A pre-chamber spark plug having a shell, an insulator disposed at least partially within the shell, a center electrode disposed at least partially within the insulator, a ground electrode forming a spark gap with the center electrode, and a pre-chamber cap connected to the shell and forming a pre-chamber. The pre-chamber cap includes two or more openings that are configured so that at least one inflowing fuel-air mixture jet is directed to a pre-chamber wall gap so as to flush out or remove gas from a previous ignition cycle. The two or more openings are angled so that a first inflowing fuel-air mixture jet of a first opening does not intersect with a second inflowing fuel air-mixture jet of a second opening.

A pre-chamber spark plug having a shell, an insulator disposed at least partially within the shell, a center electrode disposed at least partially within the insulator, a ground electrode forming a spark gap with the center electrode, and a pre-chamber cap connected to the shell and forming a pre-chamber. The pre-chamber cap includes two or more openings that are configured so that at least one inflowing fuel-air mixture jet is directed to a pre-chamber wall gap so as to flush out or remove gas from a previous ignition cycle. The two or more openings are angled so that a first inflowing fuel-air mixture jet of a first opening does not intersect with a second inflowing fuel air-mixture jet of a second opening.

A spark plug includes a ground electrode facing a distal end surface of a center electrode. In a main body of the ground electrode, a first slanted surface is formed at a portion on a side facing the distal end surface and upstream of the center electrode relative to the airflow, a facing portion, a second slanted surface is formed at a portion on a side opposite to the side facing the distal end surface and upstream of the center electrode relative to the airflow, and when T represents a thickness of the main body of the ground electrode and Su represents a distance from a connection between the first slanted surface and the second slanted surface to the facing portion, 2T/16Su8T/16.

A spark plug includes a ground electrode facing a distal end surface of a center electrode. In a main body of the ground electrode, a first slanted surface is formed at a portion on a side facing the distal end surface and upstream of the center electrode relative to the airflow, a facing portion, a second slanted surface is formed at a portion on a side opposite to the side facing the distal end surface and upstream of the center electrode relative to the airflow, and when T represents a thickness of the main body of the ground electrode and Su represents a distance from a connection between the first slanted surface and the second slanted surface to the facing portion, 2T/16Su8T/16.

An outer periphery of the tubular housing includes a parallel surface, a pressure contact surface and a connection surface. The parallel surface is formed parallel to an axial direction of the spark plug. The pressure contact surface is located closer to a tip of the spark plug and more radially inward than the parallel surface. The pressure contact surface has a tapered shape in that a diameter decreases toward the tip. The pressure contact surface is pressed against a cylinder head when installed in the internal combustion engine. The connection surface is located closer to a base of the spark plug than an extension line in a longitudinal cross-section of the spark plug parallel to the axial direction including a plug central axis. The connection surface connects an outer peripheral end of the pressure contact surface with a longitudinal end of the parallel surface.

An outer periphery of the tubular housing includes a parallel surface, a pressure contact surface and a connection surface. The parallel surface is formed parallel to an axial direction of the spark plug. The pressure contact surface is located closer to a tip of the spark plug and more radially inward than the parallel surface. The pressure contact surface has a tapered shape in that a diameter decreases toward the tip. The pressure contact surface is pressed against a cylinder head when installed in the internal combustion engine. The connection surface is located closer to a base of the spark plug than an extension line in a longitudinal cross-section of the spark plug parallel to the axial direction including a plug central axis. The connection surface connects an outer peripheral end of the pressure contact surface with a longitudinal end of the parallel surface.

A pre-chamber spark plug for an internal combustion engine having a surface discharge spark gap that is generally located at a rearward end of a pre-chamber and is configured so that sparking components will have minimal electrode obstruction and promote unhindered gas exchange between the pre-chamber and a main combustion chamber. According to one embodiment, the surface discharge spark gap includes a radial sparking portion where a majority of the sparking occurs in a generally radial direction. According to another embodiment, the surface discharge spark gap includes both a radial sparking portion and an axial sparking portion so that sparking occurs in both radial and axial directions, respectively.

A pre-chamber spark plug for an internal combustion engine having a surface discharge spark gap that is generally located at a rearward end of a pre-chamber and is configured so that sparking components will have minimal electrode obstruction and promote unhindered gas exchange between the pre-chamber and a main combustion chamber. According to one embodiment, the surface discharge spark gap includes a radial sparking portion where a majority of the sparking occurs in a generally radial direction. According to another embodiment, the surface discharge spark gap includes both a radial sparking portion and an axial sparking portion so that sparking occurs in both radial and axial directions, respectively.

An outer periphery of the tubular housing includes a parallel surface, a pressure contact surface and a connection surface. The parallel surface is formed parallel to an axial direction of the spark plug. The pressure contact surface is located closer to a tip of the spark plug and more radially inward than the parallel surface. The pressure contact surface has a tapered shape in that a diameter decreases toward the tip. The pressure contact surface is pressed against a cylinder head when installed in the internal combustion engine. The connection surface is located closer to a base of the spark plug than an extension line in a longitudinal cross-section of the spark plug parallel to the axial direction including a plug central axis. The connection surface connects an outer peripheral end of the pressure contact surface with a longitudinal end of the parallel surface.

An outer periphery of the tubular housing includes a parallel surface, a pressure contact surface and a connection surface. The parallel surface is formed parallel to an axial direction of the spark plug. The pressure contact surface is located closer to a tip of the spark plug and more radially inward than the parallel surface. The pressure contact surface has a tapered shape in that a diameter decreases toward the tip. The pressure contact surface is pressed against a cylinder head when installed in the internal combustion engine. The connection surface is located closer to a base of the spark plug than an extension line in a longitudinal cross-section of the spark plug parallel to the axial direction including a plug central axis. The connection surface connects an outer peripheral end of the pressure contact surface with a longitudinal end of the parallel surface.