Study on microstructure and extinction characteristics of particulate matter in diesel engine fueled with different biodiesels

Biodiesel combustion particulate matter (PM) is different from diesel combustion PM in terms of microscopic morphology, which directly affects the optical properties of PM. To investigate the effect of the microstructure of biodiesel PM on the extinction characteristics, an experiment was performed on a high-pressure common rail diesel engine to collect PM from three kinds of biodiesel (the main raw materials were soybean oil methyl eater (SME), palm oil methyl eater (PME), and waste cooking oil methyl eater (WME), respectively). The particle size distribution, micro morphology, and extinction characteristics of biodiesel PM were analyzed. Results show that combustion biodiesel reduces PM emissions by up to 84.2%. Compared to PM from diesel, biodiesel PM has a smaller particle size and a higher aggregation degree, which results in weaker light absorption capacity. With the iodine number of biodiesel decreasing, the number concentration of biodiesel PM decreases and the fractal dimension increases, which leads to producing a more complex agglomerate and a consequent reduction in extinction coefficient. The average particle sizes of PM from SME, PME, and WME are 5.1%, 6.7%, and 13.9% lower than that of diesel PM. Compared with diesel combustion PM, the peak absorption coefficients of SME, WME, and PME combustion PM decrease by 8.4%, 11.4%, and 13.3%, respectively. The extinction properties of particles decrease with increasing fractal dimension within the wavelength range of visible light.