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The influence of chemical mechanisms on PDF calculations of nonpremixed piloted jet flames

机译：化学机理对非预混引燃火焰PDF计算的影响

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Seven different chemical mechanisms for methane are used in PDF model calculations of the Barlow and Frank flames D, E, and F in order to investigate the ability of these mechanisms to represent the local extinction, reigni-tion, and other chemical phenomena observed in these nonpremixed piloted jet flames. The mechanisms studied range from a 5-step reduced mechanism to the GRI3.0 mechanism which involves 53 species. As in several other recent studies, we use the PDF method based on the joint probability density function of velocity, turbulence frequency, and composition. Extensive tests are performed to ensure the numerical accuracy of the calculations, to relate them to previous calculations based on the same model, and to reexamine the sensitivity of the calculations (especially of flame F) to uncertainties in the pilot temperature and the treatment of radiation. As has been observed in other studies of laminar and turbulent nonpremixed flames, we find that the GRI3.0 mechanism over-predicts the levels of NO, typically by a factor of 2. Apart from this, the GRI3.0 and GRI2.11 mechanisms yield comparably good agreement with the experimental data for all three flames, including the level of local extinction and the conditional means of major and other minor species. Two augmented reduce mechanism (ARM1 and ARM2) based on GRI2.11 and containing 16 and 19 species are slightly less accurate; while the 5-step reduced mechanism and two C_1 skeletal mechanisms containing 16 species display significant inaccuracies. An examination of the autoignition and laminar-flame behavior of the different mechanisms confirms (with some exceptions) expected trends: there is an association between long ignition delay times, small extinction strain rates, and high levels of local extinction. This study again demonstrates the ability of the joint PDF method to represent accurately the strong turbulence-chemistry interactions in these flames, and it clarifies the necessary level of description of the chemical kinetics.
机译：在Barlow和Frank火焰D，E和F的PDF模型计算中使用了七种不同的甲烷化学机理，以研究这些机理代表局部消光，重燃以及在其中观察到的其他化学现象的能力。非预混合引燃火焰。所研究的机制范围从5步简化机制到涉及53个物种的GRI3.0机制。与其他近期研究一样，我们使用基于速度，湍流频率和成分的联合概率密度函数的PDF方法。进行了广泛的测试，以确保计算的数值准确性，将其与基于同一模型的先前计算相关联，并重新检查计算（尤其是火焰F）对引燃温度和辐射处理不确定性的敏感性。正如在层流和湍流非预混火焰的其他研究中所观察到的那样，我们发现GRI3.0机制高估了NO的水平，通常高2倍。此外，GRI3.0和GRI2.11机制与所有三种火焰的实验数据（包括局部灭绝的水平以及主要物种和其他次要物种的条件性手段）的产量相比，具有相当好的一致性。基于GRI2.11并包含16和19种的两个增强还原机制（ARM1和ARM2）的准确性稍差一些。而5个步骤的还原机制和两个包含16个物种的C_1骨骼机制显示出明显的误差。对不同机制的自燃和层流行为的检查证实了（除某些例外）预期趋势：较长的点火延迟时间，较小的灭绝应变率和较高的局部灭绝之间存在关联。这项研究再次证明了联合PDF方法能够准确表示这些火焰中强烈的湍流-化学相互作用的能力，并阐明了化学动力学描述的必要水平。

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