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To improve the impinging spray's computational fluid dynamics (CFD) calculations under evaporating conditions, a detailed large eddy simulation (LES) code was constructed and examined for modeling the near-wall-velocity behavior of the impinging jet. The near-wall-velocity profile within the impinging jet was found to be different from that obtained using the steady wall functions. On the basis of this knowledge, a simple model of the wall boundary conditions was proposed for the impinging jet. The tests covered two different turbulence models. Comparing with the conventional wall functions, the proposed model improved the accuracy of the impinging spray simulations.

An auto-ignition process in a homogeneous charge compression ignition engine has been numerically solved by the Very Large Eddy Simulation (VLES) which integrates a reduced kinetic model for the low temperature oxidation of hydrocarbon fuels. We employ a new method to set the initial turbulent velocity field, reforming the velocity field so that the turbulence dissipation process may fit the results of the K-ε model simulation. The phase-averaged quantities of the VLES agree well with those of the K-ε model simulation. The VLES exhibits the spatially random appearance of auto-ignition sites, which is similar to experimental observations shown in the reference literature.

The reduced kinetics model for the low temperature oxidation and the fluid dynamics model were combined to analyze the autoignition sites. The original reduced kinetics model in the literature was modified to express a strong heat release rate on autoignition. A compression ignition of a homogeneous fuel-air mixture in a rapid compression machine was analyzed by a laminar flow computation with boundary layer resolution The computational analysis shows that the outer region of the thermal boundary layer comes to the first autoignition when it stays longer during the end phase of compression in the negative temperature dependence region of the low temperature oxidation reaction. Further analysis was made for the compression of a turbulent field simulated by a random motion flow, solving the spatially filtered transport equations. The results demonstrate that several autoignition spots appear in the numerical cells within 1 mm from the walls.