Planar Laser Light Scattering for the In-Cylinder Study of Soot in a Diesel Engine

A study has been experimentally conducted in an optically-accessible DI Diesel engine operating on 50/50 mixture of iso-octane and tetradecane to evaluate a planar laser light scattering technique for the in-cylinder study of soot. Two simultaneous images, taken with vertically and horizontally polarized scattered light, were used to determine the polarization ratio, C_HH/C_W. This magnitude of the polarization ratio was employed to distinguish soot particles from fuel droplets. The spatial and temporal variations of soot during the combustion cycle were investigated with images taken at various crank angles and swirl levels at three different planes in the combustion bowl. For the high swirl case, soot was uniformly distributed in the combustion bowl. For the non-swirl case, however, soot was mainly observed near the wall and at the top plane, and was observed to exist later into the expansion stroke. These results were consistent with combustion photography results from earlier work and provided improved spatial information and temporal resolution. The major limitations of this technique are the soot deposition on the window and multiple scattering from the fuel droplets during the fuel injection period.