6. CONCLUSIONS
Engine design is evolving such that cylinder temperatures and pressures are moving upward, thus increasing the stress levels on the lubricating oil. Under these conditions the contribution to wear of corrosive wear is a priori expected to go down and that of adhesive wear to go up.
A new set of dew point curves has been derived on basis of thermodynamic principles that predicts temperatures of condensation of aqueous sulphuric acid in relation to cylinder pressure and heavy fuel sulphur content. These new curves closely agree with earlier observations that even at liner temperatures of 270℃ and peak pressures of 180 bar cold corrosion can dominate. Previously published dew point curves predict these dew points to be about 100℃ lower.
A laboratory test procedure has been developed on basis of the well-known Cameron-Plint friction and wear testing machine that determines temperatures at which the lube oil film collapses under very high load. At the specific set of test conditions film fail temperatures of cylinder oils vary between 225 and (above) 350℃. This performance ranking has been confirmed to reasonably well agree with the known field performance of these oils. A judicious selection of the main detergent and ancillary components hence allows the lube oil formulator to optimise his formulation with respect to this load carrying capability performance aspect. The use of such oils will greatly enhance the safety margin for the engine operator.
That even at the extreme conditions of today's engines corrosive wear occurs is probably very beneficial in avoiding scuffing to occur even more frequently. It may well repair minor damage on liner and ring surfaces from hard ring-liner contact that otherwise could develop further into scuffing.
References
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