitrous oxide abatement. Moreover, the narrower spray angle of the liquid fuel facilitates positioning the liquid fuel towards an aft end of the venturi, thus reducing dwell time and coking potential. 
   Gaseous fuel injection circuit  84  is coupled to a gaseous fuel circuit such that only gaseous fuel is supplied to combustion chamber  48  during pre-determined engine operating conditions by circuit  84 . Gaseous fuel injection circuit  84  includes an annular fuel passageway  140  that extends substantially concentrically through nozzle  50  to a plurality of circumferentially-spaced discharge openings  142 . In the exemplary embodiment, fuel passageway  140  is toroidal and is positioned radially outward from water injection passageway  130 . In an alternative embodiment, water injection passageway  130  is positioned radially between primary fuel injection circuit fuel passageway  92  and gaseous fuel injection fuel passageway  140 . Within such an embodiment, secondary fuel injection circuit fuel passageway  110  is positioned radially outward from gaseous fuel injection passageway  140 . More specifically, in the exemplary embodiment, gaseous fuel injection passageway  140  is substantially concentrically aligned with respect to fuel passageways  92  and  110 , and with respect to axis of symmetry  81 . Accordingly, gaseous fuel flowing within passageway  140  flows substantially parallel to axis of symmetry  81  until being discharged through discharge openings  142 . 
   In the exemplary embodiment, gaseous fuel injection openings  142  are oriented obliquely with respect to axis of symmetry  81 . Accordingly, gaseous fuel discharged from openings  142  is expelled outwardly away from axis of symmetry  81 . 
   During initial engine operation, and through engine idle operation, only primary fuel injection circuit  88  is used to supply fuel to combustion chamber  48 . More specifically, primary fuel injection circuit  88  provides atomization of low fuel flows required for engine starting and transition to engine idle operation. 
   During higher power operations, the remaining liquid fuel required for operation is injected through secondary fuel injection circuit  90 , and gaseous fuel may be injected through gaseous fuel injection circuit  84 . In one embodiment, secondary fuel injection circuit  90  provides up to approximately 95% of total liquid fuel flow required for high power engine operations. During such operations, water is introduced to combustion chamber  48  through water injection circuit  86 . Water injection facilitates abating nitrous oxide generation within combustion chamber  48 . Moreover, in the exemplary embodiment, atomization is facilitated through a liquid water sheet formation induced by swirling the water flow within water injection circuit  86 . In an alternative embodiment, bleed air from a compressor discharge is used to facilitate atomization of the water flow. In a further alternative embodiment, natural gas flow is used to facilitate atomization of the water flow. 
   Because fuel is injected through independent injection circuits, the plurality of independent injection circuits  80  facilitates the independent optimization of each circuit for each mode of operation, including a liquid fuel dry mode, in which no water is injected into chamber  48 , a liquid fuel+NO x  water abatement mode of operation, and a gaseous fuel+NO x  water abatement mode of operation. Accordingly, optimization of the circuits  80  is facilitated at all engine operational power settings. 
   The above-described fuel nozzle provides a cost-effective and reliable means for reducing nitrous oxide emissions generated within a combustor. The fuel nozzle includes a plurality of independent injection circuits that facilitate enhanced optimization of fluids to be injected into the combustion chamber. More specifically, because water and fuel are not mixed within, or upstream from the fuel nozzle, the flows of each may be independently optimized. As a result, injection schemes are provided which facilitate reducing nitrous oxide emissions at substantially all engine operating conditions. 
   An exemplary embodiment of a fuel nozzle is described above in detail. The fuel nozzle components illustrated are not limited to the specific embodiments described herein, but rather, components of each fuel nozzle may be utilized independently and separately from other components described herein. For example, the plurality of injection circuits may be used with other fuel nozzles or in combination with other engine combustion systems. 
   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.