Description

Thermal radiation emission from a simulated black flame surface to a fuel bed is analyzed by a ray-tracing technique, tracking emission from points along the flame to locations along the fuel bed while accounting for absorption by environmental water vapor in the intervening medium. The Spectral Line Weighted-sum-of-gray-gases approach was adopted for treating the spectral nature of the radiation. The flame and fuel bed for the simulations are modeled two-dimensionally with the flame being one-tenth as long as the fuel bed. Flame heights of 1 and 10 m were explored, and the angle between the flame and the fuel bed was specified to be either 60 or 90 degrees. Simulated flame temperatures of 1000 K and 1500 K were investigated. The study reveals that water vapor at 100 percent humidity will reduce the incident radiation at the base of a 1000 K flame by 9 percent for a 1 m flame and 16 percent for a 10 m flame oriented normal to the fuel bed. Radiation from an angled flame (oriented at 60 degrees from the fuel bed) experiences slightly less attenuation from water vapor than the 90-degee flame. Further, local attenuation of the hotter flame (1500 K) from environmental water vapor is higher than for the 1000 K flame. The relative effect of the water vapor attenuation is increased with distance from the flame base.