Numerical modeling of diesel spray wall impaction phenomena

Abstract

A model for diesel spray impaction on walls is presented that is based on experimental observations. The model, which is incorporated into a two-phase CFD code employing a discrete droplet model for the liquid spray and the implicit noniterative PISO algorithm for gas equations, is assessed against experiments for a number of test cases including normal or angled injection into a quiescent space or a cross-flowing gas. In most of the cases studied, the wall spray radius is reasonably well predicted, but the wall spray height is always underpredicted. In order to capture the dispersive nature of the wall spray that contributes to the wall spray height, the original drop-drop collision model of O'Rourke and Bracco is extended to allow for the effects of multicollisions between two drop parcels in a the thick spray. The extended collision model works well in two-dimensional cases but is not fully assessed in three-dimensional cases. The wall impaction model is also implemented in the three-dimensional EPISO engine code. Preliminary results on the simulation of diesel spray impingement in an actual engine suggests that the model is there also capable of producing reasonable wall sprays.