The differences between cetane number and octane number are as follows :
| Cetane number | Octane number |
|---|---|
| Cetane number of a given diesel under test is defined as the percentage by volume of cetane in mixture of cetane and ∝-methyl naphthalene which exactly the knocking characteristics of the diesel under test. | Octane number of given petrol under petrol under test is defined as the percentage by volume of is octane in mixture of is – octane and n-heptagon which exactly matches the knocking characteristics of the petrol under test . |
| Cetane number indicates knocking characteristics of diesel in diesel engine . | Cetane number indicates knocking characteristics of diesel in diesel engine . |
| Higher the cetane number of diesel lesser is the knocking in diesel engine. | Higher the octane number of petrol lesser is the knocking in petrol engine. |
| Higher cetane number is due to less compactness, double bonds, cyclic structure and branches in straight chain hydrocarbon . | Higher octane number is due to more compactness, double bonds, cyclic hydrocarbon . |
| Fuel having higher cetane number has lower octane number and cannot be used in petrol engines. | Fuel having octane number has lower cetane number and cannot be used in diesel engines. |
| The antiknock agents have high oxygen content. | The antiknock agents do not contain oxygen. |
| Doping agents provide nascent oxygen at higher temperature to increase combustion rate and cetane number | Doping agents undergo thermal degradation to form free radicals which reduce combustion rate increase octane number. |