Cetane improvers are additives to diesel fuel that, when added at low concentrations, boost the cetane number of the blend.

The most common cetane improver is Octyl Nitrate (EHN or 2-Ethylhexyl nitrate). EHN decomposes rapidly in the high temperatures of the combustion chamber, yielding products that help initiate combustion and shorten the ignition delay period. EHN is typically added in the concentration range of 0.05-0.4 mass percent. The effect on cetane increases with a higher cetane base blend. Typical improvement is 3-10 cetane numbers. A drawback of EHN is that it can decrease thermal stability, requiring the use of a stability additive.

DTBP (di-teritary butyl peroxide) is another cetane improver. It is used less than EHN as it is less effective at increasing cetane number. However, it has the advantage of not contributing to degradation of thermal stability.