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The preparation of the air-fuel mixture represents one of the most critical tasks in the definition of a clean and efficient SI engine. Therefore it becomes necessary to consolidate the numerical methods which are able to describe such a complex physical process. Within this context, the authors developed a CFD methodology into an open-source code to investigate the air-fuel mixture formation process in PFI engines. Attention is focused on moving mesh algorithms, Lagrangian spray modeling and spray-wall interaction modeling. Since moving grids are involved and the mesh quality during motion strongly influences the computed in-cylinder flow-field, a FEM-based automatic mesh motion solver combined with topological changes was adopted to preserve the grid quality in presence of high boundary deformations like the interaction between the piston bowl and the valves during the valve-overlap period.

Computational fluid dynamics (CFD) codes today represent consolidated tools that cover most physical and chemical processes which occur during operation of internal combustion engines under steady and unsteady conditions. Despite the availability of advanced physical models, the most demanding prerequisite for a CFD engine code is its flexibility in mesh structure and geometry handling capacity to accommodate moving boundaries. In fact, while the motion is solely defined on boundary points, most CFD approaches a-priori specify the position of every mesh vertex in the mesh for every time-step. Alternatives exist, most commonly using mesh generation techniques, like smoothing. In practice this is quite limiting, as it becomes difficult to prescribe solution-dependent motion or perform mesh motion on dynamically adapting meshes. To preserve the mesh quality during extreme boundary deformation due to piston and valve motion, the number of the cells in the mesh needs to be changed.

Multi-dimensional modelling of the flow and combustion promises to become a useful optimisation tool for IC engine design. Currently, the total simulation time for an engine cycle is measured in weeks to months, thus preventing the routine use of CFD in the design process. Here, we shall describe three tools aimed at reducing the simulation time to less than a week. The rapid template-based mesher produces the computational mesh within 1-2 days. The parallel flow solver STAR-CD performs the flow simulation on a similar time-scale. The package is completed with COVISEMP, a parallel post-processor which allows real-time interaction with the data.