Characterization of mixing enhancement in swirl-spray interactions in diesel engines

Swirl in diesel engines is known to be an important parameter that affects the mixing of fuel and air, heat release, emissions, and overall engine performance. In this study, a multidimensional model for flows, sprays, and combustion in engines is employed to study the interactions between swirl and the fuel spray in a diesel engine. It is generally believed that swirl enhances mixing in a diesel engine. Previous studies have suggested that there may be an optimal level of swirl at which the mixing in the chamber is maximized for a given set of engine operating conditions. This optimal level may result from a balance between increased jet surface area and utilization of air in the chamber. In this work, those trends are clarified through a detailed evaluation of the velocity flow patterns in the chamber and by relating such patterns to those published in the literature for jets in cross-flow. It is also shown that the optimal swirl ratio for enhanced mixing may be characterized by a nondimensional parameter expressed as a ratio of the jet momentum of the azimuthal momentum.