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This paper describes recent progress towards Direct Injection Diesel engine combustion simulation, involving both engine data measurements and 3D computational fluid dynamics. Experimental data were obtained in two different engines and it includes LDV measurements as well as an extended engine combustion data base. CFD simulations were performed with a modified version of the Kiva2 code and experimental data were used to get initial and boundary conditions and to validate the numerical results. The initial version of the Kiva2 code was enhanced to allow computation of quite complex geometries with different physical sub-models for turbulence, injection and combustion. The present version of the code can compute the engine cycle from start of intake stroke to the end of combustion with any inflow and wall boundary conditions. Turbulence may be simulated using both a k-ε model and a second order uiuj-ε model which was recently implemented in the code.

Numerical simulation is now a more and more commonly used tool to investigate flows inside IC engine combustion chambers. A key parameter of these codes is to simulate accurately turbulence since it describes the flow structure and turbulence results are inputs for combustion and spray models. In usual industrial codes, in-cylinder flows are calculated with the standard k - ε model. Nevertheless, deficiencies of this model for engine flow simulations are now well known. The turbulence anisotropy due. to the volume variation in the cylinder axis direction can not be taken into account by the k - ε model since it is based on the hypothesis of a single turbulent velocity scale. Moreover, this model is deficient to simulate swirling flows and it poorly predicts recirculating zones (these two kinds of flows are frequently encountered in combustion chambers).

A flamelet model is used to calculate combustion in a diesel engine, and the results are compared to experimental data available from an optically accessible, direct-injection diesel research engine. The 3∼D time-dependent Kiva-II code is used for the calculations, the standard Arrhenius combustion model being replaced by an ignition model and the coherent flame model for turbulent combustion. The ignition model is a four-step mechanism developed for heavy hydrocarbons which has been previously used for diesel combustion. The turbulent combustion model is a flamelet model developed from the basic ideas of Marble and Broadwell. This model considers local regions of the turbulent flame front as interfaces called flamelets which separate fuel and oxidizer in the case of a diffusion flame. These flamelets are accounted for by solving a transport equation for the flame surface density, i.e., the flame area per unit volume.