The enhanced lubrication effect by ZDDP under limited lubricant supply condition

Abstract

A limited supply of lubricant can minimize energy dissipation and waste, enabling lean lubrication. However, insufficient lubricant supply can lead to a critical issue known as starved lubrication, emphasizing the need to address this concern under limited lubricant supply (LLS) condition. In this study, a ball-on-disc lubricating film test rig, with a circular contact, was employed. The impact of zinc dialkyl dithiophosphate (ZDDP) interfacial adsorption on the lubrication characteristics under LLS condition was investigated by introducing ZDDP as an anti-wear additive. A dichromatic interference intensity modulation (DIIM) approach was utilized to reveal the evolution of the lubricant film at various lubricant supply stages under LLS. Three distinct lubricant supply stages were identified: the fully flooded stage, the transition stage from fully flooded to starved lubrication, and the starved lubrication stage. The mechanism of ZDDP interfacial adsorption during different lubricant supply stages was evaluated by analyzing variations in oil reservoir morphology, lubricant film thickness, and friction coefficient. The results indicate that, under LLS conditions, changes in the oil reservoir directly influence the transition between lubricant supply stages. The adsorption effect of ZDDP was found to promote lubricant entrainment and improve the lubricant supply in the inlet area during the second and third lubricant supply stages, thereby enhancing the anti-collapse capacity of the lubricant film. Additionally, in the LLS condition, the improved anti-friction effect of ZDDP is attributed to the synergistic impact of enhanced lubricant entrainment and increased shear resistance.