Charge Motion and Mixture Formation Analysis of a DISI Engine Based on an Adaptive Parallel Mesh Approach

Mesh generation is frequently one of the most labor-intensive aspects of in-cylinder engine simulation with computational fluid dynamics (CFD). This expense makes parameter studies, such like engine geometry, valve timing or injection timing, a particularly challenging endeavor. The present paper introduces a CFD approach for the simulation of the in-cylinder processes of an internal combustion engine that minimizes user-required meshing effort and can handle almost unlimited boundary motion. The adaptation is fully automated and avoids the use of target meshes and global solution remapping. The intention of the approach is to use CFD for numerous parameter variations involving combustion system variabilities. Therefore, an open source base is chosen to avoid limitations of individual simulations due to a finite number of commercial licenses.

The approach is used here for the simulation of a modern direct injection spark igniton (DISI) engine. It enables a fast setup process for individual simulations and does not require a manual remeshing if geometric boundary conditions are changed. Here, the meshing approach shows its advantage of adaptive representation without additional user interaction. Simulations of the gas exchange, mixture preparation and combustion are conducted. The results of the presented simulations are compared against test-bench measurements for validation purposes. Furthermore, different injection strategies are investigated to analyse the mixture formation as an interaction of injection and charge motion. The results are also compared against representative CFD simulations with a commercial CFD code.