Understanding oil product inspection reports

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It is well known that the conventional testing parameters for automotive gasoline and diesel include density, boiling range, copper strip corrosion test, mercaptan sulfur content, vapor pressure, oxidation stability, benzene content, oxygen content, sulfur content, moisture and mechanical impurities, actual gum content, residue, octane number, cetane number, etc. There are also tests for diesel lubricity and polycyclic aromatic hydrocarbons. So, having a \"Test Report\" that reflects the efforts of the testers and outlines the test items and data, how can one understand the quality of the oil? Next, we will provide answers regarding the common testing items for petroleum products, especially those used for vehicle gasoline and diesel: The meanings of various properties of petroleum products. 1. The boiling range of a petroleum product – refers to the temperature range that indicates its evaporation characteristics, as determined by the initial boiling point and the final boiling point obtained through distillation under specified conditions. It is mainly used to determine the proportion of light and heavy fractions in the oil product, as well as to control product quality and performance. 2. Octane rating – a standard value that represents the resistance of a fuel for spark-ignition engines to detonation. In standard engine tests under specified conditions, it is determined by comparison with a standard fuel. It is expressed as the volume percentage of isooctane in a standard fuel that has the same anti-knock property as the fuel being tested. Different methods for measuring octane number yield different values; therefore, when citing the octane number, it is necessary to specify the method used. 3. Motor octane number – the octane number measured on a standard test engine under severe conditions of a higher air-fuel mixture temperature (usually heated to 149°C) and a higher engine speed (usually up to 900 revolutions per minute). 4. Research octane number – the octane number determined on a standard test engine under moderately severe conditions, characterized by a lower air-fuel mixture temperature (usually without heating) and a lower engine speed (usually 600 revolutions per minute). 5. Saturated vapor pressure – it is used to indicate the degree of evaporation capacity of oils, the likelihood of gas blockages forming in oil supply systems, and the tendency for loss of light fractions during storage and transportation. Gasoline has a high saturated vapor pressure, which results in high volatility and an increased likelihood of vapor blockages; as a result, there are also significant losses due to evaporation during storage and transportation. 6. Flash point – refers to the lowest temperature at which a petroleum product, under specified conditions, will ignite instantly when its vapor comes into contact with a flame upon heating. The lighter the oil, the lower its flash point. The hazard level of oils is determined by their flash point. The flash point can be used to determine the density of an oil’s composition and assess the risk of fire involving that oil. The flash point determined using a closed-cup flash point tester is called the closed-cup flash point, and it is generally used to determine light petroleum products. The higher the flash point, the safer it is. 7. Doctor test – A test carried out in the presence of sublimed sulfur, using sodium leadite and light petroleum products, to detect thiols or hydrogen sulfide in the oil. 8. Closed-cup flash point – the flash point measured using a specified closed-cup flash point apparatus, expressed in °C. 9. Open flash point – the flash point measured using a specified open flash point apparatus, expressed in °C. 10. Ignition point – the lowest temperature, expressed in °C, required for ignition and sustained combustion to occur when a flame comes into contact with the oil vapor and air mixture on the surface of the oil under specified conditions. 11. Autoignition point – the temperature at which a petroleum product catches fire spontaneously under specified conditions in the absence of a flame, expressed in °C. 12. Octane number – a standard value that represents the ignition performance of diesel in engines. In standard engine tests under specified conditions, it is determined by comparison with a standard fuel. It is expressed as the volume percentage of cetane number in a standard fuel that has the same ignition delay period as the fuel being tested. 13. Cetane number – a calculated value that indicates the ignition performance of diesel in engines. This value is calculated from the standard density of diesel and its 50% distillation temperature. It is generally used when there is no cetane rating machine or when the sample quantity is too small to conduct standard engine tests. 14. Freezing point – refers to the highest temperature at which an oil stops flowing when cooled under specified conditions. The freezing point is a parameter used to evaluate the low-temperature performance of oils. The higher the wax content in the oil, the higher its freezing point. 15. Pour point – refers to the lowest temperature at which a cooled oil sample begins to flow continuously under specified conditions. Since the pour point reflects fluidity at low temperatures better than the freezing point, China will use the pour point to indicate its low-temperature fluidity in the future. For different crude oils, the difference between their pour point and freezing point varies; generally, the pour point is 3 to 5°C higher than the freezing point. 