Diesel fuel is generally a product of the primary distillation of crude oil and, until just a few years ago, its quality depended essentially on the characteristics of the crude itself and the type of distillation. In recent years there has been an increasing use of conversion plants, such as thermal and/or catalytic cracking or hydro-cracking, which, while remaining significant, has lessened the qualitative impact of the original crude base.
The average distillation range for diesel is between 160°C and 380°C. Diesel fuel is largely used to drive internal combustion engines with spontaneous ignition or for combustion in plants for civil heating purposes.
In the case of diesel engines, the diesel is injected into the combustion chamber where, when it reaches a determined temperature and pressure, it ignites on contact with air. Consequently, diesel fuel needs to have good combustion characteristics in order to limit the gap between injection and ignition. The cetane number refers to the ignition quality of diesel fuel.