Studies of the combined effect of heat recirculation and stretch on mesoscale flame propagation

Flame propagation and extinction in two-dimensionally mesoscale channels are numerically investigated accounting for flame-wall interaction, channel width, fuel concentration, and flow velocity. A new eigenvalue approach is developed to predict the multiple flame regimes and their transitions of mesoscale combustion. The results show that at small channel widths, there is a non-monotonic dependence of flame speed on fuel concentration due to the appearance of multiple flame regimes. With the decrease of fuel concentration, the fast flame first extinguishes and then transits to the slow flame regime. At large channel widths, it is found that the two flame regimes merge together and fast flame can transit to slow flame regime smoothly without extinction. The results also demonstrate that the flow velocity has a significant impact on flame speed. A non-linear dependence of flame speed on flow velocity via the flame-wall interaction and the change of flame geometry is obtained. The present results gave a good explanation to experimental observation.