Heat release rate variations in high hydrogen content premixed syngas flames at elevated pressures: Effect of equivalence ratio
Heat release rate variations in high hydrogen content premixed syngas flames at elevated pressures: Effect of equivalence ratio
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DOI：
10.1016/j.ijhydene.2016.11.205
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发表时间：
2017-03
影响因子：
7.2
通讯作者：
K. Dinesh;H. Shalaby;K. Luo;J. A. Oijen;D. Thévenin
中科院分区：
文献类型：
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作者：
K. Dinesh;H. Shalaby;K. Luo;J. A. Oijen;D. Thévenin
采用三维直接数值模拟的方法，研究了加压湍流条件下氢气/一氧化碳膨胀球形预混火焰当量比对放热速率和火焰标志物空间变化的影响。分析和比较了贫燃料、化学计量比和富燃料中心点火球形火焰的火焰结构和放热速率。当量比改变了热扩散效应、Darrieus-Landau不稳定性和湍流之间的平衡，导致了不同的火焰动力学和放热率分布，尽管呈现出相似的胞状和皱纹火焰。Darrieus-Landau不稳定性对当量比相对不敏感，而热扩散过程受当量比的影响较大。由于热扩散效应随着当量比的减小而增大，在热扩散不稳定性和Darrieus-Landau不稳定性的共同作用下，贫燃料火焰比化学计量火焰介于两者之间的富燃料火焰更不稳定。局部放热率与曲率呈正相关关系，与化学计量比火焰呈正相关关系，与浓淡火焰呈负相关关系。此外，对于贫燃料火焰，放热率的低值和高值分别出现在负曲率和正曲率区域，而对于富燃料火焰，则呈现相反的趋势。研究发现，基于组分浓度的放热速率标记物随当量比的变化而变化很大。结果表明，在加压湍流条件下，H2/CO预混合成气体-空气化学计量火焰的HCO、CO2浓度、OH和CH2O产物浓度与局部放热速率有很好的相关性。
Three-dimensional direct numerical simulations with detailed chemistry were performed to investigate the effect of equivalence ratio on spatial variations of the heat release rate and flame markers of hydrogen/carbon monoxide syngas expanding spherical premixed flames under turbulent conditions at elevated pressures. The flame structures and the heat release rate were analysed and compared between fuel-lean, stoichiometric and fuel-rich centrally ignited spherical flames. The equivalence ratio changes the balance among thermo-diffusive effects, Darrieus–Landau instability and turbulence, leading to different flame dynamics and the heat release rate distribution, despite exhibiting similar cellular and wrinkling flames. The Darrieus–Landau instability is relatively insensitive to the equivalence ratio while the thermo-diffusive process is strongly affected by the equivalence ratio. As the thermo-diffusive effect increases as the equivalence ratio decreases, the fuel-lean flame is more unstable than the fuel-rich flame with the stoichiometric flame in between, under the joint effects of the thermo-diffusive instability and the Darrieus–Landau instability. The local heat release rate and curvature display a positive correlation for the lean flame, no correlation for the stoichiometric flame, and negative correlation for the rich flame. Furthermore, for the fuel-lean flame, the low and high heat release rate values are found in the negative and positive curvature zones, respectively, while for the fuel-rich flame, the opposite trends are found. It is found that heat release rate markers based on species concentrations vary strongly with changing equivalence ratio. The results suggest that the HCO, HO2concentrations and product of OH and CH2O concentrations show good correlation with the local heat release rate for H2/CO premixed syngas-air stoichiometric flame under turbulent conditions at elevated pressures.