Characterization of the flame spread behavior and flammability of heterogeneous fuels using a measured B number

Abstract

This study investigates the flame spread behavior of heterogeneous fuels involving polystyrene and corrugated cardboard, using a measured B number to characterize the flammability of the heterogeneous fuels. Investigations of flame spread and flammability have typically been limited to homogeneous solid fuels. However, the combustion of solid combustibles, for example, the warehouse commodities, is practically multi-fuel combustion, which has not yet been well quantified. Experiments are conducted by using 500 × 500 × 500 mm corrugated cardboard cartons, which are compartmentalized into 125 cells and filled with 125 polystyrene cups. The flame spread behavior, the mass loss rate, vertical pyrolysis length, and temperature profile have been measured and analyzed. Five distinct combustion stages are identified. Experimental results show that the first three stages are primarily the combustion of the first column cells and the latter two stages are the combustion of the second column cells. The five-stage combustion process is performed circularly until the burn out of the whole carton. A new method is proposed to estimate the combustion area on internal surface based on the measured temperature profile. By using the measured parameters as well as the estimated combustion area on internal surface, the heterogeneous fuel B numbers for the first three stages are further calculated to quantify the flammability. The average B number of stage 3, during which the combustion of inside polystyrene cups is started, is calculated to be 3.53. By comparing with the B number of single polystyrene or corrugated cardboard, the flammability is increased due to the mixing of polystyrene and corrugated cardboard. The determination of a specific B number is beneficial for the flammability evaluation of heterogeneous fuels.