CFD modeling of natural gas engine combustion with a flame area evolution model

A detailed description of the combustion process is fundamental in modern spark-ignition (SI) engines to guarantee control of pollutants formation and to meet future emission standards. Within this context, computational fluid dynamics (CFD) simulations represent an efficient and powerful tool to understand the different involved phenomena as mixture ignition, combustion development and pollutant formation. Object of this work is to find a CFD methodology to model premixed natural gas light-duty SI engines. The ignition stage is modeled by means of a simplified Eulerian spherical kernel approach (deposition model). Then, turbulent flame propagation is reproduced by means of two variables (regress variable and flame wrinkling factor) as proposed by Weller. Laminar to turbulent flame transition is taken into account using Herweg and Maly formulation and a zero-dimensional flame kernel radius evolution. Tabulated kinetics is used to estimate chemical composition of burned gases and to speed up the simulation since no chemical equilibrium calculations are necessary. The proposed CFD methodology was validated with experimental data of in-cylinder pressure, heat release rate and gross indicated work at different loads and speeds.