Measurements of the intake and in-cylinder flow field to investigate the reliability of CFD steady-state simulations for actual engines

The design of intake manifolds and valve ports in internal combustion engines is a fundamental aspect of obtaining high volumetric efficiency and originating in-cylinder flows of proper intensity. CFD calculations using the RANS approach may support steady-state flow measurements in the design of intake manifolds, valve passages, and combustion chambers. On the other hand, the geometrical complexity of these engine parts hardly allows to mesh them by means of fully hexahedral grids and the accuracy of computations is strongly compromised. The paper presents the results of an experimental and numerical study performed on the head of a motorbike high-speed spark ignition engine. The work aims at investigating the reliability of CFD RANS computations performed on polyhedral grids of different size and assessing the mesh size required for accurate computations on such a type of grid. Discharge flow coefficients of the intake valves, in-cylinder tumble intensity, and static pressure along the surface of intake manifolds have been measured in a discharge flow test rig operating in steadystate conditions. Detailed geometry of actual bell-mouth inlet, intake ports and valves, combustion chamber roof, and cylinder wall has been obtained by using a reverse engineering technique. The geometry is used to build a CFD model which allowed to simulate the steady flow field measured during the experiments for several values of valve lift