Behavior of Flame Spread on Thin PMMA near Extinction Limit at Low Oxygen Level

Abstract

The downward flame spread rate and limiting oxygen index (LOI) were investigated with varying oxygen level in normal gravity. Four kinds of diluents, nitrogen, argon, helium and carbon dioxide were used to change the thermal properties of the ambient gas. In order to clarify the impact of the properties on spread rate, simple scale analysis was developed for two-dimensional flame spread. The scale analysis predicted strong dependence of LOI on the flame temperature and the predicted LOIs agreed with the measured LOIs; the Damkohler number is the important factor for LOI of the downward spread. In the microgravity experiment, the flame spread rate was measured with varying opposed flow velocity at 18% oxygen level. The faster flame spread than that in normal gravity condition was observed when the opposed flow was about 15cm/s, which was consistent with the regime map predicted by the scale analysis.

A review of near-limit opposed fire spread

“…The recent review by Fujita [53] summarized the latest understanding of the gravity influence on the material flammability limit. A lower LOC has been observed in microgravity and reduced gravity [44,60,71]. For example, the LOC decreases from 19% (1g) to 16% (ug) for a thin copper-core wire [44] and from 18% (1g) to 16.5% (ug) for a thick PMMA rod [60].…”