INVESTIGATION ON FLOW FIELD IN SIMPLIFIED PISTON BOWLS FOR DI DIESEL ENGINE

Three-dimensional flow calculations of the in-cylinder flow for a direct-injection Diesel engine have been carried out with different combustion chambers. In order to assess the decisive factors for the formation and evolution of the in-cylinder flow field, simplified piston bowls were used. A limited number of validation calculations of the compression stroke were performed. The results show that the geometries of the piston have a significant influence on the distribution of the cross section-averaged swirl ratio. The tangential velocity profiles at the cross sections are highly nonlinear, and the rigid body rotation assumption is less admissible. Furthermore, the turbulence in four combustion chambers is analyzed for an insight of the effects of bowl shape, initial swirl ratio and squish. It is found that the squish flow plays a significant role in the turbulence generation process near the top dead center (TDC) during compression. The coupling among the swirl, squish, bowl shape and turbulence is much more pronounced in the combustion chambers.