Patent Publication Number: US-2021184437-A1

Title: Spark plug configurations for a combustion pre-chamber of an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of International Patent Application No. PCT/US19/52935 filed on Sep. 25, 2019, which claims the benefit of the filing date of U.S. Provisional Application Ser. No. 62/736,560 filed on Sep. 26, 2018, each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The subject matter of this application relates generally to internal combustion engines, and more specifically to spark plugs used in ignition systems of internal combustion engines having combustion pre-chambers for the spark plugs. 
     BACKGROUND 
     It is well documented that the use of combustion pre-chamber devices with spark plugs, such as shown in  FIG. 1 , in pre-chamber assemblies in a spark ignited, gaseous fueled, engine can result in an extended lambda (air/fuel ratio) range. Generally this allows the engine to be operated leaner than an open chamber system, resulting in lower NOx emissions while maintaining good cycle-to-cycle peak cylinder pressure variation. With these engines there is usually an operational trade-off between NOx emissions and fuel consumption. For applications that have higher NOx emissions requirements than others, better fuel consumption can be obtained by running the pre-chamber engine slightly richer (i.e., at a lower lambda value). Depending on the cost of fuel, this operation at a lower lambda value can offer substantial savings to the engine owner/operator. 
     Spark plugs are used in conjunction with various types of combustion chamber configurations to initiate a flame in a flammable fuel and air mixture. Some combustion chamber configurations include passive pre-chamber, open chamber, and fuel fed pre-chamber configurations. Pre-chambers are useful for initiating and propagating the combustion flame for pre-mixed gaseous-fueled engines. In particular, pre-chambers provide benefits as applied in lean-burn natural gas engines which can be difficult to ignite using conventional open chamber type configurations. 
     Passive pre-chambers include a combustion volume in which the spark plug is located. The combustion volume of the pre-chamber is linked to the main combustion chamber of the cylinder by the use of orifices or nozzles. The spark plugs include a central electrode and one or more outer ground or anode electrodes, which at least partially surround the central electrode to create a gap therebetween. The spark plug initiates a combustion event by generating a spark (e.g., an electron current) that spans the gap between the central electrode and one of the outer ground electrodes. More specifically, the spark initiates a flame that propagates through the pre-chamber volume. This combustion creates a sudden increase in pressure in the pre-chamber creating a large pressure difference across the orifices between the pre-chamber and main chamber. The pressure difference forces the flame to propel through the orifices into the main combustion chamber resulting in a successful combustion event. 
     After a successful combustion event, the residual exhaust gases in the main chamber are scavenged during the exhaust stroke of the piston within the cylinder. During the intake stroke, a fresh, pre-mixed air and fuel mixture (charge) is pulled into the main cylinder via an expansion event driven by the piston. However, some residual exhaust gases in the passive pre-chamber volume and between the spark plug electrodes are not completely scavenged and remain within the pre-chamber during the exhaust and intake strokes. During the subsequent compression stroke, the pressure difference between the main chamber and pre-chamber increases, forcing a fresh charge through the orifices into the pre-chamber, which compresses the residual exhaust gases towards the backside of the pre-chamber where the spark plug is located. The residual exhaust gases trapped in the area toward the back side of the pre-chamber, on the side opposite to the main chamber, can lead to pre-ignition and/or abnormal combustion, especially when the engine is operating at richer lambda (air/fuel ratio) ranges. 
     The residual gas trapped in the annular volume around the spark plug insulator nose may not be readily purged in subsequent combustion cycles and as a result can be heated to a temperature sufficient to cause pre-ignition, particularly when the engine is operated at richer lambda values. Fluid dynamics analysis shows low velocity in the spark plug annular volume nearest to the insulator nose at the rearmost portion of the pre-chamber volume. Output from CO 2  concentration analyses in a spark plug indicates evidence of unacceptably high levels of CO 2  residual gas remaining in the spark plug annular volume, particularly in zones near the base of the insulator nose. Output from temperature analyses measuring temperatures within various zones of the spark plug annular volume indicates evidence of high gas temperatures in the spark plug annular volume, especially near the base of the insulator nose, as a result of the lack of mixing or purging of the residual gas from the spark plug annular volume. 
     Improvements are needed in spark plugs to improve the purging of the residual gases in the annular spark plug volume and pre-chamber volume, thus extending the lambda operating range within which the engine may be advantageously operated. 
