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
11. System Qualification Checkout
11.1 Check the performance of the AMS at intervals in accordance with the user quality system or after any maintenance that could affect measurement system performance. Operate the system using paired check fuels to determine whether it produces the correct ΔO.N. value and does so with appropriate system stability.
11.1.1 The ΔO.N. value is dependent upon (1) knock testing unit sensitivity, (2) detonation meter sensitivity, and (3) automated analyzer span setting for the octane range to be used.
11.1.2 The knock testing unit must be able to repeatedly measure the ΔO.N. for two fuels of different octane number. The latitude of engine condition is quite broad and when the knock testing unit is no longer satisfactory for automated analyzer operation it will be evidenced as instability of knock intensity. This condition often can be rectified through carbon blasting and ultimately by cylinder overhaul.
11.1.3 Set the span according to the manufacturer's instructions for the desired octane range so that the knock intensity or compression ratios can be used to accurately calculate the ΔO.N.
11.2 Perform the qualification checkout with the AMS operating under standard conditions as specified in this method. Equal time periods of operation for each of the paired check fuels shall be used. The time period for operation on each fuel shall be 4 min or longer.
11.2.1 Sequence the AMS between the paired check fuels until a minimum of six cycles has completed. A complete cycle comprises one period of operation on one fuel (A), followed by one period on the second fuel (B). Sequence the check fuels to the analyzer measurement system so that the ΔO.N. values are determined by subtracting the fuel B result from the fuel A result.
11.3 Determination of Average ΔO.N.:
11.3.1 Discard the ΔO.N. result for the first complete cycle determination.
11.3.2 Tabulate the remaining ΔO.N. values (Fuel B from Fuel A), including the proper algebraic sign.
11.3.3 Calculate the average ΔO.N., with respect to algebraic sign.
11.4 System Accuracy Qualification:
11.4.1 Assess the accuracy of the system by comparing the measured average ΔO.N. for the paired check fuels to the expected difference O.N.
11.4.1.1 Calculate Q, the accuracy qualification value, using the following formula:
Q = measured average ΔO.N. - expected difference O.N.
11.4.1.2 Use Table 1 to determine if the calculated Q value is within the accuracy qualification acceptance limit, K, for the applicable test method operating conditions (RON or MON).
11.4.1.3 The calculated Q value would, in the long run, in the normal and correct operation of this test method, fall outside the accuracy qualification acceptance limits (K) in only 1 case in 20.
11.4.1.4 If Q is within the limits of K for the respective test method, AMS is considered to be acceptably accurate.
11.4.1.5 If Q is outside the limits of K for the respective test method, the system is considered to be inaccurate and evaluation is required to identify and correct the root cause(s) of the inaccuracy before the system is used for ΔO.N. ratings of stream samples.
11.5 System Stability Assessment:
11.5.1 Assess the stability of the system by comparing the ΔO.N. range value for the paired check fuels data to the Range Limit (L) in Table 2 for the respective test method.
NOTE 1 - Range limit (L) values listed in Table 2 are for use with data sets of five independent ΔO.N. determinations and infer a Type 1 error of approximately 1 %.
11.5.1.1 Calculate the range value, using the following formula:
Range value = maximum measured ΔO.N. - minimum measured ΔO.N.
11.5.1.2 If the ΔO.N. range value is less than the range limit (L) for the respective test method, AMS is considered to be acceptably stable.
11.5.1.3 If the ΔO.N. range value is greater than the range limit (L) for the respective method operating conditions, the system is considered to be unstable. Evaluation is required to identify and correct the root cause(s) of the instability before the system is used for ΔO.N. ratings of stream samples.
