The composition and function of lubricating system.

The lubricating oil circulation system of diesel engine is usually composed of cylinder oil lubrication, crankcase forced lubrication and crankcase oil purifying system.
The lubrication system of diesel engine is used to ensure the lubrication and cooling of the moving parts of the diesel engine power plant.
 

The main components of the crankcase forced lubrication and crankcase oil purifying system are:

1.Lubricating oil pump slide

There are two oil pumps, one of which is set aside.
Screw oil pump is usually used in order to ensure smooth oil pressure and smooth flow.
A vacuum gauge is usually installed on the suction side of the pump, and the vacuum degree is not more than 33.3Kpa (250mmHg).
The pump discharge pipe is equipped with a safety valve and a bypass valve to adjust the pressure and flow.
 

2.filter

The inlet and outlet end of the lubricating oil pump are respectively equipped with coarse and fine filter.
It is installed on the imported side as a coarse filter (sometimes with magnetic strainer). It is mounted on the outlet of the pump as a fine filter, which is equipped with a pressure gauge.
 

3.Lubricating oil cooler

The oil cooler is usually tube - shell or plate heat exchanger.
 

4.Oil slicker.

The oil separator is usually centrifugally separated. It is the most important equipment of the crankcase oil purifying system and the lubrication system of cylinder oil, which will be described in section v of this chapter.
 

The lubrication in diesel engine has the following functions:

(1) reducing friction by maintaining an oil film on the surface of each other.
This is the main function of lubrication.

(2) the cooling effect takes away the heat generated by the friction between the two moving surfaces and the heat from the outside, ensuring the proper temperature of the working surface.
 

(3) clean the surface of the moving surface and metal grit to keep the surface clean.
 

(4) the oil film produced by the sealing action can also play a sealing role.
If the oil film between piston and cylinder is lubricated, it also helps to seal the combustion chamber space.
 

(5) the oil film formed by anticorrosion is covered in the metal surface to prevent the air from contacting with the metal surface to prevent metal corrosion.
 

(6) the oil film formed by reducing the noise can act as a buffer to avoid direct contact between the two surfaces and reduce vibration and noise.
 

(7) the power oil pressure between thrust ring and thrust block in thrust bearing is transmitted.
The lubrication system of diesel engine is used to ensure the lubrication and cooling of the moving parts of the diesel engine power plant.
      

2. Performance index of lubricating oil.

Performance of the lubricating oil viscosity, viscosity index, flash point and condensation point, carbon residue, ash content, acid value (total acid value and acid value), corrosion resistance, resistance to oxidation stability, thermal oxidation stability, total base number, demulsification degree, mechanical impurities and moisture, etc. More than 10 kinds.
These indicators are measured in accordance with national test methods.
They basically reflect the quality of the oil, which plays an important role in the selection and use of lubricating oil.

Some of the above indicators are the same as the fuel performance indicators. The following are only some of the indicators that are specific to lubricating oil.
 

1.Viscosity and viscosity index (VI)

Viscosity is the most important indicator of lubricating oil.
It largely determines the formation of the wedge oil film between two friction surfaces.
For a long time, has been widely used abroad in the viscosity of lubricating oil classification of SAE taxonomy, the engine with lubricating oil according to the grades of viscosity is divided into ten, by the rise of oil viscosity with temperature, this performance said oil viscosity-temperature characteristics.
For sailing ship in different seasons and different latitude, diesel engine during cold starting and normal operation, the work of the lubricating oil temperature is different, its viscosity is not the same size, this to guarantee reliable lubrication effect greatly.
Therefore, it is not enough to judge the quality of the lubricating oil by measuring the viscosity of the temperature.
According to the research, the viscosity-temperature characteristics of different lubricating oils are different. For example, when the oil temperature increases by 10 degrees, the viscosity can be reduced by three quarters, while some of the lubricating oil can be reduced by less than half.
If the viscosity of the lubricating oil changes with the degree of temperature, it can meet the requirements of use in the larger temperature range, and the viscosity of this oil is good.
In foreign countries, viscosity index (VI) is usually used to describe the viscosity-temperature characteristics of oil.
It is obtained by comparing two standard oils.
The physical significance of viscosity index shows that the viscosity change is small when temperature changes.
In general, the viscosity index in 80 is called the high viscosity index, less than 35 is the low viscosity index, between 35 and 80 is called the intermediate viscosity index.
The best paraffin viscosity index can reach 124 and can be as high as 200 after adding the viscosifier.
Viscosity ratio is used to evaluate viscosity-temperature characteristics.
It is the lubricating oil in 50 ℃ and 100 ℃ when the ratio of kinematic viscosity.
The viscosity is smaller than that, indicating that the viscosity change is small and the quality is good.
If the viscosity ratio of the lubricating oil is known, the corresponding viscosity index can be obtained by the curve method.
 

