Computational study of the multidimensional spread of smouldering combustion at different peat conditions

Smouldering combustion is the slow, low-temperature, flameless burning of porous fuels, which propagate both laterally and in-depth. In this study, we build a physics-based two-dimensional model to simulate lateral and in-depth smouldering spread simultaneously based on open-source code Gpyro. We first validate the model against a shallow-reactor experiment (of 1.6 cm thickness) in the literature. Based on the validated model, we then investigate 2D smouldering in a 3 times deeper peat layer at different soil conditions. We found that lateral and in-depth spread rates are linearly correlated with the inverse of organic density and also with oxygen's diffusivity through soil. Due to the direct access to oxygen at the free surface, the lateral spread is approximately 10 time faster than in-depth spread. In addition, for lateral spread the influence of inorganic density and moisture can be explained by a unified parameter, heat sink density, agreeing well with previous experimental results. With the 2D model, this study well predicts the effects of peat conditions on multidimensional smouldering spread and reveals the controlling mechanism for both lateral and in-depth spread, providing a deeper fundamental understanding on this complex phenomenon.