ASTM D7170 Standard Test Method for Determination of Derived Cetane Number (DCN) of Diesel Fuel Oils - Fixed Range Injection Period, Constant Volume Combustion Chamber Method
12. Procedure
12.1 Operating Period Procedure:
12.1.1 With the combustion analyzer in shut down mode, start a new operating period as follows:
12.1.1.1 Position the combustion analyzer power switch to ON.
12.1.1.2 Open the valve at the source of the charge air supply and adjust the pressure regulators as needed to provide the specification pressures. Turn on the computer, circulation coolant system, and the pneumatic air supply.
12.1.1.3 Initiate the automated warm-up sequence using the appropriate computer command.
12.1.2 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 Prepare a test specimen of at least 220 mL.
12.2.2 Remove the reservoir cap and fill the fuel reservoir with the test specimen. Reinstall the reservoir cap hand tight.
12.2.2.1 Flush all the test specimen through the fuel injection system by pressing the appropriate button and keep it pressed until the fuel reservoir is empty. Refer to the instruction manual of the manufacturer.
12.2.2.2 Remove the reservoir cap and refill the fuel reservoir with the test specimen. Reinstall the reservoir cap hand tight and initiate the flushing sequence by pushing for 3 s the appropriate button on the apparatus.
12.2.2.3 Remove the reservoir cap and top off the fuel reservoir with the test specimen. Reinstall the reservoir cap hand tight.
12.2.3 Initiate an automatic ignition delay determination using the appropriate computer command (see Annex A2 for detailed information about the test sequence).
12.2.4 After the two pre-injections, monitor the injection period throughout the test to ensure that the injection period average is 5.00 ms +/- 0.25 ms and the injection periods all fall between 4.0 ms and 6.0 ms. If adjustments of the fuel injection pump rack are required to achieve these conditions, make the necessary adjustments and, using the same fuel test specimen contained in the fuel reservoir from the previously aborted test, start a new test by repeating steps 12.2.2.3, 12.2.3, and 12.2.4. To make these adjustments, refer to Fig. 2 and the instruction manual of the manufacturer.
NOTE 8 - The Test Output "Results Status" line will state "Test completed with errors" if the injection period is outside the specified limits.
NOTE 9 - Moving the rack towards the rear of the cabinet increases the injection period duration, and moving the rack towards the front of the cabinet reduces the injection period.
12.2.5 At the end of the test, a test output summary is automatically stored on the computer hard drive and displayed on the computer screen. The user can optionally print the results with a connected printer. The report contains detailed information about each of the 25 combustion cycles including ID, DCN, IP (injection period), and some of the important operating conditions. At the bottom ofthe printout, the average value, minimum, maximum, range, and standard deviation of critical measurements are given (see Appendix X1).
12.2.5.1 The ID result at the bottom of the printout is obtained by averaging the ID measurements of the last 25 cycles.
12.2.5.2 The DCN result at the bottom of the printout is obtained by converting the mean ID result to DCN using:
DCN = 150.4·(1/ID) + 5.3
12.2.6 Check that all standard operating conditions are in compliance. This test will also be performed by the computer software during and at the end of the test.
12.2.7 Flush the remaining test specimen through the fuel injection system by pressing the appropriate button and keep it pressed until the fuel reservoir is empty.
12.2.8 Remove the reservoir cap and visually inspect that the fuel reservoir is empty. Reinstall the fuel reservoir cap hand tight. The fuel system is now prepared for the next specimen determination (see 12.2) or unit shutdown (see 12.3).
12.3 Unit Shutdown:
12.3.1 Confirm that all specimens have been discharged from the fuel injection system (see 12.2.7) and that the fuel reservoir is empty (see 12.2.8).
12.3.2 Close the valve at the source ofthe charge air supply. Use the applicable computer command to shutdown the combustion analyzer. Turn off the computer, circulation coolant system, and the pneumatic air supply.
NOTE 10 - The shutdown procedure decompresses the combustion chamber and switches off the heating element to allow the combustion chamber to cool down.
12.3.3 Position the combustion analyzer power switch to OFF.
13. Calculation
13.1 Calculate the derived cetane number, DCN, from average ignition delay, ID (ms), recorded as in 12.2.5.2 using Eq 1.
DCN = 150.4·(1/ID) + 5.3
13.2 Record the DCN to the nearest 0.1.
13.3 The derivation and maintenance of Eq 1 is described in Annex A3.
