Evaluation of Spray Impingement Models in Multidimensional Simulation of High Speed Diesel Engines

Spray impingement on walls is an important physical process in modern DI Diesel engines as it greatly influences mixture formation, combustion process and exhaust emissions. The mixture preparation is, in fact, a crucial aspect for the correct operation of the engine as it significantly affects the combustion process. In this paper three models, among the available in literature, have been selected and implemented in the KIVA-3V code. Namely, the models by O’Rourke and Amsden (OA model) [1, 2], by Bai and Gosman (BG model) [3] and by Lee et al. (LR model) [4, 5] are compared in terms of performance and capability of representing the splash phenomenon. The model capabilities are firstly tested comparing the numerical results with four sets of experimental literature data, characterized by low injection pressures. The high injection pressures of modern Diesel engines result in droplets velocities emerging from the nozzle greater than 300 m/s. To better understand the models behavior with high injection pressures, an experimental investigation of the splash behavior of a Diesel spray emerging from a Common Rail (CR) injection apparatus, with injection pressures up to 120 MPa, is carried out. The impinging spray is lightened by a pulsed laser sheet generated from the second harmonic of a Nd - YAG laser. The images are acquired by a CCD camera at different times from the start of injection (SOI). A digital image processing software enables to extract the characteristic parameters of the impinging spray versus different operative conditions. The numerical data of the splash phenomenon, as predicted by modified versions of the proposed models are compared to the experimental ones. All the three models in their original formulation result to be inadequate to reproduce the splash phenomena. Nevertheless, after slight modifications and a proper updating phase, the BG and the LR models prove to show a good agreement with the experimental data.