Study on the tribological behavior and lubrication mechanism of piston rings and cylinder liners in hydrogen internal combustion engines

This study aims to evaluate the influence of the actual in-cylinder combustion environment of hydrogen internal combustion engines (HICEs) on the tribological behavior of piston ring-cylinder liner (PR-CL) interfaces, and to investigate the underlying lubrication mechanisms. A hydrogen engine environment simulation system was employed to accurately replicate the four characteristic stages of the hydrogen combustion process (pre-combustion, ignition, main combustion, and post-combustion), followed by reciprocating tribological tests. The worn surfaces were characterized using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that, in the PR-CL tribosystem of HICEs, the severity of wear increases noticeably as the combustion process progresses. Specifically, during the early stage of combustion, the boundary film remains relatively intact; however, as the combustion environment deteriorates, the protective film ruptures and peels off, ultimately leading to lubrication failure and a significant intensification of adhesive wear. Mechanistic analysis indicates that a decrease in hydrogen concentration within the combustion environment promotes the oxidation of Fe²⁺ to Fe³ ⁺, leading to the continuous depletion of key boundary film elements such as sulfur and phosphorus. This process severely weakens both the formation and stability of the lubricating film. Furthermore, lubricants with different base oil formulations exhibit markedly distinct adaptive responses to changes in hydrogen combustion environment parameters. This study provides important experimental support for the development of a dedicated performance evaluation system for HICEs.