Investigating the effect of oxygenated and aromatic compounds in fuel by comparing laser soot measurements in laminar diffusion flames with diesel-engine emissions

A database of fuels containing carefully graded amounts of aromatic and oxy genated compounds were used to investigate the effect of the molecular stru cture of the fuel on the sooting tendency of laminar diffusion flames. Clea r trends were found showing an increase in sooting tendency with increased aromatic content, with emphasis on the number of benzene rings. Oxygenated compounds such as diglyme were found to reduce the sooting tendency. These trends tallied closely with trends in soot emissions from a CFR IDI (Co-ope rative Fuel Research Indirect Injection) diesel engine, pointing towards an observable effect of the fuel on emissions of soot from engines. Laser tec hniques were used to measure the sooting tendency of the flame, by aiding m easurement of the threshold sooting height and by laser extinction and lase r-induced incandescence (LII) imaging. The UI technique allowed more detail ed investigation of the sooting tendency through quantitative visualisation of the soot distribution within each frame.