Abstract Soot formation, evolution and characteristics of diffusion ethylene/air flames in ψ-shaped mesoscale combustors of two different diameters with the variations of excess air ratio and flow rate were experimentally investigated. The variation in nanostructure and oxidation reactivity of soot was compared based on the results of high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results demonstrated that with an increasing excess air ratio and flow rate, the unventilated flames with bifurcated shapes were observed in both types of combustors due to the deteriorated mixing process in large flow velocity. Different effects on characteristics of soot from two combustors with the same variation of flow rate were found. For the variation in ethylene flow rate of 60–100 ml/min at excess air ratio of 0.5, the oxidation reactivity of soot from the combustor with d = 4 mm first decreased and then slightly increased, while it decreased all the time as for the soot from the combustor with d = 6 mm. Moreover, the significant distinctions in soot nanostructure due to the scale effect were observed. The soot from the combustor with d = 4 mm exhibited the partial amorphous structure aggregated by a large amount of PAHs with high reactivity. Whereas among the soot from the combustor with d = 6 mm, a typical fullerene-like structure which represented the simultaneous existence of PAHs and graphitic parts was found. The soot graphitization degree and production increased notably with the enlargement of combustor size because the higher combustion temperature and longer residence time were simultaneously obtained, which both were beneficial to soot formation and growth rate. Significantly, the lower combustion efficiency was obtained in the combustor of d = 6 mm than 4 mm at α = 0.5 because of the larger soot production and more existence of unburned gas. But the higher combustion efficiency was found for the 6 mm than 4 mm at α = 1 in the case of almost no soot generation, which was due to the longer residence time.

中文翻译：

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ψ形中尺度燃烧室中扩散乙烯/空气火焰烟尘形成、演化及特性的实验研究

摘要 通过实验研究了两种不同直径的ψ形中尺度燃烧器中，随着过量空气比和流量的变化，扩散乙烯/空气火焰的烟尘形成、演化和特性。基于高分辨率透射电子显微镜 (HRTEM)、X 射线衍射 (XRD) 和热重分析 (TGA) 的结果，比较了碳烟的纳米结构和氧化反应性的变化。结果表明，随着过量空气比和流量的增加，由于在大流速下混合过程恶化，两种类型的燃烧器都观察到了分叉形状的不通风火焰。发现具有相同流速变化的两个燃烧器对烟尘特性的不同影响。对于 60-100 ml/min 的乙烯流量变化和 0.5 的过量空气比，d = 4 mm 燃烧器中烟尘的氧化反应性先降低然后略有增加，而对于来自燃烧器的烟灰，d = 6 mm。此外，观察到由于尺度效应导致的烟灰纳米结构的显着差异。来自 d = 4 mm 的燃烧器的烟尘表现出由大量高反应性多环芳烃聚集的部分无定形结构。而在来自燃烧器的 d = 6 mm 的烟尘中，发现了一种典型的类富勒烯结构，代表 PAH 和石墨部分同时存在。随着燃烧室尺寸的增大，烟灰石墨化程度和产量显着增加，因为同时获得更高的燃烧温度和更长的停留时间，这两者都有利于烟灰的形成和生长速度。值得注意的是，d = 6 mm 燃烧器的燃烧效率低于 α = 0.5 时的 4 mm，因为产生的烟尘较多，未燃烧气体的存在较多。但在 α = 1 的情况下，6 毫米的燃烧效率高于 4 毫米，在几乎不产生烟灰的情况下，这是由于较长的停留时间。5、因为产生的烟尘较大，存在较多的未燃气体。但在 α = 1 的情况下，6 毫米的燃烧效率高于 4 毫米，在几乎不产生烟灰的情况下，这是由于较长的停留时间。5、因为产生的烟尘较大，存在较多的未燃气体。但在 α = 1 的情况下，6 毫米的燃烧效率高于 4 毫米，几乎没有烟灰产生，这是由于较长的停留时间。