Modeling of Two-Dimensional Natural Downward Smoldering of Peat

Smoldering combustion,of natural organic layers like peatlands leads to the largest fires on Earth. The multidimensional smoldering structure of peatlands is observed in the field, but the mechanism is poorly understood. In this work, a 2-D cylindrical axi-symmetric model that considers volume shrinkage is developed for the natural downward smoldering of peat with different inorganic contents. Numerical results show that the model captures the two-dimensional multisubfront structure of the peat smoldering process. For the peat with lower inorganic content, the predicted bidimensionality of wall attachment is more obvious, the mass loss rate and the spread rate are higher, and the smoldering front is thinner. For the peat with higher inorganic content, smoldering is more sensitive to lateral heat loss. Both the inorganic content and the lateral heat loss have negative effects on the volume shrinkage, peak temperature, and in-depth spread rate. Additionally, two groups of experiments using peat samples with added inorganic contents of 0% and 66.7% were conducted in an uninsulated furnace. Comparison of the numerical and experimental data shows that the model predicts the smoldering characteristics very well at lower inorganic content and qualitatively well at higher inorganic content. The predicted effects of the inorganic content and lateral heat loss on the peat smoldering process provide a theoretical basis for fire-fighting measures of smoldering peatlands with different levels of inorganics.