Flame spread over n-butanol at sub-flash temperature in normal and elevated altitude environments

Comparative tests were conducted at normal (Hefei city, 50 m, 100 kPa) and elevated altitude (Lhasa city, 3,650 m, 64 kPa) on flame spread over sub-flash n-butanol surface. Flame height, flame pulsation frequency, flame spread rate, and subsurface convection flow size and temperature are quantified to find out their behavioral changes for these two altitudes. Results show that the flame is less luminous and lower soot production, while the flame height and flame pulsation frequency are larger at the elevated altitude. A theoretical deduction of fuel diffusion process based on Fick's second law predicts that the flame pulsates more frequently at higher initial fuel temperature, which accords well with experimental results. The flame pulsation period can be well correlated with dimensionless initial fuel temperature by a semi-logarithmic fit, regardless of altitude. In addition, the flame propagates more rapidly in Lhasa, so that the fire hazard of the fuel leakage accident at the elevated altitude is greater than the normal counterpart. The variation trend of subsurface convection flow length is the inverse of initial fuel temperature at both altitudes. For a given initial fuel temperature, the subsurface convection flow temperature and size at the elevated altitude are smaller than those recorded at the normal altitude. The present findings provide a significant supplement over previous knowledge concerning liquid flame spread behaviors.