Examination of Initialization and Geometric Details on the Results of CFD Simulations of Diesel Engines

Computational Fluid Dynamic (CFD) simulations using the AVL Fire and Kiva 3v codes were performed to examine commonly accepted techniques and assumptions used when simulating direct injection diesel engines. Simulations of a steady state impulse swirl meter validated the commonly used practice of evaluating the swirl ratio of diesel engines by integrating the valve flow and torque history over discrete valve lift values [1]. The results indicate the simulations capture the complex interactions occurring in the ports, cylinder and honeycomb cell impulse swirl meter. The commonly adopted axisymmetric assumption for an engine with a centrally located injector was tested by comparing the swirl and emissions history for a motored case and a double injection low temperature combustion case. Consideration of the detailed engine geometry including valve recesses in the piston and the head lowered the peak swirl ratio at TDC by approximately 10% compared to the simplified no-recess case. The corresponding combusting cases also had different heat release and emissions predictions but could be partially compensated for by lowering the initial swirl ratio for the axisymmetric case.