LES of pulverized coal combustion with a multi-regime flamelet model

Abstract

It is well known that premixed and non-premixed flamelets coexist in the combustion system, especially for multiphase combustion (Luo et al., 2011; Bai et al., 2016). In this work, a multi-regime combustion model for partially premixed multiphase combustion (2PMC) is developed in the framework of large eddy simulation (LES). In this model, the multi-regime combustion mode is decomposed into two pure combustion regimes (i.e. premixed and non-premixed) through combustion regime indicator. Different combustion models are chosen for different combustion regimes. For example, for premixed combustion regime, the flamelet generated manifold (FGM) tabulation method in combination with the artificially thickened flame (ATF) approach is used. For non-premixed combustion regime, on the other hand, the thermo-chemical quantities will be extracted from the non-premixed chemtable generated by the flamelet/progress variable (FPV) approach. The proposed multi-regime flamelet model is then extended to adapt to the pulverized coal combustion (PCC) and applied to a laboratory-scale pulverized coal jet flame. The simulation results show that the percentage of the volume-weighted premixed combustion regime of this studied flame is up to 18%. Quantitative comparisons between the experimental data and the numerical results with the present multi-regime flamelet model, the FPV model, and the Eddy Break Up (EBU) model shows that the proposed multi-regime flamelet model has several advantages. It performs better than the FPV model in the regions where premixed combustion mode prevails and also much better than the EBU model in species concentration prediction.