Answer EKM Question 17

Q17.  Discuss the significance of cylinder lubrication in two stroke diesel engines considering the impact of Annex VI of Marpol 73/78. Explain
(a) Two level cylinder lubrication incorporated on few diesel engines.
(b) The effect of over and under lubrication on engines.

Answer: (A) Two level cylinder lubrication incorporated on few diesel engines.
Two criteria determine the control: The implementation of the below two criteria will lead to an optimal cylinder oil dosage.
1. The cylinder oil dosage must be proportional to the sulphur content in the fuel
2. The cylinder oil dosage must be proportional to the engine load, i.e. the amount of fuel entering the cylinders.
1. The cylinder oil dosage must be proportional to the sulphur content in the fuel.
(a) Optimal cylinder oil dosage proportional to the amount of sulphur entering the cylinders is calculated and the dosage is based on that.
(b) This principle is founded on the observation that the main part of the cylinder liner wear is of a corrosive nature, and the amount of neutralizing alkaline components needed in the cylinder should, therefore, be proportional to the amount of sulphur(generating sulphurous acids) entering the cylinders.
(c) However, A minimum cylinder oil dosage is set in order to account for other duties of the cylinder oil.
(d) This result especially with respect to cylinder oil consumption, particle emissions, and combustion chamber wear.
2. The cylinder oil dosage must be proportional to the engine load, i.e. the amount of fuel entering the cylinders.
(a) The load transmitter Is connected to the fuel rack, thereby continuously transmitting the fuel index % to the MCU, which calculates the engine load from this information and the detected engine rpm.
(b) Load-dependent lubrication denotes an adjustment of the stroke in the lubricator oil pumps to correspond to the mean effective pressure or the actual engine load. The system is a natural consequence of specifying the required cylinder lube oil consumption as a function of engine defined as g/kWh.
Other factors on such Sulphur & load dependent lubricators:
Timing:
(a) Timing of injection is based on two signals from the angle encoder, a Top Dead Center (TDC) cylinder marker and a crankshaft position trigger. The alpha lubricator System is normally timed to injector the cylinder oil into the piston ring pack during the compression stroke.
Feed rate:
(a) The cylinder lubrication is based on a constant amount of oil being supplied via injection.
(b) The specific feed rate is controlled by variation of the injection frequency. This frequency is calculated from index and speed, and is usually proportional to the engine (Mean Effective Power) MEP. However, a power Mode or RPM Mode is possible. Manual Mode:
(a) The system can be operated in manual mode overriding the auto mode in case of any failure or other situations where the manual mode is necessary. 

(B) The effect of over and under lubrication on engines.
The effects of over lubrication:
(a) Over lubrication of an engine means excess of additives (calcium salts for alkalinity) which burns during the combustion and produces carbonates, which keep depositing over piston.
(b) Accumulation of these hard deposits may cause liner scoring or with add on of some soft deposits it can touch the liner wall and wipe out the lubricating oil film and lead to frictional wear of the cylinder liner and piston rings.
(c) High running cost due to higher consumption.
(d) Under piston accumulation and consequential issues relating to it.
The effects of under lubrication:
(a) Causes dryness of the liner surface resulting in scuffing and clover leafing at locations on the liner where oil has not spread.
(b) Low neutralising causes higher corrosion rates.
(c) High temperature walls leads to increased NOx levels.
(d) Increased wear rate of piston, rings, liner component.