Visualization test for neutralization of acids by marine cylinder lubricants

The combustion of high-level-sulfur (2-5%) fuels generates large amounts of sulfuric acid in slow-speed crosshead marine diesel engines. In this study , a video-microscope imaging technique is used to develop an experimental p rotocol for ranking the ability of marine cylinder lubricants to neutralize sulfuric acid within microcapillaries. The technique was applied to severa l oils with known rates of acid-neutralization ability to predict these rat es. The optical observations allow one to propose a plausible mechanism by which the overbased detergent additive system performs the task of acid neu tralization. According to this mechanism the overbased sulfonate reverse mi celles are the sire for the neutralization reaction, which occurs at the oi l-acid interface. The results confirm that the detergent surfactants are ch emically bound to the micellar core. in the case of overbased calcium-carbo nate detergents reacting with sulfuric acid, the formation of solid crystal s was observed which may form a protective antiwear film on engine metal su rfaces.