sucahyo wrote:
Many thanks for the information. It is weird that misfire happen. I thought plug with many alternative spark path will have no more missfire. I have sanded an aftermarket three leg spark plug and have satisfying result. Maybe a halo around center electrode is better.
The best design I have found for plasma is a plug that has no metal above the center electrode. Just the center electrode alone with a large space between it and the ground side seems to build large volumes of plasma. Anything above the center electrode seems to hinder plasma production when it is viewed at high speed. The camera footage shows plasma develop as the spark makes contact between the center electrode and the plug body, then a plasma stream develops and builds to it's maximum. If there is something above the center electrode the plasma reaches that point and hits it, when this happens it tries to push around it, but since the J-electrode is a ground point it's like it's hitting a brick wall and cannot develop the plasma ball further.
P.S. The ball electrode design had major problems in that it would vibrate under combustion and eventually the ball would break off and fall into the cylinder until it finally got around the exhaust valve. The plugs also developed fractures in the ceramic surrounding the center stud that the ball is connected to. When the ball vibrates it cracks the ceramic and causes pieces of ceramic to fall into the cylinder until they get pushed out the exhaust port. This problem occurred with the latest design that had a larger center ball electrode.
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