Direct numerical simulation of soot formation and transport in non-premixed turbulent ethylene flames

Direct numerical simulations of two-dimensional, nonpremixed, sooting ethylene flames are presented to examine the effects of soot-flame interactions and transport in a turbulent configuration. A 15 step, 19 species reduced mechanism was used for gas chemistry, with a two-moment, four-step soot model. Flame curvature is shown to result in flames that move, relative to the fluid, either towards, or away from rich soot formation regions, resulting in soot being essentially convected into or away from the flame and transported in the mixture fraction coordinate. In regions where the flame motion relative to convection is towards the fuel stream, soot is located nearer the flame at higher temperatures, hence having higher reaction rates and radiative heat fluxes. Soot-flame breakthrough was also observed in these regions. Fluid convection and flame displacement velocity relative to fluid convection are of similar magnitudes while the thermophoretic velocity is five to ten times lower. These results emphasize the importance of both unsteady and multidimensional effects on soot formation and transport in turbulent flames.