United States
Environmental Protection Agency
Office of Transportation and Air Quality
National Vehicle and Fuel Emissions Laboratory
2565 Plymouth Road
Ann Arbor, MI 48105
Method for Calculating Cetane
Index of Diesel Fuels
This method is written for the Environmental Protection Agency, National Vehicle and Fuel
Emissions Laboratory (NVFEL) internal use. The use of specific brand names by NVFEL in
this method are for reference only and are not an endorsement of those products. This
document may be used for guidance by other laboratories.
NVFEL Reference Number
121
Implementation Approval
Original Procedure Authorized by EPCN # 322 on 05-06-2002
Revision Description
Page 1 of 4
NFVEL 121 Method for Calculating Cetane Index of Diesel Fuels Page 2 of 4
1.0 Scope ......................................................................................... 3
2.0 Summary of Method.................................................................. 3
3.0 Significance............................................................................... 3
4.0 Applicable Documents .............................................................. 3
5.0 Definitions................................................................................. 3
6.0 Interferences and/or Limitations .............................................. 3
7.0 Safety......................................................................................... 4
8.0 Apparatus .................................................................................. 4
9.0 Reagents and Materials ............................................................. 4
10.0 Sampling ................................................................................... 4
11.0 Calibration................................................................................. 4
12.0 Analytical Procedure ................................................................. 4
13.0 Calculations and Reporting ....................................................... 4
14.0 Performance Criteria ................................................................. 4
NFVEL 121 Method for Calculating Cetane Index of Diesel Fuels Page 3 of 4
1.0 Scope
The Calculated Cetane Index formula represents a means for directly estimating the ASTM
cetane number of distillate fuels from API gravity and mid-boiling point. The index value, as
computed from the formula, is termed the Calculated Cetane Index .
2.0 Summary of Method
This is a mathematical calculation method.
3.0 Significance
3.1 The Calculated Cetane Index is a useful tool for estimating ASTM cetane number
where a test engine is not available for determining this property. It may be
conveniently employed for approximating cetane number where the quantity of
sample is too small for an engine rating.
3.2 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.
3.3 Both Calculated Cetane Index and Cetane Number are required official values for
Certification Diesel Fuel. Calculated Cetane Index is not a required value for
enforcement samples.
4.0 Applicable Documents
4.1 D976, Standard Test Method for Calculating Cetane Index of Distillate Fuels.
4.2 D86, Test Method for Distillation of Petroleum Products
4.3 D4052 Standard Test Method for Density and Relative Density of Liquids by Digital
Density Meter.
5.0 Definitions - N/A
6.0 Limitations
The Calculated Cetane Index is not an optional method for expressing ASTM cetane number.
It is a supplementary tool for predicting cetane number when used with due regard for its
limitations.
NFVEL 121 Method for Calculating Cetane Index of Diesel Fuels Page 4 of 4
7.0 Safety - N/A
8.0 Apparatus
8.1 Computer
8.2 Fuel Test Database File
9.0 Reagents and Materials - N/A
10.0 Sampling - N/A
11.0 Calibration - N/A
12.0 Analytical Procedure.
12.1 The Distillation Method (as described in Step 4.1) and the API Gravity Method (as
described in Step 4.2) must be completed
12.2 The automatically calculated cetane index is determined from the following equation:
Calculated cetane index =
2 2 2
-420.34 + 0.016 G + 0.192 G log M + 65.01 (log M) - 0.0001809 M . (1)
0
G = API Degrees @ 60 F
M = D86 Temperature @ 50% volume, in 0F
13.0 Calculation and Reporting
13.1 The FTAG number of the sample is entered into Fuel Tests Data Base, the Cetane
Index Table and then the Cetane Index is automatically calculated using the T50
from Distillation Table and the API degrees from the New Gravity Table.
13.2 Print out and sign Cetane Index by Date form and place in the secured file cabinet .
14.0 Performance Criteria - N/A
