The odds against cylinder lubricating oil
At first glance it would appear that no lubricant, neither mineral nor synthetic, could withstand all above difficulties to fulfill the above requirements, but significant developments in the lubricating oil field have made it possible.
Formation of Sulphuric Acid
This is taken care of by lubricating oil of high TBN values (60-80 TBN). Further it is ensured that the cylinder liner temperature doesn’t go below the dew point temperature of sulphuric acid in the upper zone and thus the corrosion is reduced to a minimum value.
Additives to improve dispersancy and detergency have been developed to minimize abrasive wear and ring zone deposits.
Boundary Lubrication Conditions
Multilevel lubrication systems have increased oil film thickness considerably. The inclusion of additives such as polymethacrylates and ethylene-propylene co-polymers (OCP) to improve the oiliness helps in maintaining the requisite oil film thickness due to its molecular bending with porous cylinder liner.
Two stroke crosshead operation of marine engine
There is no non working stroke during which the oil film on the wall can be reformed but this problem has also been solved by improvement in timely oil injection system. A few engine manufacturers have recently developed a timely oil injection system similar to the fuel injection.
Formation of Sulphuric acid
A typical large engine developing 20000 Bhp with a daily fuel consumption of 76103 Kg burning a 3000 second Redwood No 1 fuel at 100 F and a sulphur content of 4%, the total weight of sulphur burnt would be 3048 Kg or 3 tons. If this were all converted into SO3 and then into sulphuric acid, this would produce 10 tons of highly corrosive acid. But reliable analysis indicates that only 10 to 15 % is converted into sulphuric acid, and that amounts to 450 Kg of sulphuric acid per day which may lead to highly corrosive wear.
Low spreadability of cylinder lubricating oil
Cylinder lubricating oil is highly viscous, which hampers its spreadibility thereby resulting in uneven wear on the cylinder liner. It will ultimately lead to blow down which further aggravates lubrication problems.