Temporal soot evolution and diesel engine combustion: Influence of fuel composition, injection parameters, and exhaust gas recirculation

Abstract

This study deals with the investigation of the influence of fuel composition, injection parameters, and exhaust gas recirculation on not only engine-out, NOx, and particulate matter (PM) emissions but also on the temporal behaviour of soot formation and oxidation during combustion. Based on accurate measurements of exhaust emissions (gaseous components, particle number, and size distributions), in-cylinder temporal evolution of soot and temperature (computed from multicolour-pyrometry data), and analysis of the relevant parameters in direct-injection diesel engine combustion (calculation of heat release rates and different zone temperatures in the cylinder), insight has been gained with respect to the underlying mechanisms of the observed effects. Crank-angle-resolved data of the in-cylinder soot concentration have revealed the positive influence of the addition of water or of oxygenated diesel additives in diesel fuel in terms of reducing the soot formation and enhancing the soot oxidation rate. A clear linear correlation was found between the filter smoke number and KL signal at the end of the oxidation process. With respect to the particulate number or mass an exponential fit with KL at the end of main oxidation is shown.