According to ASTM D2700, the MON Octane Engine shall be calibrated/standardized before rating a fuel sample. Every sample octane number determination shall be performed using an octane engine that has been qualified as fit-for-use by rating the appropriate TSF blend.
1. Prepare the MON Octane Engine at temperature equilibrium and in compliance with the basic engine parameter settings and standard operating conditions prescribed for ASTM D2700 MON test method.
2. Warm up the MON Octane Engine on fuel for approximately 1 h to ensure that all critical variables are stable. During the final 20 min of this warm-up period, operate the engine at a typical K.I. level.
3. Operate the MON Octane Engine to determine the appropriate TSF blend rating by bracketing procedure or compression ratio procedure. The TSF blend rating shall be performed in accordance with the following conditions:
a. At least once during each 12 h period of octane rating.
b. After the MON Octane Engine has been shut down or running at non-knocking conditions for more than 2 h.
c. 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 octane number range.
Select the appropriate TSF blend from the below table that are applicable for the octane number values of the sample fuel to be tested. Rate the TSF blend using the standard intake mixture temperature of 149 °C (300 °F).
If the untuned TSF blend rating is within the untuned rating tolerances of the below table for that TSF blend, the MON Octane Engine is fit for use to rate sample fuels within the applicable O.N. range.
If the untuned TSF blend rating is more than 0.1 O.N. from the O.N.ARV in table, it is permissible to adjust the intake mixture temperature slightly to obtain the O.N.ARV for that specific TSF blend.
If the untuned TSF blend rating is outside the untuned rating tolerance of table, adjust the intake mixture temperature within prescribed limits to obtain the O.N.ARV for that specific TSF blend.
Note: The tuned intake mixture temperature shall be no lower than 141 °C (285 °F) nor higher than 163 °C (325 °F)
Table: TSF Blend O.N.ARV, Untuned Rating Tolerances and Sample Fuel Octane Number Range of Use
Select the appropriate TSF blend from the below table that are applicable for the octane number values of the sample fuel to be tested.
Rate the TSF blend using the standard intake mixture temperature of 149 °C (300 °F). Temperature tuning is not permitted for these O.N. levels.
If the TSF blend rating is within the rating tolerance, the Octane Engine is fit for use to rate sample fuels having O.N. values within the applicable range for that TSF blend.
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 MON Octane Engine.
Table: TSF Blend O.N.ARV, Rating Tolerances and Sample Fuel Octane Number Range of Use