Appendix A
Cetane Index
Two similar methods are used to determine CI for diesel. These methods are particularly suitable for straight-run fuel, catalytically cracked stocks, and blends of the two. The correlation is best for these fuels and least satisfactory for blends containing substantial proportions of thermally cracked stocks. Neither of these standards is suitable for fuel containing pure hydrocarbons, or non-petroleum based fuels derived from coal. In addition, these methods take no account of cetane improvers used to raise CN.
ASTM D 976
ASTM D 976 is specified in the Regulations as the acceptable method for determining CI. This method uses two variable equation to determine CI from the diesel's mid-boiling point and density. Calculated Cetane Index:
CI97 = 454.74 - 1641.416D + 774.74D2 - 0.554B + 97.803(log B)2
Where:
D = density at 15°C [g/mL] determined by Test Method ASTM D 1298
B = mid-boiling temperature [°C] determined by Test Method ASTM D 86 and corrected to standard barometric pressure.
ASTM D 4737
ASTM D 4737 is a newer method which is not specified in the Regulations. This method calculates CI using a four variable equation based on diesel's low, mid and high boiling points as well as density. Calculated Cetane Index:
CI4737 = 45.2 + 0.0892T10N + [0.131 + 0.901B]T50N + [0.0523 + 0.420B]T90N + 0.00049[T210N - T290N] + 107B + 60B2
Where:
D = density at 15°C [g/mL] determined by Test Method ASTM D 1298,
B = [ e( -3.5 ) ( D - 0.85 ) ] -1,
T10 = 10% distillation temperature [°C] determined by Test Method ASTM D 86 and corrected to standard barometric pressure,
T10N = T10 - 215,
T50 = 50% distillation temperature [°C] determined by Test Method ASTM D 86 and corrected to standard barometric pressure,
T50N = T50 - 260,
T90 = 90% distillation temperature [°C] determined by Test Method ASTM D 86 and corrected to standard barometric pressure,
T90N = T90 - 310.
Back to Top