二级环流对双级贫预混火焰熄火边界的影响

Influence of secondary coflow on the extinction limit of dual-stage lean premixed flame

摘要:

为改善预混火焰的燃烧稳定性，提出双级贫预混燃烧的火焰组织思路，对预混气流进行不同当量比的径向分级，使其能在较低当量比时稳定燃烧.以一定流动条件下直管射流火焰和双级贫预混火焰的中心气流所能达到的最小稳燃当量比作为熄火边界，实验测量并分析火焰不同组织方式和环流条件变化对熄火边界的影响.结果表明：布置在射流火焰外围的环流对火焰根部附近的浓度和速度分布有一定影响；双级贫预混火焰的二级预混环流能够通过减弱外界环境气氛对锋面前预混气的稀释作用而拓宽火焰的熄火边界；环流的预混当量比是影响火焰熄火边界的关键.与均一当量比的直管射流火焰相比，双级贫预混火焰能够在更低的当量比条件下稳定燃烧，对工业上控制NO_x排放有着重要的意义.

Abstract:

Dual-stage lean premixed combustion is proposed to improve the stability of premixed flame. It is organized by dividing premixed gas into radial stages with different equivalence ratio for the purpose of stable combustion under lower global equivalence ratio. The minimum equivalence ratio of primary gas in jet flame or dual-stage lean premixed flame is defined as extinction limit and measured experimentally, and the effect of flame manner and coflow parameters on extinction limit is investigated. The result shows that the outer coflow affects the distribution of concentration and velocity near flame root. The secondary premixed coflow in dual-stage lean premixed flame can reduce the dilution effect of outside atmosphere on the premixed gas, so the flame has a wider extinction limit. The secondary equivalence ratio is key parameter affecting extinction limit of dual-stage lean premixed flame. Comparing with uniform jet flame, the dual-stage lean premixed flame can combust under lower equivalence ratio, which is important for industrial controlling of NO_x emission.