Cetannivå

Cetannivå, known in English as the cetane number, is a measure of the ignition quality of diesel fuel. It expresses how readily the fuel auto-ignites in a diesel engine under compression. In general, a higher cetane number indicates faster and more uniform ignition, while a lower number can lead to longer ignition delays, rough running, and higher emissions.

The cetane number is determined in standardized laboratory tests, most commonly using methods such as ASTM D613. In this approach, the ignition delay of the test fuel is compared to reference fuels with known cetane values. In practice, many fuels are also described by a cetane index, an estimated value derived from properties like distillation and density when a direct CN measurement is not available.

Several factors influence cetannivå. The choice of feedstock and refining process, sulfur content, and the presence of additives all affect CN. Biodiesel blends (FAME) often have lower CN on average than pure petroleum diesel, although formulations can be adjusted to meet specifications. Cetane improvers, such as certain nitrates or other additives, are used to increase CN and improve starting, combustion quality, and emissions.

Standards and market practices specify minimum cetane numbers for diesel fuels in different regions, with industry testing guiding quality control and fuel specification. The cetane number is an important parameter for engine designers and operators, affecting cold-start performance, combustion noise, efficiency, and emissions.