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Encyclopedia > Cetane number

Cetane number or CN is to diesel fuel what octane rating is to gasoline. It is a measure of the fuel's combustion quality. This article is about the fuel. ... Petrol (gasoline in the United States and Canada) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... Petrol (gasoline in the United States and Canada) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer) to release heat. ...


Cetane is an alkane molecule that ignites very easily under compression, so it was assigned a cetane number of 100. All other hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. The cetane number therefore measures how quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there are hundreds of components in diesel fuel, with each having a different cetane quality, the overall cetane number of the diesel is the average cetane quality of all the components. Hexadecane, also called cetane, is an alkane hydrocarbon with the chemical formula CH3(CH2)14CH3. ... An alkane in organic chemistry is a type of hydrocarbon in which the molecule has the maximum possible number of hydrogen atoms and so has no double bonds (they are saturated). ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ...


A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists auto-ignition and has a longer ignition delay period.


To measure cetane number properly is rather difficult, as it requires burning the fuel in a special, hard-to-find, diesel engine called a Cooperative Fuel Research (CFR) engine, under standard test conditions. For most practical purposes, people control quality using the Cetane Index, which is a calculated number based on the density and distillation range of the oil. There are various versions of this, depending on whether you use Metric or Imperial units, and how many distillation points are used. These days most oil companies use the '4-point method'.


There is very little actual cetane in diesel fuel. Diesel engines run just fine with a CN between 45 to 50. There is no performance or emission advantage when the CN is raised past 50; after this point, the fuel's performance hits a plateau.


Diesel at the pump can be found in two CN ranges: 40-46 for regular diesel, and 45-50 for premium. Premium diesel has additives to improve CN and lubricity, detergents to clean the fuel injectors and minimize carbon deposits, water dispersants, and other additives depending on geographical and seasonal needs.


  Results from FactBites:
 
Cetane number (Bruce Hamilton) (1164 words)
The cetane number is then determined by interpolation, and the higher the Cetane Number, the shorter the delay between injection and ignition.
The octane number of normal alkanes decreases as carbon chain length increases, whereas the cetane number increases as the carbon chain length increases.
The significance of the cetane number increases with the speed of the engine, and large, low speed diesel engines often only specify viscosity, combustion and contaminant levels, as Cetane Number requirement of the engine is met by most distillate and residual fuels that have the appropriate propeties.
Syntroleum - Specifications (1884 words)
A minimum cetane number of 40 is specified for diesel fuels in the United States and 50 in Europe, as well as most other parts of the world.
Such a high cetane number allows Syntroleum’s fuel to be effectively blended with lower-quality diesel fuel components to produce higher-quality fuels with positive economic benefits for the refining industry.
Yet, aromatics decrease the cetane number to the diesel fuel and have been identified as contributors of NOx and PM emissions, especially ploynuclear-aromatics.
  More results at FactBites »

 
 

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