Research on the mechanism of molten salt cleaning (MSC) for multiple contaminants in cylinder covers

Abstract Cylinder covers of diesel engines with complex structures may be contaminated by multiple contaminants, which can hardly be efficiently removed by traditional cleaning methods, and those methods may do harm to environment and human body. Fortunately, such drawbacks can be overcome by the molten salt cleaning (MSC). In the present study, it was proven that the cleaning effect of the MSC was fairly good, and the mechanism was explained by analyzing compositions and morphology of the contaminants and gas production. The contaminants could be divided into two categories: the black deposition of the organic matters in oil channels (40 μm in thickness, containing hydroxide radical and aromatic groups), and the incrustations in water channels (20 μm in thickness, consisted of CaCO3). The gas production was consisted of complex compositions, including alkanes, olefins, aromatic hydrocarbons, aldehydes, esters, alcohols, ketones and hydroxyl. Based on above analyses, it was believed that the cleaning mechanism included the thermal effect, physical flow effect, along with the pyrolysis/oxidation reactions. Thermo-gravimetric analysis (TGA) tests were conducted on either the black deposition or salt-deposition mixtures, in either the air or nitrogen atmospheres, for sake of analyzing the clean dynamic. The total weight loss of the mixtures in the air was 92.816%, and the activation energy was 150.06 kJ/mol. It was concluded that the oxidation effect was almost negligible for the contaminants only, which however accounted for 15.9688% of the contaminants removal in the presence of the molten salt.