scope:

This International Standard describes a procedure for the calculation of the cetane index of middle-distillate fuels from petroleum-derived sources. The calculated value is termed the "cetane index by four-variable equation". Throughout the remaining text of this International Standard, the term "cetane index" implies cetane index by four-variable equation.

This International Standard is not applicable to fuels containing additives for raising the cetane number, nor to pure hydrocarbons, nor to distillate fuels derived from coal. It is applicable to fuels containing non-petroleum derivatives from tar sand and oil shale.

NOTE 1 This International Standard was originally developed using a matrix of fuels, some of which contain nonpetroleum derivates from tar sands and oil shale. Other cetane index equations have since been developed which can be more applicable to tar sands products.

NOTE 2 The cetane index is not an alternative way to express the cetane number; it is a supplementary tool, to be used with due regard for its limitations.

NOTE 3 The cetane index is used to estimate the cetane number of diesel fuel when a test engine is not available to determine this property directly, or when insufficient sample is available for an engine rating. In cases where the cetane number of a fuel has been previously established, the cetane index can be used to verify the cetane number of subsequent samples of that fuel, provided the fuel's source and mode of manufacture remain unchanged.

NOTE 4 The cetane index method is used to estimate the cetane number of the fuel, but does not take into account the effects of cetane improver additives that may be present.

Within the recommended range of cetane number (32,5 to 56,5), the expected error of the prediction via the cetane index equation will be less than ± 2 cetane numbers for 65 % of the distillate fuels examined. Errors may be greater for fuels whose properties fall outside the recommended range of application.