A reminder of common sense; please refrain from criticizing if you disagree.

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I. Diesel is a type of oil product obtained from the refining of petroleum. It is composed of a mixture of different hydrocarbons. Its main components are alkanes, cycloalkanes, or aromatics with 9 to 18 carbon atoms. Its chemical and physical properties lie between those of gasoline and heavy oil; its boiling point ranges from 170°C to 390°C, and its specific gravity is 0.82–0.845 kg/l. Diesel can be used as fuel for vehicles such as cars, tanks, airplanes, tractors, and railway vehicles, as well as for other mechanical devices; it can also be used for power generation and heating. Diesel is the fuel for compression-ignition engines (i.e., diesel engines), and it is also one of the most widely used petroleum products. Due to their higher thermal efficiency, greater power output, lower fuel consumption, and improved cost-effectiveness compared to gasoline engines, diesel engines are being used more and more widely. It is primarily used as power for tractors, large vehicles, diesel locomotives, as well as construction and agricultural machinery. Diesel is a complex mixture of hydrocarbons with about 10–22 carbon atoms. It is primarily composed of diesel fractions produced through processes such as crude oil distillation, catalytic cracking, hydrocracking, visbreaking, and coking. The density range for standard diesel according to national specifications is typically 0.83 to 0.855, with different densities for various grades. For example: 0# diesel has a density of 0.835, +10# diesel has a density of 0.85, +20# diesel has a density of 0.87, –10# diesel has a density of 0.84, –20# diesel has a density of 0.83, –30# diesel has a density of 0.82, and –35# diesel also has a density of 0.82. Generally, the density of diesel is taken as 0.84; thus, one ton of diesel is approximately equivalent to 1190 liters. Light diesel No. 0 – suitable for use in high-speed diesel engines equipped with preheating systems. Light diesel No. 5 – suitable for use in areas where the minimum temperature, with a risk level of 10%, is above 8°C. Light diesel No. 0 – suitable for use in areas where the minimum temperature, with a risk level of 10%, is 4°C. Light diesel -10 – suitable for use in areas where the minimum temperature, with a risk level of 10%, is above -5°C. Light diesel -20 – suitable for use in areas where the minimum temperature, with a risk level of 10%, is above -14°C. II. Differences between non-standard diesel and Changchai diesel: Atmospheric pressure diesel is the diesel fraction obtained from the atmospheric distillation column in refineries; it contains a higher amount of unsaturated hydrocarbons. Atmospheric diesel is the diesel fraction obtained from the atmospheric distillation column in refinery vacuum distillation processes; it contains a high level of unsaturated hydrocarbons, has poor stability, tends to change color and evaporate easily, and has a low density. Catalyzed diesel is diesel produced by catalytic devices; it has a specific gravity of not less than 0.89, poor stability, and a low cetane number, so it cannot be used directly in vehicles. It is mainly used for blending with atmospheric-pressure diesel. It can be used on large machinery. It has poor quality, is prone to discoloration and volatilization, and has a low density. Catalyzed diesel is diesel produced by catalytic devices; it has a specific gravity of not less than 0.89, poor stability, and a low cetane number, so it cannot be used directly in vehicles. It is mainly used for blending with atmospheric-pressure diesel. It can be used on large machinery. So-called non-standard fuels refer to blended oils that are not produced in regular refineries and do not meet the **required standards for clean gasoline and diesel. Its origin lies mainly in fuels that are directly blended by individual gas stations using chemical materials such as naphtha, aromatics, and MTBE, or in gasoline with a lower octane rating to which MTBE is added in order to raise its octane level to meet the standards for 90-octane, or even 93-octane and 97-octane gasoline, so that it can be sold as high-octane fuel. Since the cost of using this non-standard oil is much lower than that of purchasing regular oil, some individual gas stations take the risk of doing so in order to achieve higher profits. III. How to calculate the specific gravity of diesel? The density and flowability of diesel change with temperature. The standard density is as follows: No. 0 light diesel, which is also used in vehicles, has a specific gravity of 0.84–0.86 relative to water at 20 degrees Celsius. One kilogram of diesel is approximately 1.162–1.190 liters, while one liter of diesel is about 0.84–0.86 kilograms. Light diesel is classified into three grades based on quality: high-quality, first-grade, and qualified. It is also divided into six grades according to its freezing point: No. 10, No. 0, No. -10, No. -20, No. -35, and No. -50. Light diesel with No. 10 rating means its freezing point is not higher than 10°C, and the same logic