Role of dispersant on soot-induced wear in Cummins ISB engine test

Wear performance of two fully formulated engine oils was evaluated using the Cummins ISB engine test. One of the oil formulations used a multifunctional DVII (Dispersant Viscosity Index Improver) component with enhanced antiwear characteristics to improve durability of engine components while the other formulation comprised of a conventional additive package. After the completion of engine-dynamometer tests, valvetrain components operating primarily in boundary lubrication regime were inspected for wear and weight loss in order to understand soot induced wear effects. In addition, soot was extracted and characterized using temperature resolved XRD, TEM, XANES, BET, Raman and EDS. XRD phase analysis of residue left behind after soot oxidation showed presence of crystalline compounds embedded in the soot structure (CaSO4, Ca-3(PO4)(2), Zn-3(PO4)(2) and ZnO). These species form ash pre-cursors which get trapped in the DPF (Diesel Particulate Filter) placed in the engine exhaust stream. The turbostratic structure of both soot samples remains the same prior to oxidation; however, the embedded crystalline and amorphous species in the soot structure slightly change with oil formulation. Surface area of the soot measured using BET was found to be inversely proportional to the weight of residue. Additionally, used oil analysis was performed to understand variation in viscosity, wear elements and soot content before and after the test. Findings in this study provide deeper insights into the mechanism for improved wear protection provided by DVII. (C) 2018 Elsevier Ltd. All rights reserved.