Experimental study of the effect of unheated starting segment upon flame spread over solid fuel under forced airflow
2022
Zhang, Yue | Fang, Jun | Tu, Ran | Song, Lei | Singh, Ajay V.
In the present work, to quantify the effects of an unheated starting length on the wind-driven flame spread rates, the flow field structure and flame characteristics over a horizontally placed thermally-thick poly (methyl methacrylate) slab (10 cm long, 10 cm wide, and 1.5 cm thick) are experimentally investigated for different lengths of an unheated segment (0–30 cm), where PMMA flames are stabilized under a concurrent forced airflow velocity of 0.75 m/s. The flow field, flame structure, flame spread rates, and flame standoff distances are recorded, measured, and calculated. The results show that the flow field in a reacting boundary layer is noticeably different for varying unheated lengths, which can be attributed to the reverse flow diffusion and vortex occurrence, which significantly affects the flame structure and flame spread rates. The laminar, reverse diffusion, and streaky flame regions can be easily demarcated with increasing unheated starting lengths. Eventually, the flame standoff distance, burning, and flame spread rates seem to have a non-monotonic dependence on unheated starting lengths. The work presented here reveals the functional mechanism of an unheated segment in reacting boundary layers and presents useful information that could enhance our understanding of the wind-driven flame spread rates.
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