Characteristics of diesel engine soot that lead to excessive oil thickening

This is a study of soot from a heavy duty diesel (HDD) engine test designed to evaluate the soot handling ability of a lubricant. This study aims to understand what properties of diesel soot produced under certain conditions contribute to loss of viscosity control through examination of the morphology, nanostructure and oxygen functionalization of particulates obtained from two heavy duty diesel engine tests with different levels of EGR. Particulate samples obtained from the used engine oil that lost viscosity control at relatively low soot levels showed that the soot in this case was more graphitic and had lower oxygen functionalization.

► Soot surface chemistry can contribute to loss of lubricant viscosity control.
► More ordered soot may have less active surface area to interact with soot dispersants.
► Agglomeration of soot coincided with a reduction in active surface area for ammonia chemisorption.