Effects of Velocity Profile of Combustible Gas on Stability of Boundary Layer Diffusion Flame

Abstract

The understandings of the critical condition of flame spread over combustible solids are essential for improving fire protection technology. Once the flame loses stability and moves back from the leading edge of the pyrolysis front on the solid surface during flame spread process, the flame spread stagnates, or, more likely ceases, because the unburnt part of the combustible solid loses direct heat transfer from the flame. The obstacle to the quantitative understandings of this critical condition is the complexity of the interaction between solid and gas phases. This work focuses on a portion of this interaction, namely, the effect of vaporized gas on the stability of the spreading flame. A boundary layer diffusion flame on a plate burner is adopted and the effects of velocity profile of the fuel gas ejected from the burner port are investigated. Methane is used as the fuel. The results clearly show the critical condition; the flame is stable only when both the gas velocity at the upstream edge in the ambient airflow and the two-dimensional volume flow rate exceed the critical values, which are 12 mm/s and 46 mm²/s, respectively. It is inferred from these results that the flame stability is simply determined by the gas ejected within the range of 3.8 mm from the upstream edge of the port in the tested condition.