Modeling of Pollutant Emissions Using Combined Tabulated Detailed Kinetics and Reduced Kinetics 2010-01-0628

In the context of low consumption and low emissions engines development, combustion processes modeling is a challenging subject as the requirements for accurately controlled pollutant emissions are becoming more stringent. From a scientific point of view, it is a major source of in-depth investigations as the chemical processes involved are strongly coupled to the flow characteristics. Among the various approaches developed recently to account for these processes in realistic configurations, tabulated techniques appear to be a promising way. They induce a good compromise between the accuracy of detailed chemistry and the computational time necessary to calculate complex configurations. Tabulation approaches were firstly developed to address the modeling of species concentrations in stationary combustors. They consist basically of pre-computed chemical kinetics using detailed mechanisms. It has proved to be accurate in realistic stationary conditions featuring constant volume or constant pressure combustors. A limitation of such approaches was identified in internal combustion engines where variable volume conditions are encountered: unlike in constant volume or constant pressure cases, energy or enthalpy do not remain constant during combustion in this case. To overcome this limitation, a new variable volume tabulated chemistry-based approach has been developed and is used in the present work to provide basic species and radicals concentrations (O₂, CO, CO₂, H₂O, H₂, H, O, OH...) from the start of auto-ignition to the end of expansion for compression-ignited applications. This tabulated combustion model is coupled to reduced kinetics models for soot and NOx, for which a classical definition of the progress variable is not suited. The final model is validated against homogeneous detailed chemistry computations and is finally applied to realistic compression-ignited configurations with multiple interpolation dimensions. The pollutant levels at the end of expansion are compared to experimental results on realistic diesel engine working points. Parametric variations (bowl shape, EGR rates,) are achieved. Tendencies are well reproduced for all the points. Good quantitative agreement is obtained for CO levels issued from detailed kinetics. Adapted reduced kinetics permits to reach good levels for NOx and soot emissions.