Lean Air-Fuel Ignition System Comparison in a Fast-Burn Engine

Ignition system variables investigated were: plug type, ignition energy, ignition power input, firing duration, and a plasma jet ignitor. Lean air-fuel ignition limits were determined for four different ignition system combinations. The ignition limit at a given A/F condition was determined of the peak cylinder pressure. The ignition limit of the long duration ignition system (40-60 crankangle degrees) used with a surface-air gap plug was found to have the greatest spark angle tolerance. The plasma jet ignition system had the leanest projected lean misfire limit. Adding capacitance to a conventional plug to enhance the initial discharge was found to increase the initial rate of burning, but had little effect on the ignition limit. All the high energy ignition systems had comparable ISFC values. The air-fuel ratio at which the minimum IFSC occurred, however, was observed to shift to a leaner operating condition as the burn rate of the mixture was enhanced by the ignition system.

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