An assessment of the sectional soot model and FGM tabulated chemistry coupling in laminar flame simulations

Discrete sectional method (DSM)-based soot models are computationally demanding since several transport equations are required to be solved for sectional soot variables using large chemical kinetic mechanisms. In this paper, the sectional soot model is coupled with Flamelet Generated Manifold (FGM) tabulated chemistry to achieve computationally efficient chemistry reduction for combustion simulations. Different approaches are explored for incorporating soot-gas phase coupling with FGM chemistry, and a comprehensive assessment of these FGM-DSM approaches is conducted for their predictive accuracy and computational performance in simulations of laminar ethylene counterflow flames. The accuracy of soot prediction with FGM chemistry is found to be sensitive to the tabulated concentrations of PAH species. An unaccounted consumption of PAH originating from PAH-based processes leads to significant overprediction of soot. In this context, the performance of two strategies (i) solving the transport equation of PAH species (ii) including a contribution of soot nucleation during the manifold generation stage is compared. The latter approach showed relatively better accuracy and computational efficiency than the former. Numerical results further reveal that the strategy of including the complete soot model during the manifold generation stage reproduces the detailed chemistry solutions most accurately. The influence of unsteadiness on predictive capabilities of FGM-DSM approaches is also investigated by imposing time-dependent strain rates in unsteady simulations. The computational performance analysis indicates that by adopting FGM chemistry, up to two orders of magnitude reduction in CPU time can be achieved, based on the choice of section number and simulation approach. Promising results obtained for FGM-DSM strategies in one-dimensional configuration, provide a good outset for extending the application of FGM for soot estimation in turbulent flames.