Numerical investigation of the influence of intake valve lift profile on a diesel premixed charge compression ignition engine with a variable valve actuation system at moderate loads and speeds

摘要

Variable valve actuation is attracting increasing attention for the control of diesel premixed charge compression ignition engines due to its fast-response characteristics. In this study, a three-dimensional computational fluid dynamics model, coupled with detailed chemical kinetics, is used to evaluate the influence of the intake valve lift profile on combustion and emissions of a diesel premixed charge compression ignition engine at moderate loads and speeds. The results indicate that, among all the tested variable valve actuation strategies, late intake valve closing shows the most potential for control of ignition timing and reduction of nitrogen oxide emissions, while maintaining low soot emissions and fuel consumption. A moderate decrease of intake valve lift is beneficial for the reduction of soot emissions without significant impacts on fuel consumption due to the enhanced intake flow. The enhancement of turbulence kinetic energy of the in-cylinder mixture is helpful for fuel/air mixing and soot reduction. However, the strategies for increasing turbulence kinetic energy by using intake valve reopening around the start of injection timing and one intake valve deactivation lead to deterioration in fuel efficiency due to the increased pumping work. In general, the increase of swirl ratio with various variable valve actuation strategies impedes the fuel/air mixing, resulting in rapid increases of soot emissions, and a lower swirl ratio is more beneficial for mixing and combustion in diesel premixed charge compression ignition engines with early injection timing.