Evaluation of Chlorella vulgaris modified bio-oil for improving diesel lubricity

This work studies the use of modified bio-oil derived from Chlorella vulgaris microalgae (MBOC) as lubricity improver of diesel. Microalgae-based modified bio-oils (MBOs) offer a sustainable alternative to first and second-generation sources, providing superior lubricity through their rich content of polar fatty acid methyl esters (FAMEs). The microalgae bio-oil was produced by alkaline transesterification, subsequently purified using bentonite to remove pigments and residual impurities, and finally epoxidized to enhance its properties prior to blending with diesel. High-frequency reciprocating rig tribological tests and surface analysis by confocal and scanning electron microscopies were used to evaluate the effect of various MBOC concentrations (5–20% v/v) in diesel fuel on tribological response (friction, wear scar, and wear mechanism). The results revealed a consistent friction reduction with an increase in MBOC content. This phenomenon may be attributed to the adsorption of FAME, which could foster the formation of a robust tribolayer on metallic surfaces. However, the wear exhibited distinctly non-linear behavior. Optimal tribological performance occurred at intermediate MBOC concentrations (5–10%), yielding minimal wear scar diameter (WSD), shallower wear tracks, and smoother morphology which is indicative of effective surface protection. Conversely, a higher concentration (20%) of MBOC resulted in increased wear severity, despite the ongoing reduction in friction. The SEM observation showed that abrasion was the predominant wear mechanism. These findings position MBOC from Chlorella vulgaris as a potential renewable lubricity improver for diesel, suggesting that a blending ratio between 5% and 10% could achieve an optimal balance between friction control and wear mitigation.