Cylinder head assemblies and spark plugs configured to purge gas residuals for pre-ignition mitigation

Abstract

Spark plugs are disclosed that include distal structures having a plurality of bores extending through a shell associated with the spark plug. The plurality of bores form passageways between an interior volume and a combustion chamber associated with the spark plug. The passageways provide an escape path for the purging of residual gases from the interior volume to the combustion chamber.

Description

CYLINDER HEAD ASSEMBLIES AND SPARK PLUGS CONFIGURED TO PURGE GAS RESIDUALS FOR PRE-IGNITION MITIGATIONCROSS-REFERENCE TO RELATED APPLICATION:

[0001] The present application claims priority to, and the benefit of the filing date of, U.S. Provisional Application Ser. No. 63 / 608,937 filed on December 12, 2023, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The subject matter of this application relates generally to internal combustion engines, and more specifically to spark plugs and cylinder head assemblies configured to purge residual gases in spark plugs to mitigate pre-ignition.BACKGROUND

[0003] Spark plugs are used to initiate a flame in a flammable fuel and air mixture in a combustion chamber of an engine cylinder. In some engines, a combustion pre-chamber is used in conjunction with the spark plug. After a combustion event, the residual gases around the spark plug nose volume and / or pre-chamber volume are scavenged during the exhaust stroke of the piston within the cylinder. During the intake stroke, a fresh, air and fuel mixture (charge) is pulled into the combustion chamber in an expansion event driven by the piston.

[0004] However, some residual gases in the pre-chamber volume and / or nose volume of the spark plug are not completely scavenged and remain during the exhaust and intake strokes. For gaseous fuel engines with high flammability, the residual gases can create hot surface areas associated with the spark plug and / or combustion pre-chamber that can cause pre-ignition of the air-fuel mixture in the cylinder.

[0005] For example, the volume around the nose of the spark plug provides dielectric separation between the high voltage and low voltage sides of the spark plug to maintain high voltage sparkcapability. However, this nose volume can also provide a location where the residual gases stagnate, heating the spark plug surfaces above an auto-ignition temperature that causes preignition of the charge. Improvements are therefore needed to improve the purging of the residual gases in the nose volume and / or combustion pre-chamber volume of spark plugs.SUMMARY

[0006] The present application is directed to a spark plug and / or cylinder head assembly that improves purging of residual gases from an interior volume and cooling surfaces associated with the spark plug. The interior volume can be, for example, a volume between an insulator nose and a shell of the spark plug, and / or a volume of a combustion pre-chamber associated with the spark Plug.

[0007] According to an embodiment described herein, a cylinder head assembly for an internal combustion engine is provided. The cylinder head assembly includes a cylinder head having a fire deck with a flame face, an upper deck above the fire face, and a plurality of valve ports extending through the flame face and the upper deck. The plurality of valve ports are associated with at least one combustion chamber of the internal combustion engine. The cylinder head also includes a hole opening through the flame face. The hole extends from the flame face toward the fire deck along a longitudinal axis that is obliquely oriented to the flame face at the hole. The cylinder head assembly also includes a spark plug extending through the hole along the longitudinal axis. The spark plug includes a distal structure having a plurality of bores that are transversely oriented to the longitudinal axis and located only on a first side of the longitudinal axis so that all the plurality of bores are located below the flame face.

[0008] According to another embodiment described herein, a spark plug for an internal combustion engine is provided. The spark plug includes a center electrode extending along a longitudinal axis and at least outer electrode adjacent the center electrode. The spark plug also includes a nose extending around the center electrode. The spark plug further includes a shell extending around the nose. The shell defines an interior volume around the nose. The spark plug also includes a plurality of bores extending radially from the longitudinal axis from the interior volume through the shell. The plurality of bores are located on a first side of the longitudinal axis and are configured so that when the spark plug is installed on the internal combustion engine, the plurality of bores provide a passageway for purging residual gases from the interior volume.

[0009] 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

[0010] 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:

[0011] FIG. 1 is a schematic perspective view of an internal combustion engine including a block and a cylinder head assembly;

[0012] FIG. 2 is a schematic plan view of a portion of the cylinder head assembly of FIG. 1 looking toward an upper deck of the cylinder head assemble;

[0013] FIG. 3 is schematic sectional view looking through the cylinder head along a cavity configured to receive a spark plug;

[0014] FIG. 4 is a schematic sectional view showing a distal structure of a spark plug in the cavity of the cylinder head;

[0015] FIG. 5 is a schematic cross-sectional view of an embodiment of the distal structure of the spark plug;

