Effect of nano-cerium dioxide addition in lubricating oil on particle size distribution of micro/nano-sized particulate matter in diesel engines

The application of nano-cerium dioxide (CeO₂) lubricating oil in diesel engines demonstrates excellent friction-reduction and anti-wear properties. However, the impact of nano-CeO₂lubricating oil consumption on the particle size distribution of particulate matter (PM), especially micro/nano-sized PM, remains unclear. This problem has affected the active design of the control strategy of the after-treatment system and restricted the further promotion and commercialization of nano-CeO₂lubricating oil in engine applications. This study conducts a comparative investigation on the particle size distribution and microscopic morphology of PM influenced by nano-CeO₂additives in lubricating oil. The results indicate that, compared to pure lubricating oil (PLO), the use of nano-CeO₂lubricating oil significantly increases the total number of nucleation-mode and accumulation-mode particles. Under 10%, 25%, 50%, 75% and 100% load conditions, the concentration of particles with a diameter less than 100 nm corresponding to the nano-CeO₂lubricating oil was approximately twice, seven times, twelve times, seventeen times and six times that of PLO, respectively. At rotational speeds of 2000 r min^-1, 2250 r min^-1, 2500 r min^-1, 2750 r min^-1and 3000 r min^-1, the concentration of particles with a diameter less than 100 nm corresponding to the nano-CeO₂lubricating oil is approximately five times, two times, five times, six times and five times that of PLO, respectively. Microscopic analysis reveals that PM corresponding to PLO exhibits uniform primary carbon particle sizes, whereas PM corresponding to nano-CeO₂lubricating oil contains a higher quantity of smaller primary carbon particles. This confirms that nano-CeO₂particles undergo self-nucleation during combustion, thereby increasing the risk of generating additional nucleation-mode particles.