Study on the reciprocating friction and lubrication characteristics in the EGR environment of engine cylinders

This study aims to evaluate the performance of lubricating oils under different gas environments within the engine and reveal the underlying reasons for the observed differences. In the experimental aspect, a series of friction and wear tests were conducted in a controllable simulated gas environment experimental system. Experimental verification has shown that this device can effectively simulate engine operating conditions and provide valuable reference insights, and the wear surfaces were analyzed using morphology analysis (SEM) and elemental analysis (XPS). The results show that in an inert nitrogen environment, metal sulfides and phosphates readily form friction films, exhibiting excellent anti-friction and wear-resistant properties. In contrast, an oxygen-containing environment promotes the formation of brittle oxide layers such as Fe₂O₃ while inhibiting friction film formation, significantly deteriorating lubrication performance. NO accelerates the decomposition of friction films through dual mechanisms of catalytic oxidation and acidic corrosion, leading to increased friction coefficient and aggravated wear. EGR gas exhibits a nonlinear concentration regulation characteristic, where an appropriate amount of EGR can suppress NO corrosion, but excessive EGR destroys the friction film, resulting in negative effects. These findings provide an important foundation for the development of performance evaluation standards for internal combustion engine oils.