Abstract:
A spark ignition enhancer is provided in a combustion chamber of a spark ignition direct injection engine. The combustion chamber includes a fuel injector operable to spray a fuel plume into the chamber near a spark gap. The ignition enhancer includes a diversion element that extends into the fuel plume, between the fuel injector and the spark gap, to divert some of the fuel spray toward the spark gap to provide a spark ignitable air-fuel mixture at the spark gap, located outside of the spray plume. The diversion element may be mounted on a spark plug or on an adjacent element. The ignition enhancer improves ignitability by breaking up droplets in the spray plume, enhancing fuel vaporization, and diverting some fuel vapor to a spark gap outside the spray plume or away from a spark gap in the spray plume, so that liquid fuel at the gap is reduced, small scale turbulence is increased and gradients in fuel vapor distribution at the gap are reduced.

Description:
TECHNICAL FIELD 
     This invention relates to spark ignition direct injection engines and, more particularly, to a spark ignition enhancer for altering the spray path of injected fuel within a combustion chamber to improve fuel ignitability at a spark gap portion of a spark plug. 
     BACKGROUND OF THE INVENTION 
     Location of a spark gap of a conventional spark plug in line with a direct injection fuel spray plume results in intermittent misfires under some operating conditions. Means for reducing misfires and enhancing ignition consistency are needed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a spark ignition enhancer in a spark ignition direct injection engine combustion chamber. A spark plug spark gap is located out of the direct spray plume and a mechanical diversion element is added to divert some of the fuel spray to provide a spark ignitable air-fuel mixture at the spark gap. The diversion element may also increase fuel spray turbulence and improve fuel vaporization around the spark gap. The diversion element may be carried on a spark plug to provide an ignition enhancing spark plug. 
     In a first exemplary embodiment, the spark ignition enhancer is carried on a spark plug having an axially extending body with a central insulated electrode extending from a first end. A ground electrode extends from a peripheral edge of the first end, proximate the insulated electrode. A spark gap is formed between the electrodes and is positioned in or near a direct fuel spray path or fuel plume. A mechanical diversion element (spark ignition enhancer) in the form of a metal mesh member or screen extends from the first end of the body and is positioned to shelter the electrodes and the spark gap from direct fuel spray. Fuel hitting the screen is partially deflected toward from the spark gap, or away from it, to assist formation of an ignitable air-fuel mixture at the spark gap. The screen may also improve vaporization of fuel ahead of the spark gap and create turbulence in the spark gap. The remainder of the fuel is dispersed as it passes through the openings of the screen. This reduces the velocity of the fuel cloud, reduces the size of the fuel droplets, improves fuel vaporization and reduces the gradient of fuel concentration near the spark gap. As a result, the chance of a misfire is reduced and the fuel near the spark gap easily ignites. 
     In another exemplary embodiment, a spark ignition enhancer is integrated into an extended ground electrode and a bent center electrode of a spark plug. The ground electrode extends past a point proximate to the central electrode to define a spark gap between the electrodes, which is located out of a direct fuel spray path. The ground electrode forms a mechanical diversion element (spark ignition enhancer) that extends further into a fuel spray path to direct a portion of the fuel spray toward the spark gap of the plug to provide an ignitable mixture at the spark gap. It also creates turbulence as the injected fuel passes near the spark gap. This increases fuel vaporization and reduces the velocity of the injected fuel to improve the fuel-air mixture. 
     In yet another exemplary embodiment, a spark ignition enhancer is integrated into a ground electrode of a spark plug. The spark plug includes an axially extending body having a central insulated electrode extending from a first end. An end portion of the central insulated electrode extends radially toward the ground electrode extending from a peripheral edge of the first end of the spark plug body to define a radially extending spark gap between the end portion of the central electrode and an axially extending portion of the ground electrode. The spark gap is positioned outside of a fuel spray path. An end portion of the ground electrode forms a mechanical diversion element (spark ignition enhancer) that extends into a fuel spray path. This creates turbulence in the fuel spray to improve fuel vaporization and reduce the velocity of the injected fuel to improve the fuel-air mixture. In addition, the shape of the ground electrode deflects a portion of the improved fuel-air mixture toward the spark gap of the plug. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view through a combustion chamber of a spark ignition direct injection internal combustion engine; 
         FIG. 2  is a side view of a spark plug having a spark ignition enhancer according to a first embodiment of the present invention; 
         FIG. 3  is a side view showing a variation of the spark plug of  FIG. 2 . 
