Patent ID: 7714488

Claim:
A plasma jet spark plug, comprising: a center electrode having a center electrode front end; an insulator having an insulator front end and an axial bore accommodating and holding said center electrode, said axial bore extending to an opening portion at said insulator front end, said insulator front end defining an outer circumferential surface; a metal shell having a shell front end and receiving and partially surrounding said insulator; a ground electrode having a first ground electrode end bonded to said shell front end and a second ground electrode end disposed proximate said insulator front end and forming a spark discharge gap with said center electrode front end, said spark discharge gap including an aerial discharge gap in which a spark is discharged between said second ground electrode end and said outer circumferential surface of said insulator front end, said aerial discharge gap being located where a dielectric breakdown occurs between said second ground electrode end and said outer circumferential surface of said insulator front end; and a discharge cavity defined by an inner circumferential surface of a portion of said insulator, said inner circumferential surface extending from said center electrode front end to said opening portion; wherein plasma formed in said discharge cavity is shot out from said opening portion when a spark discharge occurs in said spark discharge gap.