The application of novel injection strategies (high-pressure injection, early injection, retarded injection, etc.) in combustion engines has made the wall-wetting problem severer. As the splashed fuel dilutes the lubricating oil, the tribological performance of the cylinder liner–piston ring pair will be affected. In this research, the viscosity and wettability tests were conducted firstly by mixing diesel into lubrication oil. It was found that the dynamic viscosity of the mixture drops with more fuel diluting the oil, and a small quantity of diesel mixed will cause a remarkable decline in lubricant viscosity; also, the contact angle shows a downward trend with the increasing diluting ratio. Then based on several typical diluting ratios, the reciprocating friction tests were carried out to measure the instantaneous friction force of the production ring/liner pair. The experimental results showed that under a mixed lubrication state, the peak friction force of the ring/liner pair occurs around the dead centers, while the minimum force occurs at the middle position of the reciprocating stroke; with more fuel diluting the oil, the bearing capacity of oil film degrades, resulting in the increase of friction force. In addition, the average friction coefficient of the ring/liner pair shows an upward trend with the increasing diluting ratio, and the Stribeck curve moves toward the upper-left, which means the lubrication condition of this pair tends to transit from mixed lubrication to boundary lubrication, causing negative effects on the frictional property of the cylinder liner–piston ring pair. Therefore, the diluting ratio should be controlled under 20%.

新型喷射策略（高压喷射、提前喷射、延迟喷射等）在内燃机中的应用使壁面润湿问题变得更加严重。由于飞溅的燃油稀释了润滑油，会影响气缸套-活塞环副的摩擦学性能。在本研究中，首先将柴油混入润滑油中进行粘度和润湿性测试。发现混合油的动力粘度随着燃油稀释油量的增加而下降，少量柴油混合会导致润滑油粘度显着下降；此外，随着稀释比例的增加，接触角呈下降趋势。然后根据几个典型的稀释比例，进行往复摩擦试验以测量生产环/衬套副的瞬时摩擦力。实验结果表明，在混合润滑状态下，套环/衬套副的摩擦力峰值出现在死点附近，而最小摩擦力出现在往复行程的中间位置；随着更多的燃料稀释油，油膜的承载能力下降，导致摩擦力增加。此外，环/衬套副的平均摩擦系数随着稀释比的增加呈上升趋势，Stribeck曲线向左上方移动，表明该副润滑条件趋于从混合润滑过渡到边界润滑。润滑，对气缸套-活塞环副的摩擦性能造成负面影响。因此，稀释比例应控制在20%以下。