16. Mechanical impurities refer to precipitates or suspensions in petroleum or petroleum products that are insoluble in the oil and specified solvents, such as sediment, dust, iron filings, fibers, and certain insoluble salts. Mechanical impurities can be removed by methods such as precipitation or filtration. For light oil, mechanical impurities can block the oil passages, leading to the formation of raw rubber or corrosion ； For boiler fuel, it can clog the nozzles, reduce combustion efficiency, and increase fuel consumption ； For lubricating oil, it damages the oil film, increases wear, clogs the oil filter, and promotes the formation of carbon deposits. 17. Viscosity – refers to a measure of the internal frictional force that arises between molecules when a liquid moves under the action of an external force. It is an indicator for assessing the fluidity of oils. Viscosity decreases as temperature rises. Lubricating oil must have the appropriate viscosity to provide effective lubrication ； The fuel for internal combustion engines must have the right viscosity in order to allow for the injection of small, uniform drops of fuel that ensure complete combustion. 18. Dynamic viscosity – a measure of the internal friction force when a liquid flows under the effect of gravity; it is equal to the ratio of the dynamic viscosity at the same temperature to its density, and is expressed in meters squared per second in the International System of Units. *It is expressed in centistokes (cSt). 1 centistere = 10-6 m2/s = 1 mm2/s. 19. Calorific value – the heat released when a unit weight of oil is completely burned under specified conditions. In the International System of Units (SI), it is expressed in joules. In addition to clogging the oil filters and fuel supply lines, mechanical impurities also cause severe wear on the high-pressure fuel pumps and injectors. 21. What is sulfur content? Sulfur content is related to engine carbon deposition, corrosion, wear, and environmental pollution. The sulfur content allowed for mixed residual oil-type fuel oil used on ships at sea is 2%, but it is restricted to 1% for use on land. Methods for measuring sulfur content include the lamp burning method and the tube furnace method. Tube furnace method for fuel oil. 22. What is residue? Residue is the charred black residue formed when an oil sample is heated under specified conditions in the crucible of a residue determination apparatus, causing the oil to evaporate and decompose. The electric furnace method requires that the furnace temperature be maintained at 520±5°C to evaporate and decompose the residues. Generally, for diesel carbon residue specifications, the sample oil is distilled until only 10% remains before evaporation and decomposition occur. The 10% distillation residue is referred to as carbon residue; this value for the 10% distillation residue is much higher than that obtained from the total combustion carbon residue test, and heavy fuel oils are required to have their total carbon residue determined. Large low-speed diesel engines can use heavy fuel oil containing 10% carbon residue. The char value affects coking in the combustion chamber. However, the wear of the cylinder and piston depends not only on the amount of carbon residue but also primarily on the hardness of the carbon. Deposit with high sulfur content is hard and rigid, resulting in greater wear. 23. What is corrosivity? Corrosive substances are not allowed to be present in engine oil. The identification method involves immersing the brass sheet in an oil test tube, heating the tube to 200–220°C, removing it and allowing it to cool; if black spots or brown discoloration appear on the brass sheet, it indicates the presence of corrosive substances in the oil. Otherwise, there are no corrosive substances. 24. What is ash? Substances that cannot volatilize or burn at high temperatures are called ash. An increase in ash content in engine oil leads to increased wear of machine components. 25. What is the cold filter plugging point? It is an important indicator for measuring the low-temperature performance of light diesel; specifically, it refers to the highest temperature at which the diesel begins to clog the engine filters under specified conditions. When choosing a diesel grade, users should use the specific value of the cold filter plugging point as a reference. The cold filter points of common diesel grades are as follows: the cold filter point of No. 5 light diesel is 8°C, that of No. 0 light diesel is 4°C, that of No. -10 light diesel is -5°C, and that of No. -20 light diesel is -14°C. Therefore, when selecting diesel, it is necessary to take into account both the local temperature and the cold filter plugging point corresponding to the diesel grade; that is, diesel grade 0 should be used when the ambient temperature is 4°C, diesel grade -10 should be used when the ambient temperature is -5°C, and so on. 26. What is the condensation point? It is an important indicator for measuring the flow properties of light diesel at low temperatures. Specifically, it is the highest temperature at which light diesel oil stops moving when cooled under specified conditions. The grade of light diesel corresponds to its freezing point; that is, the freezing point of 0-grade light diesel is 0°C, that of -10-grade light diesel is -10°C, and so on. 27. What is distillation range? The distillation range refers to an indication of the quantity and temperature of a petroleum product that can be distilled within a certain temperature range. The distillation range is an important indicator for ensuring that diesel fuel evaporates and combusts rapidly in the engine combustion chamber. Full distillation range of light diesel: 160–365℃ ； Heavy diesel is used in low-speed diesel engines, where there is sufficient time for atomization and evaporation; strict requirements are not imposed on the boiling range, which is generally between 250–450°C. Currently, mixed fuel oils are being used in medium and low-speed large and medium-sized diesel engines. 28. What is density? Density is the simplest and most commonly used physical parameter for oil and its products. The density of crude oil (at 20°C) is approximately 0.7–1 kg/L. Oil with a high content of aromatic hydrocarbons, resins, and asphaltenes has the highest density; oil with a high content of naphthenes has an intermediate density, while oil with a high content of alkanes (paraffin hydrocarbons) has the lowest density. 