Spark plug for igniting a combustible fuel in an internal combustion engine, wherein the spark plug has an igniter arranged at an end of the spark plug facing the combustion chamber, when the spark plug is mounted in the internal combustion engine. The spark plug includes a wall and a sealing area. The wall at least partially surrounds the igniter. The sealing area is used for sealing the combustion chamber against the environment. The wall has the sealing area located at an end of the wall, which end faces the combustion chamber when the spark plug is mounted in the internal combustion engine.

This spark plug inhibits excessive increase in the temperature of a ground electrode to inhibit occurrence of pre-ignition. The spark plug includes: an insulator in which an axial hole extending in an axial line direction is formed; a center electrode disposed at a front end in the axial line direction of the axial hole and having a front end portion that protrudes from a front side of the axial hole; a tubular metal shell holding the insulator; and a ground electrode having one end portion that is fixed to a through hole provided in the metal shell, the ground electrode further having another end portion that forms a discharge gap between the other end portion and the front end portion of the center electrode. The through hole extends toward the front side in the axial line direction, in a direction from an outer peripheral surface toward an inner peripheral surface of the metal shell. The one end portion is located on a rear side relative to the other end portion in the axial line direction.

This spark plug inhibits excessive increase in the temperature of a ground electrode to inhibit occurrence of pre-ignition. The spark plug includes: an insulator in which an axial hole extending in an axial line direction is formed; a center electrode disposed at a front end in the axial line direction of the axial hole and having a front end portion that protrudes from a front side of the axial hole; a tubular metal shell holding the insulator; and a ground electrode having one end portion that is fixed to a through hole provided in the metal shell, the ground electrode further having another end portion that forms a discharge gap between the other end portion and the front end portion of the center electrode. The through hole extends toward the front side in the axial line direction, in a direction from an outer peripheral surface toward an inner peripheral surface of the metal shell. The one end portion is located on a rear side relative to the other end portion in the axial line direction.

A spark plug having a center electrode that includes a columnar noble metal tip at one end thereof, and a ground electrode that forms a spark gap between the ground electrode and a circular discharge surface of the tip. In the tip, a mass % of Pt is largest and a content percentage of Ni is more than or equal to 0 mass % and less than or equal to 40 mass %. In each of both a cross-section of the noble metal tip parallel to the discharge surface and a cross-section of the tip perpendicular to the discharge surface, particles each having an aspect ratio of more than or equal to 1 and less than or equal to 10 occupy more than or equal to 70% of observed particles in an area extending from an outline of the cross-section by a distance of 10% of a diameter of the discharge surface.

A spark plug having a center electrode that includes a columnar noble metal tip at one end thereof, and a ground electrode that forms a spark gap between the ground electrode and a circular discharge surface of the tip. In the tip, a mass % of Pt is largest and a content percentage of Ni is more than or equal to 0 mass % and less than or equal to 40 mass %. In each of both a cross-section of the noble metal tip parallel to the discharge surface and a cross-section of the tip perpendicular to the discharge surface, particles each having an aspect ratio of more than or equal to 1 and less than or equal to 10 occupy more than or equal to 70% of observed particles in an area extending from an outline of the cross-section by a distance of 10% of a diameter of the discharge surface.

A spark plug includes a housing, a porcelain insulator, a center electrode, a ground electrode, and a prechamber-defining portion. The prechamber-defining portion has a prechamber formed therein. The prechamber-defining portion has a plurality of spray holes. At least one of the spray holes is an upstream spray hole which is arranged upstream of a plug center axis in a gas flow within a main combustion chamber and designed such that and an angle which an extension in an opening direction makes with an inner wall surface of the prechamber is selected to be larger than 90°. A spark gap is formed upstream of a plug center axis in the gas flow within the main combustion chamber.

A spark plug includes a housing, a porcelain insulator, a center electrode, a ground electrode, and a prechamber-defining portion. The prechamber-defining portion has a prechamber formed therein. The prechamber-defining portion has a plurality of spray holes. At least one of the spray holes is an upstream spray hole which is arranged upstream of a plug center axis in a gas flow within a main combustion chamber and designed such that and an angle which an extension in an opening direction makes with an inner wall surface of the prechamber is selected to be larger than 90°. A spark gap is formed upstream of a plug center axis in the gas flow within the main combustion chamber.

A spark plug includes a first discharge chip and a second discharge chip facing the first discharge chip to define a spark gap therebetween. The spark gap has a size or distance between the first and second discharge chips which is 0.23 mm or more and 0.6 mm or less. At least one of the first and second discharge chips is made from material mainly containing iridium or platinum and an additive of tantalum of 0.5 Wt % to 5.0 Wt %. This minimizes a risk that a portion of the first or second discharge chip may be separated or such a separated portion may be redeposited on the first or second discharge portion.

A spark-ignited reciprocating piston internal combustion engine may include a pre-chamber ignition system which is arranged in the cylinder head of the reciprocating piston internal combustion engine and in which an ignition device is arranged, comprising an ignition electrode in a housing, said ignition electrode protruding into a cavity of the pre-chamber ignition system. The cavity is covered from the combustion chamber of the reciprocating piston internal combustion engine by a cover, and the cover has at least one first opening which connects the cavity and the combustion chamber together so as to conduct gas. A metal transverse brace with at least one second opening, which connects opposite sides of the housing together, is arranged in the cavity in the region of the ignition electrode, wherein the metal transverse brace is made of a first metal material in a central region and a second metal material in a region contacting the housing.

A spark plug includes a metallic shell which holds a center electrode in an insulated condition, and a ground electrode is held in a penetration hole of the metallic shell. The penetration hole includes a circular counterbore portion, and a penetrating portion extending from the counterbore portion to an inner circumferential surface of the metallic shell. The ground electrode includes a fixing portion which is fixed to the counterbore portion, and an extension portion extending from the fixing portion. The extension portion has a flat surface which faces a forward end surface of the center electrode in the axial direction. The penetrating portion restricts the extension portion such that the flat surface of the extension portion faces toward a rear end side in the axial direction.