The cetane number is one of the most important performance characteristics of diesel fuels which indicates the ignition lag of blended diesel fuel. The higher the cetane number is, the faster the fuel will ignite and the more completely it will burn.
Standard diesel engines operate on diesel fuels with a cetane number ranging from 40 to 55 units. The reduction of the cetane number usually results in ignition lag. As a result, the pressure in the combustion chamber is growing faster, and the wear rate of engine will be increased. The cetane number of the standard types of fuel is between 40-45 units. While that of high-quality fuel is between 45-50 units. High-quality diesel fuel (premium) is light and contains more flammable factions. It is therefore, desirable to use such fule to start cold engines. Additionally, the premium fuel emits less smoke while combusted. It is due to the increased ratio of hydrogen to carbon in light factions.
The increased cetane number (more than 60 units) results in a range of negative factors such as: (1) the combustion efficiency is reduced; and (2) fuel consumption and smokiness are increased.
In part, the cetane number is defined by the amount of such components as paraffins, naphthenes, and olefins. The paraffins are considered to be a desirable component of oil product due to such performance characteristic as self-ignition in cold weather.