Ventilation-controlled combustion of polymers

Abstract

Ventilation-controlled combustion in buoyant turbulent diffusion flames of polymers with CH, CHO, and CHON aliphatic and aromatic structures has been examined. Correlations have been established between equivalence ratio and combustion efficiencies (chemical, convective, and radiative), generation efficiencies of combustion products (CO, CO 2, hydrocarbons, soot, and other products) and consumption efficiency of O 2. Relationships resembling flammability limit diagrams have been developed between the generation efficiencies of CO and CO 2, and soot and CO. With increase in the equivalence ratio, chemical and convective efficiencies of combustion, generation efficiency of CO 2, and consumption efficiency of O 2 decrease, whereas radiative efficiency of combustion and generation efficiencies of CO, hydrocarbons, soot, and other carbon containing products increase. These changes in the combustion properties are due to deviations from thermodynamic equilibrium and each change is correlated in terms of the equilibrium fraction of the combustion property as a function of the equivalence ratio. For similar magnitude of increase in equivalence ratio, fuels with CHO and CHON structures show rapid increase in the generation efficiencies of CO and hydrocarbons compared to the generation efficiency of soot, whereas fuels with CH structures show rapid increase in the generation efficienty of soot, compared with the generation efficiencies of CO and hydrocarbon. This is consistent with the general understanding of the formation of soot and CO. For equivalence ratio of four or greater, flames are extinguished, but nonflaming combustion continues as long as the fuel continues to be generated as a result of external heat flux exposure. Correlations have been developed as inputs to models for enclosure fires to assess thermal and nonthermal hazards due to generation of heat, soot, CO, hydrocarbons, and corrosive and toxic products and prevention and protection from such hazards.