Contamination and Prevention of Internal Combustion Engine Lubricating Oil

The types of contaminants in lubricating oil and their hazards

Contaminants in lubricating oil include various substances mixed in the working medium that are harmful to the surface life of internal combustion engine parts, such as solid particles, water, exhaust gas, diesel (gasoline) oil and polluting energy, etc.

1) Solid particles. Solid particle contaminants are the most common type of contamination in lubrication systems. It includes metal chips that were not thoroughly removed during the processing and assembly of parts, dust and impurities that invaded the system from the outside during mechanical operation (or construction), grinding swarf and erosion spalling produced on the surface of parts themselves, as well as sediment resulting from the oxidation and decomposition of oil, etc. These solid particles mixed in the lubricating oil seep into the mating surfaces of the moving parts like abrasives, accelerating the wear of the parts' surfaces and significantly shortening their service life.

2) Water. When water seeps into the lubricating oil, the oil turns milky white and rapidly oxidizes and deteriorates. Not only does it lose its lubricating effect, but it also corrodes the metal surface.

3) Waste gas. During the operation of an internal combustion engine, there is always a certain amount of high-temperature and high-pressure exhaust gas flowing from the combustion chamber into the crankcase. The exhaust gas contains water vapor and SO2. Water vapor condenses in the engine oil to form foam, disrupting normal fuel supply. This phenomenon is particularly severe in winter. When SO2 meets water, it forms H2SO3, and when H2SO3 meets O2, it forms H2SO4, which will corrode machine parts.

4) Diesel (gasoline) oil. If diesel (gasoline) oil is mixed in the lubricating oil, it will make the lubricating oil thinner, reduce its viscosity, increase leakage, and the surface of the moving pair cannot form a thick enough oil film, thus losing its lubricating effect prematurely.

5) Polluting energy. Pollution energy refers to the thermal energy of lubricating oil. When the oil temperature is too low, the viscosity of the lubricating oil is high and its fluidity is poor, making it difficult for the oil pump to draw in oil. At the same time, it also makes it hard for the internal combustion engine to start. If the oil temperature is too high, the lubricating oil will become thinner, its viscosity will decrease, leakage will increase, dry or semi-dry friction will occur between the moving pairs, and even cause the lubricating oil to oxidize, decompose and deteriorate.

2. Basic methods and measures for preventing lubricating oil contamination

1) Selection of lubricating oil. The selection of lubricating oil with appropriate viscosity and high quality is of great significance for the normal operation of the internal gas turbine and the extension of its service life. Therefore, the basic principle for selecting lubrication is :(1) Select based on load and rotational speed. For those with heavy loads and low rotational speeds, such as some large diesel engines, lubricating oil with high viscosity should be selected. For those with low load and high speed, such as gasoline engines, lubricating oil with low viscosity should be selected. (2) Select based on the region, season and temperature. In cold winter regions such as Northeast and Northwest China, lubricating oil with low viscosity and a lower freezing point should be selected. The temperature is relatively high throughout the year. For instance, in the Jiangnan region, lubricating oil with a slightly higher viscosity should be selected. (3) Select based on the wear condition of the internal combustion engine. For those with a long service life and significant wear of parts, oils with higher viscosity should be appropriately selected. New internal combustion engines can use lubricating oils with lower viscosity. (4) Special lubricating oil should be used for internal combustion engines equipped with turbochargers. (5) According to the provisions of the internal combustion engine's user manual, select the specified brand of lubrication.

2) Lubricating oil cleaning. When adding lubricating oil, it is necessary to ensure the cleanliness of the oil filling port and the oil filling vessel to prevent the intrusion of dust and sand. Maintain the lubricating oil filter on time. Maintain the air filter and fuel filter on time to prevent impurities from entering the crankcase from the cylinder.

3) Lubricating oil temperature. The normal operating temperature of lubricating oil is 45 to 90 degrees Celsius. After starting the internal combustion engine, it should be preheated first. Only when the oil temperature exceeds 45℃ can it be put into operation or driven. When the ambient temperature is high, the working time is long, and the lubricating oil temperature exceeds 90℃, the machine should idle and wait for the temperature to drop before resuming work.

4) Prevent water from mixing into the lubricating oil. When refueling, prevent water or rainwater from entering the lubricating oil. When the oil level in the crankcase rises during operation, the cause should be analyzed promptly, and the working conditions of components such as the water pump seal, cylinder block, and cylinder head should be inspected to eliminate the fault.

5) Prevent fuel from mixing into lubricating oil. Maintain the normal operating temperature of the cooling system. The normal water temperature for water-cooled internal combustion engines is 80 to 95 degrees Celsius, and the cylinder head temperature for air-cooled internal combustion engines should be less than 120 degrees Celsius. Excessively high temperatures will accelerate the oxidation and deterioration of lubricating oil. If it is too low, some of the mixture entering the cylinder will condense into liquid and flow into the crankcase. Maintain the good working condition of the fuel system, and promptly inspect and adjust the fuel supply advance Angle and atomization quality of the high-pressure pump and fuel injector to prevent poor atomization and vaporization of the fuel from flowing into the lubricating oil along the cylinder wall.

6) Prevent the contamination of lubricating oil by exhaust gas. Install the piston rings correctly; The clearance between the piston and the cylinder liner, as well as the clearance between the valve and the guide tube, should be appropriate. Keep the crankcase well-ventilated and the seals clean.

7) Timing for lubricating oil replacement. Before starting each shift of the internal combustion engine, the quantity and quality of the lubricating oil should be checked. When any of the following situations occur, replacement should be considered: If the lubricating oil on the dipstick quickly runs out when pulled out, or if the lubricating oil drops onto the paper and quickly spreads, it indicates that the lubricating oil is too thin. When you pinch the lubricating oil with your fingers, you will feel that there is no smooth oil film and it turns black, with a smell of fuel. Excessive metal shavings in the lubricating oil, etc.

Lubrication replacement is generally carried out after a new car or machinery that has undergone major overhauls has completed its trial run. Diesel engines run for 600 hours and gasoline engines for 400 hours (approximately 14,000 kilometers); When winter or summer comes, overcome the bad phenomena of only refueling without changing the oil and replacing the oil with refueling.

8) Lubrication system cleaning. The lubrication system should be cleaned when changing the lubricating oil. The method is to drain the old lubricating oil in the lubrication system while it is still hot, add a mixture of clean lubricating oil and diesel oil (4:1) to the lower mark of the dipstick, let the engine idle for 3 to 5 minutes, then stop and drain the oil, and add new lubricating oil to the specified oil level.