1992 Volume 35 Issue 4 Pages 616-623
An experimental study was conducted to determine the time histories of fuel 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 maximum, after which it decreased during the intake and compression strokes. The concentration fluctuation was largely affected by the air fuel ratio and the engine speed.