     SUMMARY 
     The subject matter of the present application has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the spark plug and combustion pre-chamber art that have not yet been fully solved by currently available combustion pre-chamber and spark plug designs. 
     According to one embodiment as described herein, a spark plug is disclosed for use in a combustion pre-chamber assembly in a lean-burn, gaseous fueled, internal combustion engine. Various embodiments include a spark plug that is configured to improve the flow of fresh charge into the annular volume around the spark plug insulator nose to dilute or purge residual gases that are present in the annular volume. The various embodiments include arrangements in which the spacing between outer ground electrodes is increased by reducing the number of outer electrodes, arrangements in which the outer electrodes are shaped to increase the fresh charge flow into the annular volume, arrangements in which the outer electrode is shaped to convert the fresh charge flow into a swirling motion to purge residual gases from the annular volume, and combinations of two or more of these. These embodiments lower the gas temperature in the annular volume, which makes the spark plug more resistant to pre-ignition and/or abnormal combustion. 
     This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the subject matter may be more readily understood, a more particular description of the subject matter briefly described above will be rendered by reference to certain embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the subject matter and are not therefore to be considered to be limiting of its scope, the subject matter will be described and explained with additional specificity and detail through the use of the drawings, in which: 
         FIG. 1  is a cross-sectional side view of a prior art pre-chamber assembly installed in a cylinder head; 
         FIG. 2  is a cross-sectional side view of a prior art electrode end portion of a spark plug; 
         FIGS. 3A and 3B  are perspective views of electrode end portions of a spark plug embodiment to increase a flow area between electrodes; 
         FIGS. 4A and 4B  are perspective views of electrode end portions of a spark plug embodiment arranged to increase a flow area between electrodes and to further induce a swirl feature, respectively; 
         FIGS. 5A and 5B  are perspective views of electrode end portions of another spark plug embodiment arranged to induce a swirl feature 
     
    
    
     DETAILED DESCRIPTION 
     There is disclosed herein improved spark plug designs to allow for improved flow of fresh charge into the annular volume around the spark plug insulator. The improvements result in improved flow of fresh charge mix into the annular volume around the spark plug insulator, which dilutes or purges the residual gasses that are present from the previous cycle and delaying the onset of pre-ignition. The improvements have the effects of lowering the gas temperature in the annular volume, thus making the spark plug more resistant to pre-ignition and/or abnormal combustion. The improvements also result in extension of lambda (air/fuel ratio) operating range of engine, the pre-chamber, and/or the spark plug as used therein. 
       FIG. 1  shows a cross-sectional side view of an example prior art passive pre-chamber assembly mounted directly to the cylinder head  200  of an internal combustion engine. The cylinder head  200  of conventional internal combustion engines includes a plurality of spark plug recesses  202  for receiving a spark plug  10 . Typically, the conventional spark plug is fitted within a respective recess  202  such that all or part of the cathode and anode electrodes of the conventional spark plug are positioned within (e.g., directly exposed to) a respective main combustion chamber  402  of the engine or cylinder block when the cylinder head  200  is mounted to the cylinder liner  400  that is supported in the engine block. The main combustion chamber  402  is fluidly coupled to an air-fuel mixture inlet for receiving an air-fuel mixture from air intake and fuel sources (not shown). 
     As shown in  FIG. 1 , a conventional spark plug may be connected with a passive pre-chamber device  100 , which is fitted within the spark plug recess  202 . The pre-chamber device  100  includes a body  105  that defines a pre-chamber volume  115 . The pre-chamber volume  115  effectively spatially separates the spark plug (e.g., spark plug  10 ) from the main combustion chamber  402 . The body  105  includes one or more orifices or nozzles in its distal end wall that fluidly connect the pre-chamber volume  115  with the main combustion chamber  402 . As discussed above, the pre-chamber volume  115  facilitates the initiation and propagation of a combustion flame for the internal combustion engine. The body  105  may include connectors (e.g., external threads) matching or similar in dimensions the connectors (e.g., external threads) that are found on conventional spark plugs. The connectors of the body  105  mate with corresponding connectors (e.g., internal threads) formed within the spark plug recess  202  to secure the pre-chamber device  100  to the cylinder head  200 . The body  105  includes a receptacle  107  configured to receive and retain a spark plug  10  within the body  105  such that the cathode and anode electrodes of the spark plug  10  are positioned within the pre-chamber volume  115 . 
