CFD simulering av en fyrtakts Otto motorcykel motor
This thesis deals with the numerical 3D simulation of a four stroke, spark-ignited, internalcombustion engine, which is mounted on a high performance motorcycle. The work, carried outin collaboration with Politecnico di Milano and MV Agusta, focuses on the simulation of theintake, compression and expansion stroke, including combustion simulation, using an opensource CFD code.Simulation of internal combustion engines offers a great challenge in the field of CFD research.Moving boundaries of the solution domain, caused by the motion of the piston and valves, leadsto deformation of the computational grid, with decreasing quality of the solution as result. Basedon this, a previously developed mesh motion strategy was employed where a number of meshesare used to cover the whole simulation cycle. Within each mesh interval the internal cell pointsof the mesh are moved to account for the boundary motion of the piston and valves. This strategywas previously applied to simplified geometries as well as real engine geometries. The purposeof this work is to show its validity for a real and complex engine geometry, covering a longersimulation interval then previously.After an initial description of the mesh creation process, studies of the in-cylinder charge motion,created during the intake stroke, were made to investigate the presence of a tumble motion. Theresult shows that a strong tumble motion is not generated. This could also be because ofnumerical diffusion caused by the mesh structure. Furthermore, investigations were made to seewhy the present engine has a tendency to knock. The simulations showed that the in-cylinderflow field creates a temperature distribution in the cylinder that is not uniform, possibleincreasing the knock risk close to the exhaust valves. Lastly, simulations of the combustionprocess were made using the Weller combustion model. Problems causing a calculatedturbulence intensity that was too low for proper flame propagation were apparent, leading toinconsistency between the calculated cylinder pressure of the CFD calculation and the calibrated1D calculation.