Patent Publication Number: US-10317081-B2

Title: Fuel injector assembly

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates generally to fuel injectors for gas turbine engines and more particularly to a fuel injector assembly. 
     Gas turbine engines, such as those used to power modern aircraft, to power sea vessels, to generate electrical power, and in industrial applications, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. Generally, the compressor, combustor, and turbine are disposed about a central engine axis with the compressor disposed axially upstream or forward of the combustor and the turbine disposed axially downstream of the combustor. In operation of a gas turbine engine, fuel is injected into and combusted in the combustor with compressed air from the compressor thereby generating high-temperature combustion exhaust gases, which pass through the turbine and produce rotational shaft power. The shaft power is used to drive a compressor to provide air to the combustion process to generate the high energy gases. Additionally, the shaft power is used to, for example, drive a generator for producing electricity, or drive a fan to produce high momentum gases for producing thrust. 
     An exemplary combustor features an annular combustion chamber defined between a radially inboard liner and a radially outboard liner extending aft from a forward bulkhead. The radially outboard liner extends circumferentially about and is radially spaced from the inboard liner, with the combustion chamber extending fore to aft therebetween. A plurality of circumferentially distributed fuel injectors are mounted in the forward bulkhead and project into the forward end of the annular combustion chamber to supply the fuel to be combusted. Air swirlers proximate to the fuel injectors impart a swirl to inlet air entering the forward end of the combustion chamber at the bulkhead to provide rapid mixing of the fuel and inlet air. 
     Combustion of the hydrocarbon fuel in air in gas turbine engines inevitably produces emissions, such as oxides of nitrogen (NOx), which are delivered into the atmosphere in the exhaust gases from the gas turbine engine. In order to meet regulatory and customer requirements, engine manufacturers strive to minimize NOx emissions. An approach for achieving low NOx emissions makes use of a rich burning mixture in the combustor front end at high power. Such rich burning requires good mixing of fuel and air to control smoke at high power. The fuel injector must also provide a good fuel spray at low power for ignition, stability, and reduced emissions. 
     One solution for accommodating both high power and low power operations is the use of a conventional airblast fuel injector with an axial inflow swirler down the center of the fuel nozzle with radial inflow swirlers mounted to the tip of the fuel injector at the downstream end of the fuel nozzle. Having the radial inflow swirlers mounted to the tip of the fuel injector increases the size of the fuel injector, requiring more space in the dump gap between the diffuser and combustor in order to install and remove the fuel injector, which increases engine weight and cost. In addition, having the radial inflow swirlers mounted to the tip of the fuel injector makes the fuel injector heavier, which requires a thicker and heaver stem to support the fuel injector and minimize vibrations, thereby increasing the weight and cost of the fuel injector. 
     Another solution for accommodating both high power and low power operations is the use of a duplex fuel injector having a fuel nozzle surrounded by high shear air swirlers. The fuel nozzle of the fuel injector includes a primary pressure atomizing spray nozzle to provide an adequate fine primary fuel spray for ignition since, at ignition, there may be inadequate airflow shear to sufficiently atomize the fuel for reliable operation. This primary atomizing spray nozzle requires a valve at the base of the fuel injector to control flow between the primary and secondary fuel passages. So although the duplex fuel injector is lighter than the conventional airblast fuel injector having radial inflow swirlers mounted to the tip of the fuel injector eliminating some of the issues referenced previously, the external valve required by the duplex fuel injector increases the cost while reducing reliability of the duplex fuel injector. 
     BRIEF SUMMARY OF THE INVENTION 
     A fuel injector assembly for a combustor is provided, including a fuel nozzle having an axial inflow swirler and one or more radial inflow swirlers spaced radially outward of the downstream end of the fuel nozzle and mounted to the combustor, wherein the airstreams produced by the swirlers airblast atomize fuel films produced by the fuel nozzle. 
     According to one embodiment, a fuel injector assembly for a combustor is provided. The fuel injector assembly includes a fuel nozzle configured to inject fuel into the combustor, wherein the fuel nozzle comprises an axial inflow swirler configured to produce a first airstream into the combustor, and a first radial inflow swirler configured to produce a second airstream into the combustor, wherein the first radial inflow swirler is mounted to the combustor and spaced radially outward of the downstream end of the fuel nozzle. 
