Abstract:
An ignition system includes an electrical energy delivery device having a first electrode terminating at a first end portion and a second electrode positioned in the ignition system separately from the electrical energy delivery device. The second electrode terminates at a second end portion disposed a first distance from the first end portion to form an air gap therebetween. The air gap forms an area including the shortest distance between the first electrode and the second electrode.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to an ignition system and, more particularly, to an electrical energy delivery device for use in an ignition system. 
     BACKGROUND 
     Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx), and solid particulate matter, which may include unburned carbon particulates called soot. 
     Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of gaseous compounds emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions is exhaust gas recirculation (EGR). EGR systems recirculate the exhaust gas byproducts into the intake air supply of the internal combustion engine. The exhaust gas directed to the engine cylinder reduces the concentration of oxygen within the cylinder and increases the specific heat of the air/fuel mixture, thereby lowering the maximum combustion temperature within the cylinder. The lowered maximum combustion temperature and reduced oxygen concentration can slow the chemical reaction of the combustion process and decrease the formation of NOx. 
     In many EGR applications, the exhaust gas is passed through a particulate filter and catalyst containing precious metals. The particulate filter may capture a portion of the solid particulate matter carried by the exhaust. After a period of use, the particulate filter may become saturated and may require cleaning through a regeneration process wherein the particulate matter is purged from the filter. In addition, the catalyst may oxidize a portion of the unburned carbon particulates contained within the exhaust gas and may convert sulfur present in the exhaust to sulfate (SO 3 ). 
     The regeneration process may include using a regeneration device coupled within an exhaust treatment system. In some examples, the regeneration device may include an ignition system having, for example, a fuel injector and an electrical energy delivery device to facilitate combustion within the regeneration device. U.S. Pat. No. 5,189,333 issued to Kagawa et al. discloses an electrical energy delivery device which may be used with a fuel injector to ignite an air-fuel mixture such as via an electric spark. The electrical energy delivery device, or spark plug, of Kagawa et al. includes a central electrode and a parallel ground electrode. The central electrode protrudes from a lower end of an insulator. The insulator may be coupled to a main metal shell of the electrical energy delivery device. The parallel ground electrode is arranged opposite to the central electrode. One end of the ground electrode may be bonded to a main metal shell. An air-fuel mixture may be ignited by a spark discharge in an air gap between the central electrode and the parallel ground electrode. 
     However, the ignition system of Kagawa et al. may provide inconsistent ignition of the air-fuel mixture during one or more ignition attempts. For example, the amount and/or concentration of the air-fuel mixture may fluctuate around the ignition area, or air gap, in the design of Kagawa et al. Hence, a poorly positioned ground electrode, for example, one being positioned relative to the central electrode for generating an appropriate electrical current in an air gap therebetween, may not be able to provide proper ignition. The arrangement provided by Kagawa et al. may also allow fouling, such as carbon deposit build-up, to develop along components of the electrical energy delivery device. These components may include surface portions along the central and ground electrodes. Such fouling may also prevent proper ignition of the air-fuel mixture. Furthermore, the placement of the ground electrode with respect to additional components of the electrical energy delivery device of Kagawa et al., including, for example, the central electrode, may allow arcing outside of the air gap in the ignition area. This may include arcing along portions of the central or ground electrode connected to the base portion of the electrical energy delivery device. Arcing outside of the gap ignition area may also yield unfavorable and inconsistent ignition results. 
     The present disclosure is directed towards overcoming one or more shortcomings set forth above. 
     SUMMARY OF THE INVENTION 
     In accordance with one disclosed exemplary embodiment, an ignition system includes an electrical energy delivery device having a first electrode terminating at a first end portion and a second electrode positioned in the ignition system separately from the electrical energy delivery device. The second electrode terminates at a second end portion disposed a first distance from the first end portion to form an air gap therebetween. The air gap forms an area including the shortest distance between the first electrode and the second electrode. 
     In accordance with another disclosed exemplary embodiment, an ignition system for use in an aftertreatment system located downstream of an exhaust manifold of an internal combustion engine includes a combustor head, an electrical energy delivery device mounted within a passage of the combustor head, and a first electrode extending through the passage and terminating at a first end portion, the first electrode being coupled to a main body of the electrical energy delivery device. The system also includes a second electrode terminating at a second end portion outside of the passage, the second electrode positioned separately from the main body and the second end portion being disposed a first distance from the first end portion to form an air gap therebetween. 
