Width effect on upward flame spread

One previous experimental study has reported a width effect for upward flame spread rate on thermally thin fuels. A similar effect is expected for thermally thick fuels. This study revisited this topic by developing a hypothesis and performing experiments with sidewalls using 18 mm thick, 1000 mm tall PMMA slabs of widths 100, 200, 300, 500 and 700 mm. In the hypothesis, a lateral diffusion throughout the flame width was proposed to cause thicker flame along its centerline for wider flames and enhance combustion efficiency. Higher heat release rate per unit width, larger flame height, higher flame temperature and more heat feedback to the surface were consequently present. The corresponding flame spread rate was also increased and a power value of 0.35 existed between the flame spread rate and width in this study. All the experimental results clearly supported the hypothesis. This study is the first to discuss the width effect on upward turbulent diffusion flames on thermally thick materials and provide a correlation between the flame spread rate and width.