Influence of physical structure and chemistry of diesel soot suspended in hexadecane on lubrication of steel-on-steel contact

Soot generated from the combustion process in diesel engines affect engine tribology. In this paper, two diesel soot samples; from engine exhaust and oil filter are suspended in hexadecane oil and the suspension is used to lubricate a steel ball on steel flat sliding contact at a contact pressure of 1.3 GPa. The friction and wear of the steel flat are recorded. The data are compared with those recorded when the soot is generated by burning ethylene gas. The rationale for the comparatively poor tribology of diesel soot is explored by quantifying the size and shape of primary particles and agglomerates, hardness of single primary soot particles, the crystallinity and surface and near surface chemistry of soot and interparticle adhesion.

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► Diesel soot is larger, irregular shaped, harder and more adhesive than flame soot.
► Diesel soot has low graphitic and high organic contents.
► Diesel soot particles in oil suspension accommodated poorly in the sliding contact.
► Incoherent tribofilm and adhesive metal to metal contact for diesel soot leads to poor tribology.