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This paper presents a methodology for the 3D CFD simulation of the intake and compression processes of four stroke internal combustion engines.The main feature of this approach is to provide very accurate initial conditions by means of a cost-effective initialization step. Calculations are applied to a low stroke-to-bore SI engine, operated at full load and maximum engine speed. It is demonstrated that initial conditions for this kind of engines have an important influence on flow field development, particularly in terms of mean velocities close to the firing TDC. Simulation results are used to discuss the choice of a set of parameters for the flow field characterization of low stroke-to-bore engines, as well as to provide an insight into the flow patterns during the overlapping period.

The increasing of the overall engine performance requires the investigation of the unsteady engine phenomena affecting intake air flow and the air-fuel mixing process. The “standard” RANS methodology often doesn't allow one to achieve a qualitative and quantitative accurate prediction of these phenomena. The aim of this paper is to show the potential and the limits of LES numerical technique in the simulation of actual IC engine flows and to assess the influence of some basic parameters on the LES simulation results. The paper introduces the use of a merit parameter suggested by Pope for evaluating the quality of the LES solution. The CFD code used is Fluent v6.2 and two basic test cases have been simulated. The first one is the flow over a backward facing step in order to perform a preliminary parametric numerical analysis. A one-equation dynamic subgrid-scales turbulence model is used.