Assessing Validity of Diffusion Controlled Model in Acid Neutralization of Lubricant Oil

Abstract

Engine corrosion has been a long prevalent problem which is further aggravated by acids produced during combustion of fuels. Sulphur containing fuels produce sulphuric acid which must be neutralized in order to prevent corrosion at the engine cylinder lining and piston rings. In order to prevent this corrosion, lubrication oil used in combustion engines contains basic additives like CaCO₃-based reverse micelles for neutralizing the acid produced. The mechanism and rate limiting step in the reaction between acid droplets and basic reverse micelles has long been a subject of study. Literature on sulpluric acid droplets neutralization speculates that diffusion of micelles towards the acid droplet is the rate limiting step. However, through this research, we have proved that a diffusion-controlled mechanism alone is not applicable. This has been done by studying various capillary video microscopy experiments on sulphuric, nitric and acetic acid. To prove the invalidity of a diffusion-controlled mechanism, we have assessed the diffusion coefficient and the viscosity at different temperature. Models for finding the diffusion coefficient & viscosity are based on Fick’s law and Stokes Einstein equation respectively. The obtained viscosity from assuming a diffusion-controlled model is compared to observed viscosity (actual viscosity) in lubricant oil to measure deviation of diffusion-controlled model from actual neutralization kinetics. Finally, we have hypothesized alternative reaction mechanisms to explain the considerable deviation found in viscosity values.