Regan Brown
The cetane number (CN) is a measure of diesel fuel quality and performance, specifically indicating the combustion speed of the fuel and the compression needed for ignition. It is an important factor in determining the quality of diesel fuel, with higher numbers indicating better fuel performance. The CN scale ranges from 0 to 100, with pure cetane, a clear, colourless hydrocarbon, having a cetane rating of 100. The standard cetane number for diesel fuel varies across different regions, with a minimum of 40 in North America and a minimum of 46 in the European Union, Iceland, Norway, and Switzerland.
| Characteristics | Values |
|---|---|
| Definition | The cetane number (CN) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. |
| Scale | The scale for measuring CN ranges from 0 to 100, with higher numbers indicating better ignition properties. |
| Measurement | The CN is measured using a prototype CFR single-cylinder diesel engine, which varies the compression ratio until maximum knock is achieved. |
| Standards | ASTM D613 (ISO 5165) for the CFR engine, D6890 for the IQT, and D7170 for the FIT. |
| Fuel Quality | Higher CN ratings indicate better fuel quality, with improved combustion, engine performance, and reduced emissions. |
| Engine Performance | CN affects engine performance parameters such as combustion, stability, drivability, white smoke, noise, and emissions of CO and HC. |
| Fuel Economy | Higher CN fuels have increased fuel economy due to faster combustion and improved power output. |
| Ignition Delay | CN measures ignition delay, with higher CN fuels having shorter delays, resulting in more complete combustion and reduced buildup in the engine. |
| Additives | Cetane improvers are additives that increase the CN of diesel fuel, improving its combustion and performance. |
| Regional Standards | Standards vary globally; in Europe, a minimum CN of 46 is required, while in North America, the minimum is 40, and California requires a minimum of 53. |
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What You'll Learn
Cetane number measures the delay in ignition time
The cetane number (CN) is a measure of a fuel's ignition delay, or the time period between the start of injection and the first identifiable pressure increase during combustion. In other words, it measures the delay in ignition time. A higher CN indicates a shorter ignition delay, meaning the fuel ignites more quickly and easily due to compression. This results in improved fuel efficiency, fewer emissions, and better power output.
The CN is an important factor in determining the quality of diesel fuel, with higher CNs generally indicating better fuel combustion and engine performance. It plays a similar role for diesel as the octane rating does for gasoline. While a good octane rating means a fuel doesn't ignite too soon, a good CN means a fuel ignites as soon as possible. This is because diesel engines rely on compression ignition, while gasoline engines attempt to resist any ignition due to compression.
The CN of diesel fuels is typically measured using ASTM D613, which involves a prototype CFR single-cylinder diesel engine running under variable compression ratios until maximum knock is measured. The fuel is then rated against mixtures of standard hydrocarbons with known compositions, specifically n-hexadecane (cetane) and 2,2,4,4,6,8,8-heptamethyl-nonane (isocetane). The CN is calculated as the volume-weighted average of these two hydrocarbons that would result in the same ignition delay as the test sample.
The CN required for diesel fuel can vary depending on the region and the specific application. In North America, most states have adopted ASTM D975 as their diesel fuel standard, with a minimum CN of 40. In Europe, the minimum CN has increased over time, reaching 40 in 2000 and 51 under the EN 590 standard in 2001. Modern highway diesel engines typically require fuel with a CN ranging from 45 to 55, while premium diesel fuels can have CNs as high as 60 or even higher.
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Cetane number indicates the combustion speed of diesel fuel
The cetane number (CN) is an indicator of the combustion speed of diesel fuel. It plays a similar role for diesel as octane rating does for gasoline. The CN is an important factor in determining the quality of diesel fuel, but not the only one. Other measurements of diesel fuel's quality include energy content, density, lubricity, cold-flow properties, and sulfur content.
The cetane number of a fuel is defined by finding a blend of cetane and isocetane with the same ignition delay. Cetane has a cetane number defined to be 100, while isocetane's measured cetane number is 15. Once the blend is known, the cetane number is calculated as a volume-weighted average, rounded to the nearest whole number, of cetane's 100 and isocetane's 15. The higher the cetane number, the better the fuel burns within the engine of a vehicle.
The cetane rating of a specific diesel mixture is based on how much cetane—a clear, colorless hydrocarbon that ignites under high pressure—is in the fuel. Pure cetane represents the highest purity of diesel fuel possible and thus has a cetane rating of 100. The higher a fuel's cetane number, the quicker it ignites—and that carries a variety of benefits for diesel equipment. From increased fuel economy to fewer emissions to better power output, fast combustion is key to a diesel engine's performance.
The cetane number is the most significant property of diesel fuels affecting engine performance and emissions. Cetane number varies with hydrocarbon types present in diesel fuels. Normal paraffins have high cetane numbers that increase with carbon number. Isoparaffins have a wide range of cetane numbers, from about 10 to 80. Biodiesel has a higher cetane number than conventional diesel fuel, resulting in higher combustion efficiency and smoother combustion.
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Cetane number is an indicator of fuel quality
The cetane number (CN) is an important indicator of diesel fuel quality. It measures the combustion speed of diesel fuel and the compression needed for ignition. A higher cetane number indicates better fuel quality, with improved combustion and quicker ignition, resulting in improved engine performance, reduced emissions, and better power output. The CN is calculated by determining the blend of cetane and isocetane that results in the same ignition delay. The standard test method for measuring the CN of diesel fuel is ASTM D 613, using a Cooperative Fuel Research (CFR) engine.
