Establish standard K.I. by engine calibration, using a PRF blend O.N. close to the sample fuel to be rated.
Introduce the sample fuel to an empty fuel bowl. Purge the fuel line and observing that there are no bubbles in tubing. Top off the level so that the fuel level is at approximately 0.3/0.4 in the sight glass.
Operate the engine on the sample fuel and observe that the fuel level begins to fall in the sight glass.
When applying this falling level technique, stop the sequence by switching to another fuel when the K.I. reading passes its maximum value and decreases approximately ten divisions.
When using the analog detonation meter, if the K.I. reading falls outside 30 to 70, adjust the cylinder height to close to the standard K.I. condition.
When using the digital detonation meter, if the peak to peak voltage falls outside of the range of 0.05 to 0.35, adjust the cylinder height to close to the standard K.I. condition.
Refill the fuel reservoir to the appropriate rich mixture sight glass level for each successive repetition of the trial-and-error process.
When using the analog detonation meter, after the cylinder height is approximately determined. t may be necessary to make a final adjustment to ensure that the fuel level for max K.I. occurs at a sight glass level within the critical range from 0.7 in. to 1.7 in. And the max K.I. reading is between 30 and 70 divisions.
Record the max K.I. reading.
Observe the cylinder height reading, compensated to standard barometric pressure. Using the appropriate guide table determine the estimated O.N. of the sample fuel.
Reference Fuel No. 1:
Prepare a PRF blend that has an O.N. estimated to be close to that of the sample fuel.
Introduce Reference Fuel No. 1 to a fuel bowl, taking care to purge the fuel line in the same manner.
Operate the engine on Reference Fuel No. 1. Record the max K.I. reading that occurs as the fuel level falls. Observe that the max K.I. condition occurs at a fuel level within the specified 0.7 in. to 1.7 in. range.
Reference Fuel No. 2:
Select another PRF blend that can be expected to result in a maximum K.I. reading that causes the readings for the two reference fuels to bracket that of the sample fuel.
Introduce Reference Fuel No. 2 to a fuel bowl taking care to purge the fuel line in the same manner.
Operate the engine on Reference Fuel No. 2. Record the max K.I. reading that occurs as the fuel level falls. Observe that the max K.I. condition occurs at a fuel level within the specified 0.7 in. to 1.7 in. range.
If the max K.I. reading for the sample fuel is bracketed by those of the two PRF blends, continue the rating; Otherwise try another PRF blend(s) until the bracketing requirement is satisfied.
Perform the necessary steps to obtain repeat K.I. readings on the sample fuel, Reference Fuel No. 2, and finally Reference Fuel No. 1.
Perform interpolation and calculation procedure.
The two max K.I. readings for the sample fuel and two for each of the PRF blends constitute a rating provided the difference between the rating calculated from the first and second series of readings is no greater than 0.3 O.N. And the average of the sample fuel K.I. readings is between 30 and 70.
RON Octane Rating Guide Table Compliance:
Check that the cylinder height, compensated for barometric pressure, used for the rating is within the prescribed limits of the applicable guide table value of cylinder height for the sample fuel O.N. At all O.N. levels, the digital counter reading shall be within ±20 of the guide table value. The dial indicator reading shall be within ±0.014 in. of the guide table value.
If the cylinder height of the sample ocrating is outside the guide table limit, repeat the rating after readjustment of the detonation meter to obtain standard K.I. using a PRF blend whose O.N. is close to that of the sample fuel.