     According to another exemplary disclosed embodiment, a method for producing ignition of a fuel air mixture within a combustion chamber includes positioning a first electrode within a passageway so that an end portion of the first electrode is located at a first distance from a plane along an outer edge of a fuel spray, and positioning an end portion of a second electrode at a second distance from the end portion of the first electrode so as to form an air gap between the end portions, the end portion of the second electrode being at a third distance from the plane. The method also includes supplying pressurized air to the passageway and along the first electrode in a direction toward the end portion of first electrode and igniting an air-fuel mixture in the vicinity of the air gap 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  provides a diagrammatic cut away view of a combustor head and fuel nozzle assembly according to an exemplary disclosed embodiment; 
         FIG. 2  provides a rotated perspective view of the combustor head and fuel nozzle assembly of  FIG. 1 ; and 
         FIG. 3  provides an enlarged detail view of the center electrode and ground terminal in relation to the fuel spray of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an ignition system  10  which may be utilized in an aftertreatment system, such as a regeneration device. The regeneration device may include an ignition system  10  having, for example, a fuel injector and an electrical energy delivery device  14  to facilitate combustion within the regeneration device. In an exemplary embodiment, it is understood that the regeneration device may receive a supply of a combustible substance and a supply of air to facilitate combustion within the regeneration device. The combustible substance may be, for example, gasoline, diesel fuel, reformate, and/or any other combustible substance known in the art. 
     The ignition system  10  may include a combustor head  12  coupled to an electrical energy delivery device  14 . In one embodiment, a main body portion  13  of the electrical energy delivery device  14  may be mounted to the combustor head  12  by a threaded connection. Hence, a portion of the electrical energy delivery device  14  may be inserted into a receiving socket  42  of the combustor head  12  wherein threads of the electrical energy delivery device  14  may be engaged with mating threads of the receiving socket  42 . While a threaded connection has been described, other types of connections suitable for mounting the electrical energy delivery device  14  to the combustor head  12  may be utilized. 
     The electrical energy delivery device  14  may include a center electrode  16  which may be mounted, for example, to the main body portion  13 . The center electrode  16  may be inserted through an air passageway  18  of the combustor head  12  during assembly. The electrical energy delivery device  14  may be seated upon a seating element  20  such as a washer. The seating element  20  may include a thickness suitable for adjusting a mounting position of the electrical energy delivery device  14  with respect to the combustor head  12 . This may also adjust components of the electrical energy delivery device  14  relative to other components such as those within the combustion head  12 . For example, by varying the thickness of the seating element  20 , the end  38  of the center electrode  16  may be adjusted proximate to or away from a fuel spray  32 . 
     The ignition system  10  may also include an air feed assembly  24 . In one embodiment, the air feed assembly  24  may be disposed within the combustor head  12 . The air feed assembly  24  may be configured to provide pressurized air to the air passageway  18 , such as through inlet  26 , and to the an upstream side of a swirl plate  34 . The pressurized air supplied to the air feed assembly  24  may originate from an intake side of an internal combustion engine and may include pressurized air or a pressurized mixture of air and recirculated engine exhaust gases. Inlet  26  of air passageway  18  may provide an access point for allowing air to flow into the air passageway  18  and generally towards a location of the fuel spray  32 . It is understood that the air passageway  18  and inlet  26  may be omitted in an alternative embodiment consistent with this disclosure. 
     The combustor head  12  may house additional components, including, for example, a fuel nozzle  30  having a fuel passageway  28 . The fuel passageway  28  may receive a supply of a combustible substance or fuel. Thus, the combustible substance or fuel may be supplied through the fuel passageway  28  to produce a fuel spray  32  along a longitudinal axis. The fuel spray  32  may be generated within, for example, a combustion housing  36 . 
     The swirl plate  34  may be provided within the combustor head  12  in order to facilitate mixing of pressurized air from air feed assembly  24  and fuel from fuel nozzle  30  in the combustion housing  36 . For example, the disclosed embodiment shown in  FIG. 2  illustrates a plurality of holes or vents  52  disposed at prescribed locations along a surface of the swirl plate  34 . The holes or vents  52  may allow suitable passage of air (or mixture of air and engine exhaust gases) therethrough. As the air traverse through the swirl plate  34  and mixes with the fuel spray, an appropriate air-fuel mixture may be produced within the combustion housing  36 . 
