Extinguishment of Liquid Heptane and Gaseous Propane Diffusion Flames

Abstract

This paper presents a comparative study of the extinguishment of liquid heptane and gaseous propane diffusion flames caused by the addition of flame-suppressing agents (N2 and CO2) into a coflowing stream of air. Measurements included mass burning rate, concentrations of suppressants at flame extinction, inflame temperature profiles, and exhaust composition. Adiabatic equilibrium temperatures of the stoichiometric mixtures of the fuels in pure airstream, and in the airstream containing flame suppressants with the concentrations corresponding to flame extinction, were calculated. Although the extinction processes of liquid and gaseous fuel flames are markedly different, even when both are buoyancy dominated, the extinction mechanism of CO2 and N2 in both flames is primarily thermal. The reaction zone temperature in the flame-anchoring region of the heptane flame at extinction agrees well with the adiabatic flame temperature corresponding to the lean flammability limit. In propane flame, where the flame base is lifted off the burner before extinction, the reaction zone temperature at extinction is 100-200 K higher than the adiabatic flame temperature at the lean flammability limit.