A corona spark plug system for spark-ignition engines

A new spark plug design in which the spark discharge is preceded by a corona wind is studied. The plug electrodes are designed so as to produce a corona wind whenever a high voltage (but lower than the breakdown voltage) is applied. The corona wind carries the ignited mixture away from both electrodes in order to reduce heat loss from the ignited mixture by heat transfer to the electrodes. The new system facilitates the ignition of lean mixtures, and provides an efficient means for increasing ignition efficiency, improving cyclic variation and reducing HC emission. High speed photographs of the ignition process of the new system in a constant volume bomb have shown that the ignited mixture is carried out from the electrode gap at a speed of 5 m/s; a speed which has been found to be optimal in other studies. Preliminary studies with a conventional 4-cylinder engine have clearly shown promising results.