Study on the flaming-transition behavior of a downwardly smoldering biomass stick utilizing low pressure

Abstract The transition from downwardly (reverse) smoldering to flaming in a low-pressure environment during combustion of a thin-rod biomass stick with low porosity (high density and low permeability) was experimentally investigated to determine the dominant factor affecting the critical condition of this transition. After forced ignition at the top of the specimen, the downward smoldering progressed steadily, although the lengths of the luminous region slowly increased with time under certain conditions. The condition for a spontaneous transition to flaming was identified under various oxygen partial pressures. Such a spontaneous transition was not observed when the partial pressure of oxygen was sufficiently low (