Which of the following additives improves the cetane number of diesel?

The cetane number is a measure of the ignition quality of diesel fuel, indicating how quickly the fuel ignites after injection into the engine.

Higher cetane number means shorter ignition delay and better combustion efficiency in diesel engines.

Amyl nitrate is commonly used as a cetane improver because it decomposes easily under compression, helping in faster ignition of diesel fuel.

Ethyl mercaptan is mainly used as an odorant in LPG for leak detection and does not improve cetane number.

Naphthenic acid is associated with corrosion issues in petroleum refining and has no role in improving cetane number.

Tetraethyl lead is an anti-knock agent used in petrol (gasoline) to improve octane number, not cetane number.

Therefore, Amyl nitrate is the correct additive that improves the cetane number of diesel.