Characteristics of horizontal flame spread and merging of discrete fuel arrays with dual fire sources: Effect of array distribution and layout

Discrete fuel arrays in forest and built environments pose significant hazards during multiple fire source combustion. This study quantitatively investigates the influence of array distribution, through a systematic combination of eight array spacings ( S = 2–9 mm, stepped by 1 mm) and six column numbers ( n = 1–11, stepped by 2), on flame merging and key spread parameters. Experiments show that the merged flame height increases with both n and S , while the dimensionless flame height ( L f * ) exhibits an inverse-power relation with array width ( W ). The introduction of the radiative fraction ( χ rad ) reveals that heat transfer of discrete fuel arrays with dual fire sources is jointly dominated by radiation and convection (with χ rad , avg = 0.525), and the interaction between the two sources enhances convective heat transfer. In contrast to an individual fire source, dual fire sources in discrete fuel arrays exhibit a higher mean flame spread rate ( V f ). Accordingly, a segmented correlation for V f on W is derived. A theoretical formulation for predicting the MLR of discrete fuel in dual-fire-source arrays is developed, providing a quantitative basis for risk assessment and prevention in multi-source fire scenarios.