Modeling of Two-Dimensional Natural Downward Smoldering of Peat

Abstract

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.

Influence of soil conditions on the multidimensional spread of smouldering combustion in shallow layers

“…Huang and Rein [23] explained that this is because of the faster oxygen transport due to swelling. IC, on the other hand, slightly decreases in-depth spread, according to both experiments and modelling [24,25]. Notably, as the fire moves downward, in-depth spread rate decreases with depth due to the accumulation of ash above the oxidation zone reducing the oxygen supply [23,24,26].…”

Experimental study of the effect of water spray on the spread of smoldering in Indonesian peat fires

“…This data is in contrast to Prat [18] that found a range of mass consumed of 84.3 ± 4.9% −93.7 ± 2.1% for multiple moisture contents of peat. This may occur due to the different characteristics of the peat samples and also the different insulation used in the apparatus which alters the balance between heat generation and heat lost [19].…”

Downward spread of smouldering peat fire: the role of moisture, density and oxygen supply

“…As (1) the vertical dimension was clearly larger than the cross-section dimension and (2) the smouldering spread is extremely slow, the whole downward spread may be approximated as a 1-D spread phenomenon, similar to those in Benscoter et al 2011 andZaccone et al 2014). This 1-D dominated downward spread of smouldering peat fire without the wind is different from other multi-dimensional smouldering spread over small and shallow peat samples (Hadden et al 2013;Huang et al 2016;Prat-Guitart et al 2016;Yang et al 2016).…”

“…1), which plays an important role in the estimation of soil carbon emission. The DOB and critical MC for extinction ðMC Ã ex Þ at the vertical downward (or indepth) spread of peat fires have been investigated by various experiments (Benscoter et al 2011;Watts 2012;Davies et al 2013;Zaccone et al 2014) and numerical simulations Rein 2015, 2016a;Yang et al 2016). Recently, laboratory experiments on the horizontal fire spread over a shallow peat sample showed that the spread rate decreased with MC but increased with the forward wind speed (Huang et al 2016;Prat-Guitart et al 2016).…”