Katerina Swanson
Cetane is a highly combustible chemical compound that occurs naturally in diesel fuel. It ignites under high pressure, leading to the combustion of the fuel. The cetane number (CN) is a measure of the combustion quality of diesel fuel during compression ignition. It plays a similar role for diesel as the octane rating does for gasoline. The higher the CN, the quicker the ignition, leading to a more complete combustion of the fuel. This results in smoother and quieter running engines, quicker engine starts, more power, and improved fuel economy. The CN of diesel fuel is influenced by the crude oil used and the refinery's process, and it can be improved by adding aftermarket additives. However, the use of these additives involves guesswork and inherent risk. The CN of diesel fuel is important for maintaining optimal engine performance and longevity.
| Characteristics | Values |
|---|---|
| Definition | Cetane is a chemical compound found naturally in diesel fuel. |
| Combustion Speed | The higher the cetane number, the faster the combustion speed. |
| Ignition Delay | The higher the cetane number, the shorter the ignition delay. |
| Engine Performance | Cetane number impacts engine performance, including fuel economy, emissions, power output, and engine health. |
| Measurement Scale | The cetane number scale ranges from 0 to 100, with 100 representing pure cetane. |
| Fuel Standards | Fuel standards vary by region, with minimum cetane number requirements ranging from 38 to 51. |
| Premium Diesel | Premium diesel fuels typically have higher cetane numbers, ranging from 47 to 70+. |
| Additives | Cetane improvers are additives used to increase the cetane number of diesel fuel. |
| Engine Maintenance | Using diesel with an inadequate cetane number can lead to reduced efficiency, engine wear, and other issues. |
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What You'll Learn
Cetane number (CN)
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 of 100, while isocetane has a cetane number of 15. Once the blend is known, the cetane number is calculated as a volume-weighted average, rounded to the nearest whole number.
The CN is an important factor in determining the quality of diesel fuel, but it is not the only one. Other measurements of diesel fuel quality include energy content, density, lubricity, cold-flow properties, and sulfur content. Diesel fuels typically have cetane ratings ranging from 40 to 55. For most engines, a rating of 50 or above is considered excellent, providing a smoother, quieter engine operation, quicker start-up, reduced emissions, and better performance, especially in cold weather.
The use of cetane-boosting additives can improve the CN of diesel fuel. However, the effectiveness of these additives may vary, and they may not always provide significant improvements in engine performance, fuel economy, or horsepower. It is important to consult a vehicle's manual, as some manufacturers recommend specific cetane ratings.
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The impact of CN on engine performance
The cetane number (CN) is a critical factor in diesel fuel's performance and emissions. It measures the delay in ignition time, indicating how quickly a fuel ignites under compression. A higher CN means shorter ignition delays, improved combustion, and better engine performance.
Secondly, CN influences the buildup of non-ignited fuels inside the combustion chamber. Higher CN fuels have shorter ignition delays, reducing the accumulation of unburned fuel. This, in turn, minimizes the risk of excessive wear and improves engine longevity.
Additionally, CN impacts fuel economy and emissions. Higher CN fuels tend to have improved fuel economy due to more complete combustion. They also produce fewer emissions, as lower CN fuels are associated with incomplete combustion, leading to increased gaseous and particulate exhaust emissions.
Moreover, CN affects the performance of high-speed diesel engines. Higher speed engines operate more effectively with higher CN fuels. This is because higher CN fuels have shorter ignition delays, which are better suited to the faster combustion cycles of high-speed engines.
Finally, CN can influence the cold-starting capabilities of diesel engines. Higher CN fuels tend to provide improved cold-starting performance, reducing the time and effort required to start an engine in colder conditions.
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How to improve CN
Cetane number (CN) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. A higher CN indicates that the diesel fuel will ignite more readily when sprayed into hot compressed air during the fuel injection cycle. This results in better starting performance, smoother engine operation, less engine noise, and fewer emissions.
If your diesel fuel’s CN isn’t high enough, there are options to boost it. One way is to use aftermarket additives known as cetane improvers. These are highly combustible chemical compounds designed to make fuels burn more quickly. However, the amount of guesswork involved in using these products makes them inherently risky. It can be difficult to tell the difference between a legitimate product and a harmful one.
A safer approach is to use a premium diesel fuel with a cetane improver already built in. Examples include Cenex Roadmaster XL and Cenex Ruby Fieldmaster, which are both terminally injected with the optimal level of cetane improver.
