Particle Imaging Velocimetry for Sooting Flames with Scattering Suppression

Light scattering from soot particles in hydrocarbon flames presents a significant source of background noise in particle image velocimetry (PIV) measurements. To mitigate this effect, the relative scattering intensities of 200 nm PIV seed particles and soot particles in a hydrocarbon-air flame were optimized for a 90° viewing angle. A polarization control assembly-comprising a Pockels cell, vertical polarizer, and half-wave plate-was implemented to vary the incident light polarization angle relative to the scattering plane. The observed trends in scattered irradiance agree with Lorenz-Mie theory predictions for the ratio of scattered light from a single PIV seed particle to that from a single soot particle, across a range of polarization angles. Experimental single-shot PIV images qualitatively illustrate the resulting improvements. Reduced soot scattered light led to decreased velocity vector uncertainty and a lower incidence of vector dropouts in the processed PIV fields.