Enhancing the Tribological Performance of Avocado Oil With Solid Lubricant Additives: A Fractal Dimension Analysis

Abstract Natural oils exhibit effective lubricating properties, such as low friction, high viscosity, and improved wear resistance, making them suitable for a range of applications in automotive, industrial machinery, and aerospace systems. Their superior lubricating performance, combined with their eco-friendly nature, aligns with the growing need for sustainable solutions in the face of stringent environmental regulations. In addition to the base natural oil, the addition of a particulate to the natural lubricant can further boost the tribological performance. In the current investigation, the tribological performance of the avocado oil with different solids lubricant additives of different particle sizes from 70 nm to 5 µm and their combinations were evaluated by a pin-on-disk setup. A strong influence of particle type was observed where only hBN and MoS2 in the avocado lubricant mixture provided superior tribological properties compared to neat avocado oil. The results also confirmed that the smaller particle sizes of hBN and MoS2 are beneficial in reducing the coefficient of friction and wear. The influence of particle size was further analyzed by mixing multi-particle type and size which confirms that smaller particles, particularly 70 nm hBN can provide lower friction and wear when mixed with coarser hBN or MoS2 particles. A fractal dimension was also defined to quantify the relationship between the initial surface roughness and particle size of the hBN solid lubricants in the lubricant mixture.