- Method ASTM D4737
- Repeatability variable, see method
- Reproducibility variable, see method
- Blending non-linear
- Additive Correction No
When a test engine is not available for establishing this property directly and when cetane improver is not used, the Calculated Cetane Index by Four Variable Equation is useful for estimating ASTM cetane number. Also useful as a cetane number check in cases where the ASTM cetane number has been determined.
This method uses the density at 15°C and distillation recoveries at 10%,50%, and 90% to give an estimation of the cetane number within a range of 32.5 to 56.5. This equation has been proven to be accurate within +- 2 cetane numbers of the actual engine run. With this being said there are exceptions. The main exception is the use of Cetane improver. This additive will only affect the combustion properties and will not change the distillation which means the product could have a 46 on the index but 51 on the number.