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In Homogeneous Charge Compression Ignition (HCCI) as well as in conventional Diesel engine, fuel oxidation chemistry determines the ignition timing and the subsequent heat release. Auto-ignition is characterized by the production of large active intermediate radicals during the initial stage of oxidation. This makes the modeling task more complex, as it demands high computing resources to solve several hundreds of species transport equations involved in the detailed chemical mechanism. Therefore, introduction of complex chemistry details into a CFD code in a simple way is necessary. A new 3D auto-ignition model Tabulated Kinetics for Ignition with Probability Density Function (TKI-PDF) is presented. The objective is to include detailed chemical kinetics and the turbulence/chemistry interactions during auto-ignition. The model development and the validation against experiments are described in two stages.

The study of soot oxidation and CO formation in internal combustion engine applications is the subject of numerous recent investigations. Their modeling is particularly important for Diesel operating conditions. Models have been developed recently at IFP to account for the complicated kinetic processes involved in CO / soot production and oxidation. This paper presents the equations for CO formation and oxidation based on a reduced 6 step chemistry model coupled with the PSK reduced soot production and oxidation mechanism. The species are accounted for in the conservation equations. Model development is done on the framework of the ECFM3Z engine combustion model. The global CO/soot model is first validated in a constant volume high pressure cell against LII measurements. Model parameters are adjusted and kept constant for the remaining of the simulations. Then, engine simulations are used to validate the model behavior in conventional and HCCI Diesel conditions.

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.