Many researchers [1,2,3,4] have suggested that lubricants contaminated with soot result in increased rates of wear. Numerous potential mechanisms have been proposed which include abrasion via three body contact, oil starvation and deactivation of the anti-wear additives. It is commonly thought that the control of soot aggregation by the addition of appropriate dispersant additives will lead to improved wear performance .
In this paper, the kinematic behaviour of two valve train contacts are studied and a generalised wear model proposed that highlights the importance of oil film thickness, soot particle size and contact mechanics. The results of these analyses when considered alongside the detailed rheological behaviour of the soot laden oil lead us to challenge the significance of soot aggregation and viscosity control to engine wear. The dependence of oil film thickness on oil formulation parameters is explained and the wear control advantage derived from good dispersion is rationalised as an adventitious consequence of oil film thickness increases derived from certain dispersant molecules.