This spark plug includes a cap portion covering a center electrode and an end of a ground electrode from a front side. In a cross section including an axial line, where a pitch of an external thread of a metal shell is X (mm), an axial-line-direction distance between a crest of a rear-end ridge of a full thread portion of an external thread and a rear end of a contact portion of an insulator with which the metal shell contacts directly or via another member is A (mm), an axial-line-direction distance between the rear end of the contact portion and a front end of the insulator is B (mm), and an axial-line-direction distance between the rear end of the contact portion and a seating surface of the metal shell is C (mm), 0<A<4×, B≤15, and C≤3.6 are satisfied.

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.

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.

A spark plug includes a central electrode member and an outer electrode member. The central electrode member includes a central base and a plurality of electrode prongs extending in an axial direction from the central base. The outer electrode member surrounds the central electrode member. The outer electrode member includes a wall that is radially spaced from the plurality of electrode prongs to allow a series of electric arcs to form between the wall and the plurality of electrode prongs. The outer electrode member and the central electrode member are sized and positioned relative to one another such that a first rate of wear of the outer electrode member, along a longitudinal axis of the spark plug, is substantially equal to a second rate of wear of the central electrode member along the longitudinal axis.

A spark plug includes a central electrode member and an outer electrode member. The central electrode member includes a central base and a plurality of electrode prongs extending in an axial direction from the central base. The outer electrode member surrounds the central electrode member. The outer electrode member includes a wall that is radially spaced from the plurality of electrode prongs to allow a series of electric arcs to form between the wall and the plurality of electrode prongs. The outer electrode member and the central electrode member are sized and positioned relative to one another such that a first rate of wear of the outer electrode member, along a longitudinal axis of the spark plug, is substantially equal to a second rate of wear of the central electrode member along the longitudinal axis.

A spark plug includes a central electrode member and an outer electrode member. The central electrode member includes a central base and a plurality of electrode prongs extending in an axial direction from the central base. The outer electrode member surrounds the central electrode member. The outer electrode member includes a wall that is radially spaced from the plurality of electrode prongs to allow a series of electric arcs to form between the wall and the plurality of electrode prongs. The outer electrode member and the central electrode member are sized and positioned relative to one another such that a first rate of wear of the outer electrode member, along a longitudinal axis of the spark plug, is substantially equal to a second rate of wear of the central electrode member along the longitudinal axis.

A spark plug includes a central electrode member and an outer electrode member. The central electrode member includes a central base and a plurality of electrode prongs extending in an axial direction from the central base. The outer electrode member surrounds the central electrode member. The outer electrode member includes a wall that is radially spaced from the plurality of electrode prongs to allow a series of electric arcs to form between the wall and the plurality of electrode prongs. The outer electrode member and the central electrode member are sized and positioned relative to one another such that a first rate of wear of the outer electrode member, along a longitudinal axis of the spark plug, is substantially equal to a second rate of wear of the central electrode member along the longitudinal axis.

Disclosed is an ignition apparatus for an internal combustion engine. The ignition apparatus includes a spark plug, an ignition coil and a controller. The spark plug has an auxiliary combustion chamber in which a discharge gap is arranged. The ignition coil is configured to apply a voltage to the spark plug. The controller is configured to perform a multiple-discharge mode in which discharge is generated at least twice, with a discharge pause period intervening therebetween, across the discharge gap within a period from a compression stroke to an expansion stroke of the internal combustion engine.

A pre-chamber spark plug for igniting a fuel-air mixture in an internal combustion engine, in particular a gasoline engine, comprises a spark plug body (1) having a pre-chamber housing (2) and a cap (4) which at least partially closes the pre-chamber (3), and further comprises a ground electrode (11) in the spark plug body (1) as well as a central electrode (7) which protrudes into the pre-chamber (3); the ground electrode (11) has an annular shape and, on the inner surface thereof, includes at least one ignition area (17) designed as a cam (16) as well as a radially inward extending protrusion (18) as a baffle (19).

A pre-chamber spark plug for igniting a fuel-air mixture in an internal combustion engine, in particular a gasoline engine, comprises a spark plug body (1) having a pre-chamber housing (2) and a cap (4) which at least partially closes the pre-chamber (3), and further comprises a ground electrode (11) in the spark plug body (1) as well as a central electrode (7) which protrudes into the pre-chamber (3); the ground electrode (11) has an annular shape and, on the inner surface thereof, includes at least one ignition area (17) designed as a cam (16) as well as a radially inward extending protrusion (18) as a baffle (19).