Acid neutralization by marine cylinder lubricants inside a heating capillary microreactor
Description
Overbased detergents are present in marine cylinder lubricants for neutralizing combustion-generated acids in engine environment. The nature of overbased particles and the mechanisms by which they act determine their success in neutralizing acids and preventing cylinder corrosive wear. Strong-stick and weak-stick collisions are proposed to drive the acid and base transfer in oil media. The acid neutralization by overbased detergents can be a crystal-growing reaction or a crystal-solubilized reaction. With the protection of overbased particles, cylinder corrosive wear possibly occurs under conditions that facilitate a crystal-solubilized reaction, and the Ostwald ripening of acid droplets may be a decisive cause of corrosive wear. Temperature impacts on the rate of acid neutralization dramatically, while the size of an acid droplet does not affect its neutralization rate initially until the droplet shrunk to a certain level Acid neutralization experiments were carried out inside a heating-capillary, which can simulate high-temperature conditions (from ambient temperature to oil boiling point), and the progress of neutralization was recorded in real time through a video-microscope. The heating capillary microreactor was specially prepared to be electrically conductive by coating with tin-doped indium oxide and to remain transparent so that optical microscopy can be conducted inside it; when a current passes, the coated capillary could generate desired temperatures at very fast rates (75-198°C/s) In this research, the inconsistencies between 'dynamic structure' and 'rigid structure,' between 'acid-to-base' transfer and 'base-to-acid' transfer, and among the formation of acid-neutralization products, may be reconciled. It has been demonstrated that the Ostwald ripening of acid droplets works against the MCL-acid neutralization. New strategies to improve overbased detergents, marine cylinder lubricants, and engine designs may include (i) facilitating crystal-growing reactions and (ii) mitigating acid-Ostwald ripening