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International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE (Open Access)

Computational study of critical moisture and depth of burn in peat fires

Xinyan Huang A and Guillermo Rein A B
+ Author Affiliations
- Author Affiliations

A Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, United Kingdom.

B Corresponding author. Email: g.rein@imperial.ac.uk

International Journal of Wildland Fire 24(6) 798-808 https://doi.org/10.1071/WF14178
Submitted: 1 October 2014  Accepted: 11 March 2015   Published: 30 July 2015

Journal Compilation © IAWF 2015

Abstract

Smouldering combustion is the slow, low-temperature, flameless burning of porous fuels and the most important phenomenon of wildfires in peatlands. Smouldering fires propagate both horizontally and vertically through organic layers of the ground and can reach deep into the soil. In this work, we develop a one-dimensional computational model of reactive porous media in the open-source code Gpyro. We investigate the vertical in-depth spread of smouldering fires into peat columns 20 cm deep with heterogeneous profiles of moisture content (MC), inert content (IC) and density. The model solves the species, momentum and energy conservation equations with five-step heterogeneous chemistry, to predict the transient profiles of temperature, species concentration, reaction rates and depth of burn from ignition to spread and to extinction. Modelling results reveal that smouldering combustion can spread over peat layers with very high MC (>250%) if the layer is thin and located below a thick, drier layer. It is shown that the critical moisture for extinction can be much higher than the previously reported critical MC for ignition (e.g. extinction MC up to 256% for low-IC peat, with critical ignition MC of 117%). The predicted critical MC values and depths of burn are compared with experimental measurements for field samples in the literature, showing good agreement. This study provides the physical understanding of the role of moisture in the ignition and extinction of smouldering peat fires, and explains for the first time the phenomenon of smouldering in very wet peat layers.

Additional keywords: extinction, ignition, modelling, peatland, smouldering, soil moisture, surface fuel, wildfire.


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