Ammonium perfluorooctanoate (APFO) is an emerging environmental pollutant attracting significant attention due to its global distribution, high persistence, and bioaccumulation properties. The decomposition of APFO in aqueous solution with a combination of persulfate oxidant and ultrasonic irradiation was investigated. The effects of operating parameters, such as ultrasonic power, persulfate concentration, APFO concentration, and initial media pH on APFO degradation were discussed. In the absence of persulfate, 35.5% of initial APFO in 46.4 μmol/L solution under ultrasound irradiation, was decomposed rapidly after 120 min with the defluorination ratio reaching 6.73%. In contrast, when 10 mmol/L persulfate was used, 51.2% of initial APFO (46.4 μmol/L) was decomposed and the defluorination ratio reached 11.15% within 120 min reaction time. Enhancement of the decomposition of APFO can be explained by acceleration of substrate decarboxylation, induced by sulfate radical anions formed from the persulfate during ultrasonic irradiation. The SO4(-•)/APFO reactions at the bubble-water interface appear to be the primary pathway for the sonochemical degradation of the perfluorinated surfactants.

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In current lubrication analysis of piston skirt, the flooded status is generally considered in the piston skirt–cylinder liner frictional pair in all strokes of an engine operating cycle. However, the quantity of lubricating oil at the entrance of piston skirt cannot always ensure the sufficient lubrication status of piston skirt–cylinder liner frictional pair when the piston moves from the bottom dead center to the top dead center in actual engine. In this article, based on the model of piston secondary motion, fluid lubrication, and lubricating oil flow, the lubrication performance of piston skirt–cylinder liner frictional pair is analyzed, in which the quantity of lubricating oil detained on the surface of cylinder liner after the piston skirt moves from the top dead center to the bottom dead center and is considered as the quantity of lubricating oil at entrance of piston skirt when the piston moves from the bottom dead center to the top dead center. The results show that compared with current analysis, in which the sufficient lubrication of piston skirt–cylinder liner frictional pair is assumed in all strokes of engine, there are remarkable changes for the lubrication performance of piston skirt–cylinder liner frictional pair and the piston secondary motion when the lubrication status of the frictional pair in the upstroke of piston is determined by considering actual lubricating oil transport in the lubrication analysis of piston skirt.