Slow-steaming operation and an increased pressure in the combustion chamber have contributed to increased sulfuric acid (H2SO4) condensation on the cylinder liners in large two-stroke marine diesel engines, thus causing increased corrosion wear. To cope with this, lube oils are formulated with overbased detergent additives present as CaCO3 reverse micelles to neutralize the condensing H2SO4. In this present work, a mixed flow reactor (MFR) setup aims to investigate the neutralization reaction by varying Ca/S molar ratio, stirrer speed, H2SO4 inlet concentration, and residence time. Lube oil samples from the outlet of the MFR were analysed by use of Fourier Transform Infrared Spectroscopy (FTIR) and a titration method. The MFR results indicate that the CaCO3-H2SO4 reaction is very fast in a real engine, if the cylinder liner is well-wetted, the oil-film is well-mixed, and contains excess of CaCO3 compared to the condensed H2SO4. The observed corrosion wear in large two-stroke marine diesel engines could consequently be attributed to local molar excess of H2SO4 compared to CaCO3 reverse micelles on the cylinder liners.

Lubrication oil for marine diesel engines contains additives in the form of CaCO 3 -based reverse micelles, which can neutralize condensing H 2 SO 4 , 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 CaCO 3 reverse micelles and NaOH droplets for a reaction with H 2 SO 4 droplets in a lube oil emulsion was explored in a batch reactor. For the residence times investigated, the results show that CaCO 3 conversion is significantly reduced when reaching a critically low Ca/S ratio. Furthermore, a mathematical model for the neutralization of H 2 SO 4 droplets by CaCO 3 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 H 2 SO 4 droplets. Using the video-microscopy experiments of Fu et al.1 ), 221-225], it was possible to estimate kinetic parameters for the adsorption-controlled reaction. The model was used to predict conversion of H 2 SO 4 in a lube oil film at the cylinder liner surface for conditions relevant for a full-scale application. Calculations indicated that H 2 SO 4 may reach the liner surface regardless of how well-wetted the surface is.

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