关键词: 微通道, 甲烷, 凹腔, 火焰稳定性, 吹出极限, 流场, 数值模拟

Abstract: Premixed CH₄/air combustion in a mesoscale channel with cavities were experimentally investigated and compared with that without cavity. The experimental results demonstrate that no symmetric stable flame is observed in the channel without cavities and flame is prone to inclining and pulsating. In contrast, flame can be effectively anchored by the recirculation zone and low velocity zone in the channel with cavities. When the inlet velocity is close to blowout limit, curved fluctuating flames occurs. The blowout limit of the channel with cavities is 0.8, 1.35 and 1.75 m·s^-1 for the equivalence ratio of 0.8, 0.9 and 1.0 respectively, which is several times larger than the corresponding burning velocity of incoming CH₄/air mixture. These indicate that the cavities have a strong ability to anchor flame. Numerical simulation is performed to help analyzing the flame blowout mechanism, and reasonable accuracy of the numerical model adopted is confirmed. Results reveal that a large shear stress exists at the transition point between the ramped cavity wall and downstream inner wall, making flame split at high inlet velocity, and it is difficult to stabilize the flame in a straight channel. Once the second part of the reaction zone is separated from the one in the cavity, it is prone to blowout. In summary, flame behavior in the mesoscale channel with cavities strongly depends on the interactions between the reaction zone and flow field.

Key words: microchannels, methane, cavity, flame stability, blowout limit, flow field, numerical simulation