A flexible and simple device for in-cylinder flow measurements: experimental and numerical validation

Deep knowledge of intake process aerodynamics is fundamental to development and optimisation of modern internal combustion engines. In particular, the intake port flow strongly affects both volumetric efficiency, i.e. power output, and in-cylinder charge motion which influences combustion behaviour and pollutants formation. The paper presents an experimental and numerical study of intake airflow through ports and cylinder in a four-valves pent-roof motorbike high-speed engine. A very simple mechanical device specifically designed for quick and low-cost measures of swirl and tumble motions in steady-state discharge flow coefficient test rigs was developed and checked on two twin-cylinder stock production heads featuring intake ports design typical of modern motorbike high speed SI engines. Simultaneous measures of discharge flow and tumble coefficients proved the limited error due to device insertion. A detailed CFD model of cylinder, intake ports, and manifolds within the engine head was build and experimentally validated by discharge-flow coefficient measurements performed at different valve lift. The sensitivity to grid refinement and the performance of a realizable k-ε and a modified k-ω turbulence models is investigated. The numerical model is used to evaluate the reliability of tumble measurements. The correlation between experimental data and the whole CFD velocity field within cylinder volume is very good proving that the device appears well-suited for rapid and reliable analysis of aerodynamic bulk performance of engine heads.