CAREER: The Role of Electric Charges and PAHs in Molecular Clustering and Soot Inception in Laminar Premixed Flames

Combustion devices that use a range of fuels are expected to partially satisfy global energy and propulsion needs for the foreseeable future. Emissions of soot, a byproduct of combustion, have detrimental effects on air quality and human health. Models that accurately describe soot formation could be helpful in designing and optimizing the next generation of combustion devices to reduce soot emission. However, experimental data for soot formation are needed to develop and validate soot formation models, and such data are scarce. This project focuses on the inception of soot formation. Despite many years of research on soot, inception is not well understood. This project involves a series of experiments designed to uncover the necessary information about soot formation for use in soot models. Although the focus of the project is on soot, the underlying inception process is similar to the formation of carbonaceous dust in the interstellar medium and the synthesis of nanocarbon material in industrial applications. Thus, improvements in modeling generated by this project may have broad applications. The proposed project integrates research and education to build toward mitigating the environmental impact of energy conversions and usages, by unraveling the soot inception kinetics. The research objective is to quantify the electrically neutral and charged flame products including small molecules resulting from fuel oxidative pyrolysis, Polycyclic Aromatic Hydrocarbons (PAHs), weakly bonded molecular clusters, and soot nuclei. Measurements will be performed in several carbon-rich laminar premix flames with different reactant compositions and maximum temperatures. The flame products will be measured directly or after making them collide with other neutral and charged species purposely seeded either in the sampled flow or directly in the flame. The results are expected to clarify the invariably neglected effect of the electric charge on the clustering of PAHs, by characterizing the kinetics of collision charging and condensation growth occurring in the flames and post-sampling. The research efforts are complemented by an educational plan with three objectives: 1) sensitizing the public on technical aspects affecting the sustainable satisfaction of the global energy demand; 2) inspiring K-12 students to undertake college education in STEM, and 3) equipping undergraduate and graduate students with engineering skills to study reactive multiphase flows relevant to the energy sector. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.