Forced forward smolder combustion: Fid-Bau Portal

Forced forward smolder combustion

Schult, D.A. / Matkowsky, B.J. / Volpert, V.A. / Fernandez-Pello, A.C.

Samples are porous cylinders closed except at the ends, with gas forced into the sample through one end. A smolder wave is initiated at that end and propagates in the same direction as the gas flow. Asymptotic methods are used to find smolder wave solutions with two different structures. Each structure has two interior layers, i.e., regions of relatively rapid variation in temperature separated by longer regions in which the temperature is essentially constant. One layer is that of the combustion reaction, while the other is due to heat transfer between the solid and the gas. The layers propagate with constant, though not necessarily the same, velocity, and are separated by a region of constant high temperature. A so-called reaction leading wave structure occurs when the combustion layer is faster, while a so-called reaction trailing wave structure is obtained when the combustion layer is slower. The former (latter) occurs when the incoming oxygen concentration is sufficiently high (low). For each wave structure there exist stoichiometric, and kinetically controlled solutions in which the smolder velocity is determined, respectively, by the rate of oxygen supply and the rate of consumption. Stoichiometric (kinetically controlled) solutions occur when the incoming gas flux is sufficiently low (high). For each of the four solution types, there are analytical expressions for the propagation velocities of the two layers, the burning temperature, the final degree of solid conversion, and the spatial profiles of temperature, gas flux, and oxygen concentration. The solutions obtained provide qualitative theoretical descriptions of various experimental observations of forward smolder. In particular, the reaction trailing and reaction leading stoichiometric solutions correspond to experimental observations in literature.