Time Resolved Fluorescence Anisotropy Measurements of Nanoparticle Sizes in a Diffusion Flame

The growing need to control ultrafine particulate emission from combustion sources is driving the efforts in developing new diagnostic methods for in-situ determination of nanoparticle size and chemical characteristics. This work deals with the measurement of the sizes of fluorescent nanoparticles formed in flames by means of Time Resolved Fluorescence Anisotropy. Nano-sized particles are investigated in situ in a co-flow diffusion flame of ethylene. Particle fluorescence is excited by femtosecond laser pulses in the UV, detected by a fast photomultiplier tube and recorded on a digital oscilloscope. The experimental set-up allows a good time resolution allowing to measure particle sizes in the range between 2 and 30 nm. Measured axial and radial profiles of particle sizes are compared with the mean sizes of the particles detected by scattering/extinction technique.