Computed Flammability Limits and Spreading Rates of Upward Flame Spread over a Thin Solid in Low-Speed Buoyant Flows

Abstract

Upward flame spread over a thin solid in low-speed buoyant flows was studied numerically with a previous established two-dimensional model. In natural convective environments, steady flame spreading was achieved in partial gravity and reduced pressure. The effects of environmental parameters, including gravity level, ambient pressure, and oxygen percentage, on flame structures, flame spread rates, and flammability limits were investigated, especially for the pressure effects, as it was not previously examined in detail. At reduced pressure, flame is shorter but thicker. Flame length and upward flame spread rates increased with pressure to a power larger than unity. The spreading rates also increased linearly with gravity, with a slope depending on pressure. The extinction boundary using pressure and gravity level as coordinates were constructed and compared with limited available experimental results for the buoyant, reduced pressure flames.

Keywords:

• Fire safety
• Flame spread
• Flammability

The author gratefully acknowledges the support and help of NSC, Taiwan grants NSC93-2212-E-182-007 and NSC95-2221-E-182-052, and Chang Gung University.