applies to the other grades. Light diesel is used as fuel for diesel vehicles, tractors, and various high-speed diesel engines (with speeds over 1000 r/min). Different grades of light diesel are selected depending on the temperature, region, and season; lower temperatures require light diesel with a lower freezing point, while higher temperatures call for light diesel with a higher freezing point. Heavy diesel is used for medium and low-speed engines (with speeds below 1000 r/min). The fuel for diesel engines is generally classified into three grades based on its freezing point: 10, 20, and 30. The lower the engine speed, the higher the freezing point of the heavy diesel that should be used. Density: (820 kg/m3–860 kg/m3); therefore, the specific gravity is: 0.82–0.86 ± 0.2. IV. Various Questions and Answers 1. What are the differences between ordinary diesel and hydrogenated diesel in terms of properties and areas of use? Answer 1: Ordinary diesel is produced through atmospheric distillation; it contains high levels of sulfur, nitrogen, and oxygen, as well as a high amount of olefins. It changes color after standing for a short period of time. If used in vehicles, it can reduce the vehicle’s service life and cause significant pollution to the atmosphere. Hydrogenated diesel has lower levels of sulfur, nitrogen, oxygen, and olefins, offering better stability; it can be stored for long periods of time, and it also meets environmental requirements. In some hydrogenation units, a small amount of cracking agent is present, which can affect the dew point of diesel, lowering both its dew point and cold filter plugging point. The cetane number of coker diesel is generally around 50, that of Changchai diesel is around 45, and that of Cuichai diesel is around 35. Answer 2: Based on the distribution characteristics of diesel cetane numbers, straight-run diesel has a high content of alkanes and thus a high cetane number ； Catalytically processed diesel contains higher levels of isoparaffins and olefins compared to straight-run diesel; therefore, its cetane number is lower than that of straight-run diesel ； Coker diesel contains higher levels of olefins and aromatics than catalytic diesel, so its cetane number is significantly lower. Diesel refined by catalytic hydrogenation has an increased cetane number, as the olefins in it are converted into alkanes and the aromatics into naphthenes. Answer 3: Ordinary diesel has a high sulfur content; many of its components have a sulfur level of over 2000 PPM. The sulfur content in hydrogenated diesel can be reduced to very low levels; currently, a level of 800–1000 PPM is sufficient, after which it can be blended with other components. 2. The color of the diesel produced through hydrogenation refining varies (this unit carries out hydrogenation on a mixture of diesel and wax oil; the diesel obtained is a mixture of conventional diesel and catalyzed diesel) ； Wax oil is catalytic wax oil. When only diesel (either regular diesel or a mixture of regular diesel and accelerated diesel) is processed, the refined diesel is light yellow; when diesel is mixed with wax oil, the refined diesel is white. The distillation column of the unit is designed as a floating valve tray column with a total of 38 trays. The feed enters at the 8th tray, mid-column reflux is taken out at the 24th tray and sent back to the 27th tray, and diesel is also extracted at the 24th tray. (It is designed for three-stage distillation: wax oil comes from the bottom of the column, diesel from the middle section, and naphtha from the top.) The control parameters for diesel remain the same, yet the color of the output varies, which is quite puzzling. Please help analyze this issue ? ) Answer 1: The data provided by the original poster is incomplete; based on my analysis, it might be related to the reaction temperature. The reaction temperature for producing diesel fuel alone should be nearly 30 degrees lower than that for producing a mixture of diesel fuel and wax, which leads to changes in the content of basic nitrogen in the diesel product. When producing blended oil, due to the high reaction temperature, the content of basic nitrogen in diesel is low, resulting in a better color; diesel produced by hydrocracking processes is almost colorless and transparent. Answer 2: Alkaline nitrogen is the key factor affecting diesel color! ! ! An analysis of the alkaline nitrogen content in the product must be conducted, and the answer will naturally become clear! ! Answer 3: The color of the oil is related to the nitrogen content in impurities. The original poster didn’t clarify a few points; one of them is whether the processing load is the same Second, is the diesel pour point the same? When processing wax oil, the freezing point of the raw material rises again. To maintain the same freezing point, distillation separation is the only option if there is no dewaxing catalyst. Pay attention to changes in the yields of diesel and wax oil; I believe that catalytic diesel contains high levels of impurities, making it difficult to ensure a good refining quality, and as a result, the diesel has a dark color.