Experimental study on coupled combustion of PMMA counter-directional flame spread in the horizontal direction

An experimental study was carried out to address the effects of coupled combustion, and sample widths on counter-directional flame spread over poly(methyl methacrylate) (PMMA) boards in the horizontal direction. Typical flame propagation parameters were observed and analyzed, including flame form, flame front, characteristic angles, rate of spread, and radiative heat flux density. Experimental results showed that the counter-directional fire propagation process could be divided into four stages based on the flame morphology variation, and the evolution of the flame front was presented as well. The characteristic angles, defined as half of the flame front angle, show the velocity variation between the side-edge and center flame at different spread phases. Compared with unilateral flame spread, the radiative heat flux density for the counter-directional flame spread grows faster, and the maximum value is about twice. Moreover, the maximal radiative heat flux increases for a wider sample, and a positive linear relationship exists between the dimensionless mass loss rate and characteristic angle against the breadth length ratio. The research outcomes of this study offer a better understanding of the counter-directional flame spread mechanism from aspects of scale change and heat transfer.