     The body  105  includes pre-chamber inlet apertures (not shown) for receiving the air-fuel mixture from the inlet of the cylinder head  200  into the pre-chamber volume  115 . The pre-chamber volume  115  is in fluid communication with a gap  117  which is in the form of an annular space between the exterior surface of the spark plug  10  and the inner surface of the pre-chamber volume  115 , the gap  117  being positioned toward a proximal portion of an electrode end portion  12  of the spark plug  10 . 
       FIG. 2  is a cross-sectional side view of the electrode end portion  12  of the spark plug  10 . The spark plug  10  includes an outer ground electrode portion  14  with a plurality of outer ground electrodes  16 . The outer ground electrodes  16  can be defined as outer electrodes. Further, the spark plug  10  includes a central electrode  18  about which the outer electrodes  16  are positioned at a distal end  19  of the spark plug  10 . 
     Generally, the outer electrodes  16  at least partially laterally surround or are positioned laterally about the central electrode  18 . In other words, the outer electrodes  16  are radially outwardly spaced-apart from the central electrode  18 , defining a space or gap between the central electrode  18  and the outer electrodes  16 . The outer electrodes  16  extend from a proximal portion to the distal end  19  of the spark plug  10 , adjacent a head  20  of the central electrode  18 . The outer electrodes  16  may be angled radially inwardly toward a central longitudinal axis A of the spark plug  10  in a proximal to distal direction as shown in  FIG. 2 . The outer electrodes  16  may also each include an aperture  22  that facilitates the flow of fresh charge and exhaust gas into and out of the space defined between the central electrode  18  and the outer electrodes  16 . 
     The spark plug  10  includes an outer shell  24  that surrounds the body of the spark plug  10 , formed generally in a cylindrical shape at a proximal portion of the electrode end portion  14  of the spark plug  10  as shown in  FIG. 2 . The shell  24  ends at the proximal portion of the electrode end portion  14  such that the outer electrodes  16  are open to the pre-chamber volume  115 . The spark plug  10  further includes an insulator including an insulator nose  26 . The insulator nose  26  surrounds the central electrode  18  and generally is formed in the shape of a hollow tube surrounding the central electrode  18  and positioned to be concentric to the cylindrical shape of the body of the central electrode  18 . 
     The inner surfaces of the preceding structures form a space within the spark plug  10  that is generally annular in shape. Specifically, as shown in  FIG. 2 , inner surface  16   a  of the outer electrodes  16 , inner surface  24   a  of the shell  24 , surface  26   a  of the insulator nose  26 , and surface  18   a  of the central electrode  18  together form a boundary around an interior annular volume  28  that extends around insulator nose  26  inside the electrode end portion  12  of the spark plug  10 . The annular volume  28  includes a front or distal portion  28   a  formed near the distal end  19  of the spark plug  10 . The annular volume  28  further includes a rear or proximal portion  28   b  formed near the proximal portion of the electrode end portion  12  of the spark plug  10 . The proximal portion  28   b  of annular volume  28  forms an annular space surrounding the proximal portion of the insulator nose  26 . 
     Referring now to  FIGS. 3A and 3B , spark plugs  10 ′ and  10 ″ are illustrated in which the number of outer electrodes are reduced from the four outer electrodes shown in the prior art spark plug  10 . In  FIGS. 3A and 3B , components of the spark plugs  10 ′ and  10 ″ can be identical to spark plug  10  unless noted otherwise, and like components are designated with the same reference numerals. In particular, spark plug  10 ′ in  FIG. 3A  includes two outer electrodes  16 ′ positioned on opposite sides of the central electrode  18 . Outer electrodes  16 ′ are located 180 degrees opposite one another in the illustrated embodiment. The reduction in the number of electrodes from four to two increases the area of the flow path between electrodes  16 ′ as compared to electrodes  16  of spark plug  10 , allowing better purging of the annular volume  28  around insulator nose  26 . 
     Spark plug  10 ″ in  FIG. 3B  includes three outer electrodes  16 ″ positioned around the central electrode  18 . Outer electrodes  16 ″ are located 120 degrees apart from one another in the illustrated embodiment. The reduction in the number of electrodes from four to three increases the area of the flow path between electrodes  16 ″ as compared to electrodes  16  of spark plug  10 , allowing better purging of the annular volume  28  around insulator nose  26 . The three electrode arrangement also provides improved symmetry for applications in which the orientation of the spark plug is critical. 
