Multiscale Modeling\nApproach to Understand Mechanism\nof Deposit Control by Sulfonate-Based Lubricant Detergents

Protecting the material surfaces from deposits and insoluble\nsludge\nparticles extends the engine life and reduces waste. Lubricant detergents\nin engine oils are essential additive technologies that prevent deposit\nformation in internal combustion engines. In this study, the effect\nof sulfonate detergent on deposit formation in a passenger car engine\nis investigated with experimental and multiscale molecular modeling\nmethods to present a unified approach. First principles density-functional\ntheory calculations, statistical sampling methods, all-atom molecular\ndynamics simulations, and coarse-grained simulations are examined\nto elucidate deposit control mechanism of sulfonate detergents. Analysis\nof the results reveals that sludge particles in the drain oil are\nsimilar in structure to piston deposits, and they might be the precursors\nof the piston deposits. Main factor for controlling the sludge particle\ndeposition is the prevention of their colloidal aggregation at the\nmicroscale in the base oil matrix. Aggregation can be mitigated by\nthe intercalation of detergent polar groups between the particles.\nThis is followed by the extension of hydrophobic tails into the oil\nphase, which decreases further aggregation via formation of a repulsive\nlayer.