The industry standard for cetane improvers is 2-ethyl hexyl nitrate, which is effective at raising the diesel cetane rating without causing problems in the engine or harming engine materials. Other cetane improvers include nitrates, nitroalkanes, nitrocarbonates, and peroxides.
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The cost of improving CN
The cetane number (CN) of diesel fuel is a measure of its ignition quality and combustion speed. A higher CN indicates that the fuel will ignite more easily and burn more efficiently, leading to improved engine performance and reduced emissions.
The cost of improving the CN of diesel fuel can vary depending on several factors, including the type of crude oil used, the refining process, and the additives employed. Here are some key considerations regarding the costs of improving CN:
- Crude Oil Quality: The quality of crude oil used as a feedstock can impact the cost of improving CN. Refineries may incur higher costs if they use more challenging or lower-quality crudes that require additional processing to meet desired CN levels.
- Refining Processes: The refining process itself can affect costs. Implementing advanced refining techniques or technologies to improve CN may require significant capital expenditures and operational costs.
- Additives: Cetane improver additives, such as nitrates, nitroalkanes, nitrocarbonates, and peroxides, can be added to diesel fuel to increase its CN. These additives can vary in price, and their usage may depend on economic considerations. While additives offer a cost-effective way to enhance CN and engine performance, their effectiveness also relies on the quality of the base fuel.
- Market Dynamics: The market demand and pricing for diesel fuel with higher CN can influence costs. If there is a limited market for premium diesel with higher CN, the increased per-gallon cost of diesel with added cetane improvers may not be feasible for refiners or consumers.
- Equipment Maintenance: Running equipment on diesel with an insufficient CN can result in rough operation, decreased efficiency, and excessive wear and tear. This can lead to higher maintenance and repair costs for diesel equipment owners, making it essential to use diesel with an appropriate CN for their engines.
- Regulations and Standards: Diesel fuel standards and regulations, such as minimum CN requirements, can impact costs. For example, California diesel fuel has a minimum CN of 53, while Texas has implemented the TxLED program with a CN requirement of 48 or higher. Complying with these standards may influence the costs of diesel fuel production and distribution in different regions.
Improving the CN of diesel fuel can offer benefits such as enhanced engine performance, reduced emissions, and better fuel efficiency. However, the costs associated with achieving higher CN can vary based on the specific circumstances of the refining process, market conditions, and regulatory standards.
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The risks of low CN
Cetane number (CN) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It is an important factor in determining the quality of diesel fuel. The CN of diesel fuel ranges from 0 to 100, with 100 being the CN of pure cetane. The higher the CN, the better.
Fuels with low CN tend to cause diesel knocking and show increased gaseous and particulate exhaust emissions due to incomplete combustion. This can result in rough operation, lost efficiency, excessive wear, and more. Fuels with low CN also have longer ignition delays, requiring more time for the fuel combustion process to be completed. Hence, higher-speed diesel engines operate more effectively with higher CN fuels.
To improve the CN of diesel fuel, some people turn to aftermarket additives known as cetane improvers. These chemical compounds are highly combustible and are designed to make fuels burn more quickly. However, the use of these aftermarket products involves a lot of guesswork, making them inherently risky. It can be difficult to distinguish between legitimate products and harmful ones.
A safer approach to improving the CN of diesel fuel is to use Premium Diesel with a cetane improver already built in. Premium diesel fuels often use 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. For example, in North America, Neste MY Renewable Diesel has a CN of 70+.
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Frequently asked questions
Cetane number (cetane rating) (CN) is an indicator of the combustion speed of diesel fuel and compression needed for ignition. It is an important factor in determining the quality of diesel fuel. The scale for measuring cetane ranges from 0 to 100, and the higher the number, the better. Diesel fuels typically have cetane ratings ranging from 40 to 55.
Generally, diesel engines will operate better on fuels with cetane numbers above 50 compared to fuels with cetane numbers of the national average of 46. For most engines, a rating of 50 or above is considered excellent, providing a smoother, quieter engine operation, quicker start-up, reduced emissions, and better performance in cold weather.
Using diesel fuel with an inadequate cetane number can cause reduced efficiency, engine wear, and many other issues. Operating on low-cetane fuel often results in higher production of soot particulates, which forces the engine to consume more fuel to manage and expel these particulates.
