Effect of Mesh Structure in the KIVA-4 Code with a Less Mesh Dependent Spray Model for DI Diesel Engine Simulations

Abstract

Two different types of mesh used for diesel combustion with the KIVA-4 code are compared. One is a well established conventional KIVA-3 type polar mesh. The other is a non-polar mesh with uniform size throughout the piston bowl so as to reduce the number of cells and to improve the quality of the cell shapes around the cylinder axis which can contain many fuel droplets that affect prediction accuracy and the computational time. This mesh is specialized for the KIVA-4 code which employs an unstructured mesh. To prevent dramatic changes in spray penetration caused by the difference in cell size between the two types of mesh, a recently developed spray model which reduces mesh dependency of the droplet behavior has been implemented. For the ignition and combustion models, the Shell model and characteristic time combustion (CTC) model are employed. The calculated spatial distribution of droplets, fuel vapor and soot are compared against high-speed in-cylinder imaging obtained from an optical access diesel engine. Heat release rate and computational time are also compared between the two types of mesh. The results show that the uniform-sized mesh reduces computational times significantly while maintaining almost the same prediction accuracy as the KIVA-3 type polar mesh.