(218c) Role of the Soot Main Precursors in the Psds for Premixed Ethylene and Benzene Flames

Soot formation during combustion continues to be a major subject of experimental and theoretical study due to the impact of soot on human health and radiation forcing. However, soot formation is a complex process involving a great number of chemical and physical steps, and is still incompletely understood. Our previous study demonstrated the major differences in the evolution of the particle size distributions (PSDs), both measured and modeled, of soot in premixed benzene and ethylene flat flames. The most significant difference between these PSDs was the persistence of the nucleation mode with height above the burner (HAB) for ethylene flames compared to its rapid decline for benzene flames under similar temperature and C/O ratio conditions. Since conditions other than fuel changed between the flames, the question still remains as to whether the difference is accountable by the fuel change or by other flame conditions. In this study, we are measuring the concentration profiles of the soot main precursors acetylene, benzene and PAHs such as naphthalene, phenanthrene, pyrene and acenaphthalene in order to evaluate their role on the PSDs for these flames. Experimentally, samples are collected in a filter trap and cooled trap from the flames, the organic extractable material is analyzed using Gas Chromatography and the results are compared with different solutions standards prepared using benzene and light PAHs. The experimental concentrations profiles are compared with the model which employed calculations of gas phase species coupled with a discrete sectional approach for the gas-to-particle conversion. The model results showed that in the benzene flame the aromatics are consumed in the oxidation zone of the flame which might explain why the decrease in the nucleation mode in this flame. By contrast, in the ethylene flame, the acetylene and aromatics concentrations persist at even high HAB which is again consistent with the observed persistence of the nucleation mode at larger HAB

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