Multi-cycle large-eddy simulations (LES) are performed to investigate combustion cycle-to-cycle variability (CCV) in a gasoline spark ignited optical access engine operating under homogeneous stoichiometric conditions. Combustion is addressed with the Thickened Flame Model (TFM) and finite rate chemistry is accounted for through a reduced oxidation reaction mechanism. In view of the fact that computational costs of LES engine simulations are still very high today, this work investigates the use of adaptive mesh refinement (AMR) in the flame zone in conjunction with the artificial flame thickening applied by the TFM model. The paper discusses how the resulting coupled TFM-AMR combustion model allows good resolution of the flame, maintaining accuracy at acceptable costs. First, the details of the coupled model are presented and the effects of the parameters are explored, highlighting their impact on the combustion prediction. Then, computational fluid dynamics (CFD) simulation results are validated against experimental data collected in a low-speed low-load engine point, by comparing 20 LES cycles and 100 measured cycles, for mass fraction burned, combustion phasing, flame images and CCV indices. Lastly, a detailed investigation on the fastest and slowest numerical cycles is presented, analyzing instantaneous flame structures, ignition behaviors, propagation speeds, and probability density function (PDF) of the instantaneous velocity fluctuation around the spark region. The results show that combustion variability is highly correlated to the resolved velocity field and the resolved turbulence intensity, which is found to be the main cause of CCV and affects the early flame kernel growth. This work is an early attempt to use TFM-AMR combustion model for LES simulations of internal combustion engines.

进行多循环大涡模拟（LES），以研究在均质化学计量条件下运行的汽油火花点火式光学访问引擎中的燃烧循环间差异（CCV）。燃烧通过加厚火焰模型（TFM）解决，而有限速率化学通过减少的氧化反应机理解决。鉴于目前LES发动机模拟的计算成本仍然很高，这项工作研究了火焰区域中自适应网格细化（AMR）与TFM模型所应用的人工火焰增厚的结合使用。本文讨论了由此产生的TFM-AMR耦合燃烧模型如何使火焰具有良好的分辨率，并以可接受的成本保持精度。第一的，给出了耦合模型的细节，并探讨了参数的影响，突出了它们对燃烧预测的影响。然后，通过比较20个LES循环和100个实测循环，针对燃烧的质量分数，燃烧定相，火焰图像和CCV​​指数，对照在低速低负荷发动机点收集的实验数据验证计算流体动力学（CFD）模拟结果。最后，对最快和最慢的数值循环进行了详细的研究，分析了瞬时火焰结构，点火行为，传播速度以及火花区域周围瞬时速度波动的概率密度函数（PDF）。结果表明，燃烧变异性与解析速度场和解析湍流强度高度相关，被发现是CCV的主要原因，并影响火焰核的早期生长。这项工作是将TFM-AMR燃烧模型用于内燃机的LES模拟的早期尝试。