         FIG. 4  is a cross-sectional pictorial view showing a fuel spray plume in a combustion chamber with the spark plug of  FIG. 2 ; 
         FIG. 5  is a view similar to  FIG. 2  showing a second embodiment of the invention; 
         FIG. 6  is a view similar to  FIG. 4  but with the spark plug of  FIG. 5 ; 
         FIG. 7  is a view similar to  FIG. 2  showing a third embodiment of the invention; and 
         FIG. 8  is a view similar to  FIG. 4  but with the spark plug of  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1  of the drawings in detail, numeral  10  generally indicates a spark ignition direct injection internal combustion engine including a combustion chamber  11 . The combustion chamber  11  is defined by a cylinder  12 , a piston  13  reciprocable in the cylinder and a cylinder head  14  closing an end of the cylinder. A fuel injector  15  extends through the cylinder head  12  and operates to spray fuel into the combustion chamber  11  in a cone-like fuel spray plume  16 , which may be formed by multiple streams of atomized fuel droplets. 
     A spark plug  17  is positioned a distance to one side of the fuel injector and includes a spark gap  18  located at one edge of the spray plume  16 . In accordance with the present invention, the spark plug may be modified to provide various forms of ignition enhancers operative to increase the ignitability of air-fuel mixture in the spark gap at the time of ignition of a cylinder air-fuel charge. 
     Referring to  FIGS. 2 and 3  of the drawings, there are shown spark plugs  20 ,  21  illustrating two variations of a first embodiment of the invention. The spark plugs each include an axially extending body  22  having a first end  23  adapted to extend into a combustion chamber and a second end  24  adapted to extend outside the chamber. An insulated central electrode  26  extends from the first end  23  to the second end  24  for connection with an electrical ignition power source, not shown. A ground electrode  28  extends from a peripheral edge  30  of the first end, radially adjacent to the central electrode  26 , to an end  32  of the ground electrode, axially spaced from an opposite surface  34  of the central electrode, to define an axially extending spark gap  36 . In  FIG. 2 , the electrodes are made short enough to be out of the path of direct fuel spray of the fuel plume  16  in the combustion chamber. In  FIG. 3 , are made longer so they would lie in the path of the fuel plume. 
     In both  FIGS. 2 and 3 , a mechanical diversion element (spark ignition enhancer), in the form of a perforate metal screen  38  or  39  is carried on the first end  23  of the spark plug body  22  and partially or fully surrounds the spark gap  36 . The screen may take any desired form, such as a rigid metal mesh or a perforated sheet, as shown in the drawings. The screen extends beyond the spark gap  36  and into the fuel plume  16 , when the plug is installed in an engine combustion chamber  11 . In  FIG. 2 , the screen  38  partially surrounds the gap along one side of the first end. This requires locating the plug, when installed, with the screen  38  in a position between the fuel injector and the spark gap. In  FIG. 3 , the screen  39  is a cylindrical perforate sheet and extends completely around the first end  23  so that the screen is between the fuel injector  15  and the spark gap  36  in any position of the spark plug. 
     The screen may be formed of Ni-alloy or any other suitable electrode material. The size of the screen  38  or  39  should adequate to extend into the fuel injector spray plume to divert some of the fuel-air mixture to the spark plug gap  36 , as shown in  FIG. 2 , or away from the spark plug gap, as shown in  FIG. 3 . Openings  40  in the screens are sized to control the amount of fuel directed to or from the spark gap  32  of the plug  20  and to improve fuel atomization and vaporization for improved fuel ignitability. 
     As illustrated in  FIG. 4 , showing use of the spark plug  20  of  FIG. 2 , fuel is sprayed as a fuel plume  16  from the injector  15  into the combustion chamber  11  and toward the screen  38 . As the fuel contacts the screen  38 , a portion of the fuel is deflected, creating turbulence which improves fuel vaporization by mixing the fuel with air present in the combustion chamber  11 . Some of the fuel passing through the openings  40  in the screen  38  is deflected toward the spark gap  36 . 
     As the fuel passes through the openings  40 , fuel droplets are broken down into smaller droplets by the turbulence and/or the edges of the openings, improving fuel atomization. This also promotes fuel vaporization and reduces the velocity of the fuel deflected toward the spark gap  36  of the spark plug  20 . As a result, when the spark plug  20  is energized to form an arc in the spark gap  36 , the improved fuel mixture at the spark gap easily ignites. This in turn ignites air-fuel mixture throughout the combustion chamber  11  for improved combustion and reduced likelihood of a misfire. 
     When using the spark plug  21  of  FIG. 3 , the spark gap  36  would extend into the path of the fuel plume. However, the screen  39  would extend between the injector and the spark gap and would divert some of the fuel away from the spark gap, as well as improve atomization and vaporization. Thus, an ignitable air-fuel mixture may be provided at the spark gap for enhanced ignitability of the charge. It should be apparent that either screen arrangement could be applied to the differing electrode arrangements of  FIGS. 2 and 3  to direct injected fuel toward or away from the spark gap, since either screen would inherently tend to disperse fuel striking the screen. This would tend to enrich air-fuel mixture at a spark gap outside the plume and to reduce the richness of the mixture at a spark gap in the path of the fuel plume. 
