Flamelet LES modeling of coal combustion with detailed devolatilization by directly coupled CPD

A large eddy simulation (LES) with direct CPD devolatilization modeling and gas phase combustion modeling through a new flamelet approach is presented for the CRIEPI flame by Hwang et al., 2005 [1]. The devolatilization rates are directly determined from CPD for each coal particle. The flamelet is generated from non-premixed one-dimensional gaseous flames and is based on mixture fractions for volatiles and methane as well as on enthalpy and scalar dissipation rate. A transport equation for mixture fraction variance is combined with an assumed pdf approach for modeling turbulence-chemistry interaction. Special emphasis is put on the influence of devolatilization, with a comparison of LES with direct CPD coupling to empirical models with fitted and standard rate constants. The results are further analyzed by scatter plots and phase space trajectories of the quantities of interest. The results show that large deviations between CPD and the fitted model exist on the instantaneous particle level. It is shown that the direct use of CPD in the LES is feasible and that the flamelet model is able to perform well. Some weaknesses specific to the CRIEPI flame are also discussed.