Fundamental Study on Effects of Residual Fuel Droplets on Flame Propagation in SI Engines

Experimental studies on flame propagation in fuel droplet-vapor-air mixtures were performed with a constant-volume chamber. Monodispersed and mono-sized fuel droplet clouds were used for experiments as a simple model of residual fuel droplets in a gasoline SI engine. The results show that, on the fuel-lean side, the flame speed and the maximum burning pressure of the fine droplet-vapor-air mixtures exceed those of the completely gaseous premixtures with the same total equivalence ratio. It was found that the evaporation rate of fuel droplets and the slip velocity between fuel droplets and unburned gas play an important role in determining the flame speed.