Soot cloud size of a single coal particle in air/oxy combustion under forced convection

Abstract Soot cloud size is important in radiative heat transfer and particulate matter emission since it determines the integral effect in the sooty region; meanwhile, study on soot cloud size during single coal particle combustion is essential to develop theories of soot-relevant reaction pathways and mass transport. In this work, a 1-D transient coal combustion model with an empirical soot model was adopted and validated to study the effect of gas physicochemical properties and forced convection on soot cloud size (ls/r0). Tar gasification results in a larger ls/r0 at any xO2, while soot gasification has a limited effect at low xO2 and leads to a larger soot cloud size at high xO2. The effect of tar and soot diffusion becomes more important at higher oxygen mole fraction; a larger heat capacity leads to a larger soot cloud size. In O2/N2 environments, soot cloud size increases when Rep increases from 0 to 10 and decreases when Rep increases from 10 to 16. In O2/CO2 environments, soot cloud size increases dramatically when Rep increases from 0 to 13 and slightly decreases when Rep increases from 13 to 16. The ls/r0 in O2/CO2 is always larger than that in O2/N2. The effect of convection on soot cloud size has two sides. On one hand, the blow away effect tends to increase the ls/r0. On the other hand, convection may increase or decrease total soot mass, leading to an increase or decrease of ls/r0, respectively.