Analysis and identification of oil deterioration
  • Automotive

The diesel engine works under the condition of high temperature, high pressure and high speed, and the working conditions are bad. Therefore, the lubrication requirement of the diesel engine is very high. The lubricating oil (oil) must have a certain viscosity, and when the temperature changes, the viscosity changes little; it has good lubricity (commonly known as "oily"); it has good resistance. Oxidizing stability; having a lower condensation point; no glial precipitation in combustion and decomposition; no substances that cause corrosion and wear of the machine parts, without mechanical impurities and moisture. But with the increase of the use time, the quality of the oil will decrease or even deteriorate. A large number of harmful substances produced after oil deterioration are harmful to diesel engines. For example, the organic acids generated by oxidation increase the acid value of the engine oil, and the corrosion of the machine parts is rusty (with the most serious lead bronze bearing). In use, the growing oleic acid value is the sign of "aging". The film (also known as colloid) is a black sticky material, which is not only difficult to clean, but also easily causes the piston to lose its effect in the ring groove; carbon accumulation will form hot spots to make the parts overheated and wear worse; the oil mud is the result of mixing water and oil. It coagulates. In the tubing, it not only increases the flow resistance of the oil, but also blocks the oil circuit, which makes the lubrication of the diesel engine lose its function. (1) working temperature. Under normal oil temperature, oil oxidation is not obvious, but the oxidation deterioration will accelerate with the rise of temperature, and the oxidation speed of oil increases by about 1 times when the temperature rises 10 degrees C. (2) metal debris and combustion products. The worn metal powder and the burning product have a catalytic effect on the oxidation of oil. In the worn metal, the copper has the greatest influence on the oil aging, while the iron catalyst is 20% of the copper, and the other metals have no obvious catalytic action. The ferric oxide and vanadium oxide produced by combustion in the combustion chamber are all highly active oxidation. The catalyst will accelerate the oxidation of the oil. (3) water is mixed. Water in the oil will cause the formation of oil sludge and stain the oil. When the oil content of the oil is over 0.1%, the additives in the oil (antioxidants, detergent dispersants, etc.) will be invalidated, making the oil a emulsion and destroying the oil film. Thus it accelerates the oxidation of the oil. The experiment proves that when the moisture content reaches 1%, the wear of machine parts will increase 2.5 times. (4) crankcase has poor ventilation and poor oil heat dissipation. When the diesel engine works, there will be some burning gas in the crankcase. If the piston ring is seriously damaged, this phenomenon will be more serious, and the pressure in the crankcase will rise. If the pressure is higher than the external atmospheric pressure, it will cause some resistance to the operation of the piston, resulting in the leakage of oil from the joint between the oil pan and the cylinder block. In addition, sulfur dioxide leaked into the crankcase will accelerate the deterioration of the oil. For this reason, the pressure in the crankcase must be equal to the external atmospheric pressure. Some diesel engines are equipped with ventilation pipes (breathing tube), the purpose is to make the crankcase inside and outside the pressure is in a state of equilibrium. (5) improper maintenance. When cleaning the crankcase, if the oil filter or radiator is not cleaned thoroughly or leaks the seal washer of the oil filter, the diesel engine will make the oil black and dirty after adding new oil for only a few hours. In actual use, it is necessary to determine whether the oil is deteriorating, and the oil analyzer can be used conditionally, and the XD-I oil analysis box (patented product of the agricultural machinery maintenance and Research Institute of the Agricultural Ministry of Agriculture) is used to analyze the oil drop spot sign method to determine whether the oil is deteriorating, and the oil performance can be judged by experience. Break the identification. The following common methods are used: (1) hand twist rubbing sensation. That is to say, rub the oil with your hands and compare it with the new engine oil and check its viscosity by feeling. When examining, dip the index finger with a little oil, and make the index finger and thumb pairs several times. If the feeling is not sticky, it means that the oil has thinned and the viscosity has decreased. (2) the odor method. Smell the new oil with your nose, and smell the oil released from the oil pan with your nose. The odour is the manifestation of the oil pollution. If you feel a bad smell, the oil has a strong acid or a mixture of other impurities. If you feel a "burning" or an exciting smell, the oil is oxidized at a high temperature; if you feel the smell of fuel, the oil has been diluted by diesel oil. (3) appearance method. That is, directly use the test tube to take the oil sample and observe it with the naked eye. If it is clear, still keep the original color, indicating that the oil pollution is not serious; if the oil color is cloudy or emulsified, it is polluted seriously by water; if the oil color becomes black, it indicates the incomplete soot pollution by the fuel burning, and the solid substance in the oil, such as sand, metal chip, rust and dust, will sink in the static position. (4) oil flow method. Take the oil in the container and slowly pour it out. Pay attention to the oil flow. Such as oil flow can maintain slender and uniform, indicating that the oil has no sticky substance and impurities, less moisture. If the oil flow is easy to break, the thickness is uneven, turbidity and blackening, it means that the oil has deteriorated. (5) ear hearing method. Soak some oil in dry paper or cotton yarn, and then burn it with fire. If there is a slight crack or a "phenate" sound, and there is a flash phenomenon, it shows that the oil in the oil is more water and should not be used continuously, so it should be replaced in time. (6) the method of oil drop test. Drop the oil sample on the white paper to observe the spots. If there are more hard bitumen and carbon particles in the black spot in the center of the oil mark, it is indicated that the oil filter is bad and the filter should be overhauled and the oil can continue to be used. If the black spot is dark brown and no particles, it indicates that the oil has been changed and the oil has been changed; for example, the boundary of the black spot in the middle of the oil drop and the Yellow impregnated boundary of the surrounding is not obvious, and there is a spread lace It indicates that the additives are not completely invalid and can be used continuously. If the boundary clearly indicates that the additives do not work, they should be replaced. (7) light method. On a sunny day, the lubricating oil is lifted with a screwdriver, and the angle is 45 degrees with the horizontal face. Compared with the sunlight to observe the oil droplets, under the light, it can be clearly seen that no debris in the lubricating oil is good and can continue to use; if the debris is too much, the lubricating oil should be replaced.