H_2/CO/空气贫燃预混火焰的临界熄灭条件研究

Critical Extinction Condition of Lean Premixed H_2/CO/Air Flames

通过详细数值计算在较宽H_2/CO比范围内研究了H_2/CO/空气贫燃层流预混对冲火焰的熄灭极限。结果表明:H_2/CO/空气预混火焰的熄灭拉伸率随当量比和燃料H_2含量的增加而增加。分析发现主要分支反应和主要终止反应的平衡和竞争是火焰熄灭的决定性因素,对于组分确定的合成气,引入火焰面上主要分支反应的反应速率ω_B与主要终止反应的反应速率ω_T的对数比值β=ln(ω_T)/ln(ω_B)作为火焰熄灭指数,熄灭时刻所有当量比火焰的β趋近一个常数β_(ext),β_(ext)为临界熄灭指数。β随着拉伸率的增加而增加,当β=β_(ext)时,火焰熄灭。β_(ext)略大于1,随着H_2含量的增加逐渐减小并趋近于1。

The extinction limits of laminar lean premixed opposed-jet counterflow flames were numerically studied using detailed description of chemistry model and mass transport over a wide-range of H2/CO ratio.Results indicate that the extinction stretch rate increases with the increasing H2content in the fuel.The flame extinction depends on the balance and competition between the main branching and terminating reactions.A extinction exponent,β,was defined as the logarithmic ratio between the reaction rate ofthe main terminating reaction ωT and the reaction rate of the main branching reaction ωB on the flame front,i.e.,β=ln（ωT）/ln（ωB）.For a syngas with fixed composition,the β value approaches a constant βext,defined as the critical extinction exponent,at the near-extinction condition for various extinction equivalence ratios.The β value increases with the increasing stretch rate.When β=βext,the flame will extinguish.βext is slightly above1 for syngas flames,and decreases and gradually approaches 1 with the increasing H2 content in the fuel.