Effect of the Backboard on the Pyrolysis Front Morphology of Downward Flame Spread: A Simulation Study

In order to investigate the influence of the backboard on the morphology of the pyrolysis front, this study employed the fire dynamics simulator (FDS) to conduct simulation research, aiming to quantitatively analyze the reasons for the differences in the morphology of the pyrolysis front under two conditions: with and without the backboard. By comparing the surface temperature distribution, flow field, and air entrainment velocity at the bottom of the pyrolysis front made of polymethyl methacrylate (PMMA) under different conditions, it was found that the presence of the backboard not only reduced the surface temperature of PMMA at the bottom of the pyrolysis front and the temperature difference between the edge and middle, but also changed the flow field at the edge and suppressed the horizontal air entrainment velocity at that position, especially for thinner PMMA. These factors ultimately result in a larger angle of the pyrolysis front during the burning stable stage under the condition with the backboard compared to the condition without the backboard. In addition, the trend of horizontal air entrainment velocity at the edge position under different conditions also provide data support for the qualitative observation and analysis of previous experiments phenomena.