       FIG. 5  shows another embodiment of a spark plug  42 , for use in an internal combustion engine. Spark plug  42  includes an axially extending body  44  having first and second ends  46 ,  48 . A central insulated electrode  50  extends from the first end  46  of the body  44 . A ground electrode  52  extends from a peripheral edge  54  of the first end, to a point radially adjacent the central electrode  50 , to form a spark gap  56 , and beyond to an end portion  60  spaced axially from the central electrode. The spark gap  56  is positioned to one side of an adjacent fuel spray plume when the plug is installed in an engine combustion chamber. The end portion  60  extends angularly across and beyond the body  44  to intercept part of the fuel spray plume. As a result, the extended portion  60  forms a diversion element (spark ignition enhancer) which increases fuel spray turbulence and reduces fuel spray velocity, improves fuel atomization and vaporization and directs a portion of the fuel spray toward the spark gap  56 . 
     As illustrated in  FIG. 6 , the spark plug  42  is installed in an engine so that the first end  46  extends into the combustion chamber  11 . When the plug is installed, the end portion  60  of the ground electrode  52  is in the fuel spray path and the spark gap  56  is positioned adjacent the fuel spray path. As fuel is sprayed as a fuel spray plume  16  from an injector  15  into the combustion chamber, a portion of the fuel is directed onto the end portion  60  of the ground electrode  52 . This fuel is deflected in various directions to create turbulence, which reduces the velocity of the fuel and improves fuel vaporization. A portion of the deflected fuel travels toward the spark gap  56 . When the spark plug  42  is energized to form an arc in the spark gap  56 , the improved air-fuel mixture at the spark gap easily ignites. This in turn ignites the air-fuel mixture throughout the combustion chamber  11  for improved combustion and reduced likelihood of a misfire. 
       FIG. 7  shows still another embodiment of a spark plug  64 , for use in an internal combustion engine. The spark plug  64  includes an axially extending body  66  having first and second ends  68  and  70 . A central insulated electrode  72  extends from the first end  68 . A ground electrode  74  extends from a peripheral edge  76  of the first end  68 , radially adjacent the central electrode  72 . The insulated electrode  72  has an axial portion  78  extending from the first end  68  of the body  66  and a lateral portion  80  bent toward the ground electrode  74  to form a spark gap  82  adjacent the first end of the body. 
     The ground electrode  74  includes an extended connecting portion  84  joined with the first end  68  of the body  66  and a lateral portion  86  extending from the connecting portion. The connecting portion  84  of the ground electrode  74  extends axially outward from the first end  68 , past the lateral portion  86  of the insulated electrode  72 , to form the spark gap  82  adjacent a fuel spray plume when the plug is installed in an engine combustion chamber. The lateral portion  86  of the ground electrode is directed radially toward an axis of the body  66  and is adapted to extend into the fuel spray plume. Thus, the lateral portion  86  of the ground electrode  74  forms a diversion element (spark ignition enhancer). 
     As illustrated in  FIG. 8 , the spark plug  64  is installed in an engine so that the first end  68  extends into the combustion chamber  11 . The plug is installed so that the lateral portion  86  of the ground electrode  74  protrudes into the fuel plume  16  and the spark gap  82  is positioned adjacent the fuel spray path. As fuel is sprayed from an injector  15  into the combustion chamber, a portion of the fuel is directed against the lateral portion  86  of the ground electrode  74 . This fuel is deflected in various directions to create turbulence, which reduces the velocity of the fuel spray and improves fuel atomization and vaporization. A portion of the fuel is deflected to the spark gap  82 . Thus, when the spark plug  64  is energized to cause an arc in the spark gap  82 , the improved air-fuel mixture at the spark gap easily ignites, reducing the likelihood of a misfire. 
     Tests of spark plugs with an ignition enhancer similar to the embodiment  60  of  FIG. 5  in an engine combustion chamber  11  similar to  FIG. 1  were conducted with fuel injection timing held constant and spark timing varied from 20 to 60 degrees before piston top dead center. Results showed a substantial increase, compared to conventional spark plugs, in the range of spark timing values that would provide operation with stable ignition, in which there are no misfires and the coefficient of variation in combustion is less than 7 percent. 
     It should be understood, that a spark ignition enhancer or diversion element, as previously described, could be located elsewhere than on a spark plug. In such a case, a conventional spark plug may be used and the diversion element may be carried on or formed as part of the cylinder head between or adjacent to the fuel injector and the spark plug to improve the air- fuel mixture at the spark gap of the plug for improved ignitibility. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.