     In another embodiment, a fuel injector assembly for a combustor is provided. The fuel nozzle is configured to inject fuel into the combustor, wherein the nozzle comprises an axial inflow swirler configured to produce a first airstream into the combustor; a first radial inflow swirler configured to produce a second airstream into the combustor, wherein the first radial inflow swirler is mounted to the combustor and spaced radially outward of the downstream end of the fuel nozzle; and a second radial inflow swirler configured to produce a third airstream into the combustor, wherein the second radial inflow swirler is mounted to the combustor and spaced radially outward of the first radial inflow swirler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a further understanding of the disclosure, reference will be made to the following detailed description which is to be read in connection with the accompanying drawing, wherein: 
         FIG. 1  is a schematic diagram of an exemplary embodiment of a gas turbine engine. 
         FIG. 2  is a sectional view of an exemplary embodiment of a combustor of a gas turbine engine. 
         FIG. 3  is a sectional enlarged view of the exemplary fuel injector inserted into the exemplary combustor of  FIG. 2  to form a fuel injector assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram of an exemplary embodiment of a gas turbine engine  10 . The gas turbine engine  10  is depicted as a turbofan that incorporates a fan section  20 , a compressor section  30 , a combustion section  40 , and a turbine section  50 . The combustion section  40  incorporates a combustor  100  that includes an array of fuel injectors  200  that are positioned annularly about a centerline  2  of the engine  10  upstream of the turbines  52 ,  54 . Throughout the application, the terms “forward” or “upstream” are used to refer to directions and positions located axially closer toward a fuel/air intake side of a combustion system than directions and positions referenced as “aft” or “downstream.” The fuel injectors  200  are inserted into and provide fuel to one or more combustion chambers for mixing and/or ignition. It is to be understood that the combustor  100  and fuel injector  200  as disclosed herein are not limited in application to the depicted embodiment of a gas turbine engine  10 , but are applicable to other types of gas turbine engines, such as those used to power modern aircraft, to power sea vessels, to generate electrical power, and in industrial applications. 
       FIG. 2  is a sectional view of an exemplary embodiment of a combustor  100  of a gas turbine engine  10 . The combustor  100  positioned between the diffuser  32  of the compressor section  30  and the turbine section  50  of a gas turbine engine  10 . The exemplary combustor  100  includes an annular combustion chamber  130  bounded by an inner (inboard) wall  132  and an outer (outboard) wall  134  and a forward bulkhead  136  spanning between the walls  132 ,  134 . The bulkhead  136  of the combustor  100  includes a first radial inflow swirler  140  and second radial inflow swirler  150  proximate and surrounding the downstream end of an associated fuel nozzle  210  of a fuel injector  200 . The first and second radial inflow swirlers  140 ,  150  are spaced radially outward of the fuel nozzle  210 , with the second radial inflow swirler  150  spaced radially outward of the first radial inflow swirler  140 . A number of sparkplugs (not shown) are positioned with their working ends along an upstream portion  180  of the combustion chamber  130  to initiate combustion of the fuel/air mixture. The combusting mixture is driven downstream within the combustor  100  along a principal flowpath  170  through a downstream portion  180  toward the turbine section  50  of the engine  10 . As discussed previously, it is desirable to have the fuel injector  200  accommodate both high power and low power (e.g., ignition) operations, without necessarily increasing the size, weight, cost, and complexity of the fuel injector  200 . A dump gap  190  located between the diffuser  32  and the combustor  100  provides adequate space in order to install and remove the fuel injector  200 . 
     As illustrated in  FIG. 2  and in  FIG. 3 , a sectional enlarged view of the exemplary fuel injector  200  that injects fuel into the exemplary combustor  100  of  FIG. 2  through the bulkhead  136  to form a fuel injector assembly  270 , the exemplary fuel injector  200  has a fuel nozzle  210  connected to a base  204  by a stem  202 . The base  204  has a fitting  206  for connection to a fuel source. A fuel delivery passage  208  delivers fuel to the fuel nozzle  210  through the stem  202 . The fuel nozzle  210  is surrounded by the first radial inflow swirler  140  and the second radial inflow swirler  150  mounted to the bulkhead  136  of the combustor  100  to form a fuel injector assembly  270 . A radial inflow swirler inner cone  160  separates the first radial inflow swirler  140  and the second radial inflow swirler  150 . Since the first and second radial inflow swirlers  140 ,  150  are mounted to the bulkhead  136  of the combustor  100  in the fuel injector assembly  270 , and not the fuel injector  200  as in prior airblast fuel injectors, the size and weight of the fuel injector  200  is greatly reduced. 
