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Lean NOx traps are being extensively examined (Ref. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12) because they can be efficiently used to reduce the NOx emissions from port fuel injected and direct fuel injected spark ignited gasoline engines. A lean NOx trap (LNT) stores NOx during lean A/F engine operation. However, its storage capacity is limited and the LNT must be regenerated periodically by subjecting the LNT to momentary rich A/F operation for several seconds. The regeneration process releases the NOx that is chemically bonded to the washcoat and subsequently reduces it to N2 and O2. Fuel that contains a non-zero amount of sulfur will contaminate an LNT by significantly reducing its NOx storage capacity. Therefore, except for the case of a zero level of sulfur in the fuel, the LNT must be desulfated on a periodic basis. The desulfation process requires that the temperature of the LNT be raised to a temperature of about 650°C for several minutes.

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.