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首页> 外文期刊>Combustion Science and Technology >Effects of Turbulence Intensity and Biogas Composition on the Localized Forced Ignition of Turbulent Mixing Layers
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Effects of Turbulence Intensity and Biogas Composition on the Localized Forced Ignition of Turbulent Mixing Layers

机译：湍流强度和沼气组成对湍流混合层局部强制点火的影响

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Three-dimensional compressible Direct Numerical Simulations (DNS) have been used to investigate the localized forced ignition of statistically planar mixing layers of biogas/air mixtures for different levels of turbulence intensity and biogas composition. The biogas is represented by a CH/CO mixture and a two-step mechanism involving incomplete oxidation of CH to CO and HO, and an equilibrium between the CO oxidation and the CO dissociation has been used. This two-step mechanism captures the variation of the unstrained laminar flame speed with equivalence ratio and CO dilution with sufficient accuracy when compared with detailed chemistry results. A successful ignition of CH/CO/air mixing layer initially gives rise to a tribrachial flame structure involving fuel-rich and lean premixed branches on either side of the diffusion flame stabilized on the stoichiometric mixture fraction iso-surface. Long after the energy deposition has ended, the lean branch may merge with the diffusion flame, but edge flame propagation along the stoichiometric mixture fraction iso-surface is observed at all stages. The highest heat release rate (HRR) is obtained on the rich premixed branch irrespective of the turbulence intensity and biogas composition, but its magnitude decreases with increasing CO dilution. The most probable edge flame displacement speed decreases in time and converges to its theoretical value for laminar cases. As the turbulence level increases, the edge flame displacement speed assumes a larger range of values, although its mean is consistently lower than the corresponding laminar one. Furthermore, in the turbulent cases, the probability of finding negative values of the edge flame displacement speed has been found to be non-zero. This probability is larger than the one of finding positive values for the cases failing to reach a self-sustained flame propagation without the energy deposition assistance. This becomes more probable as the turbulence intensity and CO dilution increase. This is reflected in the diminished burning extent, quantified in terms of burned gas volume, with increasing turbulence intensity and CO dilution.
机译：三维可压缩直接数值模拟（DNS）已被用于研究仿真平面浆料/空气混合物的局部强制点火，用于不同水平的湍流强度和沼气组合物。沼气由CH / CO混合物和涉及不完全氧化CH至CO和HO的两步机制，以及共同氧化与共同解离的平衡。该两步机构在与详细的化学结果相比时，捕获了在等效比率和Co稀释时具有足够精度的稀释。成功点火的CH / CO /空气混合层最初产生涉及富含燃料和贫预混的分支的平坦火焰结构，在化学计量混合物级别表面上稳定在扩散火焰的任一侧上。在能量沉积结束之后，贫枝可以与扩散火焰合并，但在所有阶段观察到沿着化学计量级别馏分的边缘火焰传播。无论湍流强度和沼气组合物如何，都在富富预混分支上获得最高的热释放速率（HRR），但随着CO稀释的增加，其幅度降低。最可能的边缘火焰位移速度随着时间的推移和收敛于层流案例的理论值而降低。随着湍流水平的增加，边缘火焰位移速度是较大的值范围，尽管其平均值始终低于相应的层流。此外，在湍流情况下，已经发现发现边缘火焰位移速度的负值的可能性是非零。这种概率大于在没有能量沉积辅助的情况下未能达到自我持续的火焰传播的情况的情况下找到正值之一。这变得更可能随着湍流强度和CO稀释而增加。这反映在燃烧程度下，在燃烧的气体体积方面量化，随着湍流强度和CO稀释而定量。

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