An experimental and analytical study of the spray characteristics of an intermittent air-assisted fuel injector

Abstract

Spray characteristics of an intermittent air-assisted fuel injector (AAFI) for a four-stroke gasoline direct-injection engine were investigated using a photographic imaging system. The spatial spray structures were acquired in terms of Sauter mean diameter (D-32) and liquid mass concentration. Air entrainment motion was observed just below the poppet valve. Influence of parameters such as ambient air density, supply pressure, and injected air-liquid mass ratio (ALR) was examined. D-32 varied from 9 to 30 mu m throughout all experimental conditions. The result exhibited a similar tendency to those from diesel injectors in spray tip penetration and atomization characteristics. An intermittent injection caused temporally nonuniform ALR through an infection period. Introducing a set of plausible assumptions, the influence of instantaneous ALR (IALR) on temporary atomization quality was assessed. It showed a comparable trend with that of ALR on D-32 of overall spray. The Best-fitting curve for drop size distributions of sprays from the AAFI appeared to be a log-Boltzman function. A simple analytical modeling was introduced for predicting mean drop diameters of the AAFI with respect to various operating parameters considered in this study. The model-based equation was found to fit experimental data with an error range comparable to the empirical correlation.