Size Measurements of Fluorescent Carbon Nanoparticles in a Co-flowing Laminar Diffusion Flame by Time-Resolved Fluorescence Anisotropy

The mean size of flame-formed fluorescent carbonaceous nanoparticles was detected by insitu time-resolved fluorescence anisotropy (TRFA) measurements. A well-known and long investigated co-flowing laminar diffusion flame of ethylene was used as combustion system for both data comparison and for its importance in the field of particulate formation and emission control. Form the analysis of the decay time of the fluorescence anisotropy, we estimated the diameter of particles selected by their ability to absorb and emit visible light, as function of the flame radius for several heights form the fuel nozzle. TRFA has allowed to investigate intermediate class of compounds between the UV absorbing particles and soot studied in previous works. These compounds have average sizes ranging from 5 to 15 nm. The technique proves to be applicable to the study of soot formation mechanisms, and specifically to follow the inception phenomena based on the transition from the gas-phase to the solid particles.