Spark plug has first and second electrodes. First electrode has tip principally made of noble metal and base material principally made of Ni. The tip is joined to the base material through fusion portion. Second electrode faces discharge surface of the tip. The fusion portion has overlap portion where first interface between the tip and the fusion portion and second interface between the base material and the fusion portion overlap in first direction perpendicular to the discharge surface. When viewing cross section which passes through a center of gravity of the overlap portion projected onto virtual surface parallel to the discharge surface and is perpendicular to the discharge surface, noble metal content is greater than 50 mass % at one end portion of the overlap portion in second direction extending along the discharge surface, and Ni content is greater than 50 mass % at the other end portion of the overlap portion.

Spark plug has first and second electrodes. First electrode has tip principally made of noble metal and base material principally made of Ni. The tip is joined to the base material through fusion portion. Second electrode faces discharge surface of the tip. The fusion portion has overlap portion where first interface between the tip and the fusion portion and second interface between the base material and the fusion portion overlap in first direction perpendicular to the discharge surface. When viewing cross section which passes through a center of gravity of the overlap portion projected onto virtual surface parallel to the discharge surface and is perpendicular to the discharge surface, noble metal content is greater than 50 mass % at one end portion of the overlap portion in second direction extending along the discharge surface, and Ni content is greater than 50 mass % at the other end portion of the overlap portion.

A plasma assisted spark ignition system includes an ignitor and a power supply. The first ignitor includes: a casing having a first end, a second end that forms a first electrode, and a longitudinally extending passage, a second electrode which protrudes longitudinally outward from an opening at the second end of the casing and laterally spaced inwardly to form a spark gap, and an electrical insulator (dielectric) surrounding a portion of the second electrode, and which has a terminus that is at least closely spaced to an interior surface of the end of the casing. The power supply supplies a plurality of voltage pulses to the ignitor per ignition event to generate a flash over on the dielectric. Subsequent pulses in an ignition event may be at lower amplitude than an initial pulse in the ignition event. Pulses may, for example, have a duration on the order of a nanosecond.

There is provided a spark plug for an internal combustion engine with a simple configuration capable of ensuring stable ignitability regardless of mounting posture to the internal combustion engine. The spark plug includes a housing, an insulator, a center electrode, and a ground electrode. The ground electrode includes an erecting part that is erected from a tip part of the housing to a tip side and an inclined part that is bent from the tip of the erecting part to the center electrode side to extend obliquely toward a tip side. An end edge of the ground electrode on an opposite side to the housing side is a tip of the inclined part. The erecting part satisfies w/t1, w1.9 mm, and t2.3 mm, where t is a dimension in an alignment direction of the erecting part and the center electrode, and w is a dimension in a width direction orthogonal to each of the alignment direction and a plug axial direction. An inclination angle of the inclined part with respect to the plug axial direction satisfies 3060.

An internal combustion engine includes a fuel injection system including a fuel injector disposed to inject fuel into the combustion chamber, and a plasma ignition system including a groundless barrier discharge plasma igniter that protrudes into the combustion chamber. A controller includes an executable instruction set to control the engine in a compression-ignition mode when the output torque request indicates a low load condition, including instructions to control a variable valve actuation system and control the plasma ignition system to execute plasma discharge events subsequent to controlling the fuel injection system to execute a fuel injection event, wherein the fuel injection event achieves a cylinder charge having a lean air/fuel ratio.

An ignition plug for an internal combustion engine includes an electrode protrusion that protrudes from an electrode base material of a ground electrode toward a discharge gap. The electrode protrusion has a base part that is integrated with the electrode base material and a cover part that is joined to the base part and faces the discharge gap. The base part has an end surface facing a protrusion direction of the base part and a side peripheral surface. An outer edge of the end surface has a curved surface. The cover part is formed from a precious metal or a precious metal alloy having a lower linear expansion coefficient than that of a material for forming the base part and covers at least a part of the side peripheral surface and the end surface of the base part. While the ignition plug is attached to an internal combustion engine and the electrode protrusion is heated and then cooled, a projection is formed on an outer surface of a portion covering the side peripheral surface of the base part.

A spark plug for an internal combustion engine includes a cylindrical housing, a cylindrical insulator, a center electrode, and a ground electrode. The ground electrode includes an upright part and an inclined part. The upright part is a portion vertically provided on a tip end part of the housing to a tip end side. The inclined part is a portion that is bent from the tip of the upright part toward the center electrode side, and is extended toward an oblique tip end side. The inclined part has a ground end face, an opposed face, and a corner curved face. The corner curved face is a face that smoothly connects the ground end face and the opposed face. The corner curved face has a curved shape. The curvature radius R of the corner curved face satisfies 0.3 mmR0.7 mm. The inclination angle of the inclined part with respect to a plug axial direction (Z) satisfies 3060.

An ignition control system includes a spark plug including a cylindrical ground electrode, a cylindrical insulator having a protruding portion held inside the ground electrode and protruding toward a tip side the spark plug relative to the ground electrode, and a center electrode held inside the insulator and exposed from the insulator, an ignition coil including a primary coil and a secondary coil, and a primary current control unit performing creeping discharge control for generating a creeping discharge along a surface of the insulator, and air discharge transition control for stopping the creeping discharge occurring in the spark plug after the creeping discharge control is performed, and cutting off primary current after a discharge stop period ends, in one combustion cycle of the engine.

In order to test a semiconductor spark plug, a test method comprises a step consisting of depositing water on the head of the spark plug, between the two electrodes of same, so that the water forms a water meniscus covering the semiconductor element of the head, a step consisting of applying, between the first terminal and the second terminal of the spark plug, a voltage equal to the operating voltage of the spark plug, a step consisting of identifying at least a first characteristic of electric arcs induced between the electrodes during the application of the voltage, and a step consisting of determining the operational or defective character of the spark plug according to the first characteristic of the electric arcs. This test method is particularly reliable and does not require constraining provisions in order to ensure the safety of the operators implementing the method.

In order to test a semiconductor spark plug, a test method comprises a step consisting of depositing water on the head of the spark plug, between the two electrodes of same, so that the water forms a water meniscus covering the semiconductor element of the head, a step consisting of applying, between the first terminal and the second terminal of the spark plug, a voltage equal to the operating voltage of the spark plug, a step consisting of identifying at least a first characteristic of electric arcs induced between the electrodes during the application of the voltage, and a step consisting of determining the operational or defective character of the spark plug according to the first characteristic of the electric arcs. This test method is particularly reliable and does not require constraining provisions in order to ensure the safety of the operators implementing the method.