目的 探究离子液体(IL)对废旧发动机油摩擦学性能的影响。方法 在四球试验机上，评价了添加剂对摩擦力的影响，随后利用SEM、EDS和粗糙度轮廓仪表征了磨斑形貌、表面化学成分和粗糙度变化;利用点接触光干涉油膜厚度测量装置，研究了添加剂对成膜特性的影响。结果 在40 ℃和100 ℃下，添加离子液体的发动机油摩擦系数相较于废旧油均有所下降，分别在0.095和0.085左右，尤其是在100 ℃下，其摩擦系数(≈0.085)还低于新鲜润滑油(≈0.09)。其次，钢球的磨斑直径也均有所减小。在“轻度”和“严重”乏油的弹流润滑(Starved EHL)条件下，补加离子液体至废旧发动机油中，废旧机油可获得较好的成膜特性，其中心膜厚可增加约20 nm。结论 在边界润滑下加入IL，废旧发动机油重新获得了良好的摩擦磨损性能，高温摩擦过程中，IL在金属表面发生了复杂的化学反应，生成了一层低剪切强度的反应膜。在乏油状态下，油性添加剂IL具有较强的极性，容易在接触表面形成一层稳定的吸附膜，改变接触区润滑油的压力分布，进而引起入口区润滑油的有效黏度远大于其表观黏度，提升了废旧油的成膜能力，从而使其重新获得了较好的润滑性能。

This paper aims to explore the influence of ionic liquid on the tribological performance of used engine oil. After the evaluation for the influence of additives on friction by a four-ball experimental machine, the morphology and surface chemical composition of the wear scars are characterized by SEM, EDS and roughness profiler, and the influence of additives on film formation was studied by a measurement device of point contact light interference oil film thickness. After adding the ionic liquid, at 40 ℃ and 100 ℃, the friction coefficients are lower than those of used oil, which are about 0.095 and 0.085 respectively. Especially at 100 ℃, the friction coefficient (≈0.085) is lower than that of fresh lubrication oil (≈0.09) and the diameter of the wear scar is also reduced. Besides, under the conditions of “light” and “severe” starvation of elastohydrodynamic lubrication (Starved EHL), adding IL to the used engine oil can get better film formation and increase about 20 nm center film thickness. After the addition of IL to the lubricated boundary, the used engine oil has regained good friction and wear performance. During the friction process at high temperature, IL undergoes a complex chemical reaction on the metal surface to form a low shear strength reaction film; In the state of starvation, the oil-based additive IL has a strong polarity and it is easy to form a stable adsorption film on the contact surface, which changes the pressure distribution of the lubricating oil on the contact area and causes the effective viscosity of the lubricating oil in the inlet area to be much greater than its the apparent viscosity, so it improves the film-forming ability of used oil, thereby regaining better lubricating performance.