[0016] FIG. 6 is a cross-sectional view of a portion of an embodiment of the cylinder head with an embodiment of the spark plug in the cavity; and

[0017] FIG. 7 is a perspective view of the cylinder head portion and spark plug embodiment of FIG. 6.DETAILED DESCRIPTION

[0018] Referring to FIGs. 1-7, according to an embodiment described herein, a cylinder head assembly 20 for an internal combustion engine 10 is provided. Cylinder head assembly 20 includes a cylinder head 22 having a fire deck 32 with a flame face 36, an upper deck 34 above fire deck 32, and a plurality of valve ports 38 extending through flame face 36 and upper deck 34. The plurality of valve ports 34 are associated with at least one combustion chamber 14 of internal combustion engine 10. Cylinder head 22 also includes a hole 42 opening through flame face 36. Hole 42 extends from flame face 36 toward fire deck 32 along a longitudinal axis LI that is obliquely oriented to flame face 36 at hole 42. Cylinder head assembly 20 also includes a spark plug 50, 150 extending through hole 42 along longitudinal axis LI . Spark plug 50, 150 includes a distal structure 52, 152 having a plurality of bores 54, 154 that are transversely oriented to longitudinal axis LI. The plurality of bores 54, 154 are located only on a first side 58, 158 of longitudinal axis LI so that all the plurality of bores 54, 154 are below flame face 36.

[0019] According to another embodiment described herein, spark plug 150 for internal combustion engine 10 is provided. Spark plug 150 includes a center electrode 168 extending along longitudinal axis LI and at least one outer electrode 170 adjacent the center electrode 168. Spark plug 150 also includes a nose 164 extending around the center electrode 168. Spark plug 150 further includes a shell 166 extending around nose 164. Shell 166 defines an interior volume 156 around nose 164. Spark plug 150 also includes a plurality of bores 154 extending radially from longitudinal axis LI from interior volume 156 through shell 166. The plurality of bores 154 are all located on first side 58, 158 of longitudinal axis LI and configured so that when spark plug 150 is installed on internal combustion engine 10, all of the plurality of bores 154, provide a passageway for purging residual gases from interior volume 156.

[0020] FIG. 1 shows a perspective view of internal combustion engine 10. Internal combustion engine 10 includes a block 12 that forms one or more combustion chambers 14, such as shown in FIG. 2, that house pistons (not shown.) In an embodiment, engine 10 is a gaseous fueled engine, such as a hydrogen and / or natural gas fueled engine. A cylinder head assembly 20 is supported on an upper surface 16 of block 12. Cylinder head assembly 20 includes cylinder head 22 thatincludes opposite sides 24, 26 extending along a major axis Al of engine 10. Cylinder head 22 also includes opposite ends 28, 30 that extend between opposite sides 24, 26.

[0021] Cylinder head 22 also includes fire deck 32 and upper deck 34 above fire deck 32. One or more water jackets (not shown) can be provided between and / or in fire deck 32 and / or upper deck 34. Fire deck 32 includes flame surface 36 that is oriented toward and supported directly or indirectly on upper surface 16 of block 12. Flame surface 36 faces the combustion chambers 14 when cylinder head 22 is supported on block 12.

[0022] Cylinder head 22 further includes a number of valve ports 38 extending therethrough from flame surface 36 through upper deck 34. Valve ports 38 are configured, for example, to receive intake valves and exhaust valve that control charge flow into combustion chamber 14 and exhaust flow from combustion chamber 14. Any number and configuration of valve ports 38 are contemplated.

[0023] As further shown in FIG. 3, cavity 40 is located between valve ports 38 and extends from an opening at upper deck 34 to a hole 42 that opens at flame surface 36. As discussed further below and shown in FIG. 4, cavity 40 houses spark plug 50, and distal structure 52 of spark plug 50 is located in hole 42 and protrudes at least partially below flame surface 36 into the aligned combustion chamber 14. Cavity 40 and hole 42 are oriented along longitudinal axis LI, orienting spark plug 50 and distal structure 52 along longitudinal axis LI.

[0024] Longitudinal axis LI is obliquely oriented to flame face 36. In an embodiment, flame surface 36 includes a curvature around hole 42. A projection of the curvature of flame surface 36 across hole 42 intersects longitudinal axis LI . A tangent T1 of the projected curvature is obliquely oriented to longitudinal axis LI so that a first portion of distal structure 52 projects below flame surface 36 and a second portion of distal structure 52 directly opposite the first portion resides in hole 42. Other embodiments contemplate other configurations for flame surface 36. For example, flame surface 36 is illustrated with concave curvature. A flame surface 36 that is flat and / or includes a convex curvature are also contemplated.

