Cylinder lubrication of diesel engine is a complicated and important problem.
In large crosshead diesel engine, cylinder lubrication is an independent lubrication system, its lubrication equipment, lubricating oil quality and operation management need special consideration.
In the development of modern diesel engine with high strength and low quality of fuel, the demand for cylinder lubrication is more demanding.
 

1. Working conditions of cylinder lubrication.

The particularity of cylinder lubrication is firstly the high working temperature.
Usually, the upper cylinder liner surface temperature is about 180 ℃ ~ 220 ℃, lower part of cylinder liner surface temperature is about 90 ℃ ~ 120 ℃, according to the position of measurement point and the piston ring grooves surface temperature on the top of the design about between 100 ℃ ~ 200 ℃.
The high temperature will reduce the viscosity of the lubricating oil, accelerate the oxidation and deterioration of the oil, and make the oil film on the wall of the cylinder evaporate.
Secondly, the speed of the piston in reciprocating motion is the largest in the middle of the stroke, and zero at the top and bottom.
Therefore, it is only possible to realize the hydrodynamic lubrication in the middle of the piston stroke, while in the upper and lower stopping points, it is impossible.
Especially at the upper end point, the temperature in the cylinder is the highest, and the piston ring has the maximum radial pressure on the cylinder wall. Even if the lubricating oil can withstand the high temperature here, it can only guarantee the boundary lubrication condition.
The diesel engine USES inferior fuel oil to bring a new problem to the cylinder lubrication.
This is mainly due to the high sulfur content of inferior oil, high ash content, high residual carbon value and asphalt value.
As mentioned above, it will cause low temperature corrosion of the cylinder, the wear of solid particles, and the increase of carbon, which can lead to the failure of the piston ring adhesive and air port blockage.
In addition, the piston top and the part of the belt deformation also make the cylinder lubrication more difficult.
For the above reasons, the cylinder jacket, especially its upper part, is difficult to form a continuous and complete oil film, so the upper part of the cylinder liner is generally very badly worn.
FIG. 5-8 shows the change of cylinder sleeve wear of a two-stroke dc scavenging diesel engine.
The diesel engine USES inferior sulphur fuel.
The upper limit curve indicates the use of low alkaline cylinder oil, and the lower limit curve indicates the use of high alkaline cylinder oil.
As can be seen from the figure, the maximum wear of cylinder liner occurs in the upper part of the cylinder jacket.
The high alkaline cylinder oil can greatly reduce the corrosion amount of the cylinder liner, and the shadow line between the upper and lower limit curves can be considered as the wear caused by acid corrosion.

The function of cylinder lubrication.

(1) reduce friction loss and prevent excessive wear of cylinder sleeve and piston;
 

(2) remove impurities such as burning residue and metal abrasive particles;
 

(3) to help seal the combustion chamber space;
 

(4) forming an oil film on the metal surface to prevent gas from contacting with metal to avoid corrosion;
 

(5) reduce noise.
Cylinder lubrication can be divided into two types: splash lubrication and cylinder lubrication.