Nano-particle sizing by Laser-Induced-Incandescence (LII) in a shock wave reactor

Laser-Induced Incandescence (LII) is a relatively new optical diagnostic for particle sizing which is currently used in combustion science. Its advantage against light extinction and light scattering methods is the possibility of getting size information with high time and space resolution even for nano-particles. LII is mostly applied to particle formation or particle removal in reactive stationary flows, but it can also be used in shock-induced reactive flows. This is demonstrated in three examples: soot particle formation during high temperature pyrolysis of benzene, iron particle formation from iron pentacarbonyl, and formation of carbon-coated iron particles. From the principles of LII, it is not possible to obtain a complete particle growth curve from one individual shock tube experiment. Therefore, the kinetics of particle growth evolution must be determined from several identical shock tube experiments with a delayed triggering of the heat-up laser. The principles of LII, the in-situ measurement of particle size, and the comparison to beam-collected particles, which were visualized by a high resolution transmission electron microscope (HRTEM), are demonstrated. It was found that the energy accommodation coefficient during the particle cooling is alpha = 1 for a soot surface but is significantly lower e.g. for an iron surface.