Mixture Strength Measurements in the Combustion Chamber of SI Engine via Rayleigh Scattering : 4th Report, Concentration Fluctuation in a Motored Engine

Abstract

An experimental study was made to determine the time histories of vapor concentration and its fluctuation in the combustion chamber of a spark ignition engine. Laser Rayleigh scattering was applied for remote, nonintrusive, point probing of the vapor concentration in the combustion chamber, which was caused by the continuous injection of Freon-12 into an intake port. The conventional engine was modified to make the optical diagnostics accessible. The results showed that the concentration fluctuation consisted of a temporal concentration fluctuation in a specific cycle and a cyclic variation of the temporal mean concentration in this particular cycle, which could be separated and measured accurately by the present experimental apparatus. It was also found that the concentration fluctuation increased and reached a peak, after which it decreased during intake and compression strokes. The concentration fluctuation was largely affected by the air fuel ratio and engine speed.