ASTM D2885 Determination of Octane Number of Spark-Ignition Engine Fuels
ASTM D2885 Standard Test Method for Determination of Octane Number of Spark-Ignition Engine Fuels by On-Line Direct Comparison Technique
14. Analytical Measurement System Quality Control Checks
14.1 Confirm the operation of the analytical measurement system and CRF quality by measuring a ΔO.N. between the CRF and a paired quality control fuel at least once a week or when the CRF is used.
14.1.1 Quality control checks are intended to monitor and confirm the stability of the entire ΔO.N. measurement system over time; it is intended as a supplement to the system qualification checkout and can not be used to replace the system qualification checkout.
14.2 Perform the quality control checks with the AMS operating under standard conditions as specified in this method. Use equal time periods of operation for each of the fuels. The time period for operation on each fuel will be 4 min or longer.
14.3 Sequence the AMS between the CRF and paired quality control fuel until a minimum of two cycles has been completed. A complete cycle comprises one period of operation on one fuel (CRF), followed by one period on the second fuel (paired quality control fuel). Sequence the paired quality control fuels to the analyzer measurement system so that the ΔO.N. values are determined by subtracting the paired quality control fuel result from the CRF result.
14.4 Determination of Average ΔO.N. and Range:
14.4.1 Tabulate the ΔO.N. values including the proper algebraic sign.
14.4.2 Calculate the average ΔO.N. with respect to algebraic sign.
14.4.3 Calculate the range of data using the following formula:
Range of Data = maximum ΔO.N. - minimum ΔO.N.
14.5 Use appropriate control charts or other statistically equivalent technique to assess the average ΔO.N. and range values relative to the established expected values for that pair of quality control fuels. If an out-of-statistical situation is detected, examine the analytical measurement system operation and the CRF quality for root cause(s). The appropriate control charts are I/MR-2 for the average ΔO.N., and range chart for range.
14.6 Specifics for control chart set up and interpretation can be found in Practice D6299.
15. Precision and Bias
15.1 Repeatability:
15.1.1 O.N. for RON: 0.2
15.1.2 ΔO.N. for MON: 0.3
15.1.3 Discussion - The above limits were estimated from program 3R (see ASTM D02-1330); and can be used as an approximate (and conservative) repeatability limit as defined by ASTM (see Terminology E456), for the measured ΔO.N.
15.2 Reproducibility:
15.2.1 In the intended on-line application of this test method, where multiple ΔO.N.'s are averaged to arrive at a FPAPV (Flow-Proportioned Average Property Value) for the O.N. of a tender or batch of product, the reproducibility limit, as defined by ASTM, for individual ΔO.N. results on the same fuel pair, is of little utility since the same tender will need to be tested by another comparator system using exactly the same proto fuel in order to make meaningful comparison of the difference between the two ΔO.N. values generated by the two different systems/operators. A more useful metric is the reproducibility of the ΔO.N.-bar where the latter is calculated from n individual ΔO.N. values generated from a system under repeatability conditions.
NOTE 2 - An interlaboratory exchange test program is currently underway to estimate the reproducibility of DO.N.-bar values for n = 5.
15.2.2 Users are advised to consult the Appendix of this test method for a detailed description on how to estimate the variability associated with the FPAPV for octane number of a tender or batch of material obtained using this test method and Practice D6624.
16. Keywords
16.1 analytical measurement system; comparison reference fuel; delta octane number; stream sample fuel
