A dual spark plug may include: a metal body made of metal material, an insulating body provided inside of the metal body and made of an insulating material, a pair of central electrodes provided inside of the insulating body and electrically connected with an ignition coil, and a pair of ground electrodes respectively extended from both ends the metal body, and spaced apart from ends of the pair of central electrodes by a predetermined distance.

A dual spark plug may include: a metal body made of metal material, an insulating body provided inside of the metal body and made of an insulating material, a pair of central electrodes provided inside of the insulating body and electrically connected with an ignition coil, and a pair of ground electrodes respectively extended from both ends the metal body, and spaced apart from ends of the pair of central electrodes by a predetermined distance.

A spark plug includes a metal body member formed of a metal material, an insulating body member provided inside the metal body member and formed of an insulating material, a pair of central electrodes provided inside the insulating body member and having different polarities, and a ground electrode extending from the metal body member between a pair of central electrodes.

An apparatus for igniting a fuel mixture provides an ignition system for generating a high-voltage ignition voltage, a circuit device comprising a circuit for superimposing a high-frequency signal on to the high-voltage ignition voltage, a spark plug in an engine block, and a transmission element having a high-voltage conductor which is guided in an insulation element. The high-voltage conductor is used for transmitting the ignition voltage, onto which the high-frequency signal has been superimposed, to the spark plug. Further provided is an electrically conducting shielding element which surrounds the high-voltage conductor in an electromagnetically shielding manner at least along one portion of the longitudinal axis of the high-voltage conductor. The shielding element is connected in an electrically conducting manner to a ground potential of the circuit device and establishes a connection between the ground potential of the circuit device and a ground electrode of the spark plug.

A spark plug includes a metal body member formed of a metal material, an insulating body member provided inside the metal body member and formed of an insulating material, a pair of central electrodes provided inside the insulating body member and having different polarities, and a ground electrode extending from the metal body member between a pair of central electrodes.

In a metallic shell, cutting traces are formed on the inner circumferential surface of a trunk portion and the inner circumferential surface of an elongated leg portion. A first portion of a packing is in contact with and disposed between the rear end surface of a ledge portion of the metallic shell and the outer circumferential surface of a step portion of an insulator. A second portion of the packing is in contact with and disposed between the inner circumferential surface of a trunk portion of the metallic shell and the outer circumferential surface of a tubular portion of the insulator. A gap between the inner circumferential surface of the elongated leg portion and the outer circumferential surface of the leg portion is approximately uniform along the entire circumference.

A tip that contains a noble metal is joined to a joining surface of an electrode base material of a ground electrode via a welded portion. On cross-sections of the tip and the electrode base material in a longitudinal direction of the joining surface, the welded portion has a void above the joining surface, and a continuous distance of the welded portion on the joining surface is less than or equal to 0.5 mm, whereby thermal stress due to a difference in thermal expansion between the tip and the electrode base material can be reduced. A total of continuous distances of the welded portions on the joining surface, are 0.4 times to 0.8 times a length from an end of the tip to another end thereof, whereby joining strength of the welded portion can be assured. Peeling at the tip or falling-off of the tip due to thermal stress can be less likely to occur, whereby durability of the ground electrode can be improved.

A spark plug includes a tubular metallic shell, a tubular insulator held in the metallic shell and having an axial hole, a center electrode held at one end of the axial hole, a metallic terminal member held at the other end of the axial hole, and a resistor element disposed between the center electrode and the metallic terminal member in the axial hole and containing glass and an electrically conductive material. The resistor element has a first resistor layer disposed on the center electrode side and closest to the center electrode and containing titanium oxide, and a second resistor layer disposed on the metallic terminal member side in relation to the first resistor layer and whose titanium oxide content is lower than that of the first resistor layer. The titanium oxide content decreases from the center electrode side toward the metallic terminal member side.

A spark plug includes a tubular metallic shell, a tubular insulator held in the metallic shell and having an axial hole, a center electrode held at one end of the axial hole, a metallic terminal member held at the other end of the axial hole, and a resistor element disposed between the center electrode and the metallic terminal member in the axial hole and containing glass and an electrically conductive material. The resistor element has a first resistor layer disposed on the center electrode side and closest to the center electrode and containing titanium oxide, and a second resistor layer disposed on the metallic terminal member side in relation to the first resistor layer and whose titanium oxide content is lower than that of the first resistor layer. The titanium oxide content decreases from the center electrode side toward the metallic terminal member side.

A spark plug having an insulating body defining a longitudinal axis and including a base portion and an obstruction portion, a first electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the first electrode extending through the base portion of the insulating body, and a second electrode including a proximal portion, a sheathed portion and a distal portion, the sheathed portion of the second electrode extending through the base portion and the obstruction portion of the insulating body, wherein the obstruction portion axially extends beyond the distal portion of the first electrode.