Blockage of thermal radiation by the soot layer in combustion of condensed fuels

Abstract

Radiation blockage is considered as an important radiative characteristic in fires. In the present study, the radiation blockage effect by a soot layer between the flame and the fuel surface is investigated through two simplified models; 1) a flame with an infinitesimal thickness (a flame sheet), and 2) a flame with a finite thickness. The analysis considers a onedimensional flame in which soot particles play a dominant role in the radiation exchange. Sample calculations are performed for soot volume fractions ranging from 1×10⁻⁷ to 1×10⁻⁵. Using experimentally obtained soot volume fraction data, it is shown that for polymer fuels of polymethyl methacrylate (PMMA), polyproplyene (PP), and polyoxymethylene (POM), no significant contribution of radiation blockage due to soot exists in moderate scale fires (L≈0.5 m); however, for polystyrene (PS) fuels the contribution becomes quite significant even in small scale fires (L≈0.08 m).