【Basic Knowledge Activity】Professional \"Basic Knowledge\" in the petrochemical industry: What are the indicators used to evaluate the ignition performance of diesel?

The index used to evaluate the ignition performance of diesel is the cetane number. Cetane number refers to the volume percentage of hexadecane in a standard fuel with the same ignition properties as diesel ； Standard fuel refers to a mixture of n-hexadecane and a-methylnaphthalene in different volume ratios. It is an important quality indicator for the combustion performance of diesel. Diesel with too low a cetane number can cause knocking in diesel engines, result in excessive black smoke, and increase engine power consumption, mechanical wear, and fuel usage ； Diesel with a too high cetane number has a low auto-ignition temperature, causing it to start burning before it can mix fully with air; although this does not lead to rough operation of the diesel engine, it does result in increased fuel consumption. Problems such as power drop. For high-speed diesel engines with a normal rotational speed of over 1000 r/min, a cetane number of 40–50 is appropriate ； For medium and low-speed diesel engines with a rotational speed of less than 1000 r/min, a cetane number of 30–40 is appropriate. National standards: The cetane number of diesel fuels of grades 10, 5, 0, and -10 must be at least 49; that of grade -20 must be at least 46, and that of grade -35 must be at least 45.

The index used to evaluate the ignition performance of diesel is the cetane number. The cetane number is a measured value obtained by determining the ignition performance of diesel under specified test conditions using a standard single-cylinder tester, and comparing it with the ignition performance of a standard fuel of a certain composition (a mixture of hexane, assigned a cetane number of 100, and α-methylnaphthalene, assigned a cetane number of 0). When the ignition property of the sample is the same as that of the standard fuel used for comparison under the same conditions, the volume percentage of hexane in the standard fuel is the cetane number of the sample. The higher the content of n-alkanes in diesel, the higher its cetane number, as well as its combustion performance and cold-startability; however, its boiling point and freezing point will increase. Cetyl 20 value = 442.8–462.9d4.

Cetane number: The cetane number refers to the volume percentage of n-hexadecane in a standard fuel whose auto-ignition properties are comparable to those of diesel. Standard fuel is a mixture of n-hexadecane and 2-methylnaphthalene prepared in different volume percentages. Among them, hexadecane has good spontaneous ignition properties, so its cetane number is set at 100, while 2-methylnaphthalene has poor spontaneous ignition properties, so its cetane number is set at 0. There are also those that use 2,2,4,4,6,8,8-heptamethylnonane in place of 2-methylnaphthalene, with a cetane number of 15 set for it. The cetane number determination is carried out under specified conditions on a standard laboratory single-cylinder diesel engine. Diesel with a high cetane number starts easily, burns evenly, and delivers high power ； A low cetane number results in slow ignition, unstable operation, and a higher tendency to knock. Light diesel, commonly used in high-speed diesel engines, should have a cetane number of 40–55 ； The cetane number of heavy diesel used in medium and low-speed diesel engines can be as low as below 35. The cetane number of diesel is related to its chemical composition; n-alkanes have the highest cetane number, aromatics have the lowest, while isoparaffins and cycloparaffins fall in between. Once the cetane number exceeds 50, further increases have little effect on reducing the ignition delay period of diesel ； Conversely, when the cetane number is higher than 65, the ignition delay period is too short; the fuel ignites before it can mix evenly with the air, resulting in incomplete combustion. Some of the hydrocarbons undergo thermal decomposition to produce free carbon particles, which are then expelled with the exhaust gases. This leads to black smoke from the engine, increased fuel consumption, and reduced power output. Diesel with a high cetane number has a low auto-ignition temperature; during the ignition delay period, high-concentration peroxides are likely to form in certain areas of the combustion chamber, serving as ignition centers. Therefore, the ignition delay period is short, the heat generation is uniform throughout the combustion process, the pressure rise is gradual, the engine runs smoothly, and it exhibits good performance. Diesel with a high cetane number can prevent rough operation of the diesel engine, which reduces the additional load on the crankshaft bearings. This is beneficial for the lubrication of the crankshaft in high-speed, heavy-load diesel engines, helping to avoid bearing damage. Diesel with a high cetane number has a low auto-ignition temperature, allowing it to ignite and burn even at lower temperatures in the cylinder; as a result, it also exhibits better starting performance

The indicator used to evaluate the starting performance of diesel is the cetane number @Guan Gongyu @Hei Ren Yu Zhou @Ma Yi Yi Yi @Zhang Jun_nLlUg

The index used to evaluate the ignition performance of diesel is the cetane number.

The index used to evaluate the ignition performance of diesel is the cetane number. The cetane number is a measured value obtained by determining the ignition properties of diesel under specified test conditions using a standard single-cylinder tester, and comparing them with those of a standard fuel of a certain composition (a mixture of hexane, assigned a cetane number of 100, and α-methylnaphthalene, assigned a cetane number of 0). When the ignition property of the sample is the same as that of the standard fuel used for comparison under the same conditions, the volume percentage of hexane in the standard fuel is the cetane number of the sample. The higher the content of n-alkanes in diesel, the higher its cetane number, as well as its combustion performance and cold-startability; however, its boiling point and freezing point will increase.