Abstract A high pressure combustion chamber, housing a co-flow burner and a novel thermophoretic soot sampling system, was used to collect soot samples from methane-air diffusion flames at pressures from 5 bar to 30 bar. To have tractable diffusion flames with the same residence times, constant methane flow rate of 0.55 mg/s was maintained throughout the experiments. Soot aggregates were collected on 3 mm diameter transmission electron microscope (TEM) grids and the images of the soot aggregates were captured by a TEM device. Sampling was done at three heights above the burner rim at 3, 6, and 8 mm. An automated image processing method was used to analyze the TEM images of soot aggregates to infer the primary soot particle diameters and the aggregate morphology. The mean primary soot particle diameters increased from 5 to 15 bar at all three sampling locations and seemed to reach a peak around 15–20 bar at 6 and 8 mm height and start decreasing with further increase in pressure. On the other hand, mean primary soot diameter at 3 mm height increased slightly beyond 15 bar. In view of the measured soot concentrations and temperatures at the sampling locations at 3, 6, and 8 mm above the burner, the soot number density is argued to be increasing with increasing pressure. Throughout the all experimental conditions, fractal dimension of the aggregates in these methane diffusion flames did not exceed 1.4 which is much smaller than the accepted universal value of about 1.85. Morphological characteristics inferred from TEM images indicate that the aggregation is less prominent in methane flames in comparison to ethylene diffusion flames under similar conditions.

中文翻译：

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在压力高达 30 bar 的 coflow 层流甲烷扩散火焰中从热泳采样推导出的烟灰聚集体形态

摘要 高压燃烧室装有共流燃烧器和新型热泳烟尘采样系统，用于从 5 bar 至 30 bar 压力下的甲烷-空气扩散火焰中收集烟尘样品。为了使扩散火焰具有相同的停留时间，在整个实验过程中保持恒定的 0.55 毫克/秒的甲烷流速。在直径为 3 毫米的透射电子显微镜 (TEM) 网格上收集烟尘聚集体，并通过 TEM 设备捕获烟尘聚集体的图像。在燃烧器边缘上方 3、6 和 8 毫米的三个高度处进行采样。使用自动图像处理方法分析烟灰聚集体的 TEM 图像，以推断初级烟尘粒径和聚集体形态。在所有三个采样位置，平均初级烟尘粒径从 5 巴增加到 15 巴，似乎在 6 和 8 毫米高度处达到 15-20 巴左右的峰值，并随着压力的进一步增加而开始下降。另一方面，3 毫米高度处的平均初级烟尘直径略有增加，超过 15 巴。鉴于在燃烧器上方 3、6 和 8 毫米的采样位置测得的烟尘浓度和温度，有人认为烟尘数密度随着压力的增加而增加。在所有实验条件下，这些甲烷扩散火焰中聚集体的分形维数不超过 1.4，远小于公认的通用值约 1.85。