预混旋流多喷嘴火焰激光可视化实验研究

Laser Diagnostic on Structure of Premixed SwirlingMulti-Nozzle Flame

关键词:  多喷嘴火焰  预混燃烧  平面激光诱导荧光测量  火焰结构  火焰相互作用  当量比

Key words:  Multi-Nozzle flame  Premixed combustion  Planar laser-induced fluorescence  Flame structure  Flame interaction  Equivalence ratio

摘要:

为了研究预混旋流多喷嘴火焰结构及当量比对多喷嘴火焰结构的影响，针对当量比0.51～0.8的甲烷/空气预混旋流多喷嘴火焰开展了平面激光诱导荧光测量研究。通过实验，获得了不同当量比下预混旋流多喷嘴火焰时均火焰形态和瞬态火焰结构分布特点。实验结果表明，相邻火焰相互冲刷，在相互作用区内强化了燃烧化学反应。相邻火焰之间的相互作用随着当量比的减小逐渐减弱，当量比小于0.53时，中心火焰熄灭，相邻火焰相互作用消失。多喷嘴外侧火焰推举高度小于中心火焰，稳定范围比中心火焰宽。当量比大于0.6时火焰推举高度随当量比的变化不明显，当量比小于0.6后火焰推举高度随着当量比的减小显著增加。随着当量比的降低，湍流脉动对火焰的褶皱扭曲作用逐渐增强，湍流火焰传播速度与层流火焰传播速度之比逐渐增大。

Abstract:

In order to characterize the structure of methane/air premixed swirling multi-nozzle flames and reveal the effect of equivalence ratio on the multi-nozzle flame structure, planar laser induced fluorescence was employed at different equivalence ratios ranging from 0.51 to 0.8. The mean and instantaneous structures of premixed swirling multi-nozzle flames at different equivalence ratios were obtained during the experiment. Experimental results show neighboring swirling flames impinge with each other, generating a highly turbulent interacting zone where combustion intensity is enhanced. Flame interaction between neighboring nozzles gradually decreases as the equivalence ratio decreases. The center flame is extinguished when equivalence ratio is less than 0.53, indicating disappearance of the neighboring flame interaction. Flame liftoff height for outer nozzle is lower and the stability window is wider than that for center flame. The flame liftoff height doesn’t have any significant variations when equivalence ratio is larger than 0.6. However, the flame liftoff height increases dramatically once equivalence ratio is less than 0.6. The flame wrinkling due to flow turbulence is enhanced as equivalence ratio is decreased, which causes the ratio of turbulent flame speed to laminar flame speed being increased.