A combined numerical and experimental investigation is carried out to analyze the cycle-to-cycle variations (CCV) in an optically accessible spark-ignition engine with port fuel injection. A stable and an unstable operating condition is considered. Well-established turbulence, combustion, and ignition models are employed in the large-eddy simulations (LES). High-speed measurements of the velocity field via particle image velocimetry and flame imaging in the tumble plane are conducted in the experiments. A detailed comparison between LES and experiments is carried out, including the in-cylinder pressure, the flow fields, the spatial flame distribution, and the fields conditioned on fast and slow cycles. Good agreement is achieved for the variables considering all cycles; yet, some discrepancies are observed for the conditionally averaged quantities. A systematic quantitative correlation analysis between the selected influencing variables and the CCV is presented, in which the influencing variables are extracted from different length scales (r = 3 mm, 12 mm, and 43 mm) and the CCV are distinguished between the early flame kernel development and later flame propagation. Even though the most relevant influencing parameters are different for the two operating conditions, the location of the coherent vortex structure is found to be important for the CCV of both cases.

进行了数值和实验相结合的研究，以分析具有端口燃料喷射的光学可访问火花点火发动机中的循环到循环变化 (CCV)。考虑稳定和不稳定的操作条件。大涡模拟 (LES) 中采用了成熟的湍流、燃烧和点火模型。实验中通过粒子图像测速和滚动平面中的火焰成像对速度场进行高速测量。对 LES 和实验进行了详细比较，包括缸内压力、流场、空间火焰分布以及以快慢循环为条件的场。考虑到所有周期的变量都达到了良好的一致性；然而，观察到条件平均数量的一些差异。提出了所选影响变量与CCV之间的系统定量相关性分析，其中影响变量从不同的长度尺度（r = 3 mm、12 mm和43 mm）中提取，CCV在早期火焰核之间进行了区分。发展和后来的火焰传播。尽管两种操作条件下最相关的影响参数不同，但发现相干涡流结构的位置对两种情况下的 CCV 都很重要。