[0025] Referring further to FIG. 5, in an embodiment, distal structure 52 includes a plurality of bores 54 that extend through distal structure 52 and are in fluid communication with interior volume 56 of distal structure 52. All of the plurality of bores 54 are located on a first side 58 of the distal structure 52 and longitudinal axis LI, and the opposite, second side of distal structure 52 lacks any bores 54. As used herein, the first side 58 is the side of distal structure 52 around longitudinal axis LI located below flame face 36 when distal structure 52 is in its final engaged position in hole 42, and the second side 60 is the side of distal structure 52 around longitudinal axis LI in contact with cylinder head 22 in hole 42 in the final engaged position of distal structure 52. In an embodiment, the second side 60 includes that portion of distal structure 54 aligned along longitudinal axis LI with bores 54, for example orthogonal to longitudinal axis LI from bores 54.

[0026] The orientation of longitudinal axis LI is configured relative to flame surface 36 so that all of the plurality of bores 54 are located below flame surface 36 and are exposed to combustion chamber 14, while the second side 60 of distal structure 52 directly opposite bores 54 resides within hole 42 in contact with or adjacent to cylinder head 22. As a result, gas flow F from combustion chamber 14 can enter interior volume 56 though a distal end opening 62 of distal structure 52, and purge residual gases from interior volume 56 through the plurality of bores 54 on first side 58.

[0027] In an embodiment, distal structure 52 and interior volume 56 are formed by shell 66 that is a combustion pre-chamber device at a distal end of spark plug 50. The combustion pre-chamber device can be engaged to a housing of the spark plug 50 and / or engaged to the cylinder head 22. The combustion pre-chamber device provides an auxiliary volume, such as interior volume 56, in fluid communication with combustion chamber 14. Combustible gases are ignited in the interior volume 56 of the combustion pre-chamber device and combustion is started ahead of the main combustion chamber 14. Gas flow F purges residual gases from interior volume 56 and provides cooling of surfaces of shell 66.

[0028] In another embodiment, distal end structure 152 is formed by a shell 166 of spark plug 150, such as shown in FIGs. 6-7. Shell 166 extends around interior nose 164, such as an insulator nose around a center electrode 168 of spark plug 150. Interior volume 156 is formed between shell166 and nose 164, and gas flow F purges residual gases from the interior volume 156 while cooling surfaces of shell 166 and nose 164 in interior volume 156.

[0029] In FIGs. 6-7, spark plug 150 is shown engaged to cylinder head 22 in cavity 40. Spark plug 150 includes distal structure 152 that includes a plurality of bores 154 in fluid communication with interior volume 156. Distal structure 152 includes nose 164 and shell 166 extending around nose 164 to form interior volume 156. The oblique orientation of spark plug 150 along longitudinal axis LI with flame surface 36 exposes bores 154 on first side 158 to combustion chamber 14, while second side 160 lacks any bores and is located within hole 42.

[0030] As used herein, the first side 158 is the side of distal structure 152 around longitudinal axis LI located below flame face 36 when distal structure 152 is in its final engaged position in hole 42. The second side 160 is the side of distal structure 152 around longitudinal axis LI in contact with cylinder head 22 in hole 42 that is also aligned along longitudinal axis LI and directly opposite (for example orthogonal to longitudinal axis LI from bores 154) with bores 154 in the final engaged position of spark plug 150.

[0031] Spark plug 150 includes center electrode 168, such as a center cathode electrode, and a side electrode 170, such as a ground electrode. Nose 164 forms an insulator around center electrode 168. In the illustrated embodiment, side electrode 170 is J-shaped electrode and extends along and then below center electrode 168. However, other side and center electrode arrangements are also contemplated and not precluded.

[0032] Gas flow F can flow into interior volume 156 through a distal end opening 172. Gas flow F can purge residual gases in interior volume 156, and provide cooling to interior surfaces of shell 166 and outer surfaces of nose 164. As a result, pre-ignition issues created by residual gases in interior volume 156 are reduced or eliminated.

[0033] Various arrangements for bores 54, 154 are contemplated. For example, bores 54, 154 can be spaced around only the first side 58, 158 the corresponding distal structure 52, 152 at a regular or irregular spacing. The spacing is configured to ensure all of the bores 54, 154 are located incombustion chamber 14 at the engaged position of the distal structure 52, 152 with cylinder head 22 in hole 42.

