Fuel contamination of the lube oil, increased deposits and sludge build-up are common problems on medium and high speed diesel engines
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Medium-speed diesel engines, operating on residual fuel are among the most demanding of applications for lubricants.
The oil in these engines experiences a greater stress than that in a slow speed engine. It must lubricate the bearings and piston, keep them clean, cool under the piston crown and also protect the liner and rings from acidic combustion gasses. During this process, it is consumed and replaced with new oil top up. The Directory of Bearing Failures illustrates what can happen is a sufficient oil analysis programme is not implemented.
Total Base Number (TBN) Monitoring
Oil consumption rates have been reducing, both as a mechanism to control fouling around the rings and piston crown and also to control hydrocarbon and particulates emissions in the exhaust. This reduces the amount of new oil top up and increases the rate at which the TBN will deplete.
Very low oil consumption engines operated on high sulphur fuel can experience an oil life of less than 1000 hours (more similar to land fill fuelled gas engines). Monitoring the TBN and using a high BN oil is proven to greatly reduce the cost of lubrication under these circumstances, as exemplified by one customer operating a cement plant in India and using our equipment for this purpose.
Water in Oil & Insolubles Monitoring
After TBN depletion, the most common problem is water followed by insolubles. A rapid rise in insolubles is indicative of combustion problems. A rise in either should be investigated before the alarm limit is reached and the oil condemned.
Viscosity Testing
High speed engines can additionally experience dilution of the oil from distillate fuel. The fuel enters either via leakage at the fuel pumps or through combustion problems. Kittiwake viscosity tests are very sensitive to fuel dilution and can detect a very low contamination level. Viscosity is also affected by top up with the incorrect oil grade.
Oil Analysis Tests
The oil analysis tests that are useful for Medium & High Speed Diesel engine include:
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