Transcripción del resumen del autor. Natural forward smoldering (which normally occurs in thermochemical conversion of solid fuel) and natural reverse smoldering (which normally occurs in self-ignition fire in piled materials) have been compared theoretically using the volume reaction method. One-dimensional vertical propagation of piled char powder smoldering was used as the model case, in which upward smoldering is reverse smoldering while downward smoldering is forward smoldering. Calculation has revealed that there is significant difference between natural upward and downward smoldering. The following applies in our simulation case: (1) Upward smoldering is dominated by kinetics of char oxidation while downward smoldering is oxygen transport controlled. (2) The propagation velocity of upward smoldering is more than ten times faster than that of downward smoldering. However, the degree of carbon conversion of upward smoldering is much less than that of downward smoldering. (3) The temperature inside the fuel bed of upward smoldering (<630 K) is significantly lower than that of downward smoldering (600-900 K). (4) Char oxidation occurs at very low oxygen fractions (<5%) in either upward or downward smoldering. These characteristics predicted via theoretical analysis are in qualitative agreement with experimental observations in the literature.

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