Patent Publication Number: US-2013252185-A1

Title: Igniter air shield

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/613,735 filed Mar. 21, 2012, the contents of which are incorporated herein by reference thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to furnaces having igniter elements and, more particularly, to furnaces having shields for the igniter elements. 
     In furnace applications, igniters commonly include an igniter element. The igniter is positioned such that the “hot spot” of the igniter element, or the portion of the igniter element that reaches the hottest temperature, is placed directly in the mixture of fuel and air to create the point of ignition. If the igniter is not at a temperature hot enough to cause the fuel and air mixture to combust, the fuel flow to the furnace will automatically shut off. A predominant cause of igniter element cooling is secondary combustion airflow. Secondary combustion airflow moves quickly past the igniter causing the igniter element to cool to a temperature below that required to ignite the surrounding fuel. Systems using less power are also susceptible to igniter element cooling because less power is used to heat the igniter. Some furnace applications require the furnace to use a lower voltage power supply, such as 98V for example, rather than the typical 110V; therefore less power is applied towards heating the igniter than in a full voltage system. If the igniter is too cool to ignite the fuel and air mixture, no heat will be produced from the furnace. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to an exemplary embodiment of the invention, a burner assembly for use in a gas appliance is provided including a top plate configured to form the geometric top half of at least one burner and a bottom plate configured to form the geometric bottom half of at least one burner. The top plate and the bottom plate are joined together to form a burner and a burner carryover. An igniter air shield extends from either the top plate or the bottom plate such that the igniter air shield diverts secondary combustion air flowing around the burner. 
     According to another embodiment of the invention, a burner unit is provided including a burner assembly having a plurality of axially aligned burners. The burner unit also includes a burner box for receiving the burner assembly. An igniter assembly is mounted such that the igniter element is adjacent the burner assembly. The igniter assembly includes an igniter element extending from an insulative body. An igniter air shield extends from a portion of the burner assembly such that the igniter air shield diverts secondary air flowing around the burner assembly away from the igniter element. 
     According to yet another embodiment of the invention, a furnace is provided including a burner assembly having a plurality of axially aligned burners. A burner box receivers the burner assembly. An igniter assembly includes an igniter element connected to an insulative body. The igniter assembly is mounted such that the igniter element is adjacent the burner assembly. An igniter air shield, extending from the burner assembly, diverts secondary air flowing around the burner assembly away from the igniter element. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective cut away illustration of a gas furnace in accordance with an embodiment of the invention; 
         FIG. 2  is a perspective view of a burner unit in accordance with an embodiment of the invention; 
         FIG. 3  is a front view of a burner unit in accordance with an embodiment of the invention; and 
         FIG. 4  is a cross-sectional view taken at line  4 - 4  of  FIG. 3  in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective cutaway view of a gas-fired appliance, such as a furnace  10 . The furnace  10  includes burner assembly  14 , burner box  12 , gas valve  18 , heat exchanger assembly  20 , exhaust vent pipe  28 , induced draft blower  30 , inducer motor  32 , thermostat  34 , pressure switch assembly  42 , and furnace control  50 . In some embodiments, the furnace  10  may additionally include a combustion air pipe  16 , a condensing heat exchanger  24 , and a condensate collector box  26 . 
     Burner assembly  14  is mounted within burner box  12  and is supplied with combustion air. As will be discussed in more detail below, the burner assembly  14  includes a gas manifold  36  with a gas orifice  38  (see  FIG. 2 ) arranged at one end. Fuel gas is supplied to burner assembly  14  through gas valve  18 , which may be a solenoid-operated gas valve, and is ignited by an igniter assembly  160  (see  FIG. 2 ). The gases produced by combustion within burner assembly  14  flow through a heat exchanger assembly  20 , which includes a primary or non-condensing heat exchanger. In one embodiment, the heat exchanger assembly  20  additionally includes either a secondary or condensing heat exchanger  24 , or a condensate collector box  26 , or both. The gases are then vented to the atmosphere by inducer motor  32  through exhaust vent pipe  28 . The flow of these gases, herein called combustion gases, is maintained by induced draft blower  30 , which is driven by inducer motor  32 . Inducer motor  32  is driven in response to control signals that are generated by a furnace control circuit located within furnace control  50 , in response to the states of the pressure switch assembly  42 , and in response to call-for-heat signals received from thermostat  34  in the space to be heated. 
     Air from the space to be heated is drawn into furnace  10  by blower  52 , which is driven by blower motor  54  in response to control signals that are generated by furnace control  50 . The discharge air from the blower  52 , herein called circulating air, passes over the heat exchanger assembly  20  before being directed to the space to be heated through a duct system (not shown). 
     Referring now to  FIGS. 2 and 3 , an exploded view and a front view of a burner unit  11  are illustrated. The burner unit  11  includes a burner box  12  and a burner assembly  14  that mounts within the burner box  12 . The burner box  12  includes a top wall  110 , a bottom wall  112 , and opposing side walls  114 . Disposed horizontally along the inside surface of each of the opposing side walls  114  is an elongated opening  116  for receiving the burner assembly  14 . 
