Detailed modeling of polycyclic aromatic hydrocarbon and soot formation employing theory and experiments

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To combat the harmful effects of polycyclic aromatic hydrocarbons (PAHs) and subsequently formed soot particles on human health and the environment, many governments and institutions are introducing increasingly stringent regulations. To develop combustion control techniques that allow the compliance with these regulations, it is essential to understand and to accurately model the chemical kinetics of fuel decomposition and especially PAH formation. While most of the available literature focuses mainly on the quantitative chemical kinetic modeling of simple combustion systems, a detailed understanding of the complex PAH formation and growth mechanisms and their influence on soot production continues to be one of the central challenges in combustion research. The proposed project targets the generation and testing of new chemical kinetic mechanisms for PAH formation leading to soot production. First, the understanding of the second aromatic ring formation will be improved with theoretical and experimental methods. The Reaction Mechanism Generator (RMG) developed in the Green Group at MIT will be enhanced to allow the generation of reliable, detailed kinetic mechanisms. The combination of a time-resolved photoionization time-of-flight mass spectrometer and a laser absorption spectroscopy apparatus available in the Green Group at MIT will be employed to measure specific product-branching ratios of gas-phase radical reactions and temperature- and pressure-dependent chemical kinetics. Then, alternative pathways leading to fast soot formation will be explored, for the first time including resonantly stabilized PAH radicals. Many of the currently proposed routes appear to be too slow or too reversible to explain experimental observations. Finally, the generated chemical kinetic mechanisms will be used to compute soot production with the Hybrid Method of Moments model in laminar steady and time-dependent, one- and two-dimensional, premixed and non-premixed methane, ethylene, benzene, and acetylene flames.