Impacts of a Porous Surface on Flame Acceleration

Abstract

Deflagration-to-detonation transition (DDT) is a critical phenomenon in the development of detonation-based propulsion systems and in industrial gas safety. Recent experimental investigations by Jiang et al. and Lin et al. demonstrated that porous copper foam integrated into the walls of a square combustion channel reduced the detonation onset distance of a stoichiometric ethylene-oxygen mixture. Understanding the mechanisms responsible for this behaviour remains incomplete. This work investigates the influence of a porous boundary on flame acceleration and pressure-field development through direct numerical simulation using the compressible reacting-flow solver PeleC. Simulations were performed for a stoichiometric ethylene-oxygen mixture within a 30 mm × 30 mm square tube. The porous medium was represented using a simplified custom boundary condition consisting of evenly spaced circular outlet pores. This representation was intentionally designed to isolate surface-level mass and flow interactions while excluding combustion and transport within the internal pore structure. Post-processing techniques were developed to quantify flame propagation, shock formation, pressure-field evolution, and transport through the porous boundary. Equal-resolution comparison of the smooth-wall and porous simulations demonstrated no measurable reduction in bulk flame velocity over the available simulation interval. However, the porous boundary substantially altered pressure-wave development. Shock formation was delayed by approximately 56 μs relative to the smooth-wall simulation while occurring at a similar axial location, indicating that the porous boundary primarily influenced the rate of pressure-wave buildup. Interaction between the developing pressure field and porous boundary began prior to direct flame interaction with the pores, while mass and kinetic-energy transport increased substantially following arrival of the flame and high-pressure products. Velocity-field analysis additionally identified a reversal in transverse near-wall flow that provides a potential coupling mechanism between the bulk flame and processes occurring within the porous structure. The results demonstrate that, under the simplifying assumption of representing the porous medium as surface-level outlet pores, the experimentally observed enhancement in flame acceleration is not reproduced. The simulations instead demonstrate pressure-wave attenuation and delayed shock development while retaining similar bulk flame propagation at equal resolution. These findings indicate that physical processes excluded by the simplified boundary representation, particularly combustion and flow transport within the porous volume, may be important to reproducing the acceleration observed experimentally.