Davis Justin, Molnar Eric, Novosselov Igor
Molecular Engineering Institute, University of Washington, Seattle, WA, USA.
Mechanical Engineering Department, University of Washington, Seattle, WA, USA.
Carbon N Y. 2020 Apr 15;159:255-265. doi: 10.1016/j.carbon.2019.12.043. Epub 2019 Dec 19.
In this study, the structural properties of soot produced in diffusion flames are analyzed to elucidate the formation of mature aggregates from large young particles. Soot samples are generated in a laminar diffusion inverted gravity flame reactor (IGFR) operated on methane, ethane, and ethylene with Ar dilution to reduce the flame temperature. Soot produced in temperature ranges from 1495K-1568 K contains 100nm-300nm particles with (i) isotropic or (ii) multiple core structures, supporting a soot maturation pathway where one young soot particle evolves into a mature fractal aggregate via an internal nucleation route. During the process, these large amorphous particles can form internal voids as the particle loses mass due to pyrolysis or oxidation. Transmission electron microscopy (TEM) shows that young soot aggregates contain a higher fraction of shorter fringes and highly curved aromatics (11% vs. 23%), which is in agreement with their higher organic carbon content (3.3%-5.4% vs. 12.1%-28.8% wt.). Increasing the flame temperature reduces the curvature of polycyclic aromatic hydrocarbons (PAHs) and allows for more efficient layer stacking as indicated by a higher percent of stacked fringes. For these gaseous fuels, carbonization appears to be primarily a function of the flame temperature and independent of the fuel composition.
在本研究中，对扩散火焰中产生的烟灰的结构特性进行了分析，以阐明由大的年轻颗粒形成成熟聚集体的过程。烟灰样品在层流扩散反重力火焰反应器（IGFR）中生成，该反应器以甲烷、乙烷和乙烯为燃料，并使用氩气稀释以降低火焰温度。在1495K - 1568K温度范围内产生的烟灰包含100nm - 300nm的颗粒，具有（i）各向同性或（ii）多核结构，支持一种烟灰成熟途径，即一个年轻的烟灰颗粒通过内部成核途径演变成成熟的分形聚集体。在此过程中，由于热解或氧化导致颗粒质量损失，这些大的无定形颗粒会形成内部空隙。透射电子显微镜（TEM）显示，年轻的烟灰聚集体中较短条纹和高度弯曲芳烃的比例更高（分别为11%对23%），这与其较高的有机碳含量一致（重量百分比分别为3.3% - 5.4%对12.1% - 28.8%）。如更高比例的堆叠条纹所示，提高火焰温度会降低多环芳烃（PAH）的曲率，并允许更有效的层堆叠。对于这些气体燃料，碳化似乎主要是火焰温度的函数，与燃料成分无关。
