MIXTURE STRENGTH MEASUREMENTS IN THE COMBUSTION-CHAMBER OF SI ENGINE VIA RAYLEIGH-SCATTERING - (ENSEMBLE-AVERAGED MEAN CONCENTRATION AND CYCLIC VARIATION OF TEMPORAL MEAN CONCENTRATION 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 mean concentration an d the cyclic variation of temporal mean concentration. The results sho w that both the ensemble-averaged mean concentration and the cyclic va riation of temporal mean concentration increase and reach a peak, afte r which they decrease during the intake and compression strokes. Moreo ver, they are strongly affected by air-fuel ratio, engine speed, injec tion duration and injection timing.