Experimental Analysis on Friction and Wear Properties of 1,3-Diketone/Nano-Copper Composite Additive and DLC Piston Ring-Cast Iron Cylinder Liner

In view of the environmental restrictions of the current mainstream anti-friction and anti-wear additive zinc dialkyl dithiophosphate（ZDDP） containing phosphorus and sulfur elements, a commercial lubricating oil containing ZDDP was modified by introducing a compound additive of 1,3-diketone and nano-copper. Its tribological performance with diamond-like carbon（DLC） coated piston rings against cast iron cylinder liners, along with the interaction with ZDDP, was investigated under wide temperature （30~150 ℃） and variable load （20~40 MPa） conditions. Results showed that the compound additive exhibited the best overall tribological performance under all test conditions, where the friction coefficient was significantly reduced （with a maximum reduction of 17.4%） and effective anti-wear protection was achieved. Mechanistic analysis revealed that the boundary film formed by the compound system during friction inhibited the adsorption and dissociation of ZDDP. Although the function of ZDDP was partially weakened, it can still significantly reduce friction and wear, demonstrating potential for replacing ZDDP and developing environmentally friendly lubricants with low phosphorus and sulfur content.