SOOT VOLUME FRACTION AND PARTICLE-SIZE MEASUREMENTS WITH LASER-INDUCED INCANDESCENCE

Laser-induced incandescence from soot was analyzed with a time-depende nt, numerical model of particle heating and cooling processes that inc ludes spatial and temporal intensity profiles associated with laser sh eet illumination. For volume fraction measurements, substantial errors result primarily from changes in gas temperature and primary soot par ticle size. The errors can be reduced with the proper choice of detect ion wavelength, prompt gating, and high laser intensities. Two techniq ues for primary particle size measurements, based on ratios of laser-i nduced incandescence signals from a single laser pulse, were also exam ined. Compared with the ratio of two integration times, the newly prop osed ratio of two detection wavelengths is better suited for simultane ous volume fraction and size measurements, because it is less temperat ure sensitive and produces stronger signals with, however, a lower sen sitivity to size changes. (C) 1997 Optical Society of America