Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Tryfon T. Charalampopoulos

Abstract

The in-situ optical technique of inferring the soot agglomerate structural and optical properties from the measurements of the extinction cross section, the differential scattering cross section, the dissymmetry ratios in both planes of polarization, and the depolarization ratio, was investigated in detail by this study. A sensitivity analysis of the technique revealed that the dissymmetry ratios are insensitive to both the real and imaginary part of the refractive index. The ratio of the differential scattering to extinction cross sections was also found to be a weak function of the imaginary part of the refractive index. The sensitivity analysis results indicate that the technique is not suitable for inferring accurately the optical properties of the soot agglomerates. Therefore, a known value for the particle refractive index should be used in the agglomerate analysis to infer the morphology of the soot agglomerates. Experimental measurements of the above described quantities from a laminar premixed propane/oxygen flat flame, of fuel equivalence ratio of 2.1, were used with the appropriate agglomerate model to infer the structural agglomerate parameters. Soot samples were also extracted from the flame by using thermophoretic and sampling probes. It was found that the agglomerate model analysis of the measured scattering and extinction quantities (for four different soot refractive index values), underpredicts the degree of agglomeration of the soot particles. A quantitative analysis of the agglomerate morphology of the soot samples extracted with the sampling probe, indicates a self-preserved distribution of the primary particle sizes and the number of primary particles per agglomerate with increasing flame residence time of the agglomerate. A qualitative analysis of the electron microscopy results, of the soot samples extracted with the thermophoretic sampling probe, suggests that the degree of agglomeration is a function of flame residence time, and that the primary particle sizes in the agglomerates are fairly monosized.

Pages

261

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