Near-wall flame propagation behaviour with and without surface reactions

Abstract

Direct numerical simulations of premixed flames propagating and impinging on the wall surface are performed to investigate the near-wall flame behavior. The evolution of the flame front, which is established from an ignition kernel initially to mimic a standard experimental procedure, shows that the near-wall flame propagation has unique characteristics and following results are obtained. Displacement speed of the flame propagating normal to the wall yields a local minimum value near the wall before temporarily increases and quenches. This local minimum value becomes almost identical to a corresponding laminar flame speed when the wall temperature is close to the unburnt gas temperature initially. These trends are consistently observed for various ignition positions, equivalence ratios and fuels. Effects of radical removal by the surface reaction on the near-wall flame behaviour are also investigated. It is found that the adsorption of H-atom makes a substantial contribution for the suppression of the near-wall heat release rate under the conditions of present study. However, since the region where the radical removal affects heat release rate is much closer to the wall surface than the quenching distance, there is negligible effect on the near-wall flame displacement speed behaviour. These findings suggest that the present configuration could be used as a robust flame speed measurement technique, similar to the conventional double-kernel method, but without adverse effect of thermo-diffusive instability.