Acid and water soluble acids or bases.

Acid in lubricating oil can be divided into organic acid and inorganic acid.
There are two sources of organic acids in fresh oil:

The first is that it is not removed when it is refined in petroleum;

The second is the intentional addition of acid anti - oxygen, anti - corrosion additives.
The organic acids used in lubricating oil are mainly organic acids produced by oxidation.
When the organic acid content is small, it can not corrode the metal much, but can increase the lubricating oil of the lubricating oil to maintain good boundary lubrication property.
When its content is high, it will corrode some bearing materials (non-ferrous metals and their alloys, especially lead).
Inorganic acid refers to sulfuric acid, which has a strong corrosive effect on metals, and there is generally no sulfuric acid in the lubricating oil.
The sulfuric acid which may be contained in fresh oil is preserved after pickling and neutralization in the refining process;
The lubricating oil in use may form sulfuric acid due to the leakage of combustion products containing sulfur fuel into the crankcase.
 

In our country, the acid value is used to indicate the content of organic acids in lubricating oil, and "water-soluble acid or alkali" is used to indicate the presence of inorganic acid or strong base.
The "acid value" is denoted by the number of potassium hydroxide milligrams needed to neutralize the acid in the 1 g lubricating oil. The unit is mgKOH/g.
"Water-soluble acid" refers to the inorganic acid (strong acid) which is soluble in water and low molecular organic acid, which has a corrosive effect on almost all metals.
Water - soluble alkali is produced in the alkaline wash residue or storage of oil processing. It has a corrosive effect on aluminum.
"Water-soluble acid or alkali" only indicates that the oil is acidic or alkaline, and is only used for qualitative examination.
The Total Acid value of Total Acid Number is the sum of organic Acid and inorganic Acid, and the content of inorganic Acid is expressed separately by Strong Acid Number.
The units are all mgKOH/g.
 

3. Resistance to emulsification.

The process is called emulsification when water or fresh water leaks into the lubricating oil, which is stirred to form the emulsion and produce foam.
The emulsion affects the lubricating property, the oil is changed, and the mechanical impurities are adsorbed on the two-phase interface, and the friction surface is stained and the parts wear out.
The anti-emulsification degree of lubricating oil refers to the time required for the automatic layering of oil (oil layer and water layer) after emulsification, namely the demulsification time of the lubricating oil.
The demulsification time is short, the emulsification degree is good, and vice versa.
 

4. Thermal oxidation stability and anti-oxidation stability.

Both measures are used to measure the ability of oil to resist air oxidation under conditions of use.
The test method is different from the application object.
The former is an oxidation test of thin oil layer under high temperature condition, which is indicated by the time needed to form the paint film by oxidation.
Provisions in China standard with "ba BaoKeFa", refers to the prescribed under the condition of high temperature 250 ℃, free air flows through the thin oil reservoir test, determination of test oil generated by oxidation and 50% of the time needed for paint material (min), use this time to evaluate thermal oxidation stability test oil.
The test method is to simulate the working conditions of the oil film on cylinder wall, which is suitable for lubricating oil of diesel engine.
The antioxidant safety belongs to the thick oil layer oxidation test under the low temperature condition, which is expressed by the sediment and acid value generated after oxidation.
According to provisions of our country means under the condition of 125 ℃, to test the oil zhongtong into a certain velocity of air or pure oxygen 4 or 8 h, h, respectively test generated after the oil oxidation sediments (%) and acid value (mgKOH/g).
If the sediment is less and the acid value is small, the anti-oxidation stability of the test oil is good.
This method is used to simulate the working conditions of lubricating oil in hydraulic system.
 

