Optical properties of “young” carbonaceous particles

尽管含碳颗粒的形成在燃烧过程中的重要性，但与其形成有关的奥秘，即从分子结构到颗粒的转变，数量惊人。本项目的目的是研究和阐明碳分子和颗粒在气相向团簇和“年轻”克莱斯过渡阶段的光学性质。关于这些性质的信息具有三重相关性：（i）出于诊断目的，了解相关物质的光学性质对于解决与测量实验室规模和实际设备中的烟灰形成和烟灰形成机制相关的紧迫问题至关重要。(ii)了解早期的集群/粒子在过渡阶段与辐射的相互作用可以阐明结合力，从而形成相关物种的机制。(iii)由于碳质颗粒在大气辐射平衡（烟灰的绿色房屋贡献具有最大的总体不确定性）、沉积颗粒的吸收和再排放（例如，与火焰中的传统煤烟研究不同，在火焰中，从气相前体到颗粒的转变发生在一个非常狭窄的区域，其特点是温度和物质浓度的极端梯度，该项目的实验将在激波管中进行。在这里，粒子形成的各个阶段在时间上被很好地分开（因此在空间上也是如此，因为快速移动的冲击波引发了反应）。这将能够选择性地分析碳质颗粒形成中涉及的各种中间体。该项目利用了实验能力的独特组合。在大气压下工作的激波管配备了用于时间和空间分辨吸收测量（动力学光谱仪）以及光谱和反应时间分辨激光诱导荧光（RTR-LIF）和激光诱导白炽（RTR-LII）测量的光学诊断。这些光谱方法与高灵敏度的时间分辨消光测量相结合，该测量记录了传统上被解释为“烟灰形成的开始”以及所形成的物种的非原位表征。这些组合方法提供了关于吸收和发射特性以及允许激光加热到白炽的最小结构的全面信息。

Despite the importance of carbonaceous particle formation in combustion processes, there is a surprisingly large number of mysteries related to their formation, namely to the transition from molecular structures to particles. The objective of this project is to investigate and clarify the optical properties of carbonaceous molecules and particles in the transition phase between the gas phase towards clusters and “young” par¬ti¬cles. Information about these properties has a three-fold relevance: (i) For diagnostics purposes, knowing the optical properties of the related species is crucial to solve pressing issues related to measuring soot formation and soot formation mechanisms in lab-scale and practical devices. (ii) Understanding the interaction of the early cluster/particles in the transition phase with radiation can shed light on binding forces and thus the formation mechanism of the related species. (iii) There is a greater fundamental interest in understanding the optical properties of carbonaceous particles at all stages of their formation process because of their relevance in atmospheric radiative balancing (green house contribution of soot has the largest overall uncertainty), absorption and re-emission of deposited particles (e.g., on snow) influencing the local temperature balance, and even interstellar optical transmission.Unlike conventional soot research in flames, where the transition from gas-phase precursors towards particles occurs in a very narrow zone that is characterized by extreme gradients in temperature and species concentration, the experiments in this project will be carried out in shock tubes. Here, the various stages in particle formation are well separated in time (and thus in space because of the rapidly moving shock wave that initiates the reaction). This will enable a selective analysis of the various intermediates involved in carbonaceous particle formation. The project takes advantage of a unique combination of experimental capabilities. The shock tube operated at around atmospheric pressure is equipped with optical diagnostics for temporally- and spatially-resolved absorption measurements (kinetics spectrometer) and spectrally- and reaction-time-resolved laser-induced fluorescence (RTR-LIF) and laser-induced incandescence (RTR-LII) measurements. These spectroscopic methods are coupled with highly sensitive time-resolved extinction measurements that record what is conventionally interpreted as “the onset of soot formation” as well as with an ex situ characterization of the formed species. These combined methods provide comprehensive information about the absorption and emission properties as well as the smallest structures that allow for laser heating towards incandescence.