Numerical Analysis Of The In-Cylinder Flow In A Diesel Engine

The in-cylinder flow plays an important part in fuel-air mixture formation and combustion process for internal combustion (IC) engine, and influences the performance of IC engine. Numerical simulation with low costs and detailed information is an important method for in-cylinder flow research.The modified KIVA3V code is employed to simulate the in-cylinder flow field in this paper. The simulated results show good agreement with experiment data The combustion chamber with simplified shape is applied to investigate the influence of combustion chamber configuration on the in-cylinder flow field, and the most results are obtained as follows:Around top dead center (TDC), the swirl ratio is determined mainly by the initial angular momentum, the mean rotation radius and friction of fluid, but the vortex in the straight-cut section tends to change the mean swirl ratio in the combustion chamber. The results indicate that the shape of combustion chamber have a significant influence on the vortex in the straight-cut section. The tangential velocity field in cross-section is too complicated to be simplified as a combination of solid-body rotation and potential flow because of the effect of the vortex.Turbulence intensity is mainly detemined by the mean swirl ratio, combustion chamber configuration and squish intensity. Either one of the factors changed, turbulence intesity is strengthened. As the piston moves towards the TDC, the effect of swirl ratio on turbulence intensity is linely weakened and for the squish case is linely strengthened, while the effect of combustion chamber configuration on turbulence intensity keeps unchanged. When the three factors are changed simultaneously, the total increment of turbulence intensity doesn't equal to the sum of the change contributed by the three factors.The feature of high turbulence intensity region is also determined by the three factors. When either the swirl ratio or combustion chamber factor is enhanced, the volume percentage of high turbulence intensity region increases, but the amplitude of them becomes smaller. And when the squish flow is enhanced, the volume percentage of high turbulence intensity region declines, but the amplitude ascends quickly.When combustion chamber outline is designed to fit the turbulence structure, the utilization of fresh air in the combustion chamber is improved, with the feature of the high turbulence intensity region kept fixed.Based on the simplified combustion chamber, the in-cylinder flow of diesel engine has been investigated, and valuable guidance to the combustion chamber design has been gived in this study.