What is the cetane number of diesel

High-speed diesel engines require the diesel engine to quickly form a uniform mixture with the air after injection into the combustion chamber, and immediately burn automatically, so the fuel is required to be easy to spontaneous combustion. The time from the beginning of fuel injection into the cylinder to the start of ignition is called the ignition lag or ignition lag. If the spontaneous ignition point of the fuel (the temperature at which it can ignite automatically in the presence of air) is low, the ignition delay period is short, that is, the ignition performance is good. Cetane number is generally used as an index to evaluate the spontaneous combustion of diesel oil.

Cetane number refers to the volume percentage of n-cetane contained in a standard fuel, equal to the measured spontaneous combustion of diesel oil. Ignition performance of diesel engine is an important index to measure ignition performance of diesel engine. The higher the cetane number, the better the ignition performance of diesel, the shorter the ignition delay period, the uniform combustion and the smooth start of the engine. Low cetane number indicates difficult combustion, long ignition delay and rough engine operation. However, if the cetane number is too high, a small amount of black exhaust smoke will be produced due to partial incomplete combustion.

The cetane number is determined under specified conditions on a laboratory standard single-cylinder diesel engine. Diesel oil with high cetane number, easy to start, uniform combustion, large output power; Low cetane number, slow ignition, unstable work, easy to knock, generally used for high-speed diesel engine light diesel, cetane number of 40 ~ 55 is appropriate; The cetane number of heavy diesel for medium and low speed diesel engines can be as low as 35. The cetane number of diesel oil is related to its chemical composition: the cetane number of normal alkane is higher; The aromatics have low cetane number. The isomer and the cycloalkanes are in the middle. The cetane number of diesel oil can be increased by adding additives. The flammability of diesel oil can also be expressed by the diesel oil index, which is calculated from the formula of the aniline point and the relative density of diesel oil. Another way to characterize diesel fuel flammability is the cetane index, which is calculated from the relative density and 50% distillation temperature according to the prescribed formula.

Appropriate addition of cetane number improver can increase the cetane number of diesel oil, but the sensitivity of different oil components to the improver is different. The sensitivity of various diesel oil to cetane number improvers is not linearly related to the addition amount, but gradually tends to zero after the addition amount reaches a certain degree. When additives are added to diesel oil, the flash point of diesel oil will be affected, and the cetane number of diesel oil after adding improver will decay after storage for a period of time. Therefore, it is recommended to keep cetane number above 46 when using cetane number improver to minimize storage period.

With the increasing demand of locomotive fuel oil and the limitation of economic benefit of existing fuel oil, a new, safe and economical cetane number improver is urgently needed. Compared with diesel oil, the cetane number improver has lower viscosity, lower freezing point
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