Characterization of Carbonaceous Particles by Time-resolved Laser-induced Incandescence

Online-characterization of carbonaceous nanoscaled particles is important in different application fields, e.g., in carbon black production or in automobile raw exhaust. For the determination of mass concentration and primary particle size respectively specific surface area, a possible in situ measurement technique is time-resolved laser-induced incandescence (TIRE-LII). The basic principle of this technique is to heat the carbonaceous particles up to their sublimation temperature by means of a high-energetic laser pulse and the subsequent detection and analysis of the spectral and time-resolved enhanced thermal radiation. At later times after the laser pulse heat conduction to the ambient gas is the dominant heat loss mechanism and so particles with different specific surface area cool down differently. From the temporal signal decay the size distribution of the primary particles can be derived. Furthermore, the signal maximum is proportional to the mass concentration. Here, an overview is given on current potentials and problems using this measurement technique for the comprehensive characterization of carbon black and Diesel soot. Measurements have been performed at different carbon black reactors on the one hand and directly in the Diesel raw exhaust on the other hand. Thereby, the results were compared with established measurement methods like TEM, conventional adsorption analysis and gravimetrical techniques. Furthermore, a new approach applying this technique also for suspended particles in liquids is shown.