Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor

Tryfon Charalampopoulos


The index of refraction of soot particles is of considerable importance in many areas of research and engineering applications such as combustion diagnostics and radiative transfer from combustion systems. The present study aims toward the analysis of compositional effect on the refractive index and the spectral variation of the indices of soot particles by combining classical and dynamic light scattering measurements with the Kramers-Kronig relations in hydrocarbon flames. The particle size distribution is determined from photon correlation measurements. The number densities, volume fractions and refractive indices are then determined as a function of the height above the burner and fuel equivalence ratio for premixed propane/oxygen and methane/oxygen flames. This information is then combined with the spectral extinction measurements in the wavelength range 0.2 to 7 $\mu$m to determine the spectral variation of the refractive indices of soot. Premixed propane/oxygen and methane/oxygen flames with various fuel equivalence ratios were considered. It was found that the soot effective refractive indices change not only with the position within a given flame but they also change significantly with the fuel equivalence ratio. On the other hand, an absorption resonance exists between 0.25 $\mu$m and 0.28 $\mu$m, depending on the height above the burner surface. It was demonstrated that the Kramers-Kronig method of analysis can yield the refractive indices over the whole spectrum with the least number of assumptions as compared with the Drude-Lorentz dispersion model that has been used so far.