The Viswa group published a White Paper in April 2020 to explain the possible root cause of liner wear and scuffing issues when using Very Low Sulfur Fuels (VLSFOs).
Below is Viswa’s Addendum to its white paper on Linear Wear.
Possible causes of damage
Approximately 16% of the problem cases encountered by the shipowners in 2020 (as reported to us) were related to liner wear and scuffing issues.
Viswa’ White Paper discussed the possible causes of damage to cylinder liners and piston rings.
We concluded that the cause of liner wear was likely due to cylinder lube oil (CLO) feed rate, total base number (TBN), and detergency properties.
The damage occurred in two stages.
The first stage
The first stage of damage happened when the Base Number (BN) of the CLO was excessive with a high feed rate. In these cases, the small corrosion pits were unable to form due to the excess alkalinity. The CLO film became thinner and the friction between two surfaces increased resulting in liner wear and scuffing.
The second stage
The second stage of damage was caused by insufficient CLO detergency characteristics. The CLO did not have enough detergency properties to wash away all the scuffed liner material carried by the piston ring.
Liner wear and scuffing issues
In 2020, more than 50 cases related to liner wear and scuffing issues were reported to Viswa. We tried to isolate a single cause for the liner wear.
Causative factors considered were VLSFO, CLO, piston ring material, type of engine, and age of the ship.
- The age of the vessels facing issues varied between 3 and 38 years.
- Most of the reported cases experienced liner wear in individual units with some cases experiencing wear in all units. If all the cylinders were affected by scuffing and liner damage, the root cause of these issues could be explained totally by the effect of CLO (High TBN and feed rate).
- It is worth mentioning that Viswa did encounter some problem cases in which the piston rings were chromium coated.
- Some vessels experienced scuffing despite changing the cylinder lube oil to a higher TBN CLO.
- These problems were not related to one engine manufacturer but rather common among all engine manufacturers.
Analysis of the characteristics of VLSFOs that were in use when scuffing problems were experienced indicated that:
- VLSFOs can be divided into 2 types, Aromatic and Paraffinic fuels, based on their respective chemical characteristics and properties. About 30% of the problem VLSFOs had aromatic characteristics and 70% of them were paraffinic.
- Analysis of the ignition combustion properties of VLSFOs in general shows that more than 60% of samples had Estimated Cetane Numbers (ECN) values greater than 40 when measured on the FIA-FCA 100 instrument. Since the instrument limit is 40, the results were extrapolated and ECN values upwards of 50 and 60 were seen in some of the paraffinic VLSFOs. When such fuels are used there is a very sudden and instantaneous rise in pressure during combustion, almost generating conditions of engine knock. Under these conditions, damage to the rubbing parts of the cylinder liner and piston ring may happen.
ECN values distribution for paraffinic and aromatic VLSFOs
3. For more than 90% of aromatic VLSFOs, the ECN value was below 40. These VLSFOs may not cause a sudden and instantaneous rise in pressure that results in conditions of engine knock.
Comparison of the Ignition combustion process in HSFO, Aromatic and Paraffinic VLSFO
Root cause for Liner wear/scuffing issue
Liner wear/scuffing issue was one of the main problems experienced by vessels using VLSFOs in 2020. Various theories have been proposed to explain the root cause of these issues.
Some investigators believed that the cause of linear wear and scuffing was due to the characteristics of VLSFOs, however, they did take into full consideration the effects of CLOs.
Viswa research result
Research carried out by The Viswa Group, which was published in our white paper in 2020, indicated that Cylinder Lubricating Oil (CLO) quantity, TBN number, and a feed rate of 0.6 g/KwH of CLO may be too high for VLSFOs, which have lower sulfur content.
Therefore, we proposed that this may be the reason for liner wear and scuffing issues experienced by shipowners. It is our belief that choosing the correct CLO with TBN and feed rate is essential in preventing liner wear.
Conclusion
Examination of the cases of liner wear/ scuffing problems reported to Viswa in 2020 by ship owners, showed no inherent ISO 8217 problems with the VLSFO. Our first White paper reflected these findings.
Mechanical damages and problems
However, based on studies carried out on more samples that we have received in the lab, we found some of the VLSFO fuels have very high ECN. This results in very high peak pressures in the cylinder and may lead to certain mechanical damages and problems.
It may be asked as to why LSMGOs which also have high ECNs are not experiencing similar mechanical problems in the cylinder. The reason is that while the ECN values of LSMGOs may be high (around 40), they do not go up to very high values which we have seen in some VLSFOs (even up to 70).
Cause for the problem
To conclude, it is unlikely that the liner damage is solely due to the quality of the VLSFO fuel and has nothing to do with cylinder lubrication. We believe that the problem is predominantly due to the CLO feed rate, TBN, and detergency properties.
Poor maintenance of engine
In a few cases, the effect of VLSFO quality and the condition of the engine (poor maintenance) also contributes to the liner and piston ring damage.
Disclaimer
The content contained in this white paper is provided only for educational and informational purposes only. While Viswa Group uses reasonable efforts to accurately describe and update the information in this white paper, Viswa Group makes no warranties or representations as to its accuracy, currency or completeness. Viswa Group assumes no liability or responsibility for any errors or omissions in the content of this Advisory. To the extent permitted by applicable law, everything in this white paper is provided “as is” without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability, fitness for a particular purpose, or noninfringement. In no event will Viswa Group be liable for any damages whatsoever, including special, indirect, consequential or incidental damages or damages for loss of profits, revenue or use, whether brought in contract or tort, arising out of or connected with this white paper or the use or reliance upon any of the content or any information contained herein.
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Source: Viswa Group
