Maine Lubrication is often highly regarded and more expensive as it churns the world’s biggest mammoth structures in the toughest of the environmental conditions. Thus, marine lubricants manufactures take due care in selecting appropriate base formulations in strengthening base oils with suitable additives.
Engines, whether two stroke or four stroke offer conducive and good ambience to aggravate the depletion and disturbance of the base oil properties. Expected engine conditions are High temperature, High pressure, Agitation, Good Air supply (promotes oxidation). Thus, in spite of good formulations the oil is much prone to lose its vital base properties due to the above said environment. Among the other disturbances, Oxidation and sulfation is least considered even very often ignored in a Lube oil test report but literally these properties act behind the screens for degradation of the oil.
Sulfation and Oxidation is brought to limelight in understanding how it works and intrudes the base oil properties are drafted in the following passage.
Oxidation of lube oil is one among the most important factors that can deteriorate the Lubricating oil condition. Among various other factors, high temperature aggressively affects the Lubricating oil condition followed by prolonged usage. For every 10deg rise in the temperature the oxidation is doubling. Over the time the base formulations of the oil gets depleted eventually leads to oxidation. Oxidation resistance is much integrally visible in few of the Synthetic oils of PAO type rather than the mineral oils.
Oxidation is a very complex chemical reaction occurs primarily due to the breakdown of long chain compounds which results in byproducts that occurs in stages. Oxidation by products leads to dark colour and foul smell. On severe cases, it will result in lacquer and sludge formation. Carbon with double bonds are more vulnerable to oxidation rather than with single bonds.
On other hand, on most occasions the oxidation reaction goes unnoticed. Due to high temperature the Volatile fractions of the oil evaporates leaving behind the non-volatiles, which reflects the additives part.
During the frequent topping up of fresh oil this non-volatile portion of the oil piles up though supplied with fresh volatile part. This piling up of the non-volatile when contributes to the increase in viscosity will show up in decrease in Oxidation stability. Until then the slow process of oxidation remains unnoticed. Thus, inflation in oxidation can be confirmed by viscosity rise. Progressive increase in TAN(total acid number) values had also been noticed.
Sulfation is yet another vital parameter which is ignored but drastically influences the depletion of the alkalinity of the base oil.
Sulphur based acids are formed as by-product of the combustion due to sulphur oxides and water. At operating temperature this sulphur based acids remain in gaseous form and escape along with the exhaust gas. The remnants of the sulphur based acids find its way into the System oil in the Lube oil sump through blow past between Liner and rings.
At normal temperature these acids get transformed into liquid state due to low idle engine temperatures thereby it affects the system oil eventually depleting the additives present in the Lube oil.
Once reserve BN has got depleted completely by the above said process now this acids find its way in damaging the Oil film that is lubricating the engine parts.
As the system oil reaches the end of its service life TBN is depleted to the core. Apart from ageing of oil, reserve BN also decreases for other reasons such as poor fuel, fuel contamination with sump oil due to injector leakage will speed up the depleting process.
KnowHow to slow down oxidation and Sulfation:
Oxidation or sulfation cannot be prevented completely from happening however the reaction can be slowed down thereby the service life oil can be extended.
The following basic tips will contribute to reduce oxidation and Sulfation to a certain extent:
- Replenishing sump oil with fresh top ups in small quantity at regular intervals.
- Up keeping of engine and its operational parameters.
- Cleaning the exhaust casing at periodical intervals to avoid accumulation which will results in elevated temperatures.
- Ensuring proper combustion by overhauling Fuel injectors and Fuel pumps to have a fine atomisation of fuel to avoid early or delayed ignition.
- Replacing of Scavenge Air filters at regular intervals.
- Prompt draining of Settling tanks and service Tanks.
- Periodical testing of the used Lube oil to assess the condition.
The above measures will enable in slowing down the oxidation however as we know the oil need to be replaced completely once it has reached its end of service life and got depleted to the core.
Periodical testing of Lube oil will alone help to identify the trend of above parameters whether it is increasing. Viswa Lab, offers a comprehensive Testing of Lube oil and Cylinder oil.
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