The Calculated Cetane Index is one tool available for estimating ASTM cetane number where a test engine is not available for determining this property. It may be employed for approximating cetane number where the quantity of sample is too small for an engine rating. In cases where the cetane number of a fuel has been initially established, the index is useful as a cetane number check on subsequent samples of that fuel, provided its source and mode of manufacture remain unchanged.

Test Method D 4737 may also be used to approximate the ASTM cetane number of diesel fuels.

3.2.1 Procedure A of Test Method D 4737 was developed as a result of a larger degree of offset between Test Method D 976 Cetane Index and the results of Test Method D 613 over the entire range of the correlation. Generally, it has been found that use of Test Method D 4737 results in less offset than use of Test Method D 976, but there can be specific cases where this is not true.

3.2.2 Procedure A of Test Method D 4737 is recommended to estimate the cetane number of diesel fuels with sulfur contents above 500 ppm or No. 1-D diesel fuels.

3.2.3 Procedure B of Test Method D 4737 is recommended to estimate the cetane number of No. 2-D diesel fuels with sulfur contents at or below 500 ppm.

Calculated Cetane Index, as described in Test Method D 976-80, is recognized by the United States EPA as an alternative method to meet the U.S. Federal Diesel aromatics limit for diesel fuels containing less than 500 ppm sulfur. The equation for Calculated Cetane Index in Test Method D 976-80 and in this version (D 976-06) of the test method are the same.