Impacts of advanced diesel combustion operation on soot nanostructure and reactivity

Advanced diesel combustion, accomplished via a single pulse fuel injection and high levels of exhaust gas recirculation, is shown to be a path to reduce oxides of nitrogen and particulate matter simultaneously. This is well established in the literature. Less established is how well such dilute combustion processes influence soot formation and affect soot that is emitted from diesel engines under such combustion modes. This work focuses on characterization of the nanostructure and oxidative reactivity of soot generated by a light-duty turbodiesel engine operating under a dilute, low-temperature combustion process referred to as high-efficiency clean combustion. The high-efficiency clean combustion soot samples are shown to have a fullerenic nanostructure, characterized by high levels of tortuosity of the fringe layers as seen in transmission electron micrograph images and as quantified using an image processing algorithm. Thermogravimetric analysis of the high-efficiency clean combustion soot samples shows that they have higher rates of oxidation than soot samples from a conventional diesel combustion mode. The linkage between the nanostructure of the high-efficiency clean combustion soot samples and their oxidative reactivity reinforces and supports the structure-property relationship for soot that greater curvature on the soot nanostructure leads to significant increases in oxidative reactivity.