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
7. Apparatus
7.1 This test method utilizes a multi-component analytical measurement system (AMS). It incorporates a knock testing engine with instrumentation to measure and produce an output signal representative of the difference in knock rating or ΔO.N. An associated automated control system includes a fuel delivery system to introduce a stream sample or CRF to the engine critical carburetor components. The automated system shall also include equipment and controls for switching between the CRF and the stream sample, controls for operating the test engine and monitoring the critical operating conditions, and instrumentation to convert the compression ratio (C.R.) or knock intensity (K.I.) to a ΔO.N.
7.1.1 An appropriate CFR engine knock testing unit specified for the determination of research octane number or motor octane number and meeting the recommendations of the manufacturer of the AMS. Specific knock testing unit equipment can include the following:
7.1.1.1 For research octane number measurement, a Model CFR F-1, single cylinder engine knock testing unit assembly comprised of the appropriate critical or equivalent equipment components selected by the system manufacturer, and for which specifications are provided in Test Method D2699, Annex A2.

7.1.1.2 For motor octane number measurement, a Model CFR F-2, single cylinder engine knock testing unit assembly comprised of the appropriate critical or equivalent equipment components selected by the system manufacturer, and for which specifications are provided in Test Method D2700, Annex A2.

7.1.1.3 Instrumentation for the measurement of knock, temperatures or other knock testing unit variables as selected by the system manufacturer, and for which specifications are provided in Annex A2, of either Test Method D2699 or Test Method D2700, whichever is appropriate.

7.1.1.4 The AMS system installation requires a number of components and devices to integrate the critical or equivalent equipment items into a complete working unit. Specific items to satisfy important criteria for proper operation of the respective CFR engine unit are to comply with the appropriate non-critical equipment specifications in Annex A2, of either Test Method D2699 or Test Method D2700, whichever is appropriate.

7.1.1.5 Equipment for adjustment of engine compression ratio and a mechanism for relative measurement of this variable when the ΔO.N. value is based on differences in engine compression ratio.

7.1.2 Automated control equipment for adjustment and monitoring of the critical operating variables of the knock testing unit is required and selected in accordance with the recommendations and instructions of the system manufacturer. Specific variables and conditions to be handled by the automated control equipment can include the following:
7.1.2.1 A mechanism to vary fuel-air ratio and determine the condition that produces a maximum K.I. signal. Determination of the fuel-air ratio for maximum knock intensity can be performed using either the equilibrium or a dynamic search technique.

7.1.2.2 An adjustable octane number scaling function to convert the measured signal variable to an output signal ΔO.N. value, recognizing any non-linear relationship that can exist.

7.1.2.3 Timing controls for fuel switching and measurement functions to meet the specified operating principles of this test method.

7.1.2.4 Suitable sensors for monitoring operating conditions and system safety related functions that are incorporated in the system design.

7.1.3 A sample system to provide a continuously representative stream and deal with the unconsumed stream sample.
7.1.3.1 Equipment to treat the incoming stream sample fuel to remove particulate matter and entrained water to meet the requirements specified by the system manufacturer.

7.1.4 Storage vessels and associated equipment for storing and supplying one or more CRF materials.

8. Reagents and Reference Materials
8.1 Cylinder Jacket Coolant - Use water in the cylinder jacket for engine locations where the resultant boiling temperature will be 100 more or less 1.5°C (212 more or less 3°F). Use water with commercial glycol based antifreeze added in sufficient quantity to meet the boiling temperature requirements where altitude dictates. A commercial multifunction water treatment material can be used in the coolant to minimize corrosion and mineral scale that can alter heat transfer and rating results.
8.1.1 Water is understood to mean reagent water conforming to type IV, Specification D1193. (Warning - Ethylene glycol based antifreeze is poisonous and may be harmful or fatal if inhaled or swallowed. See Annex A1.)

8.2 Engine Crankcase Lubricating Oil - SAE 30 viscosity grade oil meeting the current API service classification for spark-ignition engines containing a detergent additive and having a kinematic viscosity of 9.3 to 12.5 mm2 per s (cst) at 100°C (212°F) and a viscosity index of not less than 85. Do not use oils containing viscosity index improvers or multigrade oils. (Warning - Lubricating oil is combustible and its vapor is harmful. See Annex A1.)

8.3 Standard Fuel - (Warning - Standard fuel is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.) A secondary comparison reference fuel that conforms to the following:
8.3.1 Octane Number - Selected to have a RONARV or MONARV with respect to the O.N. of the prototype fuel or the stream samples to be analyzed.
8.3.1.1 The difference between standard fuel and related prototype fuel shall not exceed more or less 0.5 O.N.

8.3.1.2 The difference between standard fuel and the stream samples to be analyzed shall not exceed more or less 1.0 O.N.
(1) Discussion - The difference between the standard fuel and the stream sample refers to when the standard fuel is used in direct comparison to the stream sample.

