微通道中催化段对CH_4/Air预混火焰稳定性的影响

Impact of a Catalytic Segment on the Stability of Premixed CH_4/Air Flames in a Micro Channel

微通道中的火焰传播面临巨大散热损失率带来的挑战。自从Maruta于2005年发现反复熄火又着火的不稳定火焰(FREI)以来,许多学者对此进行了研究。本文以Maruta的物理模型(内径2mm、长度80mm,具有固定壁温分布的石英圆管)为研究对象,在微通道内某个合适的位置涂覆3mm长的Pt催化剂,考察这种独特方式对CH_4/Air火焰稳定性的影响。模拟结果证实,该方法对FREI火焰有显著的抑制作用。论文从均相反应与非均相反应之间的相互作用进行了理论分析,结果表明催化段会提前消耗部分CH_4和O_2,同时,当火焰靠近催化段时,催化段对气相燃烧中间组分的吸附增强。在这两种因素的共同作用下,火焰向上游传播的范围受到限制,不会进一步传播到上游壁温过低的位置而发生熄灭。

The large heat loss ratio is a big challenge to sustain a stable flame in micro channels. The flame with repetitive extinction and ignition(FREI) has received extensive attention since it was first observed in a micro channel with a prescribed wall temperature profile by Maruta et al. in 2005. In the present work, we proposed to impose a 3-mm Platinum(Pt) segment on the channel wall to improve the flame stability of CH4/air mixtures in the identical channel(2 mm in diameter and 80 mm in length). The results manifest that flame instability can be effectively improved by a short Pt segment located at a suitable position. The effect of heterogeneous reaction on homogeneous combustion was analyzed. It is revealed that the Pt surface consumes some amount of CH4 and O2 in advance.Moreover, the adsorption of intermediate species grows stronger when flame propagates upstream. As a result, the burning velocity of homogeneous combustion is reduced and flame propagation range is restricted to the downstream of the catalyst where the wall temperature is relatively high. Hence,flame quenching can be avoided.