Effect of Lubricating Base Oil on the Morphology and Nanostructure of Diesel Particles

In this paper, the influences of lubricating base oils on diesel particles morphology and nanostructure were investigated. Four different lubricating base oils were blended in diesel at a mass ratio of 0.5% and 1.0% for combustion. Exhaust particle samples generated by a four-cylinder, four-stroke direct injection engine when employing neat diesel and four base oil dosed mixtures as the fuel were collected and compared. Primary particle diameter distributions and particle nanostructure were compared and analyzed by a High-Resolution Transmission Electron Microscope (HRTEM). Conclusions drawn from the experiments indicated that the primary particles diameter ranges from 5 nm to 70 nm and the distribution conformed to typical Gaussian distribution. Base oil II, III, IV increased the primary particles diameter, while particles from base oil I exhibited smaller size than that from neat diesel. It is mainly because that the higher content of P and S in the base oil I led to the formation of more nuclear particle emissions. Besides, particles from base oil blended fuels showed same chain-like and branch-like cluster and core-shell nanostructure with particles from neat diesel. The analysis results of particle nanostructure showed that although the chemical compositions of these four base oils were different, four different base oils led to shorter fringes with higher tortuosity and separation distance, which means that the combustion of base oils led to particles with a disordered nanostructure.