Effects of a gasoline particulate filter on the physicochemical characteristics of particulate matter from a gasoline engine

Gasoline particulate filters (GPFs) are being used increasingly in gasoline direct-injection engines because they can reduce particle emissions and allow emission regulations to be met. Therefore, understanding the particles' physicochemical properties can help with optimizing the post-processing systems and engine calibration. In this study, particles were collected both pre- and post-GPF using a Dekati® low-pressure impactor and a quartz-fiber filter membrane. High-resolution transmission electron microscopy was used to observe the morphologies of the particles, the fractal dimension was used to quantify the aggregate structure, and an image-processing program developed in MATLAB was used to analyze the nanostructures of the primary particles. Raman spectroscopy was used to study the order degree of the particles’ carbon crystal arrangement, and Fourier transform infrared spectroscopy was used to assess the changes in their surface functional-group content. After the particles were graded according to particle size, it was found that (i) the fractal dimension of all size levels and (ii) the average size of the primary particles were both smaller post-GPF than pre-GPF. Post-GPF, there was a higher proportion of nucleated particles, the particle fringe length was shorter, the tortuosity and separation were both greater, the particles were more disordered, the ratio of C–H to C–O was greater, and the proportion of organic composition of the particles and their oxidation activity were both increased.