Smoldering propagation and blow-off on consolidated fuel under external airflow

Abstract

Propagation of smoldering combustion and its blow-off phenomena are of practical importance in evaluating the fire dynamics of solid fuels, but the scientific understanding is still limited. In this work, we quantify the smoldering propagation rates on consolidated biomass and the blow-off limits under concurrent and opposed external airflows up to 50 m/s. The incense cylinders with different diameters (1.5–5.0 mm) and densities (720–1,100 kg/m3) are tested. As the airflow velocity increases, the smoldering propagation rate first increases to its maximum value (Oxygen-limited Regime) and subsequently remains stable (Thermal Regime), regardless of the airflow direction. Afterward, it slightly decreases (Chemical Regime) until blow-off, and the blow-off of opposed smoldering is easier, similar to the pattern of flame spread. The blow-off airflow velocity (13–46 m/s) of smoldering combustion is around ten times larger than that of flaming combustion, and it decreases as the fuel diameter or density increases. This work advances the fundamental understanding of the smoldering propagation, blow-off, and its persistence; thus, helping guide the fire suppression strategies of smoldering.