Relationship between pore geometry and flame dynamics in porous media burners

This work investigates the dynamics of lean premixed methane–air flames stabilized in two-dimensional, regular porous media using Direct Pore-Level Simulations (DPLS). The analysis is conducted in two stages: first, unforced flame dynamics are examined, and second, the response to externally imposed broadband velocity perturbations is assessed. Simulations are performed across multiple porous media, and a decoupling between the gas and solid thermal states is adopted to enable a systematic evaluation of the effect of porous properties on flame response. Results of unforced simulations show that, above a critical Reynolds number, vortex shedding from the solid obstacles generates coherent flame fluctuations characterized by a hydrodynamic Strouhal number St$_h$≈0.2, which is largely independent of porosity. Hydrodynamic Transfer Function (HTF) analysis further shows that the porous structure acts as a hydrodynamic filter, selectively amplifying perturbations associated with these intrinsic flow dynamics while attenuating other frequencies as perturbations propagate through the medium. The flame response to the imposed forcing is characterized using inlet- and locally-evaluated Flame Transfer Functions (FTFs). ... mehrThe inlet FTF exhibits a non-monotonic behavior reflecting modulation by hydrodynamic structures generated within the porous medium. In contrast, as the location where the FTF is evaluated approaches the flame front, the influence of hydrodynamic modulation progressively weakens and the response tends toward the low-pass behavior typical of premixed flames. When the response is represented using a Strouhal number based on geometrical properties of the porous medium related to the flame surface area, similar trends are observed across the different porous media. Overall, the present modeling framework shows that the global flame response in porous media results from the combined effect of hydrodynamic modulation within the porous structure and the intrinsic flame response to local velocity fluctuations.

Novelty and significance

This study provides a pore-scale modeling framework for premixed flame dynamics in porous media, combining unforced and forced flame analyses through Direct Pore-Level Simulations. It reveals how intrinsic vortex shedding generates coherent flow structures that selectively modulate flame response, and how porous media act as hydrodynamic filters for inlet perturbations. By decoupling hydrodynamic modulation from the intrinsic flame response, the work demonstrates a largely consistent flame behavior across different porosities, offering a framework built on dimensionless quantities for modeling flame dynamics in more complex porous configurations. These insights advance the understanding of flame–flow interactions and support the development of predictive models.