Good day team,
What BN cylinder oil are you using on MAN ME-C engines that are consuming VLSFO?
We experimented with BN 40, BN 57 and BN 70 (Total lubs) and with observed the following.
BN40: After using BN40 for a few months, we experienced scuffing more than one time.
BN70: We did not experience any problems but the residual BN was too high which as per MAN will eventually cause liner polishing.
BN57: We are using BN57 for the past 2 years. We have not experienced any problem and the scavenge drain analysis is good.
I was wondering if any of you tried a few options and which option suited better to your engines.
Over the last 2-3 years and since MAN have revised their recommendation for cylinder oils, we have used periodically cylinder oils with BN40, 70 and 100 (mixed also)
However, we did not notice any major differences and we did not have any scuffing problems.
Also the analysis results and scrapedown did not show big differences.
Our current intention is to use mainly BN40 cyl oil
The two important parameters that that would affect the choice between a high or a low BN cylinder oil when consuming VLSFO are: the cleanliness of the piston crown toplands and ringlands (detergency) and Fe (iron) content in the scrape down analysis.
MAN ES recommended the use of BN40 cylinder oils (Category I) when consuming VLSFO, however, their detergency was not as good as that of high BN cylinder oils, therefore heavy accumulation of carbon deposits was observed on ringlands and toplands of piston crowns.
At the time, Category II low BN cylinder oils where not available in the market. The newly developed Category II low BN cylinder oils have the detergency properties of high BN cylinder oils.
This is why, later on, MAN ES have revised their guidance and recommended to alternate between high- and low-BN cylinder oil, using a high-BN oil on one week and a low-BN oil the next week
(Service Letter SL2019-671/JAP).
However, this is not a practical solution.
We have used high BN oils (BN 70 up to BN 100) when consuming VLSFO and we have had a good experience. Healthy cylinder condition, no deposits, low FE content in the scrape down analyses. On average, we have seen higher values for the residual BN in the scrape down analyses and we have received alerts that this could lead to the formation of alkaline deposits however, we have not observed such phenomena during frequent M/E scavenge space inspections.
In short, high BN cylinder oils have been performing well with VLSFO.
This might be the case for the newly developed low BN Category II cylinder oils as well, but i do not think that there is a lot of experience on their use, yet.
I would conclude that there is no “hard rule” and that frequent scavenge space inspection and scrape down analyses are required in order to understand the “needs” of the M/E and act accordingly.
I would also like to cite a phrase from a correspondence with a MAN ES engineer in the MAN ES Cylinder Condition Department
“It is important to keep the FE content as low as possible and ring-lands / top-land clean and the then let the residual BN be whatever it wants”
Well said @Paraschos.Liadis. BN40 category II cylinder oils with good detergency abilities have been in production with satisfactory results. The Mark number of MAN ES engines and the vessel’s operation pattern (i.e low load, short voyages etc) are playing a great role on the selection of the BN number.
In general Engines with high combustion pressures (Mark 8 and higher) are more sensitive and require higher BN oils.