Technical Overview
Diesel Cylinder Lubrication
The piston of the 2-stroke marine diesel engine is lubricated by the injection of cylinder lubricant through quills bored into the cylinder liner wall. The lubricating
oil is of high viscosity and high alkalinity, and its functions are:
|
|
To apply a lubricating oil film onto the surface of the diesel cylinder liner and lubricate the movement of the piston up and down the cylinder liner.
|
|
|
To lubricate the movement of the piston rings in the ring grooves and provide a gas seal between rings, piston and liner wall.
|
|
|
To neutralize acid which condenses on the liner wall when burning fuels containing sulphur.
|
|
|
To carry away wear, fuel debris (fuel ash and partly burned fuel), and lubricant debris (burned and neutralized lubricant)..
|
The lubrication of the 2-stroke marine diesel cylinder is "once through" in that the lubricant passes through the diesel cylinder only once and then drains away
to a holding tank for eventual disposal by incineration or landing ashore.
Diesel Cylinder Lubricant Condition
The new cylinder lubricating oil has certain known values of viscosity, alkalinity, detergency, dispersancy etc. After its passage down the cylinder liner wall
it drips from the bottom rim of the liner, collects on the piston rod diaphragm and runs out through the drain line. As the lubricant performs its function, it
is subjected to:
|
|
High temperature and pressures in the combustion zone,
|
|
|
High shear whilst lubricating the piston rings / liner interface,
|
|
|
Acid attack,
|
|
|
Contamination by fuel and lubricant debris, wear particles and water.
|
Analysis of the used cylinder lubricating oil will show that the lubricant has undergone changes to its viscosity, alkalinity, detergency, and dispersancy values,
and provide information on the amount and type of contaminants.
Study of the changes to the lubricating oil and the degree of those changes can provide valuable information about:
|
|
Combustion conditions,
|
|
|
Adequacy of lubrication,
|
|
|
Acid condition as influenced by sulphur content in the fuel, engine loading and degree of jacket cooling,
|
|
|
Wear conditions,
|
|
|
Variations in fuel quality,
|
|
|
Efficiency of water separation,
|
|
|
Performance of piston rod glands.
|
Manufacturers recommended Cylinder Lubricant feed rate
Engine builders recommend cylinder lubricant feed rates based on the power of the engine and their field experience over the
years. The tendency has been to propose higher cylinder lubricant feed rates to combat piston deposit and liner wear problems. From 1985 until 1999, there had been
large increases in the recommended feed rate.
Daily consumption of cylinder lubricant has become a major cost item.
Since that time, engine makers have reduced their their recommended feed rates, but since 2005 cylinder lubricant prices have increased.
Daily consumption of cylinder lubricant remains a major cost item.