Numerical investigation of two-phase flame structures in a simplified coal jet flame

Abstract

The coal flame structures are investigated based on a three-dimensional compressible point-source direct numerical simulation (DNS) of a turbulent simplified coal jet flame. The coal particles are treated as point sources and tracked in the Lagrangian frame considering the interphase transfers. A comprehensive coal combustion model, including the evaporation, devolatilization and char combustion, is applied. The reaction mechanism of CH4 is adopted for gas combustion. In this paper, the general flame features and particle distributions are investigated and three typical flame structures of coal jet flames, namely interspersed flame, stripe flame and stable continuous flame, are identified. By analyzing the temporal evolution of the flame structures, the stable flame formation process is obtained intuitively. It is also found that these three typical flame zones have similar gaseous reaction and the non-premixed flame dominates. The strong reaction is more likely to appear at the locations with small vorticity and high scalar dissipation rate. Compared with purely gaseous flames, the scalar dissipation rate is not only related to turbulent micro-mixing between the fuel and oxidizer flows but also the devolatilization process. By testing the heat release rate proportion of the three zones, it is found that the contribution of interspersed flame is less. The stripe flame contributes about 26% and is important to the whole stable flame formation.