cetaneindex

Cetane Index is an empirical estimate of the cetane number (CN) of diesel fuels. The CN is a measure of ignition quality in compression-ignition engines, but direct CN determination requires specialized equipment and procedures. The Cetane Index provides a practical alternative by estimating CN from simpler, routinely measured fuel properties. It is commonly used in quality control, fuel specification, and process optimization to compare ignition quality when direct CN testing is unavailable or impractical.

Calculation of the Cetane Index relies on correlations between CN and standard fuel properties. The most common inputs are distillation characteristics, such as the temperatures at which certain percentages of the fuel boil (for example, 50% and 90%), and the density of the fuel at a reference temperature. Some methods also incorporate additional properties such as other distillation points or aromatic content. Because multiple empirical formulas exist, the exact calculation can vary by region, standard, or supplier, but all rely on readily measured properties rather than direct CN testing.

Interpretation and use: A higher Cetane Index indicates a fuel estimated to have better ignition quality, but it is not a substitute for an actual cetane number measurement. The index is used for screening, specification compliance, and comparative assessments within refinery and quality-control workflows. Limitations include that the correlation is empirical and can be affected by chemical composition, oxygenates, aromatic content, or unusual hydrocarbon profiles, which may cause discrepancies with the true CN.