This thesis investigates the effect of fuel aromatic content on soot distribution, particle morphology and internal structure inside the cylinder of an optically accessible engine. A set of custom-made jet fuels with 4%, 14% and 24% aromatic content are studied first with the 24% aromatics fuel (AR24) used for more detailed follow-up study of soot particle evolution along the flame development path. Time-resolved imaging of cool flame, OH* chemiluminescence signals and soot luminosity are

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... med to visualise the overall reaction development. Planar laser-induced fluorescence imaging of HCHO and incandescence imaging of soot are also performed to obtain detailed understanding of reactions and soot distributions. Soot is analysed at a particle level. Using the thermophoresis-based particle sampling method, soot aggregates are collected from multiple in-bowl locations. Up to four soot sampling probes are installed on the piston-bowl wall with 60° spacing angles for simultaneous sampling from the same firing cycle. These sampling locations represent a jet-wall impingement point (JW), an up-swirl point (US), a down-swirl point 1 (DS1) and a down-swirl point 2 (DS2) along the sooting flame path. The subsequent transmission electron microscope (TEM) imaging of the collected soot particles enables structural analysis of soot particles as well as sub-nano-scale carbon layers. The results showed that the aromatic content has little impact on reactions and flame development among the tested fuels. However, the soot formation starts to occur earlier, and its growth rate is much higher for a higher aromatic fuel. The carbon-layer fringe analysis shows more mature, graphitised structures with higher aromatics at both formation-dominant and oxidation-dominant stages. For a selected AR24 fuel, the carbon-layer fringe analysis indicates continued oxidation during the flame penetration along the piston-bowl wall. Regarding the particle structure evolution, it is characterised by high formation of small aggregates at JW point, s [...]