ASTM D6890 Standard Test Method for Determination of Ignition Delay and Derived Cetane Number (DCN) of Diesel Fuel Oils by Combustion in a Constant Volume Chamber
12. Procedure
12.1 Operating Period Procedure:
12.1.1 If necessary, warm-up the combustion analyzer (see A3.1).
12.1.2 Check the sealing integrity of the combustion chamber (see A3.5).
12.1.3 Check that the combustion analyzer is fit-for use by performing a quality control test (see 11.4).
12.2 Test Procedure:
12.2.1 Filter the diesel fuel sample at room temperature, using a non-reactive positive pressure delivery device such as a glass syringe or glass-lined metal syringe and single-use filter element, to prepare a test specimen of sufficient volume to complete the test method, including flushing. The recommended volume for most test purposes is 100 mL. See the instructions provided by the manufacturer for further information.
12.2.2 Flush, fill, and purge the fuel system with the specimen (see A3.2.2).
12.2.3 Initiate an automatic ignition delay determination using the appropriate computer command (see Annex A4 for detailed information about the test sequence).
12.2.4 Check that all standard operating conditions are in compliance.
12.2.5 If operating conditions are not in compliance, make the required adjustments and return to 12.2.2.
12.2.6 Record the average ignition delay to the nearest 0.001 ms for the calculation of the DCN (13.1).
12.3 Discharge unused specimen and clean the fuel system (see A3.2.3 or A3.2.4) to prepare for (1) the next specimen determination, or (2) combustion analyzer shut down (see A3.6).
13. Calculation
13.1 Calculate the derived cetane number, DCN, from average ignition delay, ID (ms), recorded as in 12.2.6 using Eq 1:
DCN = 4.460 + 186.6/ID
13.2 Record the DCN to the nearest 0.1.
13.3 The derivation and maintenance of Eq 1 is described in Annex A5.
