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A 3D Eulerian model has been developed to improve the primary break-up of an atomizing jet. The model is divided in three parts and is implemented in a modified version of KIVA II. The first part focuses mainly on the liquid dispersion, the second on the atomizing process itself, and the third on the adaptation of the model's mathematical formulation to the physics of the flow. Since the spray close to the injector is dense, an Eulerian formulation is thus chosen. However, when the spray is diluted, a Lagrangian formulation should then be applied. Different computations have been carried out using this new model and will be thoroughly discussed in this paper. The first calculation serves as a validation of the model. Those which follow demonstrate the importance of the internal liquid flow inside the injector on the spray development. They also manifest an influence of the air-co-flow, which assists the atomization of the spray.

PDF-equation approach have been extended and assessed for the diesel spray combustion computation. This approach accounts for the effects of gas turbulence and random dynamics of vaporizing liquid droplets on the chemistry. The combustion process including spray dynamics, evaporation, mixing and combustion have been treated using the combined KIVAII-PDF-equation model. Numerical computations were compared with the experimental data for spray self-ignition and combustion and with calculations using Eddy-Break-Up combustion model. Both the light-duty and heavy-duty diesel conditions have been operated in computations. Besides, the most probable self-ignition zone was computed and compared with experimental observation. It was showed that the developed here PDF model is abble to describe species concentrations, auto-ignition phenomenon and overall turbulent heat release significantly better than Eddy-Break-Up model.

A numerical submodel within the PDF-approach is developed for calculation of turbulent evaporation in liquid fuel sprays. This submodel is based on the Monte Carlo simulation of derived PDF transport equation for vapor concentration that accounts for both large scale turbulent air-fuel mixing and small scale turbulence. Evaporation-micromixing interaction is treated within coalescence-dispersion processes where evaporated mass is presented in statistical manner. The submodel is incorporated into KIVA II diesel spray codes. Computations of transient dynamics of vaporizing fuel spray were performed to assess the fluctuating structure of fuel vapor field. Discontinuous distributions of fuel vapor mass fraction are demonstrated in zones were droplets are still not evaporated. Highest intensity of vapor concentration fluctuations at the spray tip was observed.

A linked ignition-soot formation global kinetic model has been developed. The model has been adapted to the extended code CONCHAS-SPRAY. The so called Shell-model, which was successful in the representation of the ignition global kinetics has been used. Mass balanced reactions for the overall product path, soot formation and soot oxidation have been introduced. The feature to generate soot was prescribed to a stable hydrocarbon intermediate species typical for ignition. The soot surface growth rate was determined by experimental data of final soot volume fraction given by Wagner et al. for premixed flames. Soot oxidation rate is represented by Lee et al's formula. Turbulent transport properties are calculated with the help of the k-ε model. The numerical prediction of soot concentration level, generation of soot and resulting oxidation as well as a secondary soot formation at the spray axis have been demonstrated as being in qualitative agreement with known experimental data.

The modelling of a turbulent premixed flame propagating in a constant volume vessel has been studied and compared with experiments. Three models including step by step the turbulent mixing, the flamelets propagation for wrinkled flames, and the flamelets stretching, interactions and thickening when the chemistry is not very fast, have been tested. The experiment considered here allows the knowledge of the turbulent kinetic energy and the turbulence scale at the time of the spark, and avoid any problem of spark fluctuations and residual gases, but displays again “cyclic variations” and the comparison concerns ensemble averages. The results of comparisons is that the agreement concerning the flame brush propagation is improved from the simplest to the largest model, when considering a domain in which in which varies from 2. to .75 and from 2. to 0.4 .