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The high pressure injectors used in direct injection Diesel engines introduce major perturbations in the air flow field inside the combustion chamber leading to strongly strained and turbulent flow. This fuel/air mixing process plays a critical role in enhancing self-ignition. However, in most Diesel combustion models, the interaction between turbulent mixing and self-ignition is not directly taken into account. Typically, the calculated average self-ignition combustion rates are pseudo laminar reaction rates based on simplified kinetic mechanisms. The mean values of the reaction rate are determined as a function of the mean values of the reactant concentrations and temperature. But due to the high non linearity of the reaction rate during self-ignition, this assumption is not valid. A turbulent self-ignition model developed from direct numerical simulations is presented.

The flow-field of an automotive DI Diesel engine is characterized by experiments in a motored engine using Laser Doppler Velocimetry and by CFD simulations. Only one cylinder is active and a specific swirling intake duct is used. Various bowls with different shapes are investigated: fiat or W-shaped bowls, with or without re-entrant. The influence of engine speed is also studied. The mean velocity and turbulence evolutions are measured with back-scatter LDV experiments using an optical access in an extended piston. The simulations are performed using the KMB code, a modified version of KIVA-II. Along with the detailed flow-field description, integral quantities characterizing the flow are derived. The comparison between LDV data and CFD results is shown to be satisfactory. The effects of geometry and engine speed on spatial profiles and temporal evolution of mean and turbulent velocities are correctly reproduced.