Numerical study of flame tilt instability during filtration combustion with reverse flow and extra lean methane/air mixture through a multi-scale model

Currently, the thermal flow reversal reactor (TFRR) is an efficient technique for maintaining stable porous media combustion. However, the development of flame tilt during reverse flow in such reactors has rarely been investigated. This study proposes an innovative multi-scale model to investigate flame tilt dynamics in TFRRs by introducing controlled disturbances at varying factors and levels to systematically generate flame tilt angles and track their evolution. Furthermore, to capture the periodic flame behavior under reverse-flow conditions, the proposed multiscale model divides the fluid domain into five distinct sub regions.
Of these, two sub regions exhibiting alternating flame propagation are simulated with the pore-scale method, while the remaining three are modeled using the volume-averaged method. The results indicate that the magnitude of flame tilt is significantly greater during upward flow phases compared to downward flow. Among the investigated perturbations, flame tilt caused by flow rate disturbances is the most pronounced, while methane concentration perturbations induce the least pronounced tilt. Within each half-cycle, the most rapid reduction in flame tilt occurs with specific heat and porosity perturbations. ... mehrThe tilt angle of the flame front with flow rate disturbances exhibits the highest sensitivity to disturbance levels among the four factors studied. When the reversing cycle exceeds a critical duration, the tilt angle begins to decrease after reaching its peak value. Through comprehensive analysis, the optimal reversing cycle is determined to be 360 s, as this duration combines low peak tilt angles with minimal fluctuations in flame front inclination during semi-cycles. This investigation provides valuable insights for enhancing the stable operation of thermal flow reversal reactors and advancing porous media burner applications.