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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Soot formation and oxidation in a high pressure spray flame.

Author: SIVALINGAM, G

Year: 2001

Supervisor(s): Roy Crookes

The role of individual parameters in the formation and oxidation of soot particulates in spray combustion at elevated pressure, as found in diesel engines, is investigated in a high-pressure system capable of sustaining continuous combustion.

Soot particulates at various axial and radical locations within the flame and at the exhaust were examined for particle size and agglomerate morphology. Particle-size analysis and distributions are presented at three different pressures: 1.1 MPa, 1.6 MPa and 2.1 MPa and three equivalence ratios: lean, stoichiometric and rich.

Various parameters such as number density and soot volume fraction were calculated for the same locations within the flame and exhaust. A database of particle size analysis with various properties such as temperature, pressure, equivalence ratio, exhaust gas emissions is presented together with data from diesel engine exhaust samples.

The experimental results were compared with predictions from three semi-empirical mathematical models for soot formation obtained from the literature. A relatively simple and efficient spray combustion model by Nazha has been used as a platform for the soot formation models of Hiroyasu, Moss and Narasimhan.

The measured particle size distributions at early stages of soot formation were numerically oxidized and compared with measured particle distributions at later stages of soot formation, using an oxidation model based on that of Nagle and Strickland-Constable.

High magnification images showing the microstructure of soot particulates at the different stages of soot formation and oxidation are also presented. Lattice spacing were measured for some of the samples under different environmental conditions. Evidence of internal oxidation was observed in particles in some soot agglomerates.