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Preliminary test results are presented for an S.I. engine which used a focused laser beam and conventional spark ignition as ignition sources. The results show that for a steady running single-cylinder engine with MBT spark timing and fixed throttle position, engine performance and efficiency are improved, extension of the lean limit of operation by 5 air-fuel ratios is possible, and more NO is produced with laser ignition. The effects of EGR are also examined. The CO and HC emissions are essentially the same. With the laser, the spark location was found to have little effect on performance except when it was moved near the combustion chamber wall. The minimum laser pulse energy required for steady engine operation seems to be dictated by the minimum energy required to achieve breakdown of the laser pulse in air at the same pressure.

Formation of pulsed plasma jets, or puffs, was examined using several visualization techniques. Self-light streak photography was first employed to record salient global features of the development and structure of the jet. This provided information on the motion of the luminous gas particles in its core, revealing that plasma jets can have two distinct modes, being either totally subsonic or embodying a supersonic efflux manifested by the recorded streaks of Mach discs. At a fixed power pulse of electrical energy discharge in the plenum chamber, the outcome depends on the constriction imposed by an orifice at its outlet. Whereas the difference between the two types of jets was quite small, penetration in the subsonic case was found to be definitely larger than in supersonic.