- Method ASTM D976
- Repeatability variable, see method
- Reproducibility variable, see method
- Blending non-linear
- Additive Correction No
The formula for calculated cetane index provides a means for directly estimating the ASTM cetane number of distillate fuels from API gravity and boiling range. The index value, as computed from the formula is known as the Calculated Cetane Index. The Calculated Cetane Index is not an optional method for expressing ASTM cetane number. This is a supplementary tool for predicting cetane number when used with due regard for its limitations. The calculated cetane index is helpful in estimating the ASTM cetane number where a test engine is not available or when the sample is too small. When a cetane number has been determined, a cetane index is used as a check.
This version of the Cetane Index calculation uses the Api at 60°F and only the 50% versus the D4737 using 3 distillation points. It will give a calculated Cetane Index result within the range of 30-60 and is good for +- 2 numbers on the engine run. Like the D4737 if Cetane Improver is used this calculation will no longer be valid.