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The characteristics of multiple spark ignition systems with respect to engine performance, emissions, lean misfire, and tolerance to exhaust gas recirculation (EGR) have been investigated using a carbureted single-cylinder engine. The results, which were compared to those obtained with a standard single spark ignition system, show that both lean misfire limit and EGR tolerance are extended with the multiple spark system. The amount of extension varies with engine load, being largest at the lighter loads studied. Engine power and emissions at non-misfiring conditions are the same with both ignition systems.

The development of a plasma jet ignition system based on use of plasma jet spark plugs is described. Particular attention is given to systems design for automotive application. Design data for plasma jet spark plugs are given. Tests on a 37.3 CID single cylinder engine with vapor tank fuel metering indicate that plasma jet ignition produces extension of the lean misfire limit, reduction of ignition delay and burn time, higher NO, and increased torque compared to conventional ignition. Discussion of the electrical power requirements of a plasma jet ignition system is given. Operating experience for a four cylinder 2.3L test vehicle is described.