PARTICLE INCEPTION STUDY IN FUEL RICH LAMINAR PREMIXED FLAMES BY PHOTOIONIZATION MEASUREMENTS

Photoelectric charging of particles is a powerful tool for on-line characterization of submicron aerosol particles. Photoionization based techniques have high sensitivity and chemical selectivity, they yield information on electronic properties of the material and are sensitive to the state of the surface. In the present study the photoionization charging efficiency, i.e. the ratio between the generated positive ions and the corresponding neutral ones, of flame formed carbonaceous nanoparticles is measured. The fifth harmonics of a Nd:YAG laser, 213 nm (5.82eV), is used as ionization source for the collected nanoparticle, a differential mobility analyzer (DMA) and a electrometer (Faraday cup) are then used for particles classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e. D=1-10 nm, show a photoionization charging efficiency clearly dependent on the flame conditions. In particular,we observed that the richer is the flame, i.e. higher equivalent ratio, the higher is the photon charging efficiency. These results clearly show that photoionization is a powerful diagnostic tool for the physical-chemical characterization of combustion aerosol, and it may lead further insights into the soot formation mechanism.