ASTM D2700 method for motor octane number of spark-ignition engine fuel
17. Report
17.1 Motor O.N. of Spark-Ignition Engine Fuels:
17.1.1 Report the calculated bracketing procedure or the C.R. procedure result as Motor O.N.
17.1.1.1 For ratings below 72.0 O.N., report the value to the nearest integer. When the calculated O.N. ends with a 0.50, round off to the nearest even number; example, round 67.50 and 68.50 to 68 O.N.
17.1.1.2 For ratings from 72.0 through 103.5 O.N., report the value to the nearest tenth. When the calculated O.N. ends with exactly 5 in the second decimal place, round to the nearest even tenth number; example, round 89.55 and 89.65 to 89.6 O.N.
17.1.1.3 For ratings above 103.5 O.N., report the value to the nearest integer. When the calculated O.N. ends with a 0.50, round off to the nearest even number; example, round 105.50 and 106.50 to 106 O.N.
17.1.2 Report which procedure is used to determine the O.N.: bracketing - equilibrium fuel level, bracketing - dynamic fuel level, or compression ratio.
17.1.3 Report the engine room barometric pressure at the time of the rating.
17.1.4 Report the intake MIXT used.
17.2 Aviation Method Rating of Aviation Spark-Ignition Engine Fuel:
17.2.1 Report the calculated rating result as Motor O.N. rounded to the nearest tenth.
17.2.1.1 Report the engine room barometric pressure at the time of the rating.
17.2.1.2 Report the intake MIXT used.
17.2.2 Use the Motor O.N., rounded to the nearest tenth, and Table 7 to obtain the Aviation method rating. Round the converted value to the nearest tenth using the same rounding practice previously described.
17.2.2.1 Report Aviation method ratings that are 100.0 or less as O.N.
17.2.2.2 Report Aviation method ratings that are higher than 100.0 as performance number (P.N.).
18. Precision and Bias
18.1 Bracketing - Equilibrium Fuel Level Procedure A and C.R. Procedure C.
18.1.1 80.0 to 90.0 Motor O.N. Range - The precision of this test method for Motor O.N.s between 80.0 and 90.0 based on statistical examination of interlaboratory test results by the bracketing - equilibrium fuel level or compression ratio procedures is as follows:
18.1.1.1 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 0.2 O.N. only in one case in twenty.
18.1.1.2 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 0.9 O.N. only in one case in twenty.
18.1.1.3 The above repeatability is based on the replicate O.N. results obtained by the ASTM Motor National Exchange Group (NEG) participating in cooperative testing programs from 1983 through 1987 and 1994. Between 80 and 90 Motor O.N., the repeatability standard deviation is 0.09, unaffected by octane level. This average standard deviation has been multiplied by 2.772 to obtain the limit value.
18.1.1.4 The above reproducibility is based on the combined NEG monthly sample testing program data from 1988 through 1994, the Institute of Petroleum monthly sample data from 1988 through 1994, and the Institut Francais du Petrole monthly sample data from 1991 through 1994. The combination of the large number of sample sets and the fact that each sample fuel was tested by more than 30 laboratories, provides a comprehensive picture of the precision achievable using this test method. Analyzed graphically, the respective sample fuel standard deviations were plotted versus O.N. The variation in precision with respect to O.N. level, for the range of these data, is best expressed by a linear regression of the values. Between 80 and 90 Motor O.N., the reproducibility standard deviation is 0.34 unaffected by octane level. This average standard deviation has been multiplied by 2.772 to obtain the limit value.
18.1.1.5 Sample fuels containing oxygenate (alcohols or ethers), in the concentrations typical of commercial spark-ignition engine fuels, have been included in the exchange programs and the precision for these sample fuels is statistically indistinguishable from non-oxygenated fuels in the Motor O.N. range from 80.0 to 90.0.
18.1.1.6 The equivalence of this test method when performed at barometric pressures less than 94.6 kPa (28.0 in. of Hg) has not been determined. Reproducibility for the 80.0 to 90.0 O.N. range at altitude locations, based on ASTM Rocky Mountain Regional Group interlaboratory test results, would, in the long run, in the normal operation of the test method, exceed approximately 1.4 O.N. only in one case in twenty.
18.1.2 Below 80.0 Motor O.N. Range:
18.1.2.1 Precision cannot be stated for the range below 80.0 Motor O.N. because current data are not available.
18.1.3 90 to 102.0 Motor O.N. Range:
18.1.3.1 Precision cannot be stated for the 90.0 to 102.0 Motor O.N. range because sufficient current data are not available.
18.1.4 102 to 103 Motor O.N. Range - The precision of this test method at the 102 to 103 Motor O.N. level based on statistical examination of interlaboratory test results is as follows:
18.1.4.1 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 0.6 O.N. only in one case in twenty.
18.1.4.2 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 2.0 O.N. only in one case in twenty.
18.1.4.3 The above repeatability and reproducibility values are based on replicate O.N. results obtained by from 12 to 15 laboratories participating in the ASTM Aviation National Exchange Group (NEG) during the period from 1988 through 1994. The repeatability and reproducibility pooled variances for the 21 samples that rated within this range were determined. The resulting average standard deviations have been multiplied by 2.772 to obtain the respective limit values.
18.1.5 Above 103.0 Motor O.N. Range:
18.1.5.1 Precision cannot be stated for the range above 103.0 Motor O.N. because current data are not available.
18.2 Bracketing - Dynamic Fuel Level Procedure B:
18.2.1 The amount of data for the bracketing–dynamic fuel level procedure is limited. The available information includes a statistical study involving single ratings by seven laboratories that comparatively tested four gasoline samples and three TSF blends, in the 80.0 to 90.0 Motor O.N. range, by both the bracketing dynamic fuel level procedure and the bracketing - equilibrium fuel level procedure. A second phase examined repeatability using duplicate bracketing - dynamic fuel level procedure ratings by each of four laboratories on eight sample fuels.
18.2.1.1 Repeatability of the bracketing - dynamic fuel level procedure is similar to that of the bracketing - equilibrium fuel level procedure as inferred from the statistical analysis of the limited duplicate ratings data set.
18.2.1.2 Reproducibility of the bracketing - dynamic fuel level procedure is indistinguishable from that of the bracketing - equilibrium fuel level procedure based on the statistical analysis of the limited data from the round-robin study.
18.3 Standard Deviation:
18.3.1 Examination of interlaboratory test results for Motor O.N. was initiated in 1933 with the formation of the National Exchange Group that regularly tests at least one sample per month. These historical data have demonstrated that the variability (standard deviation) of the test method changes with O.N. as shown in Fig. 8. The curve for this figure is based on ASTM National Exchange Group data from 1966 through 1987.
18.4 Bias - The procedures in this test method for Motor O.N. of spark-ignition engine fuel have no bias because the value of Motor O.N. can be defined only in terms of this test method.
19. Keywords
19.1 aviation rating; guide table; isooctane; knock intensity; motor octane number; n-heptane; spark-ignition engine fuel performance; toluene standardization fuel
