| 摘要 |
PROBLEM TO BE SOLVED: To provide a plasma-jet spark plug in which structure of a through-hole of a ground electrode is regulated to allow plasma produced in a cavity to act on ignition to air-fuel mixture at a maximum, thereby improving ignitability, and its ignition system. SOLUTION: It is assumed that an imaginary conic surface of which cross section is shown by two-point chain line B has an opening angle of 60°directed to the front end side in the direction of an axial line O around the axial line O and passes through an opening end 11 of a cavity 60. In the case that the ground electrode 30 has a part (a projecting 35) projecting toward the inside rather than the second imaginary conic surface, if the part has the volume of less than 1.5mm<SP>3</SP>, it has a small volume contacting with the ground electrode 30 in the growth process of plasmas discharged from the cavity 30, so that quenching action is suppressed and deterioration of ignitability is prevented. COPYRIGHT: (C)2008,JPO&INPIT
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