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ABSTRACT
Upward flame spread over inclined solids is a classical research topic in combustion science and fire safety. However, most of previous works focused on flame spread over continuous solid. In addition, the fire hazard of extruded polystyrene (XPS) thermal insulation materials using on building façade has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of building façade, experimental research on upward flame spread over discrete XPS separated by air intervals under different inclined angles (α = 60°, 75°, 90°, 105°, 120°, and 135°) is conducted in this paper. The influence of inclined angle on discrete flame spread characteristics, including flame shape, flame height, flame spread rate, temperature distribution and heat transfer behavior, are revealed. As α ≤ 90°, there existed a flame vortex in the air interval, which may attribute to the increase of flame spread rate. The average flame height decreased with the increase of inclined angle. The time of flame spread stagnation at intervals rose with the increase of the inclined angle. However, the flame spread rate and melt zone length decreased with the increase of the inclined angle. an empirical formula concerning the flame spread rate and inclined angle was proposed. When α < 90°, the high-temperature zone was close to the wall surface. But when α > 90°, the high-temperature zone was above the air interval and on the XPS bottom. As α ≥ 90°, the average heat flux first dropped and then rose with an increase in inclined angle, while the trend was inverse for α ≤ 90°. A mathematical model was established to predict the flame spread rate of discrete XPS. The experimental results demonstrated the mathematical model was reliable.