Cetane Number - Measuring Cetane Number - Cetane Index

Cetane Index

Another method that fuel-users control quality is by using the Cetane index (CI), which is a calculated number based on the density and distillation range of the fuel. There are various versions of this, depending on whether you use metric or Imperial units, and how many distillation points are used. These days most oil companies use the '4-point method', ASTM D4737, based on density, 10% 50% and 90% recovery temperatures. The '2-point method' is defined in ASTM D976, and uses just density and the 50% recovery temperature. This 2-point method tends to overestimate cetane index and is not recommended. Cetane index calculations can not account for cetane improver additives and therefore do not measure total cetane number for additized diesel fuels. Diesel engine operation is primarily related to the actual cetane number and the cetane index is simply an estimation of the base (unadditized) cetane number.