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
1. Scope
1.1 This test method covers the quantitative online determination by direct comparison of the difference in knock rating or delta octane number of a stream sample of spark-ignition engine fuel from that of a comparison reference fuel.

1.2 This test method covers the methodology for obtaining an octane number using the measured delta octane number and the octane number of the comparison reference fuel.

1.3 The comparison reference fuel is required to be of essentially the same composition as the stream sample to be analyzed and can be a secondary fuel termed standard fuel or a tertiary fuel termed prototype fuel.

1.4 The test method utilizes a knock testing unit/automated analyzer system that incorporates computer control of a standardized single-cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine with appropriate auxiliary equipment using either Test Method D2699 Research method or Test Method D2700 Motor method operating conditions.
1.4.1 Knock measurements are based on operation of both fuels at the specific fuel-air ratio that produces maximum knock intensity for that fuel.

1.4.2 Measured differences in knock intensity are scaled to provide a positive or negative delta octane number of the stream sample from the comparison reference fuel when the fuels are compared at the same compression ratio.

1.4.3 Measured differences in compression ratio are scaled to provide a positive or negative delta octane number of the stream sample from the comparison reference fuel when the fuels are compared at the same knock intensity.

1.5 This test method is limited to testing 78 to 102 octane number spark-ignition engine fuels using either research or motor method conditions.

1.6 The octane number difference between the stream sample and the applicable comparison reference fuel is self-limiting by specifications imposed upon the standard and prototype fuels.

1.7 Specifications for selection, preparation, storage, and dispensing of standard and prototype fuels are provided. Detailed procedures for determination of an appropriate assigned octane number for both standard and prototype fuels are also incorporated.

1.8 The values of operating conditions are stated in SI units and are considered standard. The values in parentheses are historical inch-pound units. The standardized CFR engine measurements continue to be expressed in inch-pound units only because of the extensive and expensive tooling that has been created for this equipment.

1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For more specific warning statements, see Section 8 and Annex A1.

2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D2699 Test Method for Research Octane Number of Spark-Ignition Engine Fuel
D2700 Test Method for Motor Octane Number of Spark-Ignition Engine Fuel
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4814 Specification for Automotive Spark-Ignition Engine Fuel
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
D6624 Practice for Determining a Flow-Proportioned Average Property Value (FPAPV) for a Collected Batch of Process Stream Material Using Stream Analyzer Data
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics

2.2 Waukesha CFR Engine Manuals:
CFR F-1 & F-2 Octane Rating Units Operation & Maintenance FORM 847

3. Terminology
3.1 Definitions:
3.1.1 accepted reference value, n - a value that serves as an agreed-upon reference for comparison, and which is derived as: (1) a theoretical or established value, based on scientific principles, (2) an assigned value, based on experimental work of some national or international organization, or (3) a consensus value, based on collaborative experimental work under the auspices of a scientific or engineering group.
3.1.1.1 Discussion - In the context of this test method, accepted reference value is understood to apply to standard fuel or check fuel average research or motor octane numbers determined under reproducibility conditions by a recognized exchange testing organization having a minimum of 16 participants.

3.1.2 analytical measurement system, n - a collection of one or more components or subsystems, such as a sampler, test equipment, instrumentation, display devices, data handler, and printout or output transmitters that is used to determine a quantitative value of a specific property for an unknown sample.
3.1.2.1 Discussion - In the context of this test method, the analytical measurement system is comprised of the knock testing unit, automated analyzer system, and any auxiliary equipment required for the safe operation of the engine.

3.1.3 cylinder height, n - for the CFR engine, the relative vertical position of the engine cylinder with respect to the piston at top dead center (TDC) or the top machine surface of the crankcase.

3.1.4 digital counter reading, n - for the CFR engine, a numerical indication of cylinder height, indexed to a basic setting at a prescribed compression pressure when the engine is motored.

3.1.5 detonation meter, n - for knock testing, the signal conditioning instrument that accepts the electrical signal from the detonation pickup and provides an output signal for display.

3.1.6 detonation pickup, n - for knock testing, magnetostrictive type transducer that threads into the engine cylinder and is exposed to combustion chamber pressure to provide an electrical signal that is proportional to the rate-of-change of cylinder pressure.

3.1.7 fuel-air ratio for maximum knock intensity, n - for knock testing, that proportion of fuel to air which produces the highest knock intensity for each fuel in the knock testing unit, provided this occurs within the specified carburetor fuel level limits.
3.1.7.1 Discussion - In the context of this test method, the fuel-air ratio for maximum knock intensity can be determined manually or by the automated analyzer system.

3.1.7.2 dynamic fuel-air ratio for maximum knock, n - for knock testing, the changing of the mixture of fuel and air for engine combustion determined by continually varying fuel level in the carburetor delivery components, through the maximum knock intensity so that the observed peak knock intensity value can be selected as maximum knock intensity reading.

3.1.7.3 equilibrium fuel-air ratio for maximum knock, n - for knock testing, the changing of the mixture of fuel and air for engine combustion determined by making incremental step changes in fuel-air ratio, observing the equilibrium knock intensity for each step and selecting the fuel-air ratio which produces the highest knock meter reading.