     The first and second radial inflow swirlers  140 ,  150  each have a plurality of vanes  141 ,  151  respectively, forming a plurality of air passages between the vanes for swirling air traveling through the swirlers to mix the air and the fuel dispensed by the fuel nozzle  210 . The vanes  141  of the first radial inflow swirler  140  are oriented at an angle to cause the air to rotate in a first direction (e.g., clockwise) and to impart swirl to the radially inflowing airstream B. In one embodiment, the vanes  151  of the second radial inflow swirler  150  are oriented at an angle to cause the air to also rotate in a first direction (e.g., clockwise) and to impart swirl to the radially inflowing airstream C, co-swirling with airstream B. In another embodiment, the vanes  151  of the second radial inflow swirler  150  are oriented at an angle to cause the air to rotate in a second direction (e.g., counterclockwise), substantially opposite of the first direction, and to impart swirl to the radially inflowing airstream C, counter-swirling with airstream B to increase the turbulence of the air, improving mixing of fuel and air. 
     As will be described, the exemplary fuel injector assembly  270  creates films of fuel to enhance atomization and combustion performance as the fuel film is sheared between swirling airstreams, breaking up the fuel films into small droplets because of the shear and instability in the film, thereby producing fine droplets. This fuel filming enhancement breaks up fuel in a shorter amount of time and distance, minimizing the presence of large droplets of fuel that can degrade combustion performance. Referring to  FIG. 3 , the fuel delivery passage  208  delivers fuel to the fuel nozzle  210  through the stem  202  to a fuel distribution annulus  214 , which feeds fuel to the angled holes of a fuel swirler  216  and into an annular passage fuel filmer  218  to fuel filmer lip  220 , producing a swirling annular primary fuel film  250 . The fuel swirler  216  imparts a circumferential momentum to and swirls the fuel upstream of the fuel filmer lip  220 . The fuel nozzle  210  includes an axial inflow swirler  222 , which includes an air passage  212  concentric to the centerline  260  of the fuel nozzle  210  with an inlet end  226  to receive axially inflowing airstream A, a vane assembly  224  to impart swirl to the axially inflowing airstream A, and an outlet end  228  proximate the fuel filmer lip  220 . In one embodiment, the size and weight of the fuel injector  200  can be reduced by reducing the length of the fuel nozzle  210  (i.e., between the axial inflow swirler  222  and the fuel filmer lip  220 ) by shortening the length of the fuel filmer  218  and the air passage  212  downstream of the axial inflow swirler  222 . 
     Swirling the fuel with fuel swirler  216  assists in the atomization process to help produce a thin annular primary fuel film  250  that can be carried through the air passage  212  of the fuel nozzle  210  by airstream A. In one embodiment, the fuel swirler  216  can swirl the fuel in the same direction as the swirl imparted to airstream A by the axial inflow swirler  222 . The primary fuel film  250  is airblast atomized by the shear layer created between the axially inflowing airstream A of the nozzle air passage  212  and the radially inflowing airstream B of the first radial inflow swirler  140  creating a well mixed fuel spray  252  with small droplets. In one embodiment, airstream B rotates in the same direction as airstream A, causing the airstreams to be co-swirling. In another embodiment, airstream B rotates in substantially opposite of the direction of airstream A, causing counter-swirling. The high velocity swirling air on each side of the primary fuel film  250  creates a shear layer which atomizes the fuel and produces a rapidly mixing, downstream flowing fuel-air mixture. Even at low power, the fuel spray  252  provided by the fuel injector assembly  270  is sufficient to allow ignition and stability via delivery of fuel to the outer stabilization zone D without the need for a valve as in prior duplex fuel injectors. 
     Large primary droplets  254  formed within the fuel nozzle air passage  212  and not atomized by the shear layer created between the axially inflowing airstream A and the radially inflowing airstream B, reach a secondary fuel filmer  162  forming a secondary fuel film  256  on the inside of the radial inflow swirler inner cone  160  separating the first radial inflow swirler  140  and second radial inflow swirler  150 . The secondary fuel film  256  is airblast atomized by the shear layer created between the radially inflowing airstream B of the first radial inflow swirler  140  and the radially inflowing airstream C of the second radial inflow swirler  150  creating a well mixed fuel spray (not shown) with small droplets. The high velocity swirling air on each side of the secondary fuel film  256  creates a shear layer which atomizes the fuel and produces a rapidly mixing, downstream flowing fuel-air mixture. Large secondary droplets  258  not atomized by the shear layer created between the radially inflowing airstream B and the radially inflowing airstream C are transported to the stability zone by airstream C. 
     The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as basis for teaching one skilled in the art to employ the present invention. While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be recognized by those skilled in the art that various modifications may be made without departing from the spirit and scope of the invention. Those skilled in the art will also recognize the equivalents that may be substituted for elements described with reference to the exemplary embodiments disclosed herein without departing from the scope of the present invention. Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as, but that the disclosure will include all embodiments falling within the scope of the appended claims.