Impact of lubricating base oil on diesel soot oxidation reactivity

Abstract

In this study, the surface functional groups types and concentrations, graphitization degree, and oxidation reactivity of exhaust soot samples generated by a heavy-duty engine when employing neat diesel and four base oil dosed mixtures as the fuel was compared. Fourier transform infrared (FTIR), Raman spectroscopy and Thermal gravimetric analyzer (TGA) were used to characterize particle physicochemical properties. Four lubricating base oils were blended in diesel at a mass ratio of 0.5% and 1.0% for combustion. It was found that although the chemical compositions of these four base oils were different, the aliphatic CH functional groups content, graphitization degree and oxidation reactivity of exhaust soot exhibited similar trends. The combustion of base oil was found to change the graphitization degree of emitted soot and lead to soot with a more disordered nanostructure. The soot particles derived from base oil blended fuels had higher aliphatic CH groups concentration than those from neat diesel. Soot oxidation reactivity analyses showed that soot generated from base oil blended fuels had lower characteristic temperatures and lower activation energy than that from neat diesel. Besides, there was a clear correlation between the soot graphitization degree, relative concentration of aliphatic CH groups and its oxidation reactivity.