Numerical Analysis of In-Cylinder Flow in Internal Combustion Engines by LES Method

Abstract

In this research, Large Eddy Simulation of in-cylinder flow during suction and compression stroke in an axisymmetric engine is performed. A computer code using Smogorinsky subgrid model is developed to solve the governing equations of the flow. A proper understanding of flow during suction and compression strokes, gives better information for fuel/air mixture and combustion. The results show that the advantage of LES model is the ability of computing turbulence characteristics in various crank angles of engine cycle. This advantage of model is highlighted by calculating RMS values of axial velocity in comparison with experimental ones. The results show that axial velocity fluctuations during intake reaches to a higher level than in compression stroke because of the inlet jet to the cylinder and intensive gradient of variables. In this regard, the flow in 100 degree ATDC during intake stroke reaches the maximum level of turbulence intensity and then turbulence generated during intake stroke decays rapidly. During intake stroke, three main vorticities are generated inside the cylinder. In the compression stroke these three vorticities are merged together to establish a new vorticity with direction of rotation opposite to the intake flow. Some smaller recirculating regions are also generated at 90 degree BTDC.