Laboratory investigation of the ignition and spread of smouldering in peat samples of different origins and the associated emissions

Abstract

Tackling peatland wildfires, the largest fires on Earth in terms of fuel consumption, is an emerging combustion topic in the context of climate change. The understanding of fundamental smouldering dynamics and their application to peatlands are essential to mitigation methodologies’ development, but not yet fully understood in the literature. Most of the previous laboratory smouldering studies used horticultural peat which has a great advantage in controlling the influential factors, but has lower bulk density, and is not representative of some higher bulk density peat found in the field. In this thesis, a series of laboratory experiments were conducted to investigate the critical ignition conditions and governing fire spread parameters of smouldering in peat of various origins, and to quantify the associated emissions. To better understand natural variations, field samplings were conducted in Sumatra, Indonesia and Flow Country, Scotland. In addition, five types of horticultural peat were studied. The results show high bulk density peat from long-term drained peatlands experiences more extensive burning in terms of the amount of carbon and particle emitted, while newly drained peat with low bulk density is more vulnerable to fire in terms of easier ignition and faster fire spread. Evidence was found in this thesis that the heat sink density and the organic density, not only control horizontal spread and in-depth spread, but also determine ignition probability. Furthermore, as smouldering is multidimensional, a critical angle of spread direction (65˚ relative to horizontal plane) above which smouldering cannot self-sustain was found. By studying the emissions of different types of peat, the modified combustion efficiency (MCE) range for smouldering was broadened to 0.74 – 0.88, and found to be significantly dependent on the fuel composition. This thesis provides a better understanding of how smouldering wildfires start and spread in different types of peat and the associated emissions, thus contributing to prevention and mitigation.