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The analysis of the air motion inside the cylinders of an internal combustion engine constitutes a very important step during engines design. It is already known that its movement, normally decomposed in tumble and swirl motion, is totally related to the majority of phenomena which occur inside cylinder, like fuel evaporation, mixture formation or flame propagation. The use of mechanical devices in the intake system represents an interesting option in the attempt of optimizing the airflow and finding the best condition for maximum power and minimum specific fuel consumption. Devices like flow boxes, which control the airflow and change its main characteristics before entering the cylinder, by obstructing the air and changing its directions, are one possibility. Based on this idea, this paper presents a numerical analysis of the utilization of a flow box in the intake system of a spark ignition engine.

In this work, the in-cylinder flow of a spark ignited Single Cylinder Research Engine (SCRE) with variable compression ratio was simulated using STAR-CD, a Computational Fluid Dynamics (CFD) software with es-ice module for internal combustion engines. The engine used in this work was an AVL SCRE with 82 mm bore and 86 mm stroke. The simulations were made in two different configurations, one with a piston suited for wall guided direct injection and a steel liner (Configuration 1) and another with flat piston and a transparent liner (Configuration 2). Configuration 1 was simulated with the compression ratios of 9.3:1, 11.5:1 and 12.0:1 and had its in-cylinder values of tumble, Turbulent Kinetic Energy (TKE), pressure and temperature analyzed and compared between compression ratios. Configuration 2 was used for validation of in-cylinder flow field using Particle Image Velocimetry (PIV) measurements and experimental in-cylinder pressure. Both configurations were simulated for 1000 RPM.