Mixed Flow Reactor Experiments and Modeling of Sulfuric Acid Neutralization in Lube Oil for Large Two-Stroke Diesel Engines

Lubrication oil for marine diesel engines contains additives in the form of CaCO3-based reverse micelles, which can neutralize condensing H2SO4, and thereby limit uncontrolled corrosive wear of the piston rings and cylinder liner. In the present work, the neutralization mechanism was studied experimentally and through modeling.

Using a mixed flow reactor (MFR), the rate of the acid–base reaction was measured as a function of relevant process parameters. In addition, the competition between CaCO3 reverse micelles and NaOH droplets for a reaction with H2SO4 droplets in a lube oil emulsion was explored in a batch reactor. For the residence times investigated, the results show that CaCO3 conversion is significantly reduced when reaching a critically low Ca/S ratio.

Furthermore, a mathematical model for the neutralization of H2SO4 droplets by CaCO3 reverse micelles in lube oil under well-mixed conditions was developed. Both the experimental data and simulations support previous results, suggesting that the limiting step in the neutralization mechanism is adsorption of reverse micelles onto the much larger H2SO4 droplets.

Using the video-microscopy experiments of Fu et al. [ Tribol. Lett. 2006, 22 (3), 221], it was possible to estimate kinetic parameters for the adsorption-controlled reaction. The model was used to predict conversion of H2SO4 in a lube oil film at the cylinder liner surface for conditions relevant for a full-scale application.

Calculations indicated that H2SO4 may reach the liner surface regardless of how well-wetted the surface is.