[0034] In another example, bores 54, 154 additionally or alternatively extend orthogonally to longitudinal axis LI. The orthogonal orientation provides the shortest flow path for purging the residual gases from interior volume 56, 156. Further examples contemplate bores 54, 154 that are aligned with one another longitudinally along longitudinal axis LI, and extend radially outwardly from an inner surface of shell 66, 166 to an outer surface of shell 66, 166. Other embodiments contemplate other arrangements for bores 54, 154 including non-symmetrical and / or longitudinally displaced arrangements. Bores 54, 154 may all be of the same size, or have different sizes.

[0035] The distal structures 52, 152 of spark plugs 50, 150 and their arrangement with cylinder head 22 allow gas residuals to be purged from interior volumes 56, 156 eliminating or mitigating a root cause of pre-igniton due to gas residuals in spark plugs. In addition, the potential for water / ice bridging across the spark plug electrodes is reduced because of purging of gas residuals, lowering moisture concentration in the interior volumes 56, 156. Furthemore, better idle engine stability is provided due to an increase in gas flow across the spark plug electrodes. This allows for lower spark gap and higher lambdas (air / fuel ratio) to maintain engine idle stability and, as a result, less fuel consumption at idle conditions.

[0036] The cylinder head assembly 20 with spark plugs 50, 150 allow for improved flow of fresh charge into the interior volumes 56, 156 associated with the spark plugs 50, 150. As a result, fresh charge flow into the interior volumes 56, 156 dilutes or purges the residual gases that are present from the previous cycle and reduces surface temperatures, delaying or preventing pre-ignition. The improvements also result in extension of lambda operating range of engine 10, the combustion pre-chamber, and / or the spark plug as used therein.

[0037] As is evident from the figures and text presented above, a variety of aspects of the present disclosure are contemplated. According to one aspect, a cylinder head assembly for an internal combustion engine is provided that includes a cylinder head and a spark plug. The cylinder headincludes a fire deck having a flame face, an upper deck above the fire deck, a plurality of valve ports extending through the flame face and the upper deck, and a hole through the flame face. The plurality of valve ports are associated with at least one combustion chamber of the internal combustion engine. The hole extends from the flame face toward the fire deck along a longitudinal axis that is obliquely oriented to the flame face at the hole. The spark plug includes a distal structure having a plurality of bores that are transversely oriented to the longitudinal axis and located only on a first side of the longitudinal axis so that all the plurality of bores are located below the flame face.

[0038] In an embodiment, the cylinder head includes a cavity extending along the longitudinal axis from the hole through the upper deck. The spark plug is engaged to the cylinder head in the cavity. In an embodiment, the hole is located between the plurality of valve ports.

[0039] In an embodiment, the flame face has a concave curvature, the hole interrupts the concave curvature, and the longitudinal axis is obliquely oriented to a tangent of the concave curvature at the intersection of the longitudinal axis and a projection of the flame face across the hole.

[0040] In an embodiment, the plurality of bores are orthogonally oriented to the longitudinal axis. In a further embodiment, the plurality of bores are longitudinally aligned with one another along the longitudinal axis.

[0041] In an embodiment, the distal structure includes an interior volume, and the distal structure includes at least one opening at a distal end of the distal structure. The at least one opening is in fluid communication with the interior volume. The at least one opening is configured to provide a flow path for combustion gases from the at least one cylinder to purge residual gases from the interior volume through the first portion of the plurality of bores.

[0042] In a further embodiment, the distal structure includes a shell and a nose of the spark plug, the shell extends around the nose of the spark plug to form the interior volume between the nose and the shell, and the plurality of bores extend through the shell.

[0043] In a further embodiment, the distal structure of the spark plug includes a central electrode and a side electrode below the flame face. The side electrode is spaced from the central electrode.

[0044] In a further embodiment, the distal structure of the spark plug has no bores on a second side of the distal structure that is opposite the first side.

[0045] In a further embodiment, the distal structure includes a shell forming a combustion prechamber, the shell forms the interior volume, and the plurality of bores extend through the shell to the interior volume.

[0046] In an embodiment, all of the plurality of bores are located below the flame face. In an embodiment, the internal combustion engine is a gaseous fueled engine.

[0047] According to another aspect, a spark plug for an internal combustion engine is provided. The spark plug includes a center electrode extending along a longitudinal axis, at least one outer electrode adjacent the center electrode, a nose extending around the center electrode, and a shell extending around the nose. The shell defines an interior volume around the nose. The spark plug also includes a plurality of bores extending radially from the longitudinal axis from the interior volume through the shell. All the plurality of bores are located on a first side of the longitudinal axis and configured so that when the spark plug is installed on the internal combustion engine the plurality of bores provide a passageway for purging residual gases from the interior volume.

[0048] In an embodiment, each of the plurality of bores is orthogonal to the longitudinal axis. In an embodiment, the plurality of bores are spaced around the shell on the first side of the longitudinal axis. In an embodiment, the plurality of bores includes two or more bores.

