Main Difference – Octane Number vs Cetane Number
A fuel is a compound that can convert chemical energy into heat energy. Fuels can release energy through burning. Fuel is available as solids, liquids or gases. The major sources of commercially available fuel are crude oil and natural gases. These sources are processed to obtain desirable hydrocarbons that can be used in automobiles. Octane number is a value used to rate the fuel’s resistance to knocking. Cetane number is a measurement of the ignition properties of a fuel. The main difference between octane number and cetane number is that octane number gives an idea about the performance of a fuel whereas cetane number gives an idea about the ignition of a fuel.
Key Areas Covered
1. What is Octane Number
– Definition, Importance, and Applications
2. What is Cetane Number
– Definition, Importance, and Applications
3. What is the Difference Between Octane Number and Cetane Number
– Comparison of Key Differences
Key Terms: Cetane Number, Crude Oil, Fuel, Natural Gases, Octane Number, Petroleum
What is Octane Number
Octane number is a measure of the performance of a fuel. It is also called the antiknock rate of fuel. When fuel is used in an engine, the engine will generate a knocking effect. In other words, the fuel can cause the engine to undergo knocking when burnt.
The octane number is given for a certain fuel based on the relative knocking. This knocking effect is rated based on the knocking of the fuel isooctane. Isooctane has a minimal knocking effect. Therefore, the octane number of isooctane is considered as 100. In contrast, the octane number of heptane is considered as 0. This is because heptane causes the maximum knocking when used in an engine.
Figure 1: Octane Numbers of Different Fuels
The octane number is equal to the percentage of the volume of isooctane present in the fuel. For example, octane 92 is the fuel that is composed of 92% of isooctane along with 8% of heptane. Therefore, if the octane number is high, it is a good fuel to be used in an engine.
What is Cetane Number
Cetane number is the measure of the delay of the ignition of a fuel. It is measured for diesel. A higher cetane number indicates a shorter ignition delay time, which means, it ignites quickly. A lower cetane number indicates a longer ignition delay time; this means, it ignites slowly. This delay time is the time taken by the diesel for its combustion.
Cetane is a colorless liquid. It is a hydrocarbon. It ignites easily under the compression. Therefore, it is given the cetane number 100. Other diesel types are given their cetane number with comparison to the ignition of cetane liquid.
Difference Between Octane Number and Cetane Number
Definition
Octane Number: Octane number is a measure of the performance of a fuel.
Cetane Number: Cetane number is the measure of the delay of the ignition of a fuel.
Importance
Octane Number: Octane number is important for predicting the knocking of an engine.
Cetane Number: Cetane number is important for predicting the ignition of an engine.
Application
Octane Number: Octane number is given for gasoline.
Cetane Number: Cetane number is given for diesel.
Comparison
Octane Number: Octane rating is done considering the octane number of isooctane as 100.
Cetane Number: Cetane rating is done considering the ignition of cetane.
Conclusion
Octane number and cetane number are very important in determining the best fuel that can be used for engines of automobiles. The main difference between octane number and cetane number is that octane number gives an idea about the performance of a fuel whereas cetane number gives an idea about the ignition of a fuel.
References:
1. “Octane number.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 2 Aug. 2013, Available here. Accessed 15 Sept. 2017.
2. Helmenstine, Anne Marie. “Octane Number Definition.” ThoughtCo, Available here. Accessed 15 Sept. 2017.
Image Courtesy:
1. “Brighton, MI Sunoco Ethanol-Free Pump Options” By 127driver – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “9796” (CC0) via PEXELS
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