Influence of Microalgal Bio-Oil on the Lubrication Properties of Engine Oil

Abstract

In order to accelerate and expand the application of bio-energy, two kinds of microalgal bio-oils, prepared via co-liquefaction of Chlorella and Spirulina under sub- and supercritical ethanol conditions, were used as partial substitutes for the engine oil CD SAE 15W-40. The friction and wear behaviors of the oils were tested on a four-ball tribometer, referring to the ASTM D4172 standard conditions. The micro-morphology, profiles, roughness and chemical valences of typical elements on the rubbed surfaces were characterized by Scanning Electron Microscopy (SEM), surface profiler and X-ray Photoelectron Spectroscopy (XPS), respectively. The results showed that both of the bio-oils had good lubrication properties. The suitable weight content of the bio-oils in the engine oil was 10%. The lubrication properties of the Bio-Oil (BOsup) prepared in supercritical ethanol were a little better than those of the Bio-Oil (BOsub) prepared in subcritical ethanol. The lubricating mechanisms were ascribed to the combined actions of various lubricating films, including boundary lubrication, and deposited films and tribological chemical reaction films. The stronger tribological chemical effects of BOsup from higher contents of N-containing compounds contributed to its better lubrication properties than those of BOsub.