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

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

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

A Department of Mechanical Engineering, University of California, Berkeley, 60 Hesse Hall, Berkeley, CA 94720, USA.

B Department of Mechanical Engineering, Imperial College London, 614 City and Guilds Building, South Kensington, London SW7 2AZ, UK.

C Corresponding author. Email: seuhxy@gmail.com

International Journal of Wildland Fire 26(11) 907-918 https://doi.org/10.1071/WF16198
Submitted: 1 November 2016  Accepted: 6 August 2017   Published: 31 October 2017

© The Authors 2017 Open Access CC BY-NC-ND, published on behalf of IAWF

Abstract

Smouldering fires in peatland are different from the flames in wildland fires. Smouldering 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 smouldering 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 ~1 cm h−1 equivalent to a carbon emission flux of 200 tonnes day−1 ha−1. We observe that downward spread increases as MC increases substantially at least inside the range from 10 to 70%, which is not intuitive and goes against the trend observed for the horizontal spread in the same peat. We also conduct one-dimensional computational simulations to successfully reproduce the experimental observations. The analysis shows that the spread rate increases with MC and decreases with density because smouldering spread is controlled by the oxygen supply. The volume of the porous peat expands when absorbing water, which reduces the density of organic matter and decreases the heat release rate. This shows that the widely assumed conclusion that the spread rate of wildfire decreases with MC is not universal when applied to smouldering fires.

Additional keywords: carbon emission, fire spread rate, in-depth spread, modelling, peatland.


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