The Effect Of Base Oil On The Micro-morphology Of Diesel Particulate Emissions

With the rapid development of automobile industry and the fast increase in vehicle population, the main emissions, especially the particulate emissions or that nanoparticles of diesel engine, are to damage the living environment and health of human beings. The consumption of lubricating oil is inevitable during the operation process of engine and the wasting oil into cylinder would be burned impacting on the production of particulate emissions. Base oil is the main component of lube oil and its physical and chemical properties especially viscosity will mainly impact on the consumption of combustion, thereby affecting the particulate matter emissions. In view of this, two different base oils were chosen in this paper for experiments on the laboratory bench equipped with YN-4100 QB diesel engine. A thermophoretic sampling device was employed to collect particles and the particle samples were then analyzed using a high resolution transmission electron microscope(TEM), Raman spectroscopy methods and image processing acquisition system. The effect of different base oils on the performance of diesel engine and on the size distribution, morphology and microstructure of diesel particles were investigated.Firstly in this paper, two different base oils(150 and 350) were used as lubricating oil and the power, economy and emissions characteristics of the engine were recorded under external characteristics and load characteristics with EMC2020 engine control system, fuel consumption meter and AVL emissions analyzer used. The results show that the dynamic performance of engine was better when 350 base oil used under the external characteristics and load characteristics. As for economy characteristics, it was better for 350 base oil under external characteristics while under load characteristics it was better for 350 base oil in high speed condition and for 150 base oil in medium or low speed condition. As for gas emissions, it was lower for NOx and CO2 emissions when 150 base oil used but except for HC emission.For further study of the effect of base oil on particulate emission, experiments in different conditions were conducted on two different base oils. Based on the particulate matter samples, it was analyzed on the size distribution, fractal dimension, crystalline microstructure and graphitization degree of diesel particles. As for size distribution, the peak value of particulate diameter become larger for low speed or high load condition and for 150 base oil used compared with 350 base oil. As for fractal dimension, it was not affected by load or speed separately but the power. The fractal dimension value is small when the power is high or low but large when the power is moderate. For the crystal structure analysis, it is found that the average crystallite length of the carbon particle is shorter, the interlayer spacing and curvature are larger for high speed compared to low speed condition, for low load compared to high load condition and for 350 base oil used compared to 150 base oil. Raman spectroscopy was used to research the effect of base oil on the degree of graphitization of the carbon particles. It was found that the degree of graphitization become lower when speed higher or load higher and also true when 350 base oil used compared to 150 base oil condition.