An internal combustion engine is described and includes a combustion chamber formed by cooperation of a cylinder bore formed in a cylinder block, a cylinder head and a piston. A plasma ignition controller is electrically connected to a groundless barrier discharge plasma igniter that includes a tip portion disposed to protrude into the combustion chamber. A current sensor is disposed to monitor secondary current flow between the plasma ignition controller and the groundless barrier discharge plasma igniter. The plasma ignition controller is disposed to execute a plasma discharge event. A controller is disposed to monitor a magnitude of the secondary current flow via the current sensor during the plasma discharge event. The controller includes an instruction set executable to evaluate integrity of the groundless barrier discharge plasma igniter based upon the magnitude of the secondary current flow during the plasma discharge event.

An ignition device is provided, which can boost an electromagnetic wave supplied by a resonance structure, and cause a discharge by enhancing a potential difference between a discharge electrode and a ground electrode, and even though such a structure of the ignition device, a downsize and a thickness reduction, specifically, the thickness reduction can be achieved. On a main surface of a rectangular insulting substrate (2), an input electrode (3), a coupling electrode (4), a discharge electrode (6), and a ground electrode (7), are provided. The input electrode (3) is connected to an outside terminal on one shorter side. The coupling electrode (4) is capacity-coupled with the input electrode (3). The discharge electrode (6) is connected to the coupling electrode (4) on the other shorter side through a coupling line (5). The ground electrode (7) is, on both longer sides of the main surface of the rectangular insulating substrate (2), capacity-coupled with the coupling electrode (4) and capacity-coupled with the coupling line (5), and extended to the other shorter side. A resonance circuit includes a capacitor constituted by the capacity coupling and an inductor constituted by the coupling line (5). Thereby, the electromagnetic wave supplied from the outside terminal into the input electrode is resonated, a potential difference between the discharge electrode (6) and the ground electrode (7) is enhanced, and then, a discharge is caused.

A corona igniter (20) includes a metal shell (32) with a corona reducing lip (38) spaced from an insulator (26) and being free of sharp edges (40) to prevent arcing (42) in a rollover region and concentrate the electrical field at an electrode firing end (48). The corona reducing lip (38) includes lip outer surfaces (88) being round, convex, concave, or curving continuously with smooth transitions (90) therebetween. The corona reducing lip (38) includes lip outer surfaces (88) presenting spherical lip radii (r.sub.1) being at least 0.004 inches. The corona igniter (20) also includes shell inner surfaces (104) and insulator outer surfaces (75) facing one another being free of sharp edges (40).

A corona igniter (20) includes a metal shell (32) with a corona reducing lip (38) spaced from an insulator (26) and being free of sharp edges (40) to prevent arcing (42) in a rollover region and concentrate the electrical field at an electrode firing end (48). The corona reducing lip (38) includes lip outer surfaces (88) being round, convex, concave, or curving continuously with smooth transitions (90) therebetween. The corona reducing lip (38) includes lip outer surfaces (88) presenting spherical lip radii (r.sub.1) being at least 0.004 inches. The corona igniter (20) also includes shell inner surfaces (104) and insulator outer surfaces (75) facing one another being free of sharp edges (40).

A non-thermal equilibrium plasma ignition plug including a tubular metallic shell having an axial hole extending along an axial line, an insulator disposed in such a manner as to form a gap in cooperation with a wall surface of the axial hole at a forward end portion of the metallic shell, and a center electrode held at the center of the insulator, and generates nonequilibrium plasma in response to voltage applied thereto from a power supply. The insulator has a plurality of depressions or protrusions formed on a surface thereof which faces a discharge space therearound.

An ignition plug 10 comprises an elongate cylindrical body 12 of an electrically insulating material having a first end 12.1, a second end 12.2 opposite to the first end and a first face 14 at the first end. A first elongate electrode 16 having a first end 16.1 and a second end 16.2 extends longitudinally in the body. The first electrode terminates at the first end thereof a first distance d1 from the first end of the body in a direction towards the second end of the body. The body hence defines a blind bore 18 extending between the first end of the first electrode and the first end of the body. A second electrode is provided on an outer surface of the body and terminates at one of a) flush with the first face 14 of the body and b) a second distance d2 from the first end of the body in a direction towards the second end of the bod.

An ignition plug 10 comprises an elongate cylindrical body 12 of an electrically insulating material having a first end 12.1, a second end 12.2 opposite to the first end and a first face 14 at the first end. A first elongate electrode 16 having a first end 16.1 and a second end 16.2 extends longitudinally in the body. The first electrode terminates at the first end thereof a first distance d1 from the first end of the body in a direction towards the second end of the body. The body hence defines a blind bore 18 extending between the first end of the first electrode and the first end of the body. A second electrode is provided on an outer surface of the body and terminates at one of a) flush with the first face 14 of the body and b) a second distance d2 from the first end of the body in a direction towards the second end of the bod.

An igniter having at least two electrodes spaced from each other by an insulating member having a substantially continuous surface along a path between the electrodes. The electrodes extend substantially parallel to each other for a distance both above and below said surface. The insulating member has a channel (recess) for receiving at least a portion of a length of at least one of said electrodes below and to said surface of the insulating member. The surface of the insulating member may preferably be augmented with a conductivity enhancing agent. The insulating member and electrodes are configured so that an electric field between the electrodes at said surface does not have abrupt field intensity changes, whereby when a potential is applied to the electrodes sufficient to cause breakdown to occur between the electrodes, discharge occurs at said surface of the insulating member to define a plasma initiation region.

An igniter having at least two electrodes spaced from each other by an insulating member having a substantially continuous surface along a path between the electrodes. The electrodes extend substantially parallel to each other for a distance both above and below said surface. The insulating member has a channel (recess) for receiving at least a portion of a length of at least one of said electrodes below and to said surface of the insulating member. The surface of the insulating member may preferably be augmented with a conductivity enhancing agent. The insulating member and electrodes are configured so that an electric field between the electrodes at said surface does not have abrupt field intensity changes, whereby when a potential is applied to the electrodes sufficient to cause breakdown to occur between the electrodes, discharge occurs at said surface of the insulating member to define a plasma initiation region.

An igniter having at least two electrodes spaced from each other by an insulating member having a substantially continuous surface along a path between the electrodes. The electrodes extend substantially parallel to each other for a distance both above and below said surface. The insulating member has a channel (recess) for receiving at least a portion of a length of at least one of said electrodes below and to said surface of the insulating member. The surface of the insulating member may preferably be augmented with a conductivity enhancing agent. The insulating member and electrodes are configured so that an electric field between the electrodes at said surface does not have abrupt field intensity changes, whereby when a potential is applied to the electrodes sufficient to cause breakdown to occur between the electrodes, discharge occurs at said surface of the insulating member to define a plasma initiation region.