Tribological Characteristics of Stearic Acid as Base Stock Bio‐Lubricant Incorporated With Phenolic Anti‐Oxidant Tertiary‐Butyl Hydroquinone ( TBHQ )

The growing demand for sustainable energy solutions has intensified interest in hydrogen internal combustion engines (HICEs) due to their potential for zero‐carbon emissions. However, the unique operating conditions of HICEs, such as high temperatures and increased oxidative stress, pose significant challenges to the performance and durability of traditional lubricants. Developing bio‐based lubricants with enhanced thermal stability and wear resistance is critical to ensure efficient lubrication and extended engine life in hydrogen‐fueled systems. In this study, stearic acid (SA) was utilised as the base oil for a bio‐lubricant, with tertiary butylhydroquinone (TBHQ) added as an antioxidant. Tribological tests were conducted using a four‐ball tribotester in accordance with ASTM 4172B standards. The results indicated that SA with 0.5% TBHQ exhibited a stable and slightly lower coefficient of friction (COF) across temperature variations compared to industrial oil, with SA showing a significantly lower COF at 75°C, 80°C, and 85°C. As the speed increased, SA with 0.5% TBHQ demonstrated the lowest COF, followed by SA and industrial oil. At temperatures of 80°C, 85°C, and 95°C, SA with 0.5% TBHQ achieved the smallest reduction in wear scar diameter (WSD) compared to SA and industrial oil. Similarly, at speeds of 1400, 1600, and 2200 rpm, SA with 0.5% TBHQ exhibited the smallest WSD. Additionally, SA and SA with 0.5% TBHQ showed no signs of oxidative degradation and experienced mild abrasive wear, whereas the industrial oil underwent oxidation under operating conditions of 75°C, 95°C, and 1600 rpm, resulting in severe scuffing and adhesive wear.