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首页> 外文期刊>Fuel >Stabilization and blowout characteristics of lean premixed turbulent flames behind a backward-facing step in a rectangular combustor with heated propane-air mixtures
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Stabilization and blowout characteristics of lean premixed turbulent flames behind a backward-facing step in a rectangular combustor with heated propane-air mixtures

机译：矩形燃烧室中带有加热的丙烷-空气混合物的向后步骤之后的稀薄预混湍流火焰的稳定和爆燃特性

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The flame stabilization and blowout velocity of lean premixed turbulent flames in a backward-facing step combustor were investigated experimentally with well-defined stable flames. The dynamic pressure in the combustor was monitored to select a stable regime among overall flame behaviors. The responses in the flame behaviors to changes in the initial conditions of equivalence ratio, inlet temperature, and Reynolds number were simultaneously captured using high-speed CH* chemiluminescence. The results showed that the flame modes were categorized into four representative regimes according to their dynamic behavior, overall sound pressure level, and frequency spectrum: (1) stable regime, (2) unstable regime, (3) quasi-unstable regime, and (4) transition regime. For lean premixed turbulent flames in the stable regime, the flame distance, defined as distance x from the step to flame appearance, increased with the decrease in the initial equivalence ratio, and blowout occurred near the lower flammability limits. The blowout velocities linearly correlated with both the inverse of chemical reaction time (alpha(0)/S-L,0(2))(-1) and extinction strain rate eext, 0 under different initial conditions. The two chemical time scales were obtained using different flame models based on either the premixed laminar flame-speed or premixed opposed-flow flame model. In addition, the flame distances showed a linear correlation of d(f) proportional to U-0/S-L, 0(2) for all the data in the stable regime. This result implies that the lean premixed turbulent flames could be stabilized at flame distances where the local mean flow velocity is balanced with the turbulent flame speed, which is proportional to the square of laminar burning velocity.
机译：通过良好定义的稳定火焰，通过实验研究了后向阶梯燃烧室中稀薄的预混湍流火焰的火焰稳定性和吹出速度。监测燃烧器中的动态压力以在整体火焰行为中选择稳定的状态。使用高速CH *化学发光同时捕获了火焰行为对当量比，入口温度和雷诺数初始条件变化的响应。结果表明，火焰模式根据其动态行为，整体声压级和频谱分为四个代表性状态：（1）稳定状态，（2）不稳定状态，（3）拟不稳定状态和（ 4）过渡制度。对于处于稳定状态的稀薄预混湍流火焰，火焰距离（定义为从台阶到火焰出现的距离x）随着初始当量比的减小而增加，并且在较低的可燃性极限附近发生爆燃。在不同的初始条件下，喷出速度与化学反应时间的倒数（alpha（0）/ S-L，0（2））（-1）和消光应变率eext，0线性相关。基于预混合的层流火焰速度或预混合的逆流火焰模型，使用不同的火焰模型获得了两个化学时间标度。此外，对于稳定状态下的所有数据，火焰距离显示出与U-0 / S-L，0（2）成比例的d（f）线性相关。该结果表明，稀薄的预混湍流火焰可以稳定在火焰距离处，在该距离处局部平均流速与湍流火焰速度平衡，湍流火焰速度与层流燃烧速度的平方成比例。

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