Cyclic Variations in the Flame Propagation in an Spark-Ignited Engine: Multi Cycle Large Eddy Simulation Supported by Imaging Diagnostics
Cyclic Variations in the Flame Propagation in an Spark-Ignited Engine: Multi Cycle Large Eddy Simulation Supported by Imaging Diagnostics
复制标题
火花点火发动机中火焰传播的循环变化：成像诊断支持的多循环大涡模拟
DOI：
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发表时间：
2022
影响因子：
2.4
通讯作者：
Achim Kempf
中科院分区：
文献类型：
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作者：
L. Engelmann;J. Laichter;P. Wollny;M. Klein;S. Kaiser;Achim Kempf
在光学可及的四冲程火花点火发动机上进行了实验测量和多循环大涡模拟（LES），以研究循环间变化（CCV）。利用高速燃烧成像技术测量火焰的早期传播，获得火焰半径和质心。大涡模拟生成了火焰传播和柱体内动能的数据库，并用三维模拟结果证实了二维场的观测结果。对CCV的强度和分布进行了实验和仿真比较。两种方法都揭示了CCV引起的最大压力和燃烧速度的相似统计。使用10%燃烧燃料混合物的曲柄角将循环分为慢循环和快循环。对火焰质心的分析表明，与快速循环相比，慢循环向发动机进气侧移动得更远。在燃烧过程中，根据样品处于未燃烧和已燃烧混合物中，取慢循环和快循环的平均动能。通过对未燃烧和已燃烧混合气的动能水平的研究发现，快速循环时湍流动能较高，慢循环时总动能与湍流动能之间的差异较大，这为该发动机CCV变化的一个来源提供了证据。
Experimental measurements and multi-cycle large eddy simulation (LES) are performed in an optically accessible four-stroke spark-ignition engine to investigate cycle-to-cycle variations (CCV). High-speed combustion imaging is used to measure the early flame propagation and obtain the flame radius and centroids. Large Eddy Simulation generates data-bases for the flame propagation as well as the kinetic energy in the cylinder and confirms the observations from the two-dimensional fields by three-dimensional simulation results. Experiment and simulation are compared with respect to the strength and distribution of CCV. Both approaches reveal CCV causing similar statistics of maximum pressures and combustion speeds. The cycles are categorized as slow and fast cycles using the crank angle of ten percent burnt fuel-mixture. Analysis of the flame centroids shows that slow cycles move further towards the intake-side of the engine compared to fast cycles. The kinetic energy during combustion is averaged for the slow and fast cycles based on the samples being in unburnt and burnt mixture. Studying the kinetic energy level in the unburnt and burnt mixture reveals higher turbulent kinetic energy for the fast cycles as well as larger separation between the global kinetic and the turbulent kinetic energy for the slow cycles, providing evidence for a source of the CCV variations observed in this engine.