Patent Publication Number: US-9416974-B2

Title: Combustor with fuel staggering for flame holding mitigation

Description:
CROSS REFERENCE TO RELATED CASES 
     This application is a divisional of U.S. application Ser. No. 12/983,342, filed Jan. 3, 2011, which is patented and is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to gas turbine engines and more particularly relates to a combustor with fuel staggering and/or fuel injector staggering for flame holding mitigation due to local flow obstructions and other types of flow disturbances. 
     BACKGROUND OF THE INVENTION 
     In a gas turbine engine, operational efficiency generally increases as the temperature of the combustion stream increases. Higher combustion stream temperatures, however, may produce higher levels of nitrogen oxides (“NO x ”) and other types of emissions. Such emissions may be subject to both federal and state regulation in the United States and also subject to similar regulations abroad. A balancing act thus exists between operating the gas turbine engine in an efficient temperature range while also ensuring that the output of NO x  and other types of regulated emissions remain below the mandated levels. 
     Several types of known gas turbine engine designs, such as those using Dry Low NO x  (“DLN”) combustors, generally premix the fuel flows and the air flows upstream of a reaction or a combustion zone so as to reduce NO x  emissions via a number of premixing fuel nozzles. Such premixing tends to reduce overall combustion temperatures and, hence, NO x  emissions and the like. 
     Premixing, however, may present several operational issues such as flame holding, flashback, auto-ignition, and the like. These issues may be a particular concern with the use of highly reactive fuels. For example, given an ignition source, a flame may be present in the head-end of a combustor upstream of the fuel nozzles with any significant fraction of hydrogen or other types of fuels. Any type of fuel rich pocket thus may sustain a flame and cause damage to the combustor. 
     Other premixing issues may be due to irregularities in the fuel flows and the air flows. For example, there are several flow obstructions that may disrupt the flow through an incoming pathway between a flow sleeve and a liner. With a combustor having fuel injector vanes that inject fuel into the airflow upstream of the head-end, these flow disturbances may create flow recirculation zones on the trailing edge of the vanes. These recirculation zones may lead to stable pockets of ignitable fuel-air mixtures that can in turn lead to flame holding or other types of combustion events given an ignition source. 
     There is thus a desire for an improved combustor design. Such a design should accommodate flow disturbances upstream of the fuel injectors so as to avoid flame holding, flashback, auto-ignition, and the like. Moreover, an increase in the flame holding margin may allow the use of higher reactivity fuels for improved performance and emissions. 
     SUMMARY OF THE INVENTION 
     The present application thus provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. The fuel injectors may inject a flow of fuel into the air flow path such that the flows of fuel and air in the wake or the recirculation zone do not exceed a flammability limit. 
     The present application further provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. The fuel injectors may be positioned outside of the wake or the recirculation zone. 
     The present application further provides a combustor. The combustor may include an air flow path with a flow of air therein. A flow obstruction may be positioned within the air flow path and cause a wake or a recirculation zone downstream thereof. A number of fuel injectors may be positioned downstream of the flow obstruction. One or more of the fuel injectors may be downstream fuel injectors positioned downstream of but in line with the wake or the recirculation zone. 
     These and other features and improvements of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a known gas turbine engine as may be used herein. 
         FIG. 2  is a side cross-sectional view of a known combustor. 
         FIG. 3  is a partial schematic view of a combustor as may be described herein. 
         FIG. 4  is a partial schematic view of an alternative combustor as may be described herein. 
         FIG. 5  is a partial schematic view of an alternative combustor as may be described herein. 
         FIG. 6  is a partial schematic view of an alternative combustor as may be described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows a schematic view of gas turbine engine  10  as may be used herein. The gas turbine engine  10  may include a compressor  15 . The compressor  15  compresses an incoming flow of air  20 . The compressor delivers the compressed flow of air  20  to a combustor  25 . The combustor  25  mixes the compressed flow of air  20  with a compressed flow of fuel  30  and ignites the mixture to create a flow of combustion gases  35 . Although only a single combustor  25  is shown, the gas turbine engine  10  may include any number of combustors  25 . The flow of combustion gases  35  is in turn delivered to a turbine  40 . The flow of combustion gases  35  drives the turbine  40  so as to produce mechanical work. The mechanical work produced in the turbine  40  drives the compressor  15  and an external load  45  such as an electrical generator and the like. 
