Experimental study of the formation and collapse of an overhang in the lateral spread of smouldering peat fires

Huang, Xinyan; Restuccia, Francesco; Gramola, Michela

doi:10.1016/j.combustflame.2016.01.017

Cited by 83 publications

(85 citation statements)

References 23 publications

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“…After extinction, this sandwich structure of fire residue (char þ ash þ char, see (IV) End of spread in Fig. 4a) was always observed under all MCs and bulk densities, and also in previous horizontal spread experiments with the shallow samples of the same peat (Huang et al 2016). …”

Section: Resultsmentioning

confidence: 85%

“…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).…”

Section: Introductionmentioning

confidence: 97%

“…2b). Compared with the naturally sourced peat, it was readily available in large quantities, has relatively homogeneous properties and constant composition, and has been used in a series of past experiments (Belcher et al 2010;Hadden et al 2013;Huang et al 2016;Prat-Guitart et al 2016). After the oven-drying process, this moss peat has a bulk density of 135 AE 5 kg m À3 in its natural state and a low mineral content (IC ,2%).…”

Section: Methodsmentioning

confidence: 99%

“…To obtain the desired MC, the peat sample was first dried at 908C for 48 h, and then well mixed with the corresponding amount of water, the same process as in Huang et al (2016). For example, 1.7 kg of 70% MC peat requires 1 kg of dry peat mixed with 0.7 kg of water.…”

Section: Methodsmentioning

confidence: 99%

“…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). However, He et al (2014) found that the downward smouldering spread rate over the piled biomass powder was not sensitive to MC from 3 to 21%.…”

Section: Introductionmentioning

confidence: 99%

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

Huang

Rein

2017

Int. J. Wildland Fire

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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 À1 equivalent to a carbon emission flux of 200 tonnes day À1 ha À1 . 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.

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Section: Resultsmentioning

confidence: 85%