     The burner assembly  14  includes a plurality of parallel and equidistant burners  130 . In the exemplary embodiment portrayed in the FIGS., the burner assembly  14  includes four burners  130 . However, the burner assembly  14  may include any number of burners  130 . In an exemplary embodiment, the plurality of burners  130  is formed from two stamped flat metal plates, a top plate  120  and a bottom plate  122 . The top plate  120  and the bottom plate  122  of the burner assembly  14  are stamped so that the top plate  120  contains the geometry of the upper half of each burner and the bottom plate  122  contains the geometry of the lower half of each burner. Disposed between each burner half is at least one burner carryover  147  to assist in the ignition process. The plates  120 ,  122  thus divide the burners  130  and burner carryovers  147  symmetrically along the central axis Z of each burner  130  so that when the plates  120 ,  122  are assembled in face to face contact, the overall shape of each burner  130  is produced. Top and bottom plates  120 ,  122  may be fastened together by any suitable means so that the opposed flat surfaces of the plates  120 , 122  are held in close intimate contact along the length and breadth of the plates. Joining the top plate  120  and the bottom plate  122  creates a horizontal plane extending through the entire burner assembly  14  and through the center of each of the plurality of burners  130  and burner carryovers  147 . 
     Each burner  130  within the burner assembly  14  has a fuel port  132  at a first end of the burner  130 . The fuel port  132  is a cylindrical element that aligns a burner  130  with a respective fuel supply to direct pressurized fuel into the burner  130 . The fuel port  132  of each burner  130  is positioned adjacent to and in axial alignment with a tubular nozzle  138 . Each nozzle  138  has a flared inlet end  134  and a cylindrical outlet end  140 . A flame retainer housing  142  is integrally joined to the outlet end  140  of the tubular nozzle  138  and contains a generally cylindrical flame retainer  144 . The flared inlet end  134  has a larger diameter inlet opening than the fuel inlet opening defined by the fuel port  132 . An opening  146  is stamped into each of the plates  120 ,  122  between the fuel port  132  and the inlet  134  to the tubular nozzle  138 . Each opening  146  is sufficiently large so that an unimpeded airflow will be available to support the combustion when the burner is operating at capacity. The burner carryovers  147  are sized to sufficiently carry the flame to the exit of each flame retainer  144  during the ignition process. 
     A support piece  150  extends perpendicularly from the top surface  110  towards the bottom surface  112  of the burner box  12 . Fastened to this support piece  150  is an igniter mounting structure  152  having a hole in which an igniter assembly  160  is inserted. The support piece  150  and the igniter mounting structure  152  are positioned such that the mounted igniter assembly  160  is adjacent an outlet  140  of a burner  130  located at an end of the burner assembly  14 . The igniter assembly  160  includes an insulative body  162  and an igniter element  164  extending from within the insulative body  162 . The igniter element  164  is arranged to provide a hot surface to the outlet section of the burner carryover  147  at start up. The igniter element will ignite the primary air/fuel mixture moving through the burner  130  and burner carryover  147  and propagate the flame to the exit of each flame retainer  144 . 
     As the fuel is injected through the fuel port  132 , air also enters the burner  130  due to the difference of the diameter of the inlet and the diameter of the fuel port  132 . The fuel and air combine at the inlet  134  of the tubular nozzle  138  to create a primary fuel/air mixture. As the primary fuel/air mixture flows through the burner  130  and the burner carryover  147 , the primary fuel/air mixture contacts the hot surface igniter element  164  causing the mixture to ignite at the burner carryover  147  closest to the igniter element  164 . The flame is then carried across each burner carryover  147  and the exit of each flame retainer  144 . Secondary combustion air (See  FIG. 4 ) flows around the outside of the burners  130  and burner carryovers  147  and gradually mixes into the flame extending axially downstream from the exit of the flame retainers  144 . At the exit of the burner carryovers  147 , ignited fuel spreads laterally to ignite the other burners  130  in the burner assembly  14 . A flame sensor  168  is also mounted to the burner box  12 . The flame sensor  168  determines if all of the burners  130  in the burner assembly  14  are lit. If not all of the burners  130  have ignited within a given period of time, the flow of fuel to the burners  130  is shut off. 
     Referring now to  FIGS. 3 and 4 , arrows A and B represent secondary combustion air flowing around the top and bottom of the burner assembly  14  in the direction of the igniter element  164 . An igniter air shield  170  extends from the burner assembly  14  adjacent first burner  130  and igniter element  164 . The igniter air shield  170  diverts the secondary combustion air away from the igniter element  164  to reduce the cooling of the igniter element  164 . The igniter air shield  170  also improves the stability of the flame exiting the burner carryover  147  closest to the igniter element  164 . Therefore, the igniter air shield  170  improves the robustness of the ignition process within the furnace  10 . 
     The igniter air shield  170  may be formed integrally with the burner assembly  14 . In an exemplary embodiment, if the burner assembly  14  includes a stamped metal top and bottom plate  120 ,  122 , the igniter air shield  170  may be formed as part of either the top or bottom plate  120 ,  122 . To form the igniter air shield  170  as part of the bottom plate  122 , for example, the stamped metal will include an additional area extending beyond the edge forming the outlet  140  of each burner  130 . The dimensions of the area forming the igniter air shield  170  must be sufficient to create a non-turbulent flow or stable flow adjacent the outlet of the burner carryover  147  closest to the igniter element  164 , and the igniter element  164 . The area forming the igniter air shield  170  is then bent so that a portion of the igniter air shield  170  will extend into secondary combustion air flow B around the bottom plate  122  to divert it away from the igniter element  164 . The angle of the bend of the igniter air shield  170  may range from zero to ninety degrees from the horizontal plane of the plate. In an alternate embodiment, the igniter air shield  170  may be a separate part that is then attached to the portion of the burner assembly  14  adjacent the burner carryover  147  closest to the igniter element  164 . The igniter air shield  170  may be attached by welding, fastening, or any other suitable means. Additionally, a second igniter air shield  170  may extend from the top of the burner assembly  14  adjacent the igniter element  164  to divert the secondary air flow represented by arrow A away from the igniter element  164 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.