Detailed simulations of the DLR auto-igniting pulsed jet experiment
Detailed simulations of the DLR auto-igniting pulsed jet experiment
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DOI：
10.1016/j.fuel.2020.118947
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发表时间：
2021-01
期刊：
影响因子：
7.4
通讯作者：
E. Inanc;J. T. Lipkowicz;Achim Kempf
中科院分区：
文献类型：
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作者：
E. Inanc;J. T. Lipkowicz;Achim Kempf
采用高分辨率的大涡模拟方法，对德国航空航天中心（DLR）进行的一次污染并流实验中的自点火脉冲射流进行了数值模拟。实验包括两种操作模式：用于代码验证的连续喷射和用于自燃动力学基础研究的脉冲喷射。首先，参考一维自燃逆流火焰进行了研究。然后，进行了网格收敛性研究。结果表明，即使是一个粗糙的网格将足以描述点火化学，因为点火内核出现在低速度和贫燃料条件下的低标量耗散率的区域。对于统计稳定射流，数值预测与实验非常吻合，使应用模型的信心。对于脉冲射流，所有的预测点火延迟时间和位置的实验观察范围内。时间分辨的统计数据表明，在脉冲射流中的气体的热化学性质实现的状态，是不可能重现层流条件。为了进一步分析，选择羟基和甲醛分别作为建立的火焰和点燃的标记物。在层流条件下，这两种物质完全相关。然而，脉冲射流的非定常动力学使点火前次要物质化学之间的相关性失效。这产生了不同脉冲之间的自燃延迟时间和点火核的位置的差异，因为点火所需的热化学状态以随机方式发生。
Numerical simulations of an auto-igniting pulsed jet in a vitiated co-flow experiment by DLR (German Aerospace Center) are conducted by highly-resolved large-eddy simulations using direct chemistry with an augmented reduced mechanism. The experiments consist of two operation modes: continuous injection used for code-verification and pulsed injection utilized for fundamental investigation of auto-ignition dynamics. Initially, reference one-dimensional self-igniting counter-flow flames are investigated. Then, a grid convergence study has been performed. It is shown that even a coarser grid would be sufficient to describe the ignition chemistry since the ignition kernel appears at low velocities and fuel-lean conditions in zones of low scalar dissipation rates. For the statistically steady jet, numerical predictions are in a very good agreement with the experiments, giving confidence in the applied models. For the pulsed jet, all of the predicted ignition delay times and locations are in the range of the experimental observations. Time-resolved statistics reveal that thermochemical properties of the gas in a pulsed jet achieve states that are impossible to reproduce in laminar conditions. For further analysis, hydroxyl and formaldehyde are chosen as a marker for the established flame and for the ignition, respectively. In laminar conditions, these two species are perfectly correlated. However, the unsteady dynamics of the pulsed jet invalidates the correlation between the minor species chemistry prior to ignition. This yields the discrepancy in the auto-ignition delay time and the location of the ignition kernel between different pulses, as the thermochemical state needed for the ignition occurs in a random manner.