Cain Jeremy, Laskin Alexander, Kholghy Mohammad Reza, Thomson Murray J, Wang Hai
University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0101, USA.
Phys Chem Chem Phys. 2014 Dec 21;16(47):25862-75. doi: 10.1039/c4cp03330b. Epub 2014 Oct 29.
High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (λ = 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200-600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initial mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen abstraction-carbon addition mechanism currently considered in fundamental models of soot formation.
高分辨率质谱联用纳米喷雾解吸电喷雾电离技术，用于探测在三组分喷气燃料A - 1替代物的同轴流扩散火焰中心线处采集的年轻烟灰颗粒的化学成分。在颗粒对光消光（λ = 632.8 nm）透明的较低位置，发现缩聚多环芳烃（PAH）是颗粒物质的主要成分。随着颗粒质量和尺寸的增加，这些颗粒富含脂肪族成分。在碳化发生之前，年轻烟灰颗粒中的组成物种是质量为200 - 600原子质量单位的脂肪族和芳香族化合物，其中一些是含氧的。以PAH或PAH与脂肪族混合物为主的颗粒，通过电子显微镜观察可能呈现出类似液体的外观，并且对可见光透明。这里观察到的化学成分变化表明，同轴流扩散火焰中烟灰形成的分子过程可能比以前认为的更为复杂。例如，在火焰中最初主要是芳香结构且不存在氢原子或其他自由基的区域，脂肪族成分的质量增长和富集表明，除了目前在烟灰形成基础模型中考虑的氢提取 - 碳添加机制外，必定还存在至少另一种烟灰质量增长机制。
