Heat and mass transfer mechanisms during unsteady flame spread process along inclined surface under wind

This paper studies the effect of environmental wind and fuel inclined angle on concurrent flame spread behaviors along PMMA surface. During the experiments, wind velocity varies from 0 m/s (still air) to 2.0 m/s. Fuel inclined angle ranges from 0 degrees (horizontal) to 90 degrees (vertical). Measurements and analysis focus on the evolution of flame spread rate, flame shape parameters (flame height, preheating length) and heat flux distribution in preheating zone. Under wind effect, flame spread rate increases with wind velocity for 0 degrees similar to 75 degrees, and decreases for 75 degrees similar to 90 degrees, indicating the competing mechanisms of wind on flame spread process. The evolution of flame height and preheating length with wind velocity shows opposite trend at different fuel inclined angles, which is due to the coupling mechanism of environmental wind on flame diffusion combustion process. Theoretical models of flame height and preheating length are proposed combining thermal buoyancy effect and wind effect. Heat flux distribution in preheating region is shown to be of power function with downstream distance. The average pre-heating flux is constant with preheating length and fuel inclined angle for fixed flame tilt angle.