Purpose

This study aims to deal with the large eddy simulation (LES) of an ignition sequence and the resulting steady combustion in a swirl-stabilized liquid-fueled combustor. Particular attention is paid to the ease of handling the numerical tool, the accuracy of the results and the reasonable computational cost involved. The primary aim of the study is to appraise the ability of the newly developed computational fluid dynamics (CFD) methodology to retrieve the spark-based flame kernel initiation, its propagation until the full ignition of the combustion chamber, the flame stabilization and the combustion processes governing the steady combustion regime.

Design/methodology/approach

The CFD model consists of an LES-based spray module coupled to a subgrid-scale ignition model to capture the flame kernel initiation and the early stage of the flame kernel growth, and a combustion model based on the mixture fraction-progress variable formulation in the line of the flamelet generated manifold (FGM) method to retrieve the subsequent flame propagation and combustion properties. The LES-spray module is based on an Eulerian-Lagrangian approach and includes a fully two-way coupling at each time step to account for the interactions between the liquid and the gaseous phases. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for the flow field while the eddy diffusivity model is used for the scalar fluxes. The fuel is liquid kerosene, injected in the form of a polydisperse spray of droplets. The spray dynamics are tracked using the Lagrangian procedure, and the phase transition of droplets is calculated using a non-equilibrium evaporation model. The oxidation mechanism of the Jet A-1 surrogate is described through a reduced reaction mechanism derived from a detailed mechanism using a species sensitivity method.

Findings

By comparing the numerical results with a set of published data for a swirl-stabilized spray flame, the proposed CFD methodology is found capable of capturing the whole spark-based ignition sequence in a liquid-fueled combustion chamber and the main flame characteristics in the steady combustion regime with reasonable computing costs.

Research limitations/implications

The proposed CFD methodology simulates the whole ignition sequence, namely, the flame kernel initiation, its propagation to fully ignite the combustion chamber, and the global flame stabilization. Due to the lack of experimental ignition data on this liquid-fueled configuration, the ability of the proposed CFD methodology to accurately predict ignition timing was not quantitatively assessed. It would, therefore, be interesting to apply this CFD methodology to other configurations that have experimental ignition data, to quantitatively assess its ability to predict the ignition timing and the flame characteristics during the ignition sequence. Such further investigations will not only provide further validation of the proposed methodology but also will potentially identify its shortfalls for better improvement.

Practical implications

This CFD methodology is developed by customizing a commercial CFD code widely used in the industry. It is, therefore, directly applicable to practical configurations, and provides not only a relatively straightforward approach to predict an ignition sequence in liquid-fueled combustion chambers but also a robust way to predict the flame characteristics in the steady combustion regime as significant improvements are noticed on the prediction of slow species.

Originality/value

The incorporation of the subgrid ignition model paired with a combustion model based on tabulated chemistry allows reducing computational costs involved in the simulation of the ignition phase. The incorporation of the FGM-based tabulated chemistry provides a drastic reduction of computing resources with reasonable accuracy. The CFD methodology is developed using the platform of a commercial CFD code widely used in the industry for relatively straightforward applicability.

中文翻译：

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使用基于FGM的表式化学原理对涡旋稳定燃烧室中的点火序列及其产生的稳定燃烧进行大涡模拟

目的

这项研究的目的是处理点火序列的大涡模拟（LES），以及在涡流稳定的液体燃料燃烧器中产生的稳定燃烧。特别注意数值工具的易用性，结果的准确性以及所涉及的合理计算成本。该研究的主要目的是评估新开发的计算流体力学（CFD）方法检索基于火花的火焰核萌生，其传播直至燃烧室完全点火，火焰稳定和燃烧过程的能力。控制稳定的燃烧状态。

设计/方法/方法

CFD模型包括一个基于LES的喷雾模块，该模块与一个亚网格规模的点火模型耦合以捕获火焰核的萌生和火焰核生长的早期阶段，以及一个基于混合分数-进展变量公式的燃烧模型。火焰产生歧管（FGM）方法的直线以检索随后的火焰传播和燃烧特性。LES喷雾模块基于欧拉-拉格朗日方法，并且在每个时间步长包括完全双向耦合，以说明液相和气相之间的相互作用。壁自适应局部涡流粘度（WALE）模型用于流场，而涡流扩散率模型用于标量通量。燃料是液态煤油，以液滴的多分散喷雾形式喷射。使用拉格朗日程序跟踪喷雾动力学，并使用非平衡蒸发模型计算液滴的相变。Jet A-1替代物的氧化机理是通过还原反应机理来描述的，该反应机理是利用物种敏感性方法从详细机理中衍生而来的。

发现

通过将数值结果与一组稳定旋流喷雾火焰的公开数据进行比较，发现所提出的CFD方法能够捕获液体燃料燃烧室中整个基于火花的点火序列以及稳态火焰的主要火焰特征。具有合理计算成本的燃烧方式。

研究局限/意义

所提出的CFD方法论模拟了整个点火顺序，即火焰核的萌生，其蔓延以完全点燃燃烧室以及整体火焰稳定。由于缺乏这种液体燃料配置的实验点火数据，因此未对CFD方法准确预测点火正时的能力进行定量评估。因此，将这种CFD方法应用于具有实验点火数据的其他配置，以定量评估其在点火序列期间预测点火正时和火焰特性的能力，将是很有趣的。这种进一步的研究不仅将进一步验证所提出的方法，而且可能会发现其不足之处，以便进行更好的改进。

实际影响

通过定制行业中广泛使用的商业CFD代码来开发此CFD方法。因此，它直接适用于实际配置，并且不仅提供了一种相对简单的方法来预测液体燃料燃烧室中的点火顺序，而且还提供了一种稳健的方式来预测稳定燃烧状态下的火焰特性，因为已经注意到了明显的改进关于慢物种的预测。

创意/价值

将子电网点火模型与基于列表化学的燃烧模型结合在一起，可以减少点火阶段模拟所涉及的计算成本。基于FGM的列表化学的结合大大降低了计算资源的合理准确性。CFD方法论是使用商业CFD代码平台开发的，该CFD代码在行业中广泛使用，以实现相对简单的适用性。