Fuel Droplet Entrainment Studies for Minimization of Cold-Start Wall-Wetting

A method of investigating intake-port wall-wetting via liquid phase entrainment into the gas phase was developed using a single-cylinder port fuel injected CFR engine and externally-clocked single-component phase-doppler anemometry. The effects of fuel drop size, injection timing and valve timing on drop trajectory and entrainment into the gas phase flow were examined. It was found that entrainment of the liquid phase into the gas phase is a function of both drop size and of the local rate of change of the gas phase velocity vector. It is suggested that drop size distribution instead of a simple mean size should be considered when evaluating the performance of an injector. It appears that for a fuel drop to be entrained, small drops must be generated and introduced during a period of time with low gas phase velocity vector gradients.