Combustion-generated carbon black nanoparticles, or soot, have both positive and negative effects depending on the application. It is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. It also affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0°- 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz resulting in 1.4 times reduction for the total soot volume fraction.
