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
4. Summary of Test Method
4.1 The delta research (ΔRON) or delta motor (ΔMON) octane number of a stream sample is determined using a standard CFR engine operating under the appropriate test conditions, using an automated repetitive cycle that compares its knock characteristics with those of a comparison reference fuel (CRF) having an assigned octane number. The difference in knock characteristics may be measured as (1) the difference in knock intensity at constant compression ratio, or (2) the difference in compression ratio at constant knock intensity. The system draws the stream sample from a flowing stream and conditions it for delivery to the CFR engine carburetor. Comparison reference fuel is stored in a suitable container and is also appropriately conditioned for delivery to the CFR engine carburetor. System controls sequence the switching of the two fuels as well as monitoring all critical testing variables. The fuel-air ratio of each fuel is adjusted to produce the maximum knock intensity for that fuel.
5. Significance and Use
5.1 The delta octane number (ΔO.N.) measure can quantify the difference of in-line blended spark-ignition engine fuel or process stream material octane number to a desired octane number to aid in optimizing control of blender facilities or refinery process units.
5.2 The ΔO.N. measure, summed with a statistically sound comparison reference fuels O.N. provides either research or motor octane number value of the current in-line blended spark-ignition engine fuel or process stream material.
5.3 Through the use of cumulative flow-weighted averaging of the repetitive ΔO.N. results, a statistically significant octane number can be assigned to a tender or batch of in-line blended spark-ignition engine fuel.
6. Interferences
6.1 Certain gases and fumes, which can be present in the area where the knock testing unit is located, may have a measurable effect on the ΔO.N. result.
6.1.1 Halogenated refrigerant used in air conditioning and refrigeration equipment can promote knock. Halogenated solvents can have the same effect. If vapors from these materials enter the combustion chamber of the CFR engine, the octane number of spark-ignition engine fuel can be depreciated.
6.2 Electrical power subject to transient voltage or frequency surges or distortion can alter CFR engine operating conditions or knock measuring instrumentation performance and thus affect the ΔO.N. obtained for spark-ignition engine fuels.
6.2.1 Electrical noise can affect the ability of the knock testing unit/automated analytical measurement system to accurately determine the ΔO.N. of the sample stream fuel.
6.3 Precaution - Avoid exposure of sample fuels to sunlight or fluorescent lamp UV emissions to minimize induced chemical reactions that can affect octane number ratings.
6.3.1 Exposure of these fuels to UV wavelengths shorter than 550 nanometers for a short period of time may significantly affect octane number ratings.
