Analysis of spray penetration and velocity dissipation for non-steady fuel injection

Abstract

The time histories of spray penetration and velocity for conditions corresponding to non-steady fuel injection in a piston-engine cylinder are described in detail. Regions of influence are established for numerous factors affecting the spray-tip velocity curve, including injection-system characteristics, aerodynamic drag, and in-cylinder air swirl. The necessity of excluding the initial region, which is dominated by injection-system characteristics, from a generalized correlation is shown. Based on extensive experimental data, a universal curve of velocity versus penetration is then developed for the time domain in which the spray-tip velocity is decreasing. For a power-law drag formulation, general relationships for velocity and penetration are developed for any velocity exponent, and current correlations from the literature are interpreted in terms of the resulting functions. The inadequacies of the mathematical forms of both current spray-penetration correlations and correlations based upon power-law drag are then illustrated, and guidelines for developing continuously-differentiable penetration relationships are presented. Utilizing multi-term functions to describe the universal curve, an internally consistent set of relationships for spray-tip penetration and velocity is derived.