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
14. Report
14.1 Report the following information:
14.1.1 A reference to this standard,
14.1.2 The sample identification,
14.1.3 The date of the test,
14.1.4 The ID result to the nearest hundredth (0.01 ms),
14.1.5 The DCN result to the nearest tenth (0.1),
14.1.6 The test's average charge air temperature to the nearest tenth (0.1) °C, and
14.1.7 Any deviation, by agreement or otherwise, from the specified procedures.
15. Precision and Bias
15.1 General - The precision statements for ID and DCN are based on an interlaboratory study conducted in 2002 (RR:D02-1602), supplemented by interlaboratory results reported to the ASTM National Exchange Group and the Energy Institute in their monthly diesel exchanges between January 2004 and July 2009 (RR:D02-1700). The test results for the study were statistically analyzed using ASTM Practice D6300/ISO 4259 techniques and involved, from the 2002 round robin, 10 laboratories and 15 test samples, and from the exchanges, 34 laboratories and 145 samples. The totality of samples covered the ID range from 3.24 ms to 6.24 ms (DCN range from 62.0 DCN to 34.4 DCN).
NOTE 8 - The DCN and its precision have been calculated from ignition delay results using Eq 1.
15.2 Precision:
15.2.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus, under constant operating conditions, on identical test materials would, in the long run, in the normal and correct operation of the test method, exceed the values calculated using the mathematical expressions in Table 1 only in one case in twenty.
15.2.2 Reproducibility - The difference between two single and independent results, obtained by different operators working in different laboratories on identical test materials, would, in the long run, and in the normal and the correct operation of the test method, exceed the values calculated using the mathematical expressions in Table 1 only in one case in twenty.
15.2.3 Examples of repeatability and reproducibility are shown in Table 2 for user information.
15.3 Bias - The ID determined using this test method has no bias because ID is defined only in terms of this test method.
15.4 Relative Bias to Test Method D613 - The degree of expected agreement between DCN results by this test method and CN results by Test Method D613 has been assessed in accordance with Practice D6708 using the interlaboratory studies conducted in 2002 and the 2004-2009 Energy Institute IP and 2004-2009 NEG correlation schemes.
15.4.1 No bias correction considered in Practice D6708 can further improve the agreement between results from Test Method D6890 and Test Method D613. Sample specific bias, as defined in Practice D6708, was observed for some samples.
15.4.2 Reproducibility Limit between a Single DCN Result versus a Single CND613 Result:
15.4.2.1 Differences between results from Test Method D6890 and Test Method D613, for the same types and property ranges studied, are expected to exceed the following between methods reproducibility (Rxy) as defined in Practice D6708, about 5 % of the time.
15.4.2.2 As a consequence of sample-specific biases observed, the 95 % confidence limit on the differences between a single DCN result and a CND613 result can be expected to be larger than the reproducibility of either test method. Users are advised to assess the required degree of prediction agreement relative to the estimated Rxy to determine the fitness-for-use of the prediction.
15.4.2.3 Based on the results from the interlaboratory study, the difference between the single DCN result and a single CND613 result, over the long-term and correct operation of both test methods, for any sample meeting the scope of both test methods, is estimated to exceed the values calculated in Eq 2 no more than one case in twenty.
Rxy = 0.1094 x [(DCN + CND613)/2 - 11.02]
15.4.2.4 Examples of between-methods reproducibility (Rxy) are shown in Table 3 for user information.
16. Keywords
16.1 cetane number; derived cetane number; diesel performance; ignition characteristic; ignition delay