The CN plays a similar role for diesel fuel as the octane rating does for gasoline. While a higher octane rating indicates that gasoline can resist ignition due to compression, a higher cetane number means that diesel fuel ignites more easily under compression. This is because diesel engines rely on compression ignition, without the use of a spark plug, so a shorter delay between fuel injection and ignition is desirable.
The CN of diesel fuel can range from 0 to 100, with pure cetane having a CN of 100, indicating the highest purity and quality of diesel fuel. The minimum acceptable CN for diesel fuel varies by region. In North America, the minimum CN is typically 40, while in Europe, the minimum CN is 46 according to the EN 590 standard. Premium diesel fuels can have CNs as high as 60 or more.
In addition to the CN, other factors that contribute to diesel fuel quality include energy content, density, lubricity, cold-flow properties, and sulfur content. The volatility characteristics of diesel fuel can also be expressed in terms of the temperature at which successive portions are distilled under controlled heating. Biodiesel, for example, has a high cetane number but also high viscosity, which can lead to incomplete combustion and increased emissions. Therefore, it is important to consider multiple factors when evaluating diesel fuel quality.
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Cetane number is an important index for evaluating ignition behaviour
The cetane number (CN) is an important indicator of diesel fuel quality and engine performance. It measures the ignition delay of the fuel, or how long it takes for the fuel to ignite after being injected into the combustion chamber. A higher CN indicates a shorter ignition delay, which results in more complete fuel combustion and improved engine performance.
The CN is calculated by determining the blend of cetane (hexadecane, with a CN of 100) and isocetane (2,2,4,4,6,8,8-heptamethylnonane, with a CN of 15) that results in the same ignition delay as the fuel being tested. This process can be challenging as it requires a specialised diesel engine called a Cooperative Fuel Research (CFR) engine.
The CN is an essential factor in evaluating ignition behaviour as it directly impacts the performance and efficiency of diesel engines. Fuels with lower CNs tend to cause diesel knocking and increased emissions due to incomplete combustion. In contrast, fuels with higher CNs facilitate quicker ignition, leading to improved fuel efficiency, reduced emissions, enhanced engine power, and quieter engine operation.
The ideal CN range for diesel engines is generally between 40 and 55. However, the specific CN requirements may vary depending on geographical location and engine type. For example, in Europe, the minimum CN for diesel fuel was set at 40 in 2000, while in North America, most states have adopted a minimum CN of 40, with California requiring a minimum of 53.
Additionally, the CN of diesel fuel can be improved by using aftermarket additives known as cetane improvers. These additives enhance the fuel's combustibility, resulting in quicker ignition and improved engine performance. However, it is important to exercise caution when using these products due to the potential risks associated with their use.
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Cetane number is measured using ASTM D 613
The cetane number (CN) is a measure of the quality and performance of diesel fuel. It indicates the combustion speed of diesel fuel and the compression needed for ignition. The CN is an important factor in determining the quality of diesel fuel, but it is not the only factor. Other measurements of diesel fuel quality include energy content, density, lubricity, cold-flow properties, and sulfur content. The CN scale ranges from 0 to 100, with higher numbers indicating better fuel performance. Generally, diesel engines operate well with a CN from 48 to 50.
The cetane number is measured using ASTM D 613, which is a standard test method for determining the rating of diesel fuel oil in terms of an arbitrary scale of cetane numbers. ASTM D 613 uses a standard single-cylinder, four-stroke cycle, variable compression ratio, and indirect injected diesel engine. The test is run at a constant speed in a pre-combustion chamber-type compression ignition test engine. The resulting cetane number is calculated by determining the blend of cetane and isocetane that will result in the same ignition delay.
There are other methods for measuring the cetane number, such as the Ignition Quality Tester (IQT), which is a simpler and more robust approach, and the '4-point method', ASTM D4737, which is based on density and 10%, 50%, and 90% recovery temperatures. However, ASTM D 613 is the industry standard for measuring the cetane number using the CFR engine.
The cetane number is important for diesel equipment owners because it impacts the performance of their engines. Running equipment on diesel with an insufficient cetane number can result in rough operation, lost efficiency, excessive wear, and other issues. By understanding the cetane number of their fuel, equipment owners can enhance engine performance, improve fuel efficiency, reduce emissions, and improve power output.
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Frequently asked questions
The standard cetane number for diesel fuel depends on the region. In North America, the minimum cetane number is 40, with typical values in the 42-45 range. In Europe, the standard for diesel sold in the European Union, Iceland, Norway, and Switzerland is a minimum cetane index of 46 and a minimum cetane number of 51.
The cetane number (CN) is an indicator of the combustion speed of diesel fuel and the compression needed for ignition. It is an important factor in determining the quality of diesel fuel, with higher numbers indicating better ignition properties and improved engine performance.
A higher cetane number results in quicker ignition of the fuel, leading to improved fuel efficiency, reduced harmful emissions, better power output, and quieter engine operation. It also reduces the buildup of non-ignited fuels inside the combustion chamber, resulting in more complete fuel combustion.
