Estimate cetane index from density and mid-boiling point (T50) - the lab proxy for actual cetane number on distillate fuels.
Formula
$$ CI = 454.74 - 1641.416 \cdot SG + 774.74 \cdot SG^2 - 0.554 \cdot T_{50} + 97.803 \cdot (\log T_{50})^2 $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $SG$ | Specific gravity at 60 °F | - | derived from API |
| $T_{50}$ | Mid-boiling point at 50 % recovery | °F | ASTM D86 / D2887 |
| $CI$ | Cetane Index | - | result |
Sources
- ASTM D976.