29. What is the freezing point? Also known as the solidification point, it is the highest temperature at which engine oil ceases to flow. The freezing point can be determined as follows: Place the engine oil in a glass test tube and cool it continuously until, when the tube is tilted at 45°, the oil level remains unchanged for 1 minute; this temperature is the freezing point of that engine oil. 30. What is pour point? The pour point is the lowest temperature at which a petroleum product begins to flow, after being cooled under specified test equipment and conditions until it no longer flows, and then gradually heated up. Petroleum products with higher wax content have a higher pour point; gums and asphaltenes can lower their pour point. A small amount of water can cause the pour point of low-pour-point oils to rise. The pour point is 1~3°C higher than the freezing point. 31. What is the flash point? The lowest temperature at which a liquid oil produces flammable gases is called its flash point. The lower the flash point, the more volatile the oil is. The flash point can be determined using the following method: Pour the engine oil into a crucible in a wind-protected, dark area, heat the crucible, insert a thermometer into the oil, and at a temperature about 10°C below the flash point, ignite the oil using an ignition source at a distance of 8–10 mm above the oil surface; if the oil catches fire within 3 seconds, then the temperature of the oil at that moment is the flash point. 32. What is the cetane number? The cetane number is an indicator of the auto-ignition property of diesel when it burns in a diesel engine. The cetane number of pure n-hexadecane is usually set at 100, while that of pure α-methylnaphthalene is set at zero. By mixing them in various proportions, standard fuels with different anti-knock properties, having cetane numbers ranging from 0 to 100, can be obtained. These standard fuels are then compared with the diesel fuel under test on a single-cylinder test engine of a specified design. 33. What is moisture? Moisture refers to the percentage of water content in engine oil relative to the total weight of the oil. Water in engine oil not only causes rust on metal surfaces but also causes the oil to emulsify, thereby reducing its lubricating properties. To determine whether the engine oil contains water, a small amount of white powdery anhydrous copper sulfate can be added to the oil. If the copper sulfate changes from white to blue and settles at the bottom of the oil, it indicates that the oil contains water. 34. What are water-soluble acids and bases? Acids and bases in engine oil that can dissolve in water are known as water-soluble acids and bases. They are highly corrosive to engine oil components; therefore, such substances must not be present in engine oil. For more information on oils, oil-related data, and oil blending techniques, please follow the WeChat official account \"Oil Circle\" with the ID ypq0910. The method to determine whether engine oil contains water-soluble acids and bases is as follows: pour equal amounts of engine oil and distilled water into a glass test tube, heat the mixture while stirring for 1 minute to separate the oil from the water. Add 2-3 drops of a 1% phenolphthalein solution to the water; if the water turns red, it indicates the presence of water-soluble alkalis in the engine oil ； Add 2-3 drops of methyl orange solution to the water; if the water turns red, it indicates the presence of water-soluble acids in the engine oil ； Two reagents are added; if the water does not change color, it indicates that the engine oil is neutral. 35. What is the acid value? The acid value of an oil is the number of milligrams of potassium hydroxide required to neutralize 1 gram of that oil; it is an indicator that shows whether the oil is acidic or not. A simple way to determine whether there is an acid value in engine oil is to soak a copper plate in the oil for 2-3 days; if the copper plate turns green, it indicates the presence of acid value in the oil. 36. What is viscosity? Viscosity is a measure of a fluid’s viscosity; it represents the resistance to flow caused by internal friction within the fluid. High viscosity indicates high internal friction; the greater the molecular weight, the more carbon-hydrogen bonds there are, and thus the greater this force becomes. Viscosity is decisive for various lubricants in terms of quality identification and application determination, as well as for the combustion performance and efficiency of various fuel oils. At the same distillation temperature, petroleum products with alkanes as their main components have low viscosity and good viscosity-temperature behavior, that is, a high viscosity index; in other words, the change in viscosity due to temperature variations is small ； Oils with a higher content of naphthenic (or aromatic) components have higher viscosity, that is, they exhibit poorer viscosity-temperature behavior ； Oils with higher levels of gums and aromatics have the highest viscosity and the worst viscosity-temperature behavior, that is, the lowest viscosity index. Viscosity is commonly expressed as dynamic viscosity, with the unit of mm2/s. Heavy fuel oil has high viscosity; preheating it to a dynamic viscosity of 18–20 mm2/s (at 40°C) facilitates uniform fuel injection by the injectors. 37. The meaning of the octane number figure: Octane number is determined by setting the octane value of isooctane at 100 and that of n-heptane at 0. In standard engine tests, any gasoline is compared with these reference fuels; if the level of knocking produced by a particular gasoline in an engine is identical to that produced by a mixture of 98% isooctane and 2% n-heptane, then the octane number of that gasoline is deemed to be 98.