Plasma jet spark plug
A plasma jet plug has a cavity defined by a surface of a center electrode, an inner surface of an insulator, and a surface of a ground electrode. When a volume of a portion of the cavity on a front side of a front portion of the center electrode is a first volume V 1 and a volume of a portion of the cavity on a rear side of the front end of the center electrode is a second volume V 2 , the following expression is satisfied: V 1/ V 2≧0.20.
1. A plasma jet plug comprising:
a tubular insulator having an inner surface that defines an axial hole that extends along an axis;
a rod-shaped center electrode that is disposed in the axial hole of the insulator and extends along the axis;
a metallic shell disposed around an outer periphery of the insulator;
a ground electrode that is electrically connected to the metallic shell, said ground electrode having a through hole and being abutted on a front side of the insulator; and
a cavity that is defined by a surface of the center electrode, the inner surface of the insulator, and a surface of the ground electrode facing a rear side of the insulator,
wherein an inner diameter of the through hole is smaller than an inner diameter of a portion of the insulator which abuts the ground electrode; and
wherein, a following expression is satisfied:
V 1 /V 2 ≧0.20, where a first volume V 1 is a volume of a portion of the cavity on the front side of a front end of the center electrode, and a second volume V 2 is a volume of a portion of the cavity on a rear side of the front end of the center electrode.
2. The plasma jet plug according to claim 1 ,
wherein the through hole has a maximum width that is smaller than or equal to 0.7 mm.
3. The plasma jet plug according to claim 1 ,
wherein the front end of the center electrode has a maximum width that is greater than or equal to 1.3 mm.
4. The plasma jet plug according to claim 1 , wherein the cavity includes;
a first portion provided at the front side of the front end of the center electrode, and
a second portion that is located on a rear side of the first portion and has a small diameter portion whose outer diameter is smaller than an inner diameter of the first portion.
5. The plasma jet plug according to claim 4 ,
wherein the second portion is located on a rear side of the front end of the center electrode.
6. The plasma jet plug according to claim 1 ,
wherein a following expression is satisfied:
V 1 /V 2 ≦0.62.
7. The plasma jet plug according to claim 2 ,
wherein the front end of the center electrode has a maximum width that is greater than or equal to 1.3 mm.
8. The plasma jet plug according to claim 2 , wherein the cavity includes;
a first portion provided at the front side of the center electrode, and
a second portion that is located on a rear side of the first portion and has an inner diameter smaller than an inner diameter of the first portion.
9. The plasma jet plug according to claim 3 , wherein the cavity includes;
a first portion provided at the front side of the center electrode, and
a second portion that is located on a rear side of the first portion and has an inner diameter smaller than an inner diameter of the first portion.
10. The plasma jet plug according to claim 2 ,
wherein a following expression is satisfied:
V 1 /V 2 ≦0.62.
11. The plasma jet plug according to claim 3 ,
wherein a following expression is satisfied:
V 1 /V 2 ≦0.62.
12. The plasma jet plug according to claim 4 ,
wherein a following expression is satisfied:
V 1 /V 2 ≦0.62.
13. The plasma jet plug according to claim 5 ,
wherein a following expression is satisfied:
V 1 /V 2 ≦0.62.
14. The plasma jet plug according to claim 4 , wherein the outer diameter of the second portion is defined by the inner surface of the insulator.