Enhanced optical methods of soot characterization for application to diesel emission measurements.

摘要

The first part of this thesis addresses the enhancement of the available optical methods used in flame research for soot characterization. A method that combines Laser Extinction and Laser Elastic Scattering that can yield the soot volume fraction, primary particle diameter, number density, and soot structure parameters in flames was developed using a laminar diffusion flame and a laminar premixed flame. The albedo (the ratio of the scattering cross section to the extinction cross section) from an extinction and three scattering measurements is calculated first. This enables the determination of the contributions to extinction from absorption and scattering before performing calculations for other soot characteristics.; The fractal dimension and the fractal prefactor of soot aggregates were considered as constants in the initial analysis of this study. This approach yielded results that were consistent in the mid-flame region of the diffusion flame with those of a previous study in this laboratory. However, results for the lower part and higher elevations in the flame did not compare well with those of the previous study. It was observed that the calculations were very sensitive to the value of the fractal dimension and therefore the assumption that the fractal dimension and the prefactor were constant at all heights in the flame was evaluated.; The fractal dimension was obtained from experimental measurements. A method for obtaining the value of the fractal prefactor if the value of the fractal dimension is available is also developed. It was observed that the values of the fractal dimension obtained from experimental data were significantly lower than the constant assumed value of 1.74 in the lower part and higher elevations of the diffusion flame where the anomaly in the results was observed in the initial analysis. Based on the evidences found in this study, it was concluded that the value of the fractal dimension is not the same at all heights in the flame and the variation of the fractal dimension needs to be considered in the analysis.; It was also observed that the lognormal distribution function did not provide a good fit for the probability density function for the number of primary particles in an aggregate (pdf(n)) when the experimentally determined value of the fractal dimension was significantly lower than 1.74. (Abstract shortened by UMI.)