ASTM D613 standard test method for cetane number of diesel fuel oil
14. Report
14.1 Report the calculated result as cetane number.
14.2 If the sample was filtered before testing, include this information in the report.
15. Precision and Bias
15.1 Handwheel Bracketing Procedure Precision - The precision of this test method and procedure based on statistical examination of interlaboratory test results is as follows:
15.1.1 Repeatability - The difference between two test results, obtained on identical test samples under repeatability conditions would, in the long run, in the normal and correct operation of the test method, exceed the values in Table 2 only in 1 case in 20.
15.1.2 Reproducibility - The difference between two single and independent results obtained on identical test samples under reproducibility conditions would, in the long run, in the normal and correct operation of the test method, exceed the values in Table 2 only in 1 case in 20.
15.1.3 Repeatability precision limits are based on the ASTM National Exchange Group (NEG) monthly sample testing program data from mid-1978 through 1987. During this period each exchange sample was rated twice on the same day by the same operator on one engine in each of the Member laboratories.
15.1.4 Reproducibility precision limits are based on the combined NEG monthly sample testing program data from mid-1978 through mid-1992, the Institute of Petroleum monthly sample data for 1988 through mid-1992 and the Institut Francais du Petrole monthly sample data for 1989 through early 1992.
15.1.5 The combination of the large number of sample sets and the fact that each sample is tested by 12 to 25 laboratories provides a comprehensive picture of the precision achievable using this test method. Analyzed graphically, the respective sample standard deviations were plotted vs cetane number. The variation in precision with respect to cetane number level for these data is best expressed by a linear regression of the values. The average standard deviation for each cetane number level has been multiplied by 2.772 to obtain the respective limit values.
15.2 Bias - The procedure in this test method for cetane number of diesel fuel oil has no bias because the value of cetane number can be defined only in terms of the test method.
16. Keywords
16.1 cetane number; diesel performance; ignition delay
