PEPICO in combustion chemistry research II

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A detailed knowledge of the most important reactions plays a key role for the development of a predictive understanding of combustion processes and it is particularly important for ignition processes and the mitigation of pollutants. The goal of this project is to investigate the initial steps of fuel destruction in detail. A key reaction is the formation of a fuel radical by hydrogen abstraction from the carbon frame of the fuel because it leads to isomeric radicals, which in subsequent reactions cause branching in the reaction network. To describe the complete reaction network correctly, the first branching steps must be understood. At low temperatures, the fuel radicals typically react by oxygen addition to peroxides and subsequently oxygenated intermediates. At high temperatures, beta-scissions and unimolecular decomposition form hydrocarbon intermediates. A combination of molecular-beam mass spectrometry (MBMS) and photoelectron-photoion-coincidence spectroscopy (PEPICO) is used to detect the reactive key species experimentally in laminar low pressure flames and in a plug-flow reactor. The experiments with photoionization at the Swiss Light Source are complemented with laboratory based MBMS experiments using electron ionization. The teams of both applicants showed that their flame experiment at the Swiss Light Source features exceptional sensitivity and can identify and quantify isomers better than comparable MBMS instruments. As a consequence, this experiment is ideally suited to detect the mostly radical species in the complex matrix of the flame gases. A Mercator-fellowship for Dr. Hemberger is requested to ensure a high quality of data evaluation. Because the pressure and the reaction times at a specified temperature can be controlled easier and more systematically in a flow reactor than in a model flame, it is one target of this project to build and connect a plug-flow reactor to the MBMS PEPICO system. The goal of these experiments is to characterize the intermediates formed via low-temperature reaction pathways in a wider parameter range by temperature-dependent concentration profiles.A combination of both experiments yields experimental data sets for a series of hydrocarbons (Propene, Propane, 1-Butene, 2-Butene, i-Butene, n-Butane, i-Butane, n-Heptane, Methylhexane, Propylbenzene und Propylcyclohexane) that can be used to develop and validate reaction mechanisms for low and high temperature combustion. The focus of the work in this project is the identification of intermediates that lead to branching in the initial steps of the reaction network. The experimental results obtained in this project will be provided to the scientific community and interpreted in cooperation with model developers.