Analysis Of Lubricating Oil Pollution In Internal Combustion Engines

1 Types of lubricating oil pollutants and their hazards

Pollutants 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 polluted energy.

1) Solid particles. Solid particle pollutants are the most common type of pollutants in the lubrication system. It includes metal chips left behind that are not cleaned during parts processing and assembly, dust and debris that invade the system from the outside during mechanical driving (or construction), wear debris and erosion peelings generated on the surface of the part itself, and oil oxidation and sediments produced by decomposition, etc. These solid particles mixed in the lubricating oil penetrate into the mating surfaces of the moving parts like abrasives, accelerating the wear of the parts’ surfaces and greatly shortening their service life.

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

3) Exhaust gas. During the operation of an internal combustion engine, a certain amount of high-temperature and high-pressure exhaust gas always escapes from the combustion chamber into the crankcase. The exhaust gas contains water vapor and SO2. Water vapor condenses to form foam in the engine oil, destroying the normal oil supply. This phenomenon is especially serious in winter; SO2 generates H2SO3 when it meets water, and H2SO3 generates H2SO4 when it meets O2, which will corrode mechanical parts.

4) Diesel (gasoline) oil. If the lubricating oil is mixed with diesel (gasoline) oil, the lubricating oil will become thinner, the viscosity will decrease, leakage will increase, and a thick enough oil film will not be formed on the surface of the moving pair, causing the lubricating effect to be lost prematurely.

5) Pollution energy. Contamination energy refers to lubricating oil thermal energy. The oil temperature is too low, the viscosity of the lubricating oil is high, and the fluidity is poor, making it difficult for the oil pump to absorb oil, and it also makes it difficult to start the internal combustion engine; the oil temperature is too high, the lubricating oil becomes thinner, the viscosity decreases, leakage increases, and dry friction or half friction occurs between the kinematic pairs. Dry friction may even cause lubricating oil to oxidize, decompose and deteriorate.

2 Basic methods and measures to prevent lubricating oil pollution

1) Selection of lubricating oil. Choosing lubricating oil with appropriate viscosity and good quality is of great significance to the normal operation of the internal combustion engine and extending its service life. Therefore, the basic principles for selecting lubrication are: (1) Select according to load and speed. Those with large load and low speed, such as some large diesel engines, should use lubricating oil with high viscosity; while those with small load and high speed, such as gasoline engines, should use lubricating oil with small viscosity. (2) Choose according to the region, season and temperature. In cold winter regions, such as the Northeast and Northwest regions, lubricating oil with small viscosity and low freezing point should be selected; in areas with higher temperatures throughout the year, lubricants with slightly higher viscosity should be selected in regions south of the Yangtze River. (3) Select according to the wear condition of the internal combustion engine. If the engine has a long service life and the parts wear out a lot, it is appropriate to choose oil with a higher viscosity. For new internal combustion engines, lubricating oil with a lower viscosity can be used. (4) Internal combustion engines equipped with superchargers should use special lubricating oil. (5) According to the internal combustion engine operating instructions, select the specified brand of lubrication.

2) Clean the lubricating oil. When filling lubricating oil, ensure that the filling port and refueling container are clean 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 working temperature of lubricating oil is 45~90℃. After the internal combustion engine is started, it should be preheated first, and the standby oil temperature should be higher than 45°C before being put into operation or driving. When the ambient temperature is high, the working time is long, and the lubricating oil temperature is higher than 90°C, it should be operated at idle speed and wait until the temperature drops before starting work.

4) Prevent moisture from mixing into the lubricating oil. When refueling, prevent moisture or rain from intruding into the lubricating oil. When the crankcase oil level is found to rise during operation, the cause should be analyzed in time, the working conditions of the water pump water seal, cylinder block, cylinder head and other components should be checked, and the fault should be eliminated.

5) Prevent fuel from mixing into lubricating oil. Maintain the normal operating temperature of the cooling system. The normal water temperature of water-cooled internal combustion engines is 80~95℃, and the cylinder head temperature of air-cooled internal combustion engines should be less than 120℃. If the temperature is too high, the oxidation and deterioration of the lubricating oil will be accelerated; if the temperature is too low, part of the mixture entering the cylinder will condense into liquid and flow into the crankcase. Maintain the good working condition of the fuel system, promptly check and adjust the fuel supply advance angle and fuel injection atomization quality of the high-pressure pump and injector to avoid poor fuel atomization and vaporization, and the flow of lubricating oil along the cylinder wall.

6) Prevent exhaust gas from contaminating lubricating oil. Install the piston rings correctly; the gap between the piston and the cylinder liner, and the gap between the valve and the guide should be appropriate; keep the crankcase well ventilated and the seal clean.

7) Timing of lubricating oil replacement. The quantity and quality of the lubricating oil should be checked before starting each shift of the internal combustion engine. Replacement should be considered when one of the following conditions occurs: when the oil dipstick is pulled out, the lubricating oil on the dipstick runs away quickly, or the lubricating oil drops on the paper and spreads quickly. It means that the lubricating oil is too thin; when you pinch the lubricating oil with your fingers, it feels smooth and black, with a smell of fuel; there are too many metal shavings in the lubricating oil, etc.

The lubrication is usually replaced after the new car or the overhauled machinery has completed the test run; the diesel engine runs every 600 hours and the gasoline engine runs every 400 hours (approximately 14,000km traveled); in winter or summer, it is necessary to only refuel without changing the oil, and replace the oil with oil replenishment. adverse phenomena.

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