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Abstract
The attenuation of radiation transfer from wildland flames to fuel by environmental water vapor is investigated. Emission is tracked from points on an idealized 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 employed 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 both vertical and angled flames were studied. Simulated flame temperatures of 1000 K and 1500 K were investigated. The study reveals that the effect of absorption of flame radiation by environmental water vapor is quite modest locally. For the worst-case scenario of 100% relative humidity, water vapor was found to reduce the incident radiant flux at the base of a vertically oriented flame at 1000 K flame by 9% for a 1 m flame and 16% for a 10 m flame. Radiation from the angled flame (30 deg from the vertical) experiences less attenuation from water vapor than the vertical 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 increases with distance from the flame base.