     Referring to  FIG. 4A , there is shown another embodiment spark plug  100  which includes another electrode arrangement to provide for increased charge air flow as compared to spark plug  10 . Elements of spark plug  100  that are the same or similar to spark plug  10  are designated with the same reference numerals. Spark plug  100  includes four electrodes  116  each including a blade  118  that extends from a proximal end  120  to a distal end  122 . Blade  118  includes opposite channels  122   a ,  122   b  in the sidewalls of blade  118  that provide for an increased flow area between adjacent electrodes  116  into and out of annular volume  28 . Channels  122   a ,  122   b  are located closer to proximal end  120  than distal end  122  to be closer to the annular volume  28 . The blade  118  has a T shape to provide a wider flow area and facilitate purging of residual exhaust gases in annular volume  28 . The shape of the electrodes  116  can be adjusted to increase the heat transfer and flow area as compared to electrodes  16 . 
     Referring to  FIG. 4B , there is shown another embodiment spark plug  100 ′ which includes an electrode arrangement to provide for increased charge air flow into annular volume  28  that is similar to spark plug  100 , except the blade  118 ′ of each electrode  116 ′ includes swirl inducing surfaces  124   a ′,  124   b ′ along each of the channels  122   a ′  122   b ′. The opposite channels  122   a ′,  122   b ′ provide for both an increased flow area between adjacent electrodes  116 ′ into and out of annular volume  28  and for generating a swirl flow in the annular volume  128  around insulator nose  126 . The swirl flow improves removal of the residual exhaust gases. The dimensions and shape of the surfaces  124   a ′  124   b ′ can be adjusted depending on the application. 
     Each outer or ground electrode  116  includes an outer surface  132  that extends from proximal end  120  to distal end  122  and is angled obliquely toward central longitudinal axis A in the distal direction. Inner surface  130  extends from proximal end  120  to a distally tapered end member  121  that is positioned adjacent to head  20  of central electrode  18 . In one embodiment, the surfaces  124   a ,  124   b  of each channel  122   a ,  122   b  of spark plug  100  extends along a plane that intersects or nearly intersects central longitudinal axis A and is perpendicular or nearly perpendicular to the parallel inner and outer surfaces  130 ,  132  of the respective electrode  116 . In contrast, the swirl inducing surfaces  124   a ′,  124   b ′ of spark plug  100 ′ are arranged on a plane that does not intersect central longitudinal axis A, and these surfaces  124   a ′,  124   b ′ extend at an oblique angle to the inner and outer surfaces  130 ′,  132 ′ of the electrodes  116 ′. 
     Referring to  FIGS. 5A and 5B , another embodiment spark plug  200  is shown that includes another embodiment electrode arrangement in the form of electrode  216 . Electrode  216  includes a proximal support member  218  supported on a distal end of shell  24  and a distal support member  220  extending around the head  20  of central electrode  18 . A number of spirally oriented electrode blades  222  extend between and connect support members  218 ,  220  with gaps  226  formed between adjacent electrode blades  222 . Each of the support members  218 ,  220  can be ring-shaped, although other shapes are not precluded. 
     As shown in  FIG. 5B , each electrode blade  222  is oriented so that an inner part of the proximal end of electrode blade  222  lies on a line B extending radially outwardly from central longitudinal axis A. The remaining part of each electrode blade  222  is curved distally away from line B to distal ring member  220 . The number of electrode blades  222  and spacing between blades  222  can be varied as may be needed based on the operating requirements and/or to produce the desired performance results. The blades  222  and/or the channels  122   a ′,  122   b ′ can be arranged to induce clockwise or counterclockwise swirl flow. The range of lambda values at which the engine may be operated increases, with less instances of pre-ignition and/or abnormal combustion. 
     As is evident from the figures and text presented above, a variety of aspects of the present disclosure are contemplated. For example, according to one aspect, a spark plug for an internal combustion engine is provided, The spark plug includes a distal end portion comprising a center electrode and at least one outer electrode and an insulator nose extending around the center electrode. The insulator nose has a distal end that is spaced proximally from a distal end of the center electrode and a shell extending around a body of the spark plug. The shell defines an annular volume around the insulator nose and the at least one outer electrode includes a blade extending between a proximal end and a distal end. The blade includes opposite channels extending into opposite sides of the blade that direct charge flow into and out of the annular volume. 
