Ignition device

An ignition device for an internal combustion engine comprising:

• a columnar center electrode;
• a center dielectric having a shape of a bottomed cylinder and covering the center electrode;
• a housing accommodating therein the center dielectric;
• a ground electrode disposed at a distal end of the housing so as to form a discharge space with the center dielectric;
• and
• a high energy source for applying an AC voltage of a predetermined frequency between the center electrode and the ground electrode so that an AC electric field is formed between the center electrode covered by the center dielectric and the ground electrode to generate a streamer discharge for igniting an air-fuel mixture introduced into a combustion chamber of the internal combustion engine;
• wherein
• a distal end portion of the center electrode covered by the center dielectric projects beyond a distal end of the ground electrode to an inside of the combustion chamber to make a dielectric discharge portion exposed in the discharge space,
• the ground electrode is formed with an airflow inlet and an airflow outlet at lateral portions thereof for enabling an in-cylinder airflow flowing in the combustion chamber to be introduced into the discharge space, and
• a distal end portion of the ground electrode projects radially inward to make a ground electrode projecting portion so that a discharge space narrow portion is formed with the dielectric discharge portion.