The influence of fuel molecular structure on particulate emission investigated with isotope tracing

This thesis is concerned with the formation of particulate matter, a topic of scientific and practical importance due to the toxicity of particulate emissions from automotive and other combustion sources. At present, fuels are predominantly derived from fossil sources, but as production technology improves, biofuels and synthetic fuels are expected to emerge as scalable long-term sources of liquid fuels. Efforts are being made to ensure that this next-generation of fuels is cleaner burning than the last. In order to inform the production and processing of cleaner burning fuels, more needs to be known about how molecular structure influences the formation of pollutant emissions. This thesis presents research that has been carried out in order to better understand the role of functional group chemistry on the conversion of carbon atoms in the fuel to the particulate matter (PM). In particular, the propensity of individual molecules or carbon atoms within molecules to form PM is reported quantitatively. To this end, a technique using carbon-13 (13C) labelled fuel molecules was used so to track the labelled carbon atoms in the fuel to PM. The technique required only very low levels of 13C enrichment, and isotope ratio mass spectrometry equipment (IRMS) was used as a means of 13C detection. Samples of particulate matter were formed using a tube reactor, and also in a compression ignition diesel engine. The tube reactor was designed and commissioned in order to study the pyrolysis of various fuel molecules under well-controlled, homogenous conditions. The contribution to PM of a number of molecules containing various functional groups was assessed, including: alcohols, esters, aromatics, double bonded carbon atoms, a ketone, and a carboxylic acid. Tests were conducted using single-component fuels, and blended in a binary mixture with n−heptane. The results show that the contribution of carbon atoms within molecules to PM, is not equal, but depends on the local molecular structure. For example, oxygenated molecules significantly reduced the contribution to PM of the carbon atoms directly attached to oxygen. The thesis presents one of only a handful of investigations that have been published on the conversion of specific carbon atoms of various molecules to soot and particulate. It advances the field of study by providing data for validation, at the sub-molecular level, for chemical kinetic models of soot formation, and advances fundamental understanding of how fuels convert to soot and particulates.

本论文关注颗粒物的形成，由于汽车和其他燃烧源排放的颗粒物具有毒性，这是一个具有科学和实际重要性的课题。目前，燃料主要来源于化石能源，但随着生产技术的提高，生物燃料和合成燃料有望成为可大规模使用的长期液体燃料来源。人们正在努力确保下一代燃料比上一代燃烧更清洁。为了给更清洁燃烧燃料的生产和加工提供信息，需要更多地了解分子结构如何影响污染物排放的形成。本论文介绍了为更好地理解官能团化学在燃料中的碳原子向颗粒物（PM）转化过程中的作用而进行的研究。特别是，对单个分子或分子内的碳原子形成PM的倾向进行了定量报告。为此，使用了一种用碳 - 13（13C）标记燃料分子的技术，以便追踪燃料中标记的碳原子到PM的过程。该技术只需要极低水平的13C富集，并使用同位素比质谱仪（IRMS）作为13C检测手段。颗粒物样品是在管式反应器中以及压燃式柴油发动机中形成的。设计并调试管式反应器是为了在良好控制的均匀条件下研究各种燃料分子的热解。评估了许多含有不同官能团的分子对PM的贡献，包括：醇、酯、芳烃、双键碳原子、一种酮和一种羧酸。使用单一组分燃料进行了测试，并与正庚烷以二元混合物的形式混合。结果表明，分子内的碳原子对PM的贡献并不相等，而是取决于局部的分子结构。例如，含氧化合物显著降低了直接与氧相连的碳原子对PM的贡献。本论文是为数不多的已发表的关于各种分子的特定碳原子向烟灰和颗粒物转化的研究之一。它通过在亚分子水平上为烟灰形成的化学动力学模型提供验证数据，推动了该研究领域的发展，并增进了对燃料如何转化为烟灰和颗粒物的基本理解。