5. Corrosion,

Corrosion is used to measure the degree of corrosion to metal (lead) when the lubricating oil under high temperature is in full contact with oxygen.
It is an important index of lubricating oil of diesel engine.
The copper, lead and other alloy bearing materials in modern diesel engines are very sensitive to corrosion, so long as a small amount of acid in the lubricating oil can seriously corrode the bearing.
Provisions in China standard corrosion experiment with "the Yugoslavia method", namely the test oil heated to 140 ℃, with a certain area of a special pieces of metal at a speed of 15 to 16 times per minute alternately immersed in the oil and the dew in the air, after 50 h, determination of the weight of the sheet metal to reduce (g/m2).
The greater the weight, the more corrosive the oil, the worse the quality.
 

Alkali value 6.

The Base Number is Base Number.
It has the same units as the acid value, but also with mgKOH/g, but the opposite is true.
The basic value is the number of milligrams of potassium hydroxide in a gram of oil.
Natural mineral oil itself is not alkaline, only after adding alkaline additive is alkaline.
In the course of use, the base value will gradually decrease due to the loss of additives.
 

7. Floatability

Planktonicity means that the surface colloidal carbon residue is used to clean the surface of the parts with additive lubricating oil, so that it can be dispersed as small particles and the ability of suspension is carried.
It is usually carried out on a special test machine for a certain amount of time under specified conditions. Then, according to the paint film condition on the piston, the evaluation is conducted from 0 to 6 levels.
Level 0 is the piston is very clean, no paint film formation;
Level 6 is seriously dirty, the piston is completely covered with paint film.
 

8. Anti-foam

Foam resistance is used to measure the bubbling volume and defoaming time of a special foam head and a certain amount of air measurement test oil.
When the oil is running, it is agitated violently so that the air is mixed into oil to form a foam.
Excessive foam, in addition to the loss of lubricating oil, will also cause the oil pump and bearing to cause cavitation corrosion, the lubrication efficiency is reduced, the bearing burnt.
   

Iii. Quality grade of lubricating oil.

Some foreign countries and related societies have divided the lubricating oil into several quality grades according to the performance characteristics and working conditions of the lubricating oil.
A quality classification method jointly published by SAE, ASTM and API in the United States is commonly referred to as the API taxonomy.
This classification method can be divided into four quality grades: CA, CB, CC and CD according to the characteristics of oil quality and applicable model.
CA -- light loading diesel engine oil.
A diesel engine that is fired with high quality fuel and operates under moderate to moderate conditions.
Under the condition of non - pressurization and high - quality fuel, it has the properties of anti - bearing corrosion and preventing high temperature formation of sediment (paint film, carbon deposition).
CB - diesel oil for general load.
A diesel engine used for moderate to moderate operation.
In the non-pressurization and the use of sulfur-containing fuel, it has the properties of anti-bearing corrosion and the formation of precipitates under high temperature.
CC - medium load diesel engine oil.
High pressure diesel engine for medium to harsh conditions.
It has the properties of anti - corrosion and anti - corrosion.
CD - heavy load diesel engine oil.
It is used for supercharging, high speed, high power, and the requirement can be very effective to restrain the wear and prevent the formation of the sediment diesel engine.
The performance of anti - bearing corrosion and anti - temperature formation in the supercharged diesel engine with various quality fuel is used.
The API classification provides strict engine test methods and standards for diesel engine lubricating oil. The lubricating oil must pass the specified assessment items and be qualified to meet a certain level.
Currently, this classification has been recognized and used internationally.
Because of the development of high - pressure diesel engine, the use of CD - grade oil can not meet the requirements.
In recent years, it has developed more oil than CD, but it has not been formally named CE.
In addition, the oil of Marine cylinder oil and high power medium speed machine are still developed by each oil company, and there is no uniform standard.