Towards understanding the effect of sub-atmospheric pressure on flame height, gas-phase temperature and radiation characteristics of turbulent diffusion flames in high-altitude areas

Sub-atmospheric pressure in plateau poses a significant threat to energy safety during fire events. Understanding the flame length scales, gas-phase temperature and radiation characteristics of turbulent diffusion flames at sub-atmospheric pressures is necessary to ensure fire safety in energy facilities and increase energy utilization efficiency on high-altitude areas. This work presents a comprehensive experimental investigation of turbulent diffusion flames in sub-atmospheric pressures P (30–100 kPa). Results show that time-averaged turbulent diffusion flame height elongates due to a lower air entrainment rate (α˜) as pressure reduces, resulting in a two-thirds power law dependence on the product of dimensionless heat release rate and α˜. Axial gas-phase temperature becomes lower in fuel-rich region with a lower air-fuel mixing rate, while it is higher in thermal plume region under sub-atmospheric pressures. A piece-wise function between axial temperature rise and dimensionless height divided into 5 stages was obtained at different pressures. Radiative fraction and near-field radiative heat flux decrease with the decreasing pressure as the soot formation is suppressed in reduced pressures. Radiative fraction is deduced as a function of α˜−1/3P1/3 using the optically thin flame approximation. Based on solid flame model, near-field radiative heat fluxes received by horizontal targets are well predicted considering the axial gas-phase temperature change. The results of this work contribute to an in-depth understanding of the impact of sub-atmospheric pressure on plateau fires, and provide key scientific support for fire prevention and the sustainability of energy systems in high-altitude areas.