     The ignition system  10  may also include another electrode such as ground terminal  22 . The ground terminal  22  may be provided as a separately connected element from the main body portion  13  of the electrical energy delivery device  14 . Hence, the ground terminal  22  may be mounted at a separate location from other components of the electrical energy delivery device  14 . For example, in one disclosed embodiment, the ground terminal  22  may be mounted integrally with the swirl plate  34 . The ground terminal  22  may extend in a direction toward the center electrode  16  and terminate at an end  40 . With this configuration, the end  40  of ground terminal  22  may be separately fixed in position at a desired location from the fuel spray  32  irrespective of the location of the center electrode  16 . This separately fixed location of the end  40  of the ground terminal  22  allows for variations in the location of the center electrode  16 , while maintaining a location of the ignition area or air gap (distance  46  in  FIG. 3 ) between the ground terminal end  40  and the center electrode end  38 . While one embodiment has been described to include the ground terminal  22  being mounted integrally with the swirl plate  34 , other suitable mounting locations separate from the center electrode  16  may be provided for the ground terminal  22 . 
     Turning to  FIG. 3 , an enlarged detail view of the center electrode  16  and ground terminal  22  relative to the fuel spray  32  is illustrated. Again, the end  38  of the center electrode  16  may be disposed, for example, in a final assembly, at a distance  44  away from an outer plane of the fuel spray  32 . As discussed above, one disclosed embodiment may include adjusting the end  38  of the center electrode  16  proximate to or away from the outer plane along the length of the fuel spray  32  by varying the thickness of the seating element  20 . In some embodiments, the distance  44  may include a range of approximately 1.0-10.0 mm. 
     As noted above, the end  40  of the ground terminal  22  may be disposed at a distance  46  from the end  38  of the center electrode  16  to form an air gap or ignition area. In some embodiments, the distance  46  may include a range of approximately 1.2-4.4 mm. One disclosed embodiment of the ground terminal  22  may include a curved surface  56 . An extension of the surface  56  relative to the center electrode  16  may form a gap  54  therebetween. A configuration of the gap  54  may include a portion which radially increases, for example, as measured from a point along a length  50  of the center electrode  16  while traversing a distance along surface  56  of the ground terminal  22  (e.g., such as from end  40  towards the mounted location of the ground terminal  22 ). In one embodiment, a measured distance from a point along the length  50  of the center electrode  16  to the surface  56  within the gap  54  may be greater than the distance  46 . While a curved surface  56  has been described as part of an extension of the ground terminal  22 , other surface designs and shapes suitable for extending the end  40  of the ground terminal  22  proximate to the end  38  of the center electrode and forming a radial gap  54  with respect to the center electrode  16  may be utilized. 
     The end  40  of the ground terminal  22  may also be disposed, for example, in a final assembly, at a distance  48  away from the outer plane of the fuel spray  32 . In some embodiments, the distance  48  may also include a range of approximately 1.0-10.0 mm 
     INDUSTRIAL APPLICABILITY 
     The ignition system  10  of the present disclosure may be used with any combustion-type device such as, for example, an engine, a furnace, or any other device known in the art where ignition of a combustible substance is desired. By way of example, the ignition system  10  may be used in an aftertreatment system downstream of an exhaust manifold of an internal combustion engine, such as a diesel engine. In such an aftertreatment system, ignition system  10  would be used to facilitate the heating of exhaust gases exiting the engine to temperatures sufficient to regenerate a particulate filter located downstream of the ignition system  10 . 
     The ignition system  10  may be useful in enhancing the probability of ignition, and the formation of an ignition area in a desired location. This is due to the prescribed location of components of the ignition system  10  and their respective design. In particular, the separate nature and particular shape of the ground terminal  22  with respect to the center electrode  16  of the electrical energy delivery device  14  provides for a substantially fixed or consistent location of the ignition area with respect to the fuel spray provided by the fuel nozzle  30 . Because the ignition area is defined by the electrical energy or arc that bridges the gap between the end  38  of central electrode  16  and the end  40  of ground terminal  22 , the location of the ignition area is a function of the location of both the electrical energy device  14  and the ground terminal  22 . Thus, by locating the ground terminal  22  on a component separate from the electrical energy delivery device  14 , and at a particular location with respect to the fuel spray, the ground terminal  22  may provide for a substantially fixed or consistent location of the ignition area regardless of variations in the location of the end  38  of central electrode  16 . Variations in the location of the central electrode  16  may occur due to variations associated with the coupling the electrical energy delivery device  14  to the combustion head  12 . In addition to these advantages, location of the ground terminal  22  separate from the electrical energy delivery device  14  also allows the opening for housing the electrical energy delivery device to be smaller in size because the opening does not have to be large enough to also house the ground terminal  22 . 
