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Downward Spread of Smoldering Peat Fire: the Role of Moisture, Density and Oxygen Supply
Smoldering fires in peatland are different from the flames in wildland fires. Smoldering peat fire is slow, low-temperature and more persistent, releasing large amounts of smoke into the atmosphere. In this work, we experimentally and computationally investigate the vertical downward spread of smoldering fire in a column of 30-cm tall moss peat under variable moisture content (MC) and bulk density. The measured downward spread rate decreases with depth and wet bulk density, and is about 1 cm∙h-1 with respect to a carbon emission flux of 1 kg∙h-1∙m-2 or 200 ton∙day-1∙ha-1. Moreover, we observe that downward spread increases as MC increases within the range of this study, which is not intuitive and opposite to the trend observed for the horizontal spread in the same peat. We also propose a one-dimensional numerical model of porous media and computational simulations successfully reproduce the experimental observations. The model shows that the vertical spread rate decreases with depth because of the formation and accumulation of a char layer. Modeling results further reveal that the vertical spread rate increases with MC because the fuel density decreases, thus confirming that oxygen supply controls the smoldering spread. This study provides novel physical understanding of how peat fires spread.
WF16198 Accepted 06 August 2017
© CSIRO 2017