本生灯层流预混火焰稳定点与熄火机理

采用速度匹配法结合壁面淬熄分析甲烷本生灯层流预混火焰稳定点与熄火机理,得到了贫油与富油状态下火焰稳定点不同的移动规律,定量预测了火焰吹熄特性关系,并通过实验验证.火焰稳定点在本生灯出口附近的边界层中,该处的火焰传播速度与预混气来流速度相平衡;而在边界层中,以火焰稳定点为起点,存在一个可点火区域.随着来流预混气流速的增大或者当量比远离恰当比,这一可点火区域逐渐缩小,直至成为一个点,此时即为熄火的临界状态.通过比较近壁面的当地气流速度与火焰传播速度,并采用非耦合的方法分析壁面淬熄的影响,得到了火焰稳定点的移动规律.在径向上,火焰稳定点随来流速度增大向射流中心线方向移动;在轴向上,随流速增大,贫油工况下稳定点向下游移动,富油工况时则向上游移动.根据火焰稳定点移动规律结合可点火区域分析定量预测了吹熄特性,通过了实验验证,证明了火焰的熄火机理.

Anchoring point and blow-off mechanism of Bunsen laminar premixed flame

A velocity-matching method (VM Method) combined with the wall quenching effect was used to analyze the anchoring point movements and the blow-off characteristics of a methane-air laminar premixed Bunsen flame in lean and rich conditions. A blow-off model was achieved and proved by experiments. The flame was anchored in the shearing layer near the burner exit, where the local velocity was equilibrium with the flame speed; there was also an ignition area in the boundary layer. This ignition area was diminished when the flow velocity increased or the equivalence ratio was away from the stoichiometric ratio. When the ignition area became a point, the blow-off occurred. The anchoring point movements were predicted by comparing the local flow velocity and the flame speed, and considering the wall quenching effect in a decoupled method. With the increasing incoming velocity, in radial direction the anchoring point moves towards the jet center line, and in flow direction it moves downstream in fuel-lean conditions and upstream in fuel-rich conditions, respectively. This movement and the ignition area analysis predict the blow-off characteristics, and are validated by experiments. The result shows a good precision and proves the blow-off mechanism.