3.1.8 guide tables, n - for knock testing, the specific relationship between cylinder height (compression ratio) and octane number at standard knock intensity.

3.1.9 knock, n - in a spark-ignition engine, abnormal combustion, often producing audible sound, caused by auto-ignition of the air/fuel mixture.

3.1.10 knock intensity, n - for knock testing, a measure of the level of knock.

3.1.11 knockmeter, n - for knock testing, the 0 to 100 division indicating meter that displays the knock intensity signal from the detonation meter.
3.1.11.1 Discussion - In the context of this test method, the knock intensity signal may also be displayed using digital or recording instrumentation.

3.1.12 motor octane number, n - for spark-ignition engine fuel, the numerical rating of knock resistance obtained by comparison of the fuel's knock intensity with that of primary reference fuel blends when both are tested in a standardized CFR engine operating under the conditions specified in Test Method D2700.

3.1.13 repeatability conditions, n - conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.
3.1.13.1 Discussion - In the context of this test method, application of repeatability conditions is primarily applied to the determination of variability of delta octane numbers generated by repeating the comparison measurements within a short time, by the same operator, using the same comparator, on the same fuel pair.

3.1.14 reproducibility conditions, n - conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment.

3.1.15 research octane number, n - for spark-ignition engine fuel, the numerical rating of knock resistance obtained by comparison of the fuel's knock intensity with that of primary reference fuel blends when both are tested in a standardized CFR engine operating under the conditions specified in Test Method D2699.

3.1.16 spread, n - in knock measurement, the sensitivity of the detonation meter expressed in knockmeter divisions per octane number.

3.1.17 site assigned value, n - a value that serves as an agreed-upon reference for comparison, determined from multiple test results obtained under site precision conditions.
3.1.17.1 Discussion - In the context of this test method, site assigned value is understood to apply to prototype fuel average research or motor octane number determined under site precision conditions using direct comparison delta octane number cycles comparing the prototype fuel to a standard fuel having an accepted reference value octane number.

3.1.18 site precision conditions, n - conditions under which test results are obtained by one or more operators in a single location practicing the same test method on a single measurement system using test specimens taken at random from the same sample of material over an extended period of time spanning at least a 15 day interval.
3.1.18.1 Discussion - In the context of this test method, application of site precision conditions is primarily applied to the determination of the variability of delta octane average results, obtained by different operators, over different days, for the same fuel pair, using the same comparator. Each delta octane average result is obtained from repetitive comparisons of the same fuel pair under repeatability conditions.

3.1.19 stream sample, n - the material to be evaluated by an analytical measurement system, typically drawn from a flowing stream of either blended spark-ignition engine fuel or process unit material.

3.2 Definitions of Terms Specific to This Standard:
3.2.1 comparison reference fuel, n - for direct comparison knock testing, a spark-ignition engine fuel having an assigned octane number that is the reference for the determination of the delta octane number of stream samples.
3.2.1.1 standard fuel, n - for direct comparison knock testing, a spark-ignition engine fuel having an octane number accepted reference value (RONARV or MONARV) which is used as a secondary comparison reference fuel for (1) determination of the octane number site assigned value (RONSAV or MON-SAV) of prototype fuels, (2) determination of the ΔO.N. of a stream sample, or (3) pairing with another standard fuel for analytical measurement system qualification checkout.

3.2.1.2 prototype fuel, n - for direct comparison knock testing, a spark-ignition engine fuel or process unit material having an octane number site assigned value (RONSAV or MONSAV) referenced to an appropriate standard fuel, which is used as a tertiary comparison reference fuel for determination of the ΔO.N. of a stream sample.

3.2.2 delta octane number, n - for direct comparison knock testing, the algebraic difference in octane number between two fuels under research or motor engine conditions, when determined by the direct comparison technique.

3.2.3 paired check fuels (A and B), n - for on-line knock testing system qualification checkout, two standard fuels used for system qualification checkout of a analytical measurement system.
3.2.3.1 expected difference O.N., n - for on-line knock testing system qualification checkout, the absolute octane number difference between paired check fuels (A-B) based on the O.N.ARV for both fuels.

3.2.4 paired quality control fuels, n - for on-line system quality control, a pair of fuels, one of which is a comparison reference fuel, to be used in the repetitive testing for ΔO.N. as a quality control check of the analytical measurement system.

3.2.5 span, n - for direct comparison knock testing, a measure of the overall sensitivity of the analyzer. The ratio of the change in delta octane reported produced by a given change in either compression ratio or knock intensity.

3.3 Acronyms:
3.3.1 AMS - analytical measurement system

3.3.2 ARV - accepted reference value

3.3.3 RONARV - research octane number accepted reference value

3.3.4 MONARV - motor octane number accepted reference value

3.3.5 SAV - site assigned value

3.3.6 RONSAV - research octane number site assigned value

3.3.7 MONSAV - motor octane number site assigned value

3.3.8 C.R. - compression ratio

3.3.9 K.I. - knock intensity

3.3.10 O.N. - octane number

3.3.11 ΔO.N. - delta octane number

3.3.12 PRF - primary reference fuel

3.3.13 CRF - comparison reference fuel

3.4 Symbols:
3.4.1 Q - accuracy qualification value

3.4.2 K - accuracy qualification acceptance limit