Stick–Slip Friction of Stainless Steel in Sodium Dodecyl Sulfate Aqueous Solution in the Boundary Lubrication Regime

The service life of a diesel fuel injector is highly affected by the tribological properties of the fuel. This study aims to investigate the friction and wear behaviors of emulsified bio-oil (EBO), which is a very promising alternative fuel for engines. Sliding wear tests were performed with a ball-on-disk tribometer using a GCr15 steel ball and a flat specimen as a counterpart. In these tests, the total sliding distance was 500 m, the load ranged from 10 to 20 N, and the oscillation frequency ranged from 30 to 50 Hz. Experimental results showed that EBO had better tribological properties than diesel oil and crude bio-oil. Contact load and oscillation frequency significantly influenced friction coefficient, wear volume, and wear damage pattern. The friction coefficient decreased with an increase in load and increased with an increase in oscillation frequency. Furthermore, the wear volume slightly increased with an increase in load or oscillation frequency. The damage mechanism is attributed to adhesive wear under low load and to abrasive wear under high load. The transition in the wear mechanism is related to the adsorption of the molecules in the EBO, the microstructural contact surface, and the mechanical actions.