A spark plug includes: a center electrode; an insulator having a through hole around a part of the center electrode; and a metal shell holding the insulator from an outer peripheral side thereof. The metal shell includes a shelf portion that projects radially inward. The insulator includes an engagement portion engaged with the shelf portion from the front side, and a front end portion at the front side with respect to a front end of the metal shell. The front end portion has an outer diameter larger than an inner diameter of the metal shell at the front side with respect to the shelf portion. The front end portion of the insulator has a diameter-enlarged portion at which a diameter of the through hole increases and which is spaced apart from an outer peripheral surface of the center electrode.

An igniter, such as a corona igniter for an internal combustion engine, and a method of manufacturing the igniter, are provided. The igniter includes an insulator with enlarged upper and lower end regions extending axially beyond opposite ends of a constrained, reduced diameter region of a shell through passage. The enlarged lower end region of the insulator is disposed axially outwardly of a lower end of the shell. The insulator is hermetically sealed to the shell and is permanently fixed against being removed axially outwardly from the shell. The method can include conforming the shell to the contour of the insulator by plastically deforming the shell, or casting the shell about the insulator. Alternatively, separate pieces of metal can be disposed around the insulator to form the shell which is conformed to the insulator.

An igniter, such as a corona igniter for an internal combustion engine, and a method of manufacturing the igniter, are provided. The igniter includes an insulator with enlarged upper and lower end regions extending axially beyond opposite ends of a constrained, reduced diameter region of a shell through passage. The enlarged lower end region of the insulator is disposed axially outwardly of a lower end of the shell. The insulator is hermetically sealed to the shell and is permanently fixed against being removed axially outwardly from the shell. The method can include conforming the shell to the contour of the insulator by plastically deforming the shell, or casting the shell about the insulator. Alternatively, separate pieces of metal can be disposed around the insulator to form the shell which is conformed to the insulator.

A corona comprises a central electrode surrounded by an insulator, which is surrounded by a conductive component. The conductive component includes a shell and an intermediate part both formed of an electrically conductive material. The intermediate part is a layer of metal which brazes the insulator to the shell. An outer surface of the insulator presents a lower ledge, and the layer of metal can be applied to the insulator above the lower ledge prior to or after inserting the insulator into the shell. The conductive inner diameter is less than an insulator outer diameter directly below the lower ledge such the insulator thickness increases toward the electrode firing end. The insulator outer diameter is also typically less than the shell inner diameter so that the corona igniter can be forward-assembled.

A corona comprises a central electrode surrounded by an insulator, which is surrounded by a conductive component. The conductive component includes a shell and an intermediate part both formed of an electrically conductive material. The intermediate part is a layer of metal which brazes the insulator to the shell. An outer surface of the insulator presents a lower ledge, and the layer of metal can be applied to the insulator above the lower ledge prior to or after inserting the insulator into the shell. The conductive inner diameter is less than an insulator outer diameter directly below the lower ledge such the insulator thickness increases toward the electrode firing end. The insulator outer diameter is also typically less than the shell inner diameter so that the corona igniter can be forward-assembled.

An apparatus comprises a coaxial cavity resonator; a radio frequency power source coupled to the coaxial cavity resonator; a direct current power source coupled to the coaxial cavity resonator; a combustion process feedback module configured to sense a condition in a combustion environment by measuring a characteristic of the coaxial cavity resonator; and a controller configured to modulate operation of the coaxial cavity resonator based at least in part on combustion process feedback information from the combustion process feedback module.

In certain embodiments, a time-varying spark current ignition system can be applied to improve spark plug ignitability performance and durability as compared to conventional spark ignition systems. Two performance parameters of interest are spark plug life (durability) and spark plug ignitability. In certain embodiments, spark plug life can be extended by applying a spark current amplitude as low as possible without causing quenching of the flame kernel while it is traveling within an electrode gap and/or by applying spark current of a long enough duration to allow the spark/flame kernel to clear a spark plug gap. In certain embodiments, ignitability can be improved by applying a high enough spark current amplitude to sustain the flame kernel once outside the spark plug gap and/or by applying a spark current for long enough to sustain the flame kernel once outside the spark plug gap.

In certain embodiments, a time-varying spark current ignition system can be applied to improve spark plug ignitability performance and durability as compared to conventional spark ignition systems. Two performance parameters of interest are spark plug life (durability) and spark plug ignitability. In certain embodiments, spark plug life can be extended by applying a spark current amplitude as low as possible without causing quenching of the flame kernel while it is traveling within an electrode gap and/or by applying spark current of a long enough duration to allow the spark/flame kernel to clear a spark plug gap. In certain embodiments, ignitability can be improved by applying a high enough spark current amplitude to sustain the flame kernel once outside the spark plug gap and/or by applying a spark current for long enough to sustain the flame kernel once outside the spark plug gap.

In an ignition plug, since a ground electrode is formed in a thin-rod-shape or a mesh-like shape, sufficiently strong radicals are locally generated by a barrier discharge, an anti-inflammation effect by the electrode is small, and the growth of a flame is hardly hindered. Furthermore, by making the thickness dimension of a second dielectric facing a discharge region uniform, the barrier discharge is spread over the surface of the second dielectric, the generation of the radicals is maintained, and combustibility after ignition is promoted. Furthermore, because an end portion of a high voltage electrode and a ground electrode are disposed to face each other within a combustion chamber, a fuel gas introduced into the combustion chamber is liable to flow into the discharge region, and is easily ignited by the radicals generated due to the discharge.

An ignition device for an extraneously igniting combustion piston engine with an ignition chamber located between a cylinder head and a piston, wherein the cylinder head has an end surface which defines the ignition chamber and which is at least partially formed as a cylinder head electrode, and wherein an ignition chamber electrode is disposed within the ignition chamber and forms an ignition gap with the cylinder head electrode.