     The gas turbine engine  10  may use natural gas, various types of syngas, and/or other types of fuels. The gas turbine engine  10  may be anyone of a number of different gas turbine engines offered by General Electric Company of Schenectady, N.Y., including those such as a heavy duty 9FA gas turbine engine and the like. The gas turbine engine  10  may have different configurations and may use other types of components. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together. 
       FIG. 2  shows a simplified example of a known combustor  25  that may be used with the gas turbine engine  10 . Generally described, the combustor  25  may include a combustion chamber  50  with a number of fuel nozzles  55  positioned therein. Each of the fuel nozzles  55  may include a central fuel passage  60  generally for a liquid fuel. The fuel nozzles  55  also may include a number of fuel injectors  65 . The fuel injectors  65  may be positioned about one or more swirlers  70 . The swirlers  70  aid in the premixing of the flow of air  20  and the flows of fuel  30  therein. The fuel injectors  65  may be used with a premix fuel and the like. Other types of fuels and other types of fuel circuits may be used herein. 
     The flow of air  20  may enter the combustor  25  from the compressor  15  via an incoming air path  75 . The incoming air path  75  may be defined between a liner  80  of the combustion chamber  50  and an outer casing  85 . The flow of air  20  may travel along the incoming air path  75  and then reverse direction about the fuel nozzles  55 . The flow of air  20  and the flow of fuel  30  may be ignited downstream of the fuel nozzles  55  within the combustion chamber  50  such that the flow of the combustion gases  35  may be directed towards the turbine  40 . Other configurations and other components may be used herein. 
     The combustor  25  also may have a lean pre-nozzle fuel injection system  90  positioned about the incoming air path  75  between the liner  80  and the casing  85 . The lean pre-nozzle fuel injection system  90  may have a number of fuel pegs or fuel injectors  92 . The fuel injectors  92  may have an aerodynamic airfoil or streamline shape. Other shapes may be used herein. The fuel injectors  92  each may have a number of injector holes  94  therein. The number and positioning of the fuel injectors  92  and the injection holes  94  may be optimized for premixing. A premix fuel or other types of fuel flows  30  may be used therein. 
     As described above, a number of flow obstructions  96  also may be positioned within the incoming air path  75 . These flow obstructions  96  may be structures such as a number of crossfire tubes  98 . Other types of obstructions  96  may include liner penetrations, liner stops, and the like. These flow obstructions  96  may create a low velocity wake or a low or negative velocity recirculation zone. The wake or the recirculation zone may envelop one or more of the fuel injectors  92  and/or create other types of local flow disturbances. A flow of the fuel  30  from the holes  94  of the fuel injectors  92  thus may be pulled upstream within the wake or recirculation zone. Although these flow obstructions  96  may cause these flow disturbances, the structures are otherwise required for efficient combustor operation. 
       FIG. 3  shows portions of a combustor  100  as may be described herein. Specifically, an air path  110  may be configured between a liner  120  and a casing  130 . The air path  110  also may be configured between other structures. The combustor  100  may include a number of fuel pegs or fuel injectors  140  positioned in the air path  110 . The fuel injectors  140  likewise may have an aerodynamic airfoil or streamlined shape  150  to optimize flame holding resistance. Other shapes may be used herein. Any number of the fuel injectors  140  may be used in any size or position. The fuel injectors  140  each may have a number of injector holes  160  therein. The injector holes  160  may be on one or both sides of the fuel injectors  140 . Any number of the injector holes  160  may be used in any size or position. Other configurations and other components may be used herein. 
