An experimental study of ejected flames and combustion efficiency

Abstract

This paper describes a series of fire experiments in a 0.9m by 0.6m by 0.4m high compartment. A single rectangular opening is set for the ventilation with opening factors (AH 0.5 ) ranging from 0.02 m 5/2 to 0.10 m 5/2. Propane gas and three kinds of solid fuel (wood crib, PMMA and polyurethane flexible foam) are used as fuels. Mass loss rates are measured and net heat release rates are estimated with a furniture calorimeter to examine combustion efficiency, which effects ejected flame formation. Results indicate that the combustion efficiency of gas fuel depends on 'fuel to air' global equivalence ratios (φ ) and the efficiency starts to decrease at about the 0.75 of φ. Moreover, the efficiency reaches 77 % when φ is at 1.27. However, when more fuel is supplied, the efficiency is improved to 100 % at the 2.0 point, because combustion is promoted within externally ejected flames. In the case of solid fuels, maximum heat release rates become 1.5 to 2.5 times higher than the suppositional maximum heat release rate determined by the opening factor. Under these cases, flames are ejected longer and the efficiency of the combustion also recovers as well as gas fuel combustion. Copyright © International Association for Fire Safety Science.