     In one embodiment, the at least one outer electrode includes four outer electrodes positioned around the center electrode and each of the four outer electrodes includes a pair of opposite channels formed in the blade thereof. In a refinement of this embodiment, each of the blades of the four outer electrodes is T-shaped. 
     In another embodiment, the body of the spark plug extends along a central longitudinal axis and the opposite channels in the blade each include a swirl inducing surface that extends along a plane that does not intersect the central longitudinal axis. In yet another embodiment, the blade of the at least one outer electrode includes an inner surface facing the center electrode and an opposite outer surface, and the opposite channels in the blade of the at least one outer electrode each include a swirl inducing surface that is obliquely oriented to the inner and outer surfaces of the blade. 
     According to another aspect, a spark plug for an internal combustion engine that includes a distal end portion comprising a center electrode and at least one outer electrode and an insulator nose extending around the center electrode. The insulator nose has a distal end that is spaced proximally from a distal end of the center electrode and a shell extending around a body of the spark plug. The shell defines an annular volume around the insulator nose. The at least one outer electrode includes a proximal support member adjacent a distal end of the shell, a distal support member around the center electrode, and a plurality of blade members extending between and connecting the proximal support member and the distal support member. 
     In one embodiment, the proximal support member and distal support member are ring-shaped. In another embodiment, the blade members are spirally oriented between the proximal and distal support members. In yet another embodiment, the blade members are curved between the proximal and distal support members. In a further embodiment, a gap is provided between each of the adjacent blade members. 
     According to another aspect, a spark plug for an internal combustion engine includes a first and second end portion, the first end portion including a center electrode and at least one outer electrode. The spark plug also includes an outer body extending between the first and second end portion and an insulator provided around a portion of the center electrode that is spaced apart from an inner portion of the outer body to form an annular space between the insulator and outer body. The at least one outer electrode includes a blade configured with a channel at opposite sides thereof to direct charge flow into and out of the annular space. 
     In an embodiment, the insulator extends along a central longitudinal axis of the spark plug. In another embodiment, the at least one outer electrode extends along a plane in a direction toward a central longitudinal axis of the spark plug that intersects with the central longitudinal axis. In yet another embodiment, the blade comprises a distal and proximal end and configured to extend between the distal and proximal end. In a refinement of this embodiment, the channel is provided between the distal end and the proximal end at the opposite sides of the blade. In a further refinement, the channel is positioned closer to the proximal end of the blade than the distal end to increase purging of residual exhaust gasses in the annular space. 
     In another embodiment, the blade includes an inner surface facing the center electrode and an opposite outer surface, and the channel in the blade includes a swirl inducing surface obliquely oriented to the inner and outer surfaces. In yet another embodiment, the channel includes a swirl inducing surface that extends along a plane that is parallel to the central longitudinal axis of the spark plug. In still another embodiment, the at least one electrode includes four electrodes positioned around the center electrode such that at least two of the four electrodes are spaced 180° opposite one another. In another embodiment, the blade is T-shaped. 
     In the above description, certain relative terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” “proximal,” “distal,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object. 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. Similarly, the use of the term “implementation” means an implementation having a particular feature, structure, or characteristic described in connection with one or more embodiments of the present disclosure, however, absent an express correlation to indicate otherwise, an implementation may be associated with one or more embodiments. 
     The described features, structures, advantages, and/or characteristics of the subject matter of the present disclosure may be combined in any suitable manner in one or more embodiments and/or implementations. In the following description, numerous specific details are provided to impart a thorough understanding of embodiments of the subject matter of the present disclosure. One skilled in the relevant art will recognize that the subject matter of the present disclosure may be practiced without one or more of the specific features, details, components, materials, and/or methods of a particular embodiment or implementation. In some instances, the benefit of simplicity may provide operational and economic benefits and exclusion of certain elements described herein is contemplated as within the scope of the invention herein by the inventors to achieve such benefits. In other instances, additional features and advantages may be recognized in certain embodiments and/or implementations that may not be present in all embodiments or implementations. Further, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the subject matter of the present disclosure. The features and advantages of the subject matter of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the subject matter as set forth hereinafter. 
     The present subject matter may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.