Impacts of lubricating oil and its formulations on diesel engine particle characteristics

Abstract

© 2020 Lubricating oil-related engine emission reduction is now a key path to further control the engine-out emission level and to meet the restrict regulations, especially in the manner of particulate number emission. This work experimentally studied the contribution of lubricating oil and its key constituents to the particle emission via monitoring the combustion process and analyzing the particle physic-chemical characteristics. Two sets of experiments were conducted to understand how the lubricating oil alters the regular combustion cycles and to study the effects of oil sulfur and metallic-ash constituents on the particle chemical characteristics, respectively. Details of the surface oxygenated functional groups and carbon chemical state on the particle surface were analyzed by XPS, while the FTIR was employed to characterize the possible functional groups in the bulk particle samples and the bonding patterns of the sulfur element. The effects on the particle morphology and elemental compositions were analyzed by SEM-EDS. Results show that the lubricating oil could shorten the ignition-delay phase combustion effectively, for instance, by 20% when 1wt% oil is burned along with diesel. Furthermore, more oxygenated surface functional groups and relatively more sp3 hybridization carbon shows up in the oil-derived particles. The sulfur element in the oil increases the oxygenated functional groups and lowers the aliphatic C[sbnd]H group by forming –SH radical. On the contrary, the metallic-ash fraction reduces the amount of oxygenated functional groups because the inorganic sulfates/phosphates occupy some oxygen atoms during the combustion reaction. Both the sulfur and ash tend to generate more un-substituted and meta-disubstituted benzene instead of the mono-disubstituted benzene structure, which is popular in diesel fuel-related particles mainly. Last but not the least, the sulfur and ash content significantly increase the concentration of the sulfates and phosphates of Iron, Calcium, and Zinc in the particles.