Combustion regimes in inert porous media: From decoupled to hyperdiffusive flames

Abstract

Based on the classical volume-averaged equations, this work proposes a classification of porous media combustion in three distinct regimes for increasing interphase heat transfer, namely: decoupled, intermediate and hyperdiffusive. In the decoupled regime, flames behave as preheated free-flames. In the intermediate regime, large superadiabaticities are found. In the hyperdiffusive regime, flames are governed solely by an increase in thermal conductivity. The transition between these regimes is shown to be driven by two dimensionless parameters. The extent of the intermediate regime and the maximal superadiabaticity are proven to be related to the ratio between the diffusive and reactive length scales of the reference free-flame. Eventually, it is emphasized how the heat-recirculating system acts locally as a Lewis-changing device, whose effect harmonizes in the hyperdiffusive regime.