     The air path  110  also may include one or more flow obstructions  170  therein. The flow obstructions  170  may be a crossfire tube  180  or any other type of flow obstruction including liner penetrations, liner stops, and the like. The flow obstruction may be any structure that may create a flow disturbance in the flow of air  20 . The flow disturbance may be a wake or other type of region with a reduced or negative velocity that may serve as a wake or a recirculation zone  190  and the like. 
     In this example, the fuel injectors  140  may include a number of unfueled fuel injectors  200  positioned downstream of the flow obstruction  170  in the wake or the recirculation zone  190  thereof. The remaining fuel injectors  140  may be fueled fuel injectors  210 . By removing the flow of fuel  30  in the fuel injectors  140  within the wake or the recirculation zone  190 , the possibility of fuel entrainment therein that may lead to flashback and the like may be reduced. To the extent that the flow of fuel  30  enters the wake or the recirculation zone  190 , the maximum fuel-air mixture may never exceed a flammability limit for a number of given conditions because of the unfueled fuel injectors  200  therein. A position outside or downstream or otherwise out of the wake or the recirculation zone  190  thus means that the position of the fuel injector  140  is in an acceptable velocity range with respect to an overall bulk velocity in the air path  110 . Other configurations and other components may be used herein. 
       FIG. 4  is an alternative embodiment of a combustor  220  as may be described herein. As above, the combustor  220  includes a number of the fuel pegs or fuel injectors  140  positioned within the air path  110 . In this example, there are no fuel injectors  140  positioned downstream of the wake or the recirculation zone  190  caused by the flow obstruction  170 . Rather, an unobstructed path  230  may be used. The unobstructed path  230  likewise eliminates the possibility of fuel entrainment in the wake or the recirculation zone  190  by removing the flow of fuel  30  therein. To the extent that the flow of fuel  30  enters the wake or the wake or the recirculation zone  190 , the maximum fuel-air mixture may never exceed a flammability limit for a number of given conditions because of the unobstructed path  230 . Other configurations and other components may be used herein. 
       FIG. 5  shows a further embodiment of a combustor  240  as may be described herein. In this example, the combustor  240  includes a number of the fuel injectors  140  positioned within the air path  110  downstream of the flow obstruction  170 . In this example, a number of reduced fuel flow fuel injectors  250  may be positioned within the wake or the recirculation zone  190 . Fueled fuel injectors  210  may be positioned outside of the wake or the recirculation zone  190 . Reducing the flow of fuel  30  through the reduced fuel flow fuel injectors  250  within the wake or the recirculation zone  190  thus may prevent flame holding and the like because the maximum fuel-air mixture may never exceed a flammability limit for a number of given conditions. Other configurations and other components may be used herein. 
       FIG. 6  shows a further example of a combustor  260  as may be described herein. The combustor  260  also may include a number of the fuel injectors  140  positioned within the pathway  110  downstream of the flow obstruction  170 . In this example, the fuel injectors  140  may include a number of downstream fuel injectors  270 . The downstream fuel injectors  270  may be positioned further downstream from, for example, the fueled fuel injectors  210  and downstream of the wake or the recirculation zone  190  caused by the flow obstruction  170 . The downstream fuel injectors  270  also may be fueled fuel injectors  210 . Removing the fuel injectors  140  and the flow of fuel  30  from the wake or the recirculation zone  190  also removes the possibility of fuel entrainment while maintaining a uniform fuel profile. To the extent that the flow of fuel  30  enters the wake or the recirculation zone  190 , the maximum fuel-air mixture may never exceed a flammability limit for a number of given conditions because of the lack of fuel injectors  140  therein. Other configurations and other components may be used herein. 
     In use, the combustors described herein thus reduce the possibility of fuel entrainment downstream of the flow obstructions  170  so as to reduce the possibility of flame holding and other types of combustion events about the fuel injectors  140 . The fuel injectors  140  may vary the fuel-air ratio that could feed a wake or a recirculation zone caused by the flow obstructions  170 . The fuel injectors  140  also may have an increased flame holding margin such that the overall gas turbine engine  10  may be able to use higher reactivity fuels. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.