The study of ignition and flame spread over a thick solid fuel in a forced convective environment

This study explores numerically the flame behaviors, which include ignition and subsequent flame spread over thermally thick solid fuel in a forced convection environment. The entire process is divided into two distinct stages. In the heating stage, the maximum temperature, occurring at the interface, increases with time. The flame development stage consists of ignition and transition processes. Ignition process consists of an induction period and a thermal run-away period. During the induction period, a flammable mixture is established adjacent to the pyrolyzing fuel surface, but its chemical reaction is not strong enough to generate significant heat release. The temperature rises sharply due to a burning of premixed flame in the thermal run-away period. In the transition process, the flame is initially in a transition from a premixed flame to a diffusion flame. Subsequently, the flame spreads upstream and downstream simultaneously, and grows with time. Eventually, a steady opposed flame spread is reached. For the parametric studies, the ignition delay time is found to decrease with the opposed flow temperature (T_in) and the peak of input radiant heat flux (q_exp), but it is independent of the opposed flow velocity (u_∞). The maximum interface temperature at ignition decreases as T_in increases or q_exp decreases. The flame spread rate decreases as u _∞ increases and a recirculation flow is identified just ahead of the flame front. A comparison with a previous work, whose environment is natural convection, is given as well.