The virtual development of future Spark Ignition (SI) engine combustion processes in three-dimensional Computational Fluid Dynamics (3D-CFD) demands for the integration of detailed chemsitry, enable - additionally to the 3D-CFD modeling of flow and mixture formation - the prediction of fuel-dependent SI engine combustion in all its complexity. the conflict of goal arising in coupling 3D-CFD calculations with detailed chemistry is to keep computational costs low while achieving accurate results.
This work presents an approach which constitutes a coupled solution for flame propagation, autoignition and emission formation modeling incorporating detailed chemsitry, while exhibiting low computational costs.
For modeling the regular flame propagation, a laminar flamelet approach, the G-equation is used. This approach describes the flame propagation based on the turbulent flame speed, which is determined by the turbulence and the fuel-specific laminar flame speed. The latter one is incorporated using an adequate fitting function.
Auto-ignition phenomena are addressed using an integrated flamelet approach, which bases on the tabulation of fuel-dependant reaction kinetics. By introducing a progress variable for the autoignition - the Ignition progress Variable (IPV) - detailed chemistry is integrated in 3D-CFD. the tabulation approach only demands for the soltuion of the IPV transport equation, thus keeping the computational demand low, while allowing the consideration of local effects on auotigntion chemsitry on cell level.
The modeling of emissions formation bases on an interactively coupled flamelet approach, the Transient interactive Flamelet model. By transforming the species balance equations into a one-dimensional form, the numerical effort incorporated with the solution of small chemical time-scales is separated from the 3D-CFD flow field solution. Thus, the emission formation is calculated under representative boundary conditions. the description of the soot formation bases on a detailed soot model, and the properties of the soot Particle Size Dsitribution Function are calculated using the method of moments.
The coupling between the G-equation, integrated flamelet, and interactive flamelet models is done based on the IPV. The functionality of the combined approach to model the variety of SI enigne combustion phenomena is prooved first in terms of fundamentals and standalone sub-model functionality studies. For standalone and model coupling functionality studies, a simplified test case is introduced, representing an adiabatic pressure vessel without moving meshes. the vessel is initialised homogeneously, allowing the selective investigation of different parameters on combutsion process and direct comparison with direct numerical solution of the detailed chemistry in 0D homogeneous reactor calculations. Following the basic functionality studies, the standalone and combined sub-model functionalities are investigated in adequate engine test cases.