8.3.1.3 Determine the appropriate O.N.ARV of standard fuel under reproducibility conditions using a minimum of 16 different exchange participants (see Annex A3).

8.3.2 Volatility - Or use with blended stream samples, the standard fuel can be slightly less volatile than the stream samples to be analyzed in the interest of minimizing weathering.
8.3.2.1 A vapor pressure, as defined in Test Method D4814, of less than 68.9 kPa (10 psi) is preferred but, in any case, it shall not exceed 82.7 kPa (12 psi).

8.3.3 Hydrocarbon Composition - Similar to that of a related prototype fuel or the stream samples to be analyzed. Users are cautioned to investigate the O.N. effect of any significant differences in composition matrix between these related fuels.

8.3.4 Antiknock Compound - The same organometallic lead or manganese additive compound, in a similar concentration, shall be present in the standard fuel if it is present in the prototype fuel or stream sample to be analyzed.

8.3.5 Octane Enhancers - Compounds such as oxygenates shall be present in the standard fuel, in similar concentration, to that present in the prototype fuel or stream sample to be analyzed.

8.3.6 Antioxidant - Add at the treat-rate recommended by the additive supplier to ensure maximum storage stability.
8.3.6.1 Add antioxidant prior to distribution of standard fuel for the determination of the O.N.ARV.

8.3.7 Metal Deactivator - Add in accordance with supplier recommendations if it is deemed necessary.

8.3.8 Storage and Handling - Controlled conditions to minimize the possibility of octane number change or contamination. Systems and procedures shall conform to the requirements set forth in Annex A2 of this test method.

8.4 Prototype Fuel - (Warning - Prototype fuel is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.) A tertiary comparison reference fuel that conforms to the following:
8.4.1 Octane Number - The difference between prototype fuel and the stream samples to be analyzed shall not exceed more or less 1.0 O.N.
8.4.1.1 Determine the appropriate O.N.SAV of prototype fuel based on the average value of a minimum of 10 direct match knock characteristic comparisons, obtained either manually or automatically, under site precision conditions (see Annex A4).

8.4.2 Volatility - For use with blended stream samples, the prototype fuel can be slightly less volatile than the stream samples to be analyzed in the interest of minimizing weathering.
8.4.2.1 A vapor pressure, as defined in Test Method D4814, of less than 68.9 kPa (10 psi) is preferred but, in any case, it shall not exceed 82.7 kPa (12 psi).

8.4.3 Hydrocarbon Composition - Similar to that of the stream samples to be analyzed. Users are cautioned to investigate the O.N. effect of any significant differences in composition matrix between these related fuels.

8.4.4 Antiknock Compound - The same organometallic lead or manganese additive compound, in a similar concentration, shall be present in the prototype fuel if it is present in the stream sample to be analyzed.

8.4.5 Octane Enhancers - Compounds such as oxygenates shall be present in the prototype fuel, in similar concentration, to that present in the stream sample to be analyzed.

8.4.6 Antioxidant - Add at the treat-rate recommended by the additive supplier to ensure maximum storage stability.

8.4.7 Metal Deactivator - Add in accordance with supplier recommendations if it is deemed necessary.

8.4.8 Storage and Handling - Control conditions to minimize the possibility of octane number change or contamination. Systems and procedures shall conform to the recommendations set forth in Annex A2.

8.5 Paired Check Fuels - The paired check fuels will have an expected difference O.N. ranging from 0.2 to 1.0 and be coded so the difference in the accepted reference values (Fuel A-Fuel B) is a positive value.
8.5.1 The fuel characteristics, including those for antiknock compound, octane enhancers, and antioxidant protection are to be similar for the two check fuels of a pair.

8.6 Paired Quality Control Fuels - The two quality control fuels, one of which is a comparison reference fuel, shall have ΔO.N. ranging from 0.2 to 1.0.

8.7 Primary Reference Fuels - Reference fuel grade isooctane, heptane, the 80 O.N. blend of the two meeting the specifications given in Test Method D2699 or Test Method D2700, or both. (Warning - Primary reference fuels are flammable and the vapors are harmful. Vapors may cause flash fire. See Annex A1.)

9. Sampling
9.1 Collect stream samples for on-line analysis in accordance with Practice D4177.
9.1.1 Collect, treat, and deliver stream samples to the CFR engine carburetor in a way that minimizes exposure to light of any form.

9.2 Collect stream sample material for preparation, storage and laboratory testing as comparison reference fuels in accordance with Practices D4057, D4177, and D5842.
9.2.1 Collect and store sample fuels in an opaque container, such as a dark brown glass bottle, metal can, or a minimally reactive plastic container to minimize exposure to UV emissions from sources such as sunlight or fluorescent lamps.