Large eddy simulation of a reacting spray flame with multiple realizations under compression ignition engine conditions
Large eddy simulation of a reacting spray flame with multiple realizations under compression ignition engine conditions
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DOI：
10.1016/j.combustflame.2015.08.010
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发表时间：
2015-12
影响因子：
4.4
通讯作者：
Y. Pei;S. Som;E. Pomraning;P. Senecal;S. Skeen;J. Manin;L. Pickett
中科院分区：
文献类型：
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作者：
Y. Pei;S. Som;E. Pomraning;P. Senecal;S. Skeen;J. Manin;L. Pickett
采用δ函数燃烧模型沿着动态结构大涡模拟（LES）模型对正十二烷喷雾火焰（来自发动机燃烧网络的喷雾A）进行了模拟，以评估其在发动机相关条件下的性能并了解该湍流火焰的瞬态行为。液体喷雾采用传统的拉格朗日方法处理，气相反应采用δ函数燃烧模型。正十二烷化学动力学模型采用103种骨架机理。显着不同的火焰结构和点火过程中观察到的LES相比，雷诺平均Navier-Stokes（RANS）的预测。LES数据表明，第一次点火开始于贫混合气中并传播到富混合气，并且主要点火发生在富混合气中，优选地在混合气分数空间中小于0.14。LES被观察到有多个点火点在混合层同时，而主要的点火启动在一个明显的不对称的方式。火焰发展的时间也表明火焰稳定机制是自动点火控制。与RANS相比，LES的碳烟预测在定性和定量上与实验吻合得更好。进行LES的多个实现，以了解实现到实现的变化，并建立最佳实践的整体平均柴油喷雾火焰。相关性指数分析表明，平均5和6个实现可以达到99%的相似性的目标平均16个实现的混合物分数和温度场，分别。然而，更多的实现是必要的氢氧化物（OH）和烟尘的质量分数，由于他们的高波动。
An n-dodecane spray flame (Spray A from Engine Combustion Network) was simulated using a δ function combustion model along with a dynamic structure large eddy simulation (LES) model to evaluate its performance at engine-relevant conditions and to understand the transient behavior of this turbulent flame. The liquid spray was treated with a traditional Lagrangian method and the gas-phase reaction was modeled using a δ function combustion model. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. Significantly different flame structures and ignition processes are observed for the LES compared to those of Reynolds-averaged Navier− Stokes (RANS) predictions. The LES data suggests that the first ignition initiates in a lean mixture and propagates to a rich mixture, and the main ignition happens in the rich mixture, preferably less than 0.14 in mixture fraction space. LES was observed to have multiple ignition spots in the mixing layer simultaneously while the main ignition initiates in a clearly asymmetric fashion. The temporal flame development also indicates the flame stabilization mechanism is auto-ignition controlled. Soot predictions by LES present much better agreement with experiments compared to RANS, both qualitatively and quantitatively. Multiple realizations for LES were performed to understand the realization to realization variation and to establish best practices for ensemble-averaging diesel spray flames. The relevance index analysis suggests that an average of 5 and 6 realizations can reach 99% of similarity to the target average of 16 realizations on the mixture fraction and temperature fields, respectively. However, more realizations are necessary for the hydroxide (OH) and soot mass fractions due to their high fluctuations.