Fuel Droplets inside the Cylinder of a Spark Ignition Engine with Axial Stratification

An axially stratified, fuel-air mixture can be produced in an engine cylinder using inlet-port fuel injection and air swirl. Past work has shown that stratification decreased as fuel volatility decreased. This paper shows that the reason for this relationship is the entry of fuel droplets into the cylinder prior to the start of fuel injection. This phenomenon, presumably caused by wall wetting in the inlet port, increased the mixing of the fuel and air which reduced the stratification. Also, it was shown that (a) droplets were not uniformly distributed throughout the cylinder, (b) droplets were completely vaporized prior to ignition, and (c) the largest droplets entered the cylinder under low inlet flow conditions.