Numerical and experimental study of downward flame spread along multiple parallel fuel sheets

In the present study, downward flame spread over multiple parallel fuel sheets is investigated experimentally and numerically to understand the mechanism that controls the flame spread process and compare that with the flame spread over a single fuel sheet. A 2D numerical model, based on OpenFOAM is used to simulate the flame spread in a natural convective environment under normal gravity. The model is validated with detailed experimental data involving spatial distributions of temperature and species, and flame spread rates. Flame spread rates on central fuel sheet have been measured in 3 parallel fuel sheets configurations, considering spacing (s) between the fuel sheets in the range of 0.5 cm–3 cm. The flame spread rate varies non-monotonically with spacing, with a peak spread rate at 1 cm spacing between the fuel sheets. Conduction is the dominant mode of heat transfer to the single fuel sheet case. However, in the case of multiple fuel sheets, radiation contributes almost to the same order as that of conduction. The non-monotonic trend in the flame spread rate with spacing is attributed to two opposing effects, namely, increase in oxygen availability and decrease in heat transfer to the fuel, with an increase in the spacing between the fuel sheets.