Smouldering in fixed beds of oil shale grains: governing parameters and global regimes

This paper examines the various regimes that may prevail in a smouldering process in a combustible porous medium, and their consequences from a physical point of view and for the formulation of a macroscopic description. A set of governing parameters are first identified, by use of a dimensional analysis. Then, their influence is illustrated by direct and detailed numerical simulations on the microscale. In particular, the lack of local thermodynamic equilibrium is demonstrated in many situations, which prevents a rash application of simple homogenized models. Finally, an application of matched microscopic and macroscopic descriptions in separate domains is presented, together with a determination of the associated effective coefficients for the latter.