An experimental apparatus to measure soot morphology at high pressures using multi-angle light scattering

In this work, a novel experimental setup is described which is designed and built specifically to study soot morphology using light scattering and extinction techniques at elevated pressures. The experimental setup consists of a counterflow burner housed inside a pressure vessel. A unique feature of this pressure vessel is the four curved optical windows which can provide the required optical access for light scattering measurements in order to infer the morphological parameters of soot. Using this setup, N2-diluted ethylene and air counterflow flames are stabilized from 3 to 5 atm. Global strain rate (a) of 30 s−1 is maintained at all conditions and all the flames studied are soot formation (SF) flames. Light scattering by soot is measured between 15° to 165° at different locations along the axis of the burner. Ratio of total scattering to absorption (ρsa), path averaged soot volume fraction (f v), mean primary particle size (dp), mean radius of gyration of aggregates (Rgm) and fractal dimension (Df) are calculated from multi-angle light scattering and extinction data using Rayleigh–Debye–Gans theory for fractal aggregates (RDG-FA). ρsa, f v, dp, and Rgm increase as the pressure is raised. The scattering contribution in these measurements vary from 1.3% to 16% of absorption which suggests that wide angle optical access is essential for accurate measurements of f v. Df equal to 1.27 is measured near the flame at 3 atm which increases as the particles are convected away from the flame and Df increases to 1.98 at 5 atm.