Experimental Investigation and Theoretical Analysis of Flame Spread Dynamics over Discrete Thermally Thin Fuels with Various Inclination Angles and Gap Sizes

Abstract

Flame spread over discrete fuels is a typical phenomenon in fire scenes. Experimental and theoretical research on flame spread over discrete thermally thin fuels separated by air gaps with different inclination angles was conducted in the present study. Experiments with six inclination angles ranging from 0° to 85° and various fuel coverage rates from 0.421 to 1 were designed. The flame spread behavior, the characteristic flame size, and the flame spread rate were analyzed. The results show that the flow pattern, stability, and flame size exhibit different characteristics with different inclination angles and gap sizes. As the inclination angle increases, particularly with smaller gaps, turbulent and oscillating flames are observed, while larger gap sizes promote flame stability. The mechanism of flame propagation across the gap depends on the interplay between the flame jump effect and heat transfer, which evolves with gap size. Average flame height, average flame width, and flame spread rate initially increase and then decline with the increase in fuel coverage, peaking at fuel coverage rates between 0.93 and 0.571 for different inclination angles. A theoretical model is proposed to predict the flame spread rate and the variation in the flame spread rate with inclination angle and fuel coverage. Furthermore, the map determined by inclination angle and fuel coverage is partitioned into distinct regions, comprising the accelerated flame spread region, the flame spread weakening region, and the failed flame spread region. These findings provide valuable insights into flame spread dynamics over discrete thermally thin fuels under diverse conditions.