Soot nucleation in diffusion flames and the role of aromatic hydrocarbons
Soot nucleation in diffusion flames and the role of aromatic hydrocarbons
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DOI：
10.1016/j.combustflame.2023.112899
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发表时间：
2023-09
影响因子：
4.4
通讯作者：
Kevin Gleason;A. Gomez
中科院分区：
文献类型：
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作者：
Kevin Gleason;A. Gomez
我们对大气压逆流扩散火焰中煤烟的光散射进行了空间分辨测量，以补充先前报道的煤烟热学、温度和气体物种直至三环多环芳烃(PAHs)的数据。我们比较了两种火焰：基线乙烯火焰和甲苯种子火焰，在这两种火焰中，进料流中的等量乙烯被3500ppm的预汽化甲苯取代。目标有两个：直接添加芳烃燃料以绕过第一芳环的形成，第一芳环被广泛认为是脂肪族燃料形成碳烟的主要瓶颈，以及评估运输燃料替代品的一种常见成分对碳烟形成的影响。燃料和氧化剂流的组成被调整以确保温度-时间历史的不变性，从而使燃料替代的化学效应与其他因素分离。除了温度-时间历史之外，掺杂方法还可以比较非常相似的火焰的燃烧产物、自由基和芳香族形成的关键前体(C2-C5物种)。与基准乙烯火焰相比，掺入甲苯提高了火焰的芳烃含量和碳烟体积分数，但令人惊讶的是，碳烟数密度和成核率受到的影响不大。因此，在掺甲苯火焰中观察到的体积分数的差异反映了在碳烟成核开始时较大的初始颗粒。煤烟首次出现在火焰附近时的成核速率与单环芳烃的二聚化速率处于同一数量级，而不是预期较大的多环芳烃的二聚化启动了这一过程。尽管成核本身对总体烟尘负荷的贡献不大，但成核作用通过影响初始颗粒的大小来调节总体烟尘负荷，最终影响后续的生长。
We perform spatially resolved measurements of light scattering of soot in atmospheric pressure counterflow diffusion flames to complement previously reported data on soot pyrometry, temperature and gaseous species up to three-ring polycyclic aromatic hydrocarbons (PAHs). We compare two flames: a baseline ethylene flame and a toluene-seeded flame in which an aliquot of ethylene in the feed stream is replaced with 3500 ppm of pre-vaporized toluene. The goal is twofold: directly adding an aromatic fuel to bypass the formation of the first aromatic ring, widely regarded as the main bottleneck to soot formation from aliphatic fuels, and assessing the impact of a common component of surrogates of transportation fuels on soot formation. The composition of the fuel and oxidizer streams are adjusted to ensure invariance of the temperature-time history, thereby decoupling the chemical effects of the fuel substitution from other factors. The doping approach enables the comparison of very similar flames with respect to combustion products, radicals and critical precursors to aromatic formation (C2–C5 species), in addition to the temperature-time history. Doping with toluene boosts the aromatic content and soot volume fraction relative to the baseline ethylene flame, but, surprisingly, the soot number density and nucleation rate are affected modestly. As a result, the observed difference in volume fraction in the toluene-doped flame is reflective of larger initial particles at the onset of soot nucleation. The nucleation rate when soot first appears near the flame is of the same order as the dimerization rate ofsingle-ringaromatics, in contrast with the expectation that the dimerization of larger PAHs initiates the process. Even though in and of itself nucleation contributes modestly to the overall soot loading, nucleation conditions the overall soot loading by affecting the size of theinitialparticle, which ultimately affects subsequent growth.