Source: Dissertation Abstracts International, Volume: 78-07(E), Section: B.

Adviser: Marshall B. Long.

In this thesis, optical diagnostics and particle sampling techniques were applied in a standardized series of nitrogen-diluted ethylene diffusion flames stabilized on the Yale Coflow Burner. These flames are designed to provide a multi-dimensional and yet computationally tractable environment to study the formation, growth, and oxidation of soot particles. Chemically reacting flows, such as the sooting flames studied in this thesis, are the product of several highly coupled phenomena that includes chemical reaction, fluid dynamics, heat transfer, and mass transport. As such, it can be difficult to directly compare computational results to an experimentally measured parameter given the myriad details that affect the computed parameter. In this thesis, the two-dimensional temperature field of the Yale coflow flames was measured experimentally and used to constrain a numerical simulation by fixing the temperature at each grid point. Thus, the computed temperature field was not driven by heat release from the chemical model, and differences may be observed in species concentration or soot volume fraction. The two- dimensional scalar temperature field of the axisymmetric flames was measured using soot and thin filament pyrometry, Rayleigh structured laser illumination planar imaging, and thermographic phosphor thin filaments. Some of the temperature-time history of soot particles in the flames remains unmeasured and the effect on the constrained numerical solution is discussed.

Modeling the in-flame evolution of soot particles often relies on simplified models of particle morphology or empirical parameters to capture fundamental processes such as particle nucleation. A sectional model of soot morphology is common and approximates particles with a spheroid geometry wherein particles coalesce upon impact. However, this is not consistent with the known morphology of mature soot aggregates, which are comprised of nearly spherical primary particles that connect to form a mass fractal structure. The number of primary particles in these aggregates follows a power law scaling dependence in which surface area is preserved during the agglomeration of two particles (to first order). The aforementioned sectional model incorrectly suggests that particles coalesce upon impact, thereby not preserving surface area (to first order). Therefore, in order to capture surface area dependent processes such as particle oxidation, experimental data must be provided regarding the morphology of soot aggregates in order to assist in the development of an aggregation soot model. In this thesis, the effective radius of gyration of soot aggregates was optically measured in two dimensions for flames stabilized on the Yale burner. The optical measurement was validated through thermophoretic sampling of soot aggregates at targeted locations; information about particle polydispersity and additional morphological parameters was also obtained. An additional study is presented that investigates the optical properties of soot particles in the Yale Coflow Burner. The optical properties were used to validate our knowledge of soot volume fraction and to provide accurate experimental data for comparison to results from numerical models.