REACTION OF SULFURIC ACID IN LUBE OIL: IMPLICATIONS FOR LARGE TWO- STROKE DIESEL ENGINES

摘要

Slow-steaming operation and an increased pressure in the combustion chamber have contributed to increased sulfuric acid (H_2SO_4) 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 CaCO_3 reverse micelles to neutralize the condensing H_2SO_4. In this present work, a mixed flow reactor (MFR) setup aims to investigate the neutralization reaction by varying Ca/S molar ratio, stirrer speed, H_2SO_4 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 CaCO_3-H_2SO_4 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 CaCO_3 compared to the condensed H_2SO_4. The observed corrosion wear in large two-stroke marine diesel engines could consequently be attributed to local molar excess of H_2SO_4 compared to CaCO_3 reverse micelles on the cylinder liners.