MIXTURE STRENGTH MEASUREMENTS IN THE COMBUSTION-CHAMBER OF SI ENGINE VIA RAYLEIGH-SCATTERING - (ENSEMBLE-AVERAGED CONCENTRATION FLUCTUATIONAND CYCLIC VARIATION OF TEMPORAL CONCENTRATION FLUCTUATION NEAR THE SPARK PLUG)

Laser Rayleigh scattering was applied for remote, nonintrusive point p robing of the vapor concentration and its fluctuation near the spark p lug of a motored spark ignition engine, which was caused by the interm ittent injection of Freon-12 vapor into an intake port. The theoretica l analysis showed that the instantaneous fuel vapor concentration can be split into three components: the ensemble-averaged mean concentrati on, the cyclic variation of temporal mean concentration and the tempor al concentration fluctuation in a specific cycle. This paper concentra tes on the measurements of the ensemble-averaged concentration fluctua tion and the cyclic variation of temporal concentration fluctuation. T he results show that the cyclic variation of temporal concentration fl uctuation is too large to be neglected, and both the ensemble-averaged concentration fluctuation and the cyclic variation of temporal concen tration fluctuation increase and reach a peak after which they decreas e during the intake and compression strokes. They are strongly affecte d by air fuel-ratio, engine speed, injection duration and injection ti ming.