Cold-Corrosion

Spatial distribution of high temperature flame (indicated by yellow colour) and sulfuric acid vapour (indicated by blue colour) at 20 crank angle degree after top dead center.

The numerical model serves as an important prerequisite to study the temporal and spatial sulphur oxides and sulphuric acid distribution in the combustion system. These are particularly significant since heavy fuel oil which is commonly used in large low speed marine diesel engines, can comprise up to 4.5% of sulphur (by mass fraction). During the in-cylinder combustion process where air is excessive, the fuel sulphur is oxidised to sulphuric dioxide (SO2). A fraction of SO2 is then oxidised to form sulphuric trioxide (SO3) and SO3 subsequently reacts with water vapour to form vapour sulphuric acid. The latter condenses as aqueous sulphuric acid near engine cylinder liners where the local temperature is cold. This promotes corrosive wear on cylinder liners. In order to understand these phenomena, the three-dimensional CFD model is incorporated with a new surrogate fuel model which includes a skeletal sulphur subset mechanism. Thermal boundary layers near the engine wall liner are carefully resolved in order to provide reasonable local temperatures, by which are significant for the predictions of the sulphuric acid formation and the associated condensation rate.

Updated by Jens Honore Walther on 28 May 2016