Abstract A new multi-location soot sampling method is used to enhance the knowledge about the structural evolution of in-flame particles in a light-duty optical diesel engine. Through thermophoresis-based particle sampling performed at multiple in-bowl locations, the soot structures are shown for both early formation stage and later stage from the same combustion event. Three different jet-spacing angles of 45°, 90° and 180° were studied to analyse how different levels of jet–jet interaction impact the soot particle morphology and internal structure. One selected jet–jet interaction condition was further analysed to show differences in soot structures between the up-swirl side and down-swirl side of the wall jets. From transmission electron microscopes (TEM) images of the sampled soot particles and their statistical size analysis, it was found soot particles initially formed within 45∘ separated jet–jet interaction region have un-solidified premature aggregates due to limited carbonisation in the locally fuel-rich mixtures. When these soot particles travelled on the down-swirl side of the jets, they became solidified and carbonised while the oxidation was evident from the smaller soot primary particle and longer carbon-layer fringe and lower tortuosity. The higher mixing on the up-swirl side of the jets further enhanced the soot oxidation, resulting in even smaller soot primary particle, fragmentation of large soot aggregates, and even longer and less curved carbon-layer fringes. Regarding jet–jet interaction, the 180° jet spacing angle created no jet–jet interaction condition on the soot sampler locations. For smaller jet-spacing angles, the increase in jet–jet interaction promoted the soot formation as evidenced by larger and more complex soot aggregates formed due to more active soot aggregation and agglomeration. The soot oxidation became limited at higher jet–jet interaction conditions, which led to more amorphous soot internal structures.

中文翻译：

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柴油燃烧环境中射流-涡流和射流-射流相互作用影响下烟尘颗粒的形态和内部结构

摘要 一种新的多位置烟尘采样方法被用于增强对轻型光学柴油发动机中燃烧颗粒结构演变的认识。通过在多个碗内位置进行的基于热泳的粒子采样，显示了来自同一燃烧事件的早期形成阶段和后期阶段的烟尘结构。研究了 45°、90° 和 180° 三种不同的射流间距角度，以分析不同水平的射流相互作用如何影响烟尘颗粒形态和内部结构。进一步分析了一种选定的射流-射流相互作用条件，以显示壁射流的向上涡流侧和向下涡流侧之间的烟尘结构差异。从采样烟尘颗粒的透射电子显微镜 (TEM) 图像及其统计尺寸分析，发现最初在 45∘ 分离的射流-射流相互作用区域内形成的烟灰颗粒由于局部富含燃料的混合物中的碳化有限而具有未固化的过早聚集体。当这些烟灰颗粒在射流的下旋流侧行进时，它们变得凝固和碳化，而氧化作用从更小的烟灰初级颗粒和更长的碳层边缘和更低的曲折度中可见一斑。射流向上涡旋侧的更高混合进一步增强了烟尘氧化，导致更小的烟尘初级粒子、大烟尘聚集体的碎裂，以及更长和更少弯曲的碳层边缘。关于射流-射流相互作用，180° 射流间隔角在烟尘采样器位置没有产生射流-射流相互作用条件。对于较小的喷射间距角，射流-射流相互作用的增加促进了烟尘的形成，正如由于更活跃的烟尘聚集和附聚而形成的更大和更复杂的烟尘聚集体所证明的那样。在较高的射流相互作用条件下，烟灰氧化变得有限，这导致更多的无定形烟灰内部结构。