Direct numerical simulation of ignition of a single particle freely moving in a uniform flow

In this study, a direct numerical simulation (DNS) of the ignition of a single particle freely moving in a uniform flow is performed to investigate the particle's ignition behavior in detail. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to compute the six degrees of freedom motion of a particle (Zhang et al., 2015). The computational setting follows the experiment designed by Lee and Choi (2015). The volatile gas that is composed of methane blows out at the particle surface. Its velocity is calculated by Ex-CPD model (Umemoto et al., 2017) and its direction is set perpendicular to the particle surface. The ignition behavior is compared with that observed in the experiment. The effect of the particle's shape is also investigated. Results show that the ignition delay of the particle and the flame inclined angle are in good agreement with that of the experiment. While examining the combustion of the gas phase by considering the variation of Flame Index (FI), it is found that a premixed and diffusion regions are formed around the particle after the devolatilization starts. The gas phase ignites at the boundary of the premixed and diffusion regions and the flame propagates towards the particle. This causes a rapid increasing of the temperature and the volatile velocity on the particle surface. Finally, a diffusion flame is formed and reaches a stable state around the particle. It is also revealed that the flame keeps spherical despite the spheroidal shape of the particle.