Mixture Strength Measurements in the Combustion Chamber of SI Engine via Rayleigh Scattering. (Ensemble-Averaged Concentration Fluctuation and Cyclic Variation of Temporal Concentration Fluctuation near the Spark Plug).

Abstract

Laser Rayleigh scattering was applied for remote, nonintrusive point probing of the vapor concentration and its fluctuation near the spark plug of a motored spark ignition engine, which was caused by the intermittent injection of Freon-12 vapor into an intake port. The theoretical analysis showed that the instantaneous fuel vapor concentration can be split into three components : the ensemble-averaged mean concentration, the cyclic variation of temporal mean concentration and the temporal concentration fluctuation in a specific cycle. This paper concentrates on the measurements of the ensemble-averaged concentration fluctuation and the cyclic variation of temporal concentration fluctuation. The results show that the cyclic variation of temporal concentration fluctuation is too large to be neglected, and both the ensemble-averaged concentration fluctuation and the cyclic variation of temporal concentration fluctuation increase and reach a peak after which they decrease during the intake and compression strokes. They are strongly affected by air fuel-ratio, engine speed, injection duration and injection timing.