Effect of Fuel Spacing on Horizontal Flame Spread and Merging in Discrete Fuel Arrays with Dual Fire Sources

This study focuses on flame spread and merging in discrete fuel arrays composed of birch rods under dual fire source conditions. Tests were performed with five fuel spacings (nL/W = 1, 2, 3, 4, single source) and eight array spacings (S = 2 mm to 9 mm) to quantitatively evaluate the influence of these parameters on the flame merging behavior and key spread characteristics. The results indicate that the probability of flame merging decreases with increasing fuel spacing and is strongly affected by array spacing. Both the inter-fire temperature and dimensionless temperature rise were found to follow distinct power-law relationships with spacing. Flame height is governed by both spacing parameters. In contrast, the flame spread rate responded to array spacing but exhibited minimal sensitivity to fuel spacing. In this study, heat flux between the two arrays is demonstrated to be dominated by thermal radiation. A predictive model was formulated for the merged flame height, demonstrating close agreement with the experimental results.