ASTM D2700 method for motor octane number of spark-ignition engine fuel
11. Engine Standardization
11.1 Unit Compliance - Operate the properly commissioned knock test unit at temperature equilibrium and in compliance with the basic engine and instrument settings and standard operating conditions prescribed for this test method.
11.1.1 Operate the engine on fuel for approximately 1 h to ensure that all critical variables are stable. During the final 10 min of this warm-up period, operate the engine at a typical K.I. level.
11.2 Fit-for-Use Qualification for Each Operating Period:
11.2.1 Every sample fuel O.N. determination shall be performed using an engine that has been qualified as fit-for-use by rating the appropriate TSF blend.
11.2.2 Qualify the engine using the appropriate TSF blends in accordance with the following conditions:
11.2.2.1 At least once during each 12 h period of rating.
11.2.2.2 After an engine has been shut down for more than 2 h.
11.2.2.3 After an engine has been operated at non-knocking conditions for more than 2 h.
11.2.2.4 After a barometric pressure change of more than 0.68 kPa (0.2 in. Hg) from that reading made at the time of the previous TSF blend rating for the specific O.N. range.
11.2.3 When either bracketing procedure is utilized to determine the TSF blend rating, establish standard K.I. using a PRF blend whose whole O.N. is closest to that of the O.N. accepted reference value of the selected TSF blend.
11.2.4 When either bracketing procedure is utilized to determine the TSF blend rating, set the cylinder height, compensated for the prevailing barometric pressure, to the guide table value for the O.N.ARV of the selected TSF blend.
11.2.5 When the compression ratio procedure is utilized to determine the TSF blend rating, first establish standard K.I. using the PRF blend whose whole O.N. is closest to that of the O.N.ARV of the selected TSF blend.
11.3 Fit-for-Use Procedure 79.8 to 94.5 O.N.:
11.3.1 Select the appropriate TSF blend(s) from Table 3 that are applicable for the O.N.s of the sample fuel ratings tested or to be tested during the operating period.
11.3.2 Rate the TSF blend using the standard intake MIXT of 149°C (300°F).
11.3.2.1 If the engine standardization during the last operating period required MIXT tuning to be fit-for-use and maintenance has not taken place, it is permissible to start fit-for-use testing for a new operating period using approximately the same MIXT tuning adjustment applied for the previous operating period.
11.3.3 If the untuned TSF blend rating is within the untuned rating tolerances of Table 3 for that TSF blend, the engine is fit for use to rate sample fuels within the applicable O.N. range. Intake MIXT tuning is not required.
11.3.4 If the untuned TSF blend rating is more than 0.1 O.N. from the O.N.ARV in Table 3 for that TSF blend, it is permissible to adjust the intake MIXT slightly to obtain the O.N.ARV for that specific TSF blend.
11.3.5 If the untuned TSF blend rating is outside the untuned rating tolerance of Table 3, adjust the intake MIXT, within prescribed limits, to obtain the O.N.ARV for that specific TSF blend.
11.3.5.1 The tuned intake MIXT shall be no lower than 141°C (285°F) nor higher than 163°C (325°F).
NOTE 1 - A TSF blend rating change of 0.1 O.N. requires an intake mixture temperature adjustment of approximately 1°C (2°F). Increasing the temperature decreases the O.N.
11.3.5.2 If the temperature tuned TSF blend rating is within +/- 0.1 O.N. of the O.N.ARV in Table 3, the engine is fit for use to rate sample fuels within the applicable O.N. range.
11.3.5.3 If the temperature tuned TSF blend rating is more than +/- 0.1 O.N. from the O.N.ARV in Table 3, the engine shall not be used for rating sample fuels having O.N. values within the applicable range until the cause is determined and corrected.
11.4 Fit-for-Use Procedure - Below 79.8 and Above 94.5 O.N.:
11.4.1 Select the appropriate TSF blend(s) from Table 4 that are applicable for the O.N. values of the sample fuel ratings tested or to be tested during the operating period.
11.4.2 The rating tolerances of Table 4 are determined by multiplying the standard deviation of the data that established the O.N.ARV of the TSF blend and a statistical tolerance limit factor K for normal distributions. Using the standard deviation values for the TSF blend data sets of 100 or more values and K = 1.5, it is estimated that in the long run, in 19 cases out of 20, at least 87 % of the test engines would rate the TSF blend within the rating tolerances listed in Table 4.
11.4.3 Rate the TSF blend using the standard intake MIXT of 149°C (300°F). Temperature tuning is not permitted for these O.N. levels.
11.4.4 If the TSF blend rating is within the rating tolerance, the engine is fit for use to rate sample fuels having O.N. values within the applicable range for that TSF blend.
11.4.5 If the TSF blend rating is outside the rating tolerance, conduct a comprehensive examination to determine the cause and required corrections. It is expected that some engines will rate outside the rating tolerance, at one or more of the O.N. levels, under standard operating conditions. Control records or charts of these TSF blend ratings can be helpful to demonstrate the ongoing performance characteristic of the unit.
11.5 Checking Performance on Check Fuels:
11.5.1 While engine standardization is dependent solely on TSF blend determinations, further rating using Check Fuels can provide additional credibility. Regular testing of Check Fuels and the use of standard quality control charting provide the means to document the overall effectiveness of the engine and operating personnel.
11.5.1.1 Test one or more Check Fuels.
11.5.1.2 Compare the octane rating obtained for the Check Fuel to the Check Fuel O.N.ARV.
11.5.1.3 Update the selected quality control charts to be maintained for the specific engine.
11.5.1.4 Interpret the performance depicted on the control charts in a timely manner so that investigation and corrective action can be taken if either a bias begins to develop or the variability of the engine begins to depreciate.
