燃料/空气混合距离对非预混燃烧中燃烧不稳定性的影响

Jiaying Cheng, Bofan Liu, Tong Zhu
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摘要

在几种燃烧类型中,燃烧不稳定性已被广泛报道;然而,关于非预混合燃烧中不同燃料/空气混合距离的信息却很有限。设定空气管和燃料管之间的不同距离,燃料/空气混合距离(δ)会因喷嘴的结构变化而改变。在热负荷和当量比保持不变的情况下,本研究旨在探讨燃料/空气混合距离对非预混燃烧中燃烧不稳定性的影响。实验观察表明,与其他类型的非预混合燃烧相比,火焰在喷嘴外点燃的非预混合燃烧会出现燃烧振荡。在三种燃料/空气混合距离的非预混合燃烧中发现了准周期振荡、极限循环模式和间歇模式。本研究建立了非预混合燃烧对流时间的计算方法。然后计算了极限循环振荡的对流时间,进一步发现该时间触发了燃烧系统的第二共振模式。进一步的分析表明,不同的燃料/空气混合距离会对局部等效比分布产生影响,对流时间也会相应变化。对流时间的变化会影响燃烧室内热释放率波动与声学模式之间的耦合特性。当热声耦合发生时,燃烧不稳定性就会出现。这项工作建立了非预混合燃烧中燃烧不稳定性与燃料/空气混合距离之间的联系,并强调了局部等效比空间分布和对流时间的影响,可为各种燃料/空气混合类型的实际应用提供技术指导。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Effects of fuel/air mixing distances on combustion instabilities in non-premixed combustion
Combustion instability has been widely reported in several combustion types; however, there is limited information on different fuel/air mixing distances in non-premixed combustion. Setting different distances between air tube and fuel tubes, the fuel/air mixing distances (δ) are changed by structural variations of nozzles. Keeping the heat load and equivalence ratios constant, the present work aims to examine the effects of fuel/air mixing distances on combustion instability in non-premixed combustion. Experimental observations suggest that combustion oscillations occur in non-premixed combustion with flame ignited outside the nozzle rather than other types of non-premixed combustion. Quasiperiodic oscillations, limit cycle modes, and intermittency modes are found in three fuel/air mixing distances in non-premixed combustion. The calculation methods of convection time for non-premixed combustion are established in the present work. The convection time of the limit cycle oscillations is then calculated, which is further found to trigger the second resonance modes of the combustion system. The further analysis reveals that varying fuel/air mixing distances can cause influences on local equivalence ratio distributions, and the convection time are correspondingly varied. The changes in convection time affects the coupling characteristics between heat release rate fluctuations and the acoustic modes in the combustion chamber. When the thermoacoustic coupling occurs, combustion instabilities appear. This work establishes a link between combustion instability and fuel/air mixing distances in non-premixed combustion and highlights the influences on spatial distributions of local equivalence ratios and then convection time, which can provide technical guidance for actual applications in various fuel/air mixing types.
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