One example provides a spark plug having a center electrode including at least one of a first material and a second material, the second material having a hardness rating greater than a hardness rating of the first material. The center electrode includes a region of first material disposed beyond an end surface of an insulative nose toward a firing end. The center electrode includes an electrode head, at least a portion of the electrode head disposed beyond the end surface of the insulative nose toward the firing end and having a cross-sectional area perpendicular to an axial centerline greater than a cross-sectional area of the end surface of the insulative nose. A shield element of the second material covers exposed surfaces of the region of first material disposed beyond the end surface of the insulative nose. An electrode wire extends from the electrode head into a central bore.

One example provides a spark plug having a center electrode including at least one of a first material and a second material, the second material having a hardness rating greater than a hardness rating of the first material. The center electrode includes a region of first material disposed beyond an end surface of an insulative nose toward a firing end. The center electrode includes an electrode head, at least a portion of the electrode head disposed beyond the end surface of the insulative nose toward the firing end and having a cross-sectional area perpendicular to an axial centerline greater than a cross-sectional area of the end surface of the insulative nose. A shield element of the second material covers exposed surfaces of the region of first material disposed beyond the end surface of the insulative nose. An electrode wire extends from the electrode head into a central bore.

A spark plug has an insulator having a through hole formed along an axial direction, a center electrode which is partially inserted into a portion of the through hole on a forward end side in the axial direction, and a glass seal portion which is in contact with the insulator and the center electrode within the through hole, in which the glass seal portion contains glass and an electrically conductive substance. The glass contains an Si component and a B component in a total amount of 50 mass % or more, as reduced to SiO.sub.2 and B.sub.2O.sub.3, a Zn component in an amount of 20 mass % to 35 mass % as reduced to ZnO, and an alkali metal component. The glass contains, as the alkali metal component, an Na component in an amount less than 1 mass % as reduced to Na.sub.2O.

A spark plug has an insulator having a through hole formed along an axial direction, a center electrode which is partially inserted into a portion of the through hole on a forward end side in the axial direction, and a glass seal portion which is in contact with the insulator and the center electrode within the through hole, in which the glass seal portion contains glass and an electrically conductive substance. The glass contains an Si component and a B component in a total amount of 50 mass % or more, as reduced to SiO.sub.2 and B.sub.2O.sub.3, a Zn component in an amount of 20 mass % to 35 mass % as reduced to ZnO, and an alkali metal component. The glass contains, as the alkali metal component, an Na component in an amount less than 1 mass % as reduced to Na.sub.2O.

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.

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 wire includes a boot of electrically insulative material defining a central bore configured to receive a spark plug, an electrical connector disposed in the central bore and configured to connect with the spark plug, and a cylindrical heat shield circumscribing the boot. The heat shield has retaining features extending past a distal end of the boot and configured to radially flex to engage with a hex of the spark plug to increase a retaining force of the spark-plug wire to the spark plug.

A spark-plug wire includes a boot of electrically insulative material defining a central bore configured to receive a spark plug, an electrical connector disposed in the central bore and configured to connect with the spark plug, and a cylindrical heat shield circumscribing the boot. The heat shield has retaining features extending past a distal end of the boot and configured to radially flex to engage with a hex of the spark plug to increase a retaining force of the spark-plug wire to the spark plug.

A spark plug has an insulator having a through hole formed along an axial direction, a center electrode which is partially inserted into a portion of the through hole on a forward end side in the axial direction, and a glass seal portion which is in contact with the insulator and the center electrode within the through hole, in which the glass seal portion contains glass and an electrically conductive substance. The glass contains an Si component and a B component in a total amount of 50 mass % or more, as reduced to SiO.sub.2 and B.sub.2O.sub.3, a Zn component in an amount of 20 mass % to 35 mass % as reduced to ZnO, and an alkali metal component. The glass contains, as the alkali metal component, an Na component in an amount less than 1 mass % as reduced to Na.sub.2O.

A spark plug has an insulator having a through hole formed along an axial direction, a center electrode which is partially inserted into a portion of the through hole on a forward end side in the axial direction, and a glass seal portion which is in contact with the insulator and the center electrode within the through hole, in which the glass seal portion contains glass and an electrically conductive substance. The glass contains an Si component and a B component in a total amount of 50 mass % or more, as reduced to SiO.sub.2 and B.sub.2O.sub.3, a Zn component in an amount of 20 mass % to 35 mass % as reduced to ZnO, and an alkali metal component. The glass contains, as the alkali metal component, an Na component in an amount less than 1 mass % as reduced to Na.sub.2O.