Role of the intake generated thermal stratification on the temperature distribution at top dead center of the compression stroke

摘要

This work investigates the role of the intake generated thermal stratification in the temperature field evolution during the compression stroke using direct numerical simulation. The analysis compares two direct numerical simulations during the compression stroke, from which one is initialized with a homogeneous temperature distribution and the other one with a stratified temperature field resulting from a precursor direct numerical simulation of the intake stroke. All other initial and boundary conditions are identically imposed. The results show that the thermal situation at bottom dead center has nearly no impact on the evolution of the temperature field and the wall heat transfer during compression. Dominating mechanism for the temperature field evolution is found to be the convective transport of cold gases from the boundary layers toward the cylinder center. As a consequence, the wall temperature and the flow field are the main influencing parameters controlling the evolution of the temperature distribution during compression. This finding can assist practical engine experiments, since it points out which mechanisms are promising to affect the temperature field during the compression stroke. In addition, it explains why the stratification of the temperature field during intake by varying the gas temperatures in the two intake channels showed only a minor impact on the thermal situation at top dead center.