Trunk Piston Engine Crankcase Oils

Medium speed engines <1000 rpm often operate on residual fuel and are a demanding of applications for lubricants. High speed engines have less fuel related issues (distillates) with the challenge being the load cycles under which they are operated with frequent idling of low load operation.

The oil in these engines experience a greater stress than that in a larger 2-Stroke Slow Speed Engine. It must lubricate bearings and pistons, keep them clean, cool under the piston crown and also protect the liner and rings from acidic combustion gases. During this process, it is consumed and replaced with new oil top up. The failed machinery images illustrate what can happen if a sufficient oil analysis programme is not implemented. 

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Base Number (BN - formally TBN)
Oil consumption rates are historically low, both as a mechanism to control fouling around the rings and piston crown plus hydrocarbon and particulates emissions. This reduces the amount of new oil top up leaing to low BN being a reason to change the oil out. (Similar to land fill gas fuelled engines.) This is typically more of an issue with engines run on residual fuel with a mismatched BN as most distillates have low sulphur levels. We have seen it become an issue though especially in the Oil & Gas sector that operates in remote regions where fuel choice is limited.  Monitoring the BN in and using a high BN oil is proven to greatly reduce the cost of lubrication under these circumstances.

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Water in Oil & Insolubles Monitoring
After BN depletion, the most common problem is water, followed by insolubles. Water can come from adulteration, atmospheric moisture of internal leakage. A rapid rise in insolubles is indicative of combustion problems. A rise in either should be investigated before the alarm is reached and the oil condemned.

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Viscosity
All engines can 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 and lube oil additive depletion.

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Ferrous Wear Debris
Testing for ferrous wear debris often highlights the earliest visible onset of failure. Worn engine parts will leave trace particles in the oil which, when trended using simple onsite test equipment, will provide extremely useful data that helps save your critical plant. However, wear partciles are typically small (frictional wear) so this is not a good parameter to monitor On-Line line as the sensors are less sensitive than On-site options. 

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Glycol 
This is only an issue with high speed engines that operate with collant using antifreeze.  Coolant leaks are usually detected by an increase in water but this can be driven off in a hot operating engine leaving the glycol behind with resultant problems.  The Kittiwake On-Line Oil Condition Sensor is a sensitive method to detect glycol contamination even if no additional water is present.  

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