     As noted above, the air feed assembly  24  may be configured to supply a flow of pressurized air into the air passageway  18  generally towards a location of the fuel spray  32  and through holes or vents  52  formed in swirl plate  34 . The pressurized air flow through passageway  18  may generally traverse a length of the center electrode  16  which may also be disposed through the air passageway  18 . The direction of air flow supplied by the air feed assembly  24  through the air passageway  18  may facilitate preventing the fuel spray  32  from traversing up along the length  50  of the center electrode  16  and into the air passageway  18  and may reduce the build up of soot within passageway  18 . In particular, by supplying a flow of pressurized air into the air passageway  18  generally towards a location of the fuel spray  32 , the disclosed ignition system  10  may also be capable of reducing fouling, such as carbon deposit build-up, along various components thereof. These components may include, for example, build-up along a length  50  of the central electrode  16  and along the extended surface  56  of the ground terminal  22 . 
     As the pressurized air (or air and exhaust gases) is supplied through the swirl plate  34  and through air passageway  18 , air mixes with the fuel of the fuel spray in the combustion housing  36 , including the region of the ignition area between the end  38  of the center electrode  16  and the end  40  of the ground terminal  22 . As discussed earlier, the swirl plate  34  may enhance the quality of the air-fuel mixture. This enhanced quality of air-fuel mixture may include an even more combustible air-fuel mixture which may be provided in the region of the ignition area  46  by the disclosed configuration. Because an enhanced air-fuel mixture may be located in the ignition area  46 , the probability of ignition during one or more ignition attempts may be improved. This probability may be further optimized by adjusting the gap distance  46  of the ignition area, the gap distance  44  away from a plane along a location of the fuel spray  32  to the end  38  of the center electrode  16 , and the gap distance  48  away from a plane along a location of the fuel spray  32  to the end  40  of the ground terminal  22 . These distances  44 ,  46 , and  48  may include the distances within the prescribed ranges of approximately 1.0-10.0 mm, 1.2-4.4 mm, and 1.0-10.0 mm, respectively. 
     The extension design and mounting location of the ground terminal  22  relative to the center electrode  16  may also increase ignitability and reduce or prevent arcing outside of the ignition area  46 . For example the design of the disclosed ground terminal  22  provides an end  40  proximate to an end  38  of the center electrode  16  thus defining an air gap or ignition area  46  therebetween. A radial gap  54  may be formed between a length  50  of the center electrode  16  and a radial surface  56  of the ground terminal  22 . Thus, during a combustion process, a voltage difference may be generated between the end  38  and  40  to initiate the ignition of the air-fuel mixture. Another voltage difference may also be produced within the radial gap  54  between the ground terminal  22  and the center electrode  16  during the combustion process. However, since the distance of the radial gap  54  is greater than the distance of the ignition area  46 , the electrical resistance provided by the quantity of air in the radial gap  54  is greater than the electrical resistance provided by the quantity of air in the ignition area  46 . This higher concentration can increase the probability of ignition occurring within the ignition area  46 . This may also reduce or eliminate the probability of arcing occurring outside of the ignition area  46 , including, for example, in the radial gap  54 . 
     The configuration of additional components of the disclosed ignition system  10  may also facilitate preventing the combustible substance from igniting within the radial gap  54 . For example, the flow of air supplied into the air passageway  18  along the length  50  of the center electrode  16  and towards the fuel spray  32  may also reduce or eliminate the air-fuel mixture from accumulating within the radial gap  54  and becoming ignited. As noted above, this may also facilitate the reduction or elimination of contaminants, such as carbon deposit build-up, along surfaces within the radial gap  54 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed apparatus and method without departing from the scope of the disclosure. Additionally, other embodiments of the apparatus and method will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.