Influence of sidewalls on width effects of upward flame spread

[[abstract]]A previous study has reported width effects for turbulent diffusion upward flame spread on thermally thick materials with sidewalls. However, sidewalls are not realistic. The present study has revisited this topic by performing experiments without sidewalls using 9 mm thick and 1000 mm tall PMMA slabs with widths of 100, 200, 300, 500 and 700 mm and by providing a hypothesis of the sidewall effects. Experimental data have revealed that the width effects still exist when sidewalls are absent. Flame heights and spread rates were higher for wider flames, although heat feedback to the fuel did not vary much with flame width. Compared to flames without sidewalls, the existence of sidewalls lengthened flame heights and generally reduced heat feedback along the central lines of the flames, resulting in higher flame spread rates for narrower flames and lower flame spread rates for wider flames. In addition, the absence of sidewalls enhanced the delivery of pyrolyzate towards the central line of the flames throughout the whole flame width