This paper provides a numerical study on n-dodecane flames using Large-Eddy Simulations (LES) along with the Flamelet Generated Manifold (FGM) method for combustion modeling. The computational setup follows the Engine Combustion Network Spray A operating condition, which consists of a single-hole spray injection into a constant volume vessel. Herein we propose a novel approach for the coupling of the energy equation with the FGM database for spray combustion simulations. Namely, the energy equation is solved in terms of the sensible enthalpy, while the heat of combustion is calculated from the FGM database. This approach decreases the computational cost of the simulation because it does not require a precise computation of the entire composition of the mixture. The flamelet database is generated by simulating a series of counterflow diffusion flames with two popular chemical kinetics mechanisms for n-dodecane. Further, the secondary breakup of the droplet is taken into account by a recently developed modified version of the Taylor Analogy Breakup model. The numerical results show that the proposed methodology captures accurately the main characteristics of the reacting spray, such as mixture formation, ignition delay time, and flame lift-off. Additionally, it captures the “cool flame" between the flame lift-off and the injection nozzle. Overall, the simulations show differences between the two kinetics mechanisms regarding the ignition characteristics, while similar flame structures are observed once the flame is stabilised at the lift-off distance.

本文使用大涡模拟 (LES) 以及用于燃烧建模的小火焰生成歧管 (FGM) 方法对正十二烷火焰进行了数值研究。计算设置遵循发动机燃烧网络喷雾 A 操作条件，其中包括将单孔喷雾喷射到恒定体积容器中。在这里，我们提出了一种将能量方程与 FGM 数据库耦合以进行喷雾燃烧模拟的新方法。也就是说，能量方程是根据显焓求解的，而燃烧热是从 FGM 数据库中计算出来的。这种方法降低了模拟的计算成本，因为它不需要对混合物的整个组成进行精确计算。小火焰数据库是通过用两种流行的正十二烷化学动力学机制模拟一系列逆流扩散火焰而生成的。此外，最近开发的泰勒类比破碎模型的修改版本考虑了液滴的二次破碎。数值结果表明，所提出的方法准确地捕捉了反应喷雾的主要特征，例如混合物形成、点火延迟时间和火焰升空。此外，它还捕获了火焰升起和喷射喷嘴之间的“冷火焰”。总体而言，模拟显示了两种动力学机制在点火特性方面的差异，而一旦火焰在升程处稳定，就会观察到类似的火焰结构-关闭距离。