Octane vs. Cetane

Gasoline vs. diesel engines

• Gasoline engines 
• the ignition temperature is very low. 
• So, it has the property of easily exploding with the heat generated when the piston compresses. 
• If the piston explodes without sufficiently compressing the fuel, the engine can of course not run normally. 
• So octane is a substance added to prevent the fuel from exploding before it reaches the specified compression ratio.
• Diesel engines 
• It is the opposite; Diesel does not ignite even if you put a lit matchstick. 
• It is a fuel with a high ignition point, and therefore, the desired ignition temperature can be reached only by applying high pressure. 
• Sometimes the explosion does not occur even when the desired pressure is applied; this happens mainly when the temperature is low or the quality of the fuel itself is poor. 
• Cetane, as opposed to octane, serves to lower the ignition point of diesel fuel.

Common features of octane rating and cetane rating

• The higher the number, the better the fuel burns within the engine of a vehicle. 
• The difference is that octane rating rates gasoline whereas cetane rates diesel.

Octane rating (or octane number)

• A measurement of the quality or performance of gasoline
• The higher the number, the better the fuel burns within the engine of a vehicle. 
• Higher performance vehicles require fuels with a higher octane rating.
• The octane rating represents how well a fuel can resist pre-ignition due to compression—ensuring the fuel ignites only from a spark from the spark plug.
• Gasoline engines which attempt to resist any ignition due to compression

Cetane rating (or cetane number)

• Measures the delay in the ignition time of the fuel. 
• In other words, it is how minimized the delay is between when the fuel is injected into the chamber and when the combustion begins. 
• Diesel engines rely on this compression ignition and thus no spark is involved. 
• A higher cetane number simply means the time between when the fuel is injected into the combustion chamber and when the fuel ignites is minimized.
• This shorter delay time results in more complete fuel combustion.
• Diesel fuel has a higher explosive power than gasoline, so it is a lot heavier as the main parts of the engine are made stronger to withstand the explosive power. 
• For this reason, the engine speed is lower than that of gasoline, but the efficiency of the fuel itself is higher than that of gasoline, and it has a strong explosive power, so it has been mainly used in trucks and SUVs.