[0049] In an embodiment, the at least one outer electrode is a J-shaped electrode extending along and below the center electrode. In an embodiment, a second side of the shell opposite the first side does not include any of the plurality of bores. In an embodiment, the passageway extends from a distal end opening of the spark plug, into the interior volume, and out the plurality of bores.

[0050] In the above description, certain relative terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” 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.

[0051] 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.

[0052] 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 becomemore fully apparent from the following description and appended claims, or may be learned by the practice of the subject matter as set forth hereinafter.

[0053] 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.

Claims

WHAT IS CLAIMED IS:

1. A cylinder head assembly for an internal combustion engine, the cylinder head assembly comprising: a cylinder head including: a fire deck having a flame face; an upper deck above the fire deck; a plurality of valve ports extending through the flame face and the upper deck, the plurality of valve ports associated with at least one combustion chamber of the internal combustion engine; a hole opening through the flame face, the hole extending from the flame face toward the fire deck along a longitudinal axis that is obliquely oriented to the flame face at the hole; and a spark plug extending through the hole along the longitudinal axis, the spark plug including a distal structure having a plurality of bores that are transversely oriented to the longitudinal axis and located only on a first side of the longitudinal axis so that all the plurality of bores are located below the flame face.

2. The cylinder head assembly of claim 1, the cylinder head further comprises a cavity extending along the longitudinal axis from the hole through the upper deck, wherein the spark plug is engaged to the cylinder head in the cavity.

3. The cylinder head assembly of claim 1, wherein the hole is located between the plurality of valve ports.

4. The cylinder head assembly of claim 1, wherein: the flame face has a concave curvature; the hole interrupts the concave curvature; and the longitudinal axis is obliquely oriented to a tangent of the concave curvature at the intersection of the longitudinal axis and a projection of the flame face across the hole.

5. The cylinder head assembly of claim 1 , wherein the plurality of bores are orthogonally oriented to the longitudinal axis.

6. The cylinder head assembly of claim 5, wherein the plurality of bores are longitudinally aligned with one another along the longitudinal axis.

7. The cylinder head assembly of claim 1, wherein: the distal structure includes an interior volume; and the distal structure includes at least one opening at a distal end of the distal structure, the at least one opening in fluid communication with the interior volume, the at least one opening configured to provide a flow path for combustion gases from the at least one cylinder to purge residual gases from the interior volume through the first portion of the plurality of bores.

8. The cylinder head assembly of claim 7, wherein: the distal structure includes a shell and a nose of the spark plug; the shell extends around the nose of the spark plug to form the interior volume between the nose and the shell; and the plurality of bores extend through the shell.

9. The cylinder head assembly of claim 8, wherein the distal structure of the spark plug includes: a central electrode; and a side electrode below the flame face, wherein the side electrode is spaced from the central electrode.

10. The cylinder head assembly of claim 8, wherein the distal structure of the spark plug has no bores on a second side of the distal structure that is opposite the first side.

11. The cylinder head assembly of claim 7, wherein: the distal structure includes a shell forming a combustion pre-chamber; the shell forms the interior volume; andthe plurality of bores extend through the shell to the interior volume.

12. The cylinder head assembly of claim 1, wherein all of the plurality of bores are located below the flame face.

13. The cylinder head assembly of claim 1, wherein the internal combustion engine is a gaseous fueled engine.

14. A spark plug for an internal combustion engine, the spark plug comprising: a center electrode extending along a longitudinal axis; at least one outer electrode adjacent the center electrode; a nose extending around the center electrode; a shell extending around the nose, the shell defining an interior volume around the nose; and a plurality of bores extending radially from the longitudinal axis from the interior volume through the shell, wherein all the plurality of bores are located on a first side of the longitudinal axis and configured so that when the spark plug is installed on the internal combustion engine the plurality of bores provide a passageway for purging residual gases from the interior volume.

15. The spark plug of claim 14, wherein each of the plurality of bores is orthogonal to the longitudinal axis.

16. The spark plug of claim 14, wherein the plurality of bores are spaced around the shell on the first side of the longitudinal axis.

17. The spark plug of claim 14, wherein the plurality of bores includes two or more bores.

18. The spark plug of claim 14, wherein the at least one outer electrode is a J-shaped electrode extending along and below the center electrode.

19. The spark plug of claim 14, wherein a second side of the shell opposite the first side does not include any of the plurality of bores.

20. The spark plug of claim 14, wherein the passageway extends from a distal end opening of the spark plug, into the interior volume, and out the plurality of bores.

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