Characterization of nanoparticles generated in reacting flows

Abstract

In this thesis, particle formation in reacting flows is investigated experimentally. Two separate systems are considered. First, silica particle synthesis is characterized in a cold, turbulent jet doped with trace amounts of silane gas that issues into a vitiated co-flow. Additionally, soot formation is characterized in a laminar ethylene diffusion flame. Laser diagnostic techniques are the cornerstone of this work and make it possible to perform measurements with minimal disruption to the system. In both scenarios, elastic light scattering (ELS) and OH-PLIF are employed to obtain experimental signals that contain information about temperature, particle formation, OH concentration and other physical quantities. Additionally, line-of-sight extinction is used in the soot-forming system to recover integrated soot volume fraction profiles and multi-angle light scattering (MALS) is demonstrated on the silica-forming system to obtain in-situ information about particle size. Laser-based datasets are supplemented by probe measurements, including temperature profiles measured using radiation-corrected thermocouples and TEM analysis of particle samples obtained by location-specific thermophoretic sampling. Fully-defined numerical models, available in both scenarios, are validated following an unconventional approach based on the comparison of “predicted signals” with experimentally-obtained signals, as a means to avoid introducing additional assumptions. Satisfactory agreement is found, even though some discrepancies remain concerning silica particle formation, which are likely related to uncertainties in precursor chemistry and nucleation. Nevertheless, this is one of a few joint numerical and experimental studies that address particle formation under turbulent conditions. Regarding soot formation in laminar flames, a consistent underprediction of soot formation on the centreline is identified, which is believed to be a limitation of the acetylene-based model. In summary, this work uses optical diagnostic techniques to generate extensive datasets of particle-forming reacting jets, making a major contribution towards the validation of computational tools to predict particle formation in turbulent reacting flows as well as soot formation in laminar flames.