Orientation effect on upward flame propagation over rigid polyurethane foam

Inclined upward (concurrent) flame spread over rigid polyurethane (RPU) foam which can exhibit great fire hazard in real high-rise building fire disasters has attracted more and more attentions in the previous studies. In this work, a series of bench-scale experiments and theoretical analyses were conducted to explore the orientation effect on upward flame spread of RPU foam with sample inclination ranging from 10° to 85°. Results show that the fitted correlations between flame length and pyrolysis length are different due to the increasing inclinations, and can be categorized by a modified Rayleigh number. Meanwhile, the power exponents of the fitted expressions between flame length and heat release rate per unit width can also be classified: the power exponent n = 1, n<1 and n>1, when 10° ≤ θ ≤ 40°, 50° ≤ θ ≤ 70°, and θ ≥ 80°, respectively. Furthermore, the dimensionless mass loss rate is approximately proportional to the quarter power of the modified Rayleigh number. The relationship between upward flame spread rate and sine of inclined angle is approximately exponential, and a critical modified Rayleigh number at which no flame spread can be sustained is proposed. The results of this study can provide a reference to high-rise building fire risk assessment and energy conservation system design.