This study shows how the structure of soot particles within the flame changes due to the relative direction of the swirl flow in a small-bore diesel engine in which significant flame–wall interactions cause about half of the flame travelling against the swirl flow while the other half penetrating in the same direction. The thermophoresis-based particle sampling method was used to collect soot from three different in-flame locations including the flame–wall impingement point near the jet axis and the two 60° off-axis locations on the up-swirl and down-swirl side of the wall-interacting jet. The sampled soot particle images were obtained using transmission electron microscopes and the image post-processing was conducted for statistical analysis of size distribution of soot primary particles and aggregates, fractal dimension, and sub-nanoscale parameters such as the carbon layer fringe length, tortuosity, and spacing. The results show that the jet-wall impingement region is dominated by many small immature particles with amorphous internal structure, which is very different to large, fractal-like soot aggregates sampled from 60° downstream location on the down-swirl side. This structure variation suggests that the small immature particles underwent surface growth, coagulation and aggregation as they travelled along the piston-bowl wall. During this soot growth, the particle internal structure exhibits the transformation from amorphous carbon segments to a typical core–shell structure. Compared to those on the down-swirl side, the soot particles sampled on the up-swirl side show much lower number counts and more compact aggregates composed of highly concentrated primary particles. This soot aggregate structure, together with much narrower carbon layer gap, indicates higher level of soot oxidation on the up-swirl side of the jet.

这项研究表明，在小口径柴油机中，火焰中烟尘颗粒的结构如何由于旋流的相对方向而发生变化，在该发动机中，显着的火焰-壁相互作用导致大约一半的火焰逆着旋流流动。一半以相同的方向穿透。基于热泳的颗粒采样方法用于从三个不同的火焰内位置收集烟灰，包括靠近喷射轴的火焰壁撞击点和位于燃烧室上旋和下旋侧的两个60°偏轴位置。与壁相互作用的射流。使用透射电子显微镜获得采样的烟尘颗粒图像，并对图像进行后处理，以便对烟尘一次颗粒和聚集体的尺寸分布，分形维数，以及亚纳米级参数，例如碳层边缘长度，曲折度和间距。结果表明，射流壁的撞击区域被许多具有非晶形内部结构的未成熟小颗粒所占据，这与从向下旋流侧的60°下游位置采样的大的，分形的烟灰聚集体非常不同。这种结构变化表明，未成熟的小颗粒沿着活塞碗壁行进时会发生表面生长，凝结和聚集。在这种烟ot生长过程中，颗粒的内部结构表现出从无定形碳链段到典型的核-壳结构的转变。与向下旋转的那些相比，向上旋流侧采样的烟灰颗粒显示出低得多的数量，并且由高浓度的初级颗粒组成的聚集体更紧密。这种烟灰聚集体结构以及更窄的碳层间隙表明，在喷流的向上旋流侧，烟灰氧化程度更高。