The oil used to lubricate the cylinders of large 2-stroke marine diesel engines has to contend with high temperatures and acidic products formed during the combustion of sulphur-rich bunker oils; for this reason cylinder oil is used on a continuous loss basis. In recent times ship operators have taken to running engines at reduced speeds (so-called slow steaming) as a means of improving fuel consumption. Unfortunately slow steaming is accompanied by a drop in engine temperature which allows sulphuric acid to build up on the cylinder liners thereby promoting their "cold corrosion". The iron compounds formed by this process are then flushed from the engine by the cylinder oil. The iron found in used cylinder oil samples typically exists in various forms, each one having its own particular properties. For example, metallic iron particles worn off the cylinder liner by cat fines exhibit strong ferromagnetism and may be detected using magnetometry. On the other hand, compounds such as iron sulphate and rust, which are formed during the combustion process by reactions involving the cylinder liner, cannot be detected magnetically. This paper will demonstate a novel technique for quantifying the concentration of iron due to corrosion and therefore help engine operators to make well-informed adjustments to running parameters.
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