scope:

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". Througout the remaining text of this Standard, the term "cetane index" will imply cetane index by four-varibale equation. This 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 sands and oil shale.