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
12. Procedure
12.1 Detailed operating procedures shall conform to the recommendations of the AMS manufacturer.
13. Calculation of Delta Octane Number and Octane Number
13.1 ΔO.N. calculation involves taking the signed difference in knock intensity or compression ratio signals between the reference fuel (standard or prototype) and the stream sample fuel and then dividing it by the appropriate span.
13.1.1 Differential Knock Intensity at a Constant Compression Ratio:
ΔO.N. = (K.I. reference - K.I. sample) / Span (K.I./octane)
Example:
K.I. Reference Fuel = 50
K.I. sample fuel = 57
Span (K.I./Octane) = 20
ΔO.N. = (50-57) / 20
ΔO.N. = -0.35
13.1.2 Differential Compression Ratio at a Constant Knock Intensity:
ΔO.N. = (C.R. sample - C.R. reference) / Span (C.R./octane)
Example:
Reference Fuel C.R. = 756
Sample Fuel C.R. = 764
Span(C.R./Octane) = 14
ΔO.N. = (764-756) / 14
ΔO.N. = +0.57
13.2 Octane number using the measured delta octane number and the octane number of the comparison reference fuel:
13.2.1 O.N. stream sample = ΔO.N. + O.N. comparison reference fuel.
