In this work, a one-dimensional (1-D) model of a reactive porous media is developed to solve the heat and mass transfer equations with heterogeneous chemistry. The model first predicts the smouldering thresholds, relating to the critical moisture and inert contents. Modelling results show a good agreement with experiments for a wide range of peat types. Then, the model is optimized to investigate the in-depth spread of peat fire into layers of heterogeneous profiles of moisture, mineral and density. Modelling results reveal that smouldering combustion can spread over peat layers of very high moisture content (> 250%), and the critical moisture for extinction can be much higher than that for ignition. The predicted critical moisture values and depths of burn show a good agreement with measurements of 20-30 cm thick peat samples in the literature. Afterwards, the model reproduces the mass loss rate of a bench-scale peat fire under various oxygen concentrations, and predicts that the minimun oxygen concentration for smouldering of dry peat is around 11 %, much lower than flaming wildfires. This is the first time that the in-depth spread of peat fires is systemically studied based on a computational model to bridge the experimental data in last decades, thus helping to understand this important natural and widespread phenomenon.
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