LES/FGM Modeling of the ECN Spray a Flame: Effects of Progress Variable Definition and Chemical Mechanism

A large eddy simulation/flamelet generated manifold (LES/FGM) method is employed to investigate the influence of progress variable definition and chemical kinetic mechanisms on Diesel spray combustion under Engine CombustionNetwork (ECN) Spray A conditions. Two commonly used progress variable definitions and three chemical mechanisms are considered. The LES/FGM method iscoupled with a spray model and implemented in OpenFOAM. The spray model is first validated against non-reactive case, followed by reactive simulations to examine the effects of progress variable definition and chemical kinetics on flame structure and ignition behavior, with particular emphasis on key species and reaction pathways. Results show significant sensitivity to the progress variable definition and indicate that the Yao mechanism (Yao et al. 2015) underpredicts, whereas the Narayanaswamy (Narayanaswamy et al. 2014) mechanism overpredicts the ignition delay time (IDT); the Polimi-reduced mechanism (Frassoldati et al. 2015) shows the best agreement with experimental measurements. When employing different progress variable definitions, discrepancies in ignition behavior are attributed to variations in the temporal evolution of the respective progress variable source terms. The predicted flame lift-off length (FLOL) agrees reasonably well with measurements and exhibits limited sensitivity to both progress variable definition and chemical mechanism. The results demonstrate that both ignition and evolution of combustion are sensitive to the choice of chemical kinetic mechanism and the definition of the progress variable.