On the Modeling of a Spray Impingement Onto a Hot Surface

Abstract

The present investigation addresses the impingement of a spray onto a heated solid surface under crossflow conditions at low pressure injection - typical of port-injection engines - during cold start. The characteristics of the initial spray are established by employing an empirical procedure, which relies on a comprehensive set of free spray measurements. This computational study considers the presence of a crossflow moving perpendicularly to an interposed surface and the formation of a dynamic liquid film over the impingement wall. Both previous conditions are often neglected in numerical simulations, despite their importance on the final outcome. Distinct wall and crossflow temperatures are analyzed systematically to evaluate the influence of droplets evaporation on the final outcome of spray impingement, and, particularly, on the distribution of the thin liquid film over the surface. The present computational model already proved to deliver accurate predictions of the spray/wall interactions under different conditions. In this work, the conditions are extrapolated to a heated environment, which reproduce more adequately what is found in in-cylinder situations. The computational model is adapted to meet the new requirements and perform within the range of conditions for which it is now formulated. The analysis shows that higher temperatures lead to smaller impinging droplets, an increase in the number of depositing droplets but a decrease in the fraction of mass of particles contributing to the liquid film; and a more uniform distribution of the liquid layer over the surface.