Flame attachment state and control mechanism in inclined trench condition

Author：Li, M. M., Liu, N. A., Xie, X. D., Gao, W.

Journal：Proceedings of the Combustion Institute

DOI:  10.1016/j.proci.2024.105419

Keywords: Flame attachment, Slope, Trench, Flame geometry, needle fuel bed, fire, spread, flow, Thermodynamics, Energy & Fuels, Engineering

Abstract: 

This paper investigates the flame attachment characteristics in inclined trenches through experimental and theoretical analyses. The experimental data include the flame geometry, pulsation, upslope gas temperature, and velocity with different sidewall heights, heat release rates, and slopes. We focus on four distinct states and two crucial critical angles of flame attachment at different slopes. The effects of heat release rate and trench configuration parameters on flame attachment are discussed. Four different flame states were observed: I-Vertical; II-Inclined without flame attachment; III-Inclined with flame attachment; and IV-Fully attached. It is revealed that the changes in the flame attachment state result from competing buoyancy and pressure differences between the two sides of the flame. For slopes without sidewalls (with experimental slope angles from 0 degrees to 40 degrees in this work), the flame attachment state significantly depends on the heat release rate, with more inhibition of flame attachment as the heat release rate increases. Trench sidewalls facilitate flame attachment, and the flame attachment state weakly depends on the heat release rate. The flame geometry is characterized using dimensionless parameters based on mechanism analysis. The heat release rate affects both flame height and attachment length in all attachment states. In addition, flame height is affected by slope in State III, while flame attachment length is affected by slope in State III and by trench sidewalls in State IV. Furthermore, the presence of the trench enhances the convective heat transfer, resulting in accelerated velocity growth ahead of the flame front. The flame pulsation conforms to a normal distribution only in sloped conditions since, in sloped trench conditions, the flame is mainly controlled by momentum in State IV.