ASTM D2699 test method for Research Octane Number of Spark-Ignition Engine Fuel
1. Scope
1.1 This laboratory test method covers the quantitative determination of the knock rating of liquid spark-ignition engine fuel in terms of Research O.N., except that this test method may not be applicable to fuel and fuel components that are primarily oxygenates. The sample fuel is tested using a standardized single cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions. The O.N. scale is defined by the volumetric composition of PRF blends. The sample fuel knock intensity is compared to that of one or more PRF blends. The O.N. of the PRF blend that matches the K.I. of the sample fuel establishes the Research O.N.

1.2 The O.N. scale covers the range from 0 to 120 octane number but this test method has a working range from 40 to 120 Research O.N. Typical commercial fuels produced for spark-ignition engines rate in the 88 to 101 Research O.N. range. Testing of gasoline blend stocks or other process stream materials can produce ratings at various levels throughout the Research O.N. range.

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

1.4 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 specific hazard statements, see Section 8, 13.4.1, 14.5.1, 15.6.1, Annex A1, A2.3.9, A2.4.8, A3.2.7.2(7), A4.2.3.1, A4.2.3.3(6) and (9), A4.3.5, X2.3.7, X3.2.3.1, X3.3.4.1, X3.3.9.3, X3.3.11.4, and X3.5.1.8.

2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D1744 Test Method for Determination of Water in Liquid Petroleum Products by Karl Fischer Reagent
D2268 Test Method for Analysis of High-Purity n-Heptane and Isooctane by Capillary Gas Chromatography
D2360 Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons by Gas Chromatography
D2700 Test Method for Motor Octane Number of Spark-Ignition Engine Fuel
D2885 Test Method for Determination of Octane Number of Spark-Ignition Engine Fuels by On-Line Direct Comparison Technique
D3703 Test Method for Peroxide Number of Aviation Turbine Fuels
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
D5842 Practice for Sampling and Handling of Fuels for Volatility Measurements
E 1 Specification for Liquid-in-Glass ASTM Thermometers
E 456 Terminology for Relating to Quality and Statistics
E 542 Practice for Calibration of Laboratory Volumetric Apparatus

2.2 ANSI Standard:
C-39.1 Requirements for Electrical Analog Indicating Instruments

2.3 Energy Institute Standard:
IP 224/02 Determination of Low Lead Content of Light Petroleum Distillates by Dithizone Extraction and Colorimetric Method

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 or certified value, based on experimental work of some national or international organization, or (3) a consensus or certified 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 the Research octane number of specific reference materials determined empirically under reproducibility conditions by the National Exchange Group or another recognized exchange testing organization.

3.1.2 Check Fuel, n - for quality control testing, a spark-ignition engine fuels of selected characteristics having an octane number accepted reference value (O.N.ARV) determined by round-robin testing under reproducibility conditions.

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 machined surface of the crankcase.

3.1.3.1 dial indicator reading, n - for the CFR engine, a numerical indication of cylinder height, in thousandths of an inch, indexed to a basic setting at a prescribed compression pressure when the engine is motored.

3.1.3.2 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.

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

3.1.5 detonation pickup, n - for knock testing, a 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.

3.1.6 dynamic fuel level, n - for knock testing, test procedure in which the fuel-air ratio for maximum knock intensity for sample and reference fuels is determined using the falling level technique that changes carburetor fuel level from a high or rich mixture condition to a low or lean mixture condition, at a constant rate, causing knock intensity to rise to a maximum and then decrease, thus permitting observation of the maximum knockmeter reading.

3.1.7 equilibrium fuel level, n - for knock testing, test procedure in which the fuel-air ratio for maximum knock intensity for sample and reference fuels is determined by making incremental step changes in carburetor fuel level, observing the equilibrium knock intensity for each step, and selecting the level that produces the highest knock intensity reading.

3.1.8 firing, n - for the CFR engine, operation of the CFR engine with fuel and ignition.

3.1.9 fuel-air ratio for maximum knock intensity, n - for knock testing, that proportion of fuel to air that produces the highest knock intensity for each fuel in the knock testing unit, provided this occurs within specified carburetor fuel level limits.

3.1.10 guide tables, n - for knock testing, the specific relationship between cylinder height (compression ratio) and octane number at standard knock intensity for specific primary reference fuel blends tested at standard or other specified barometric pressure.

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

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

3.1.13 knockmeter, n - for knock testing, the 0 to 100 division indicating meter that displays the knock intensity signal from the detonation meter.

3.1.14 motoring, n - for the CFR engine, operation of the CFR engine without fuel and with the ignition shut off.

3.1.15 octane number, n - for spark-ignition engine fuel, any one of several numerical indicators of resistance to knock obtained by comparison with reference fuels in standardized engine or vehicle tests.

3.1.15.1 research octane number, n - for spark-ignition engine fuel, the numerical rating of knock resistance obtained by comparison of its knock intensity with that of primary reference fuel blends when both are tested in a standardized CFR engine operating under the conditions specified in this test method.

3.1.16 oxygenate, n - an oxygen-containing organic compound, which may be used as a fuel or fuel supplement, for example, various alcohols and ethers.

3.1.17 primary reference fuels, n - for knock testing, isooctane, n-heptane, volumetrically proportioned mixtures of isooctane with n-heptane, or blends of tetraethyllead in isooctane that define the octane number scale.

3.1.17.1 primary reference fuel blends below 100 octane, n - the volume % of isooctane in a blend with n-heptane that defines the octane number of the blend, isooctane being assigned as 100 and n-heptane as 0 octane number.

3.1.17.2 primary reference fuel blends above 100 octane, n - the millilitres per U.S. gallon of tetraethyllead in isooctane that define octane numbers above 100 in accordance with an empirically determined relationship.

3.1.18 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.

3.1.18.1 Discussion - In the context of this test method, a short time interval between two ratings on a sample fuel is understood to be not less than the time to obtain at least one rating on another sample fuel between them but not so long as to permit any significant change in the sample fuel, test equipment, or environment.

3.1.19 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.

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

3.1.21 standard knock intensity, n - for knock testing, that level of knock established when a primary reference fuel blend of specific octane number is used in the knock testing unit at maximum knock intensity fuel-air ratio, with the cylinder height (dial indicator or digital counter reading) set to the prescribed guide table value. The detonation meter is adjusted to produce a knockmeter reading of 50 for these conditions.

3.1.22 toluene standardization fuels, n - for knock testing, those volumetrically proportioned blends of two or more of the following: reference fuel grade toluene, n-heptane, and isooctane that have prescribed rating tolerances for O.N.ARV determined by round-robin testing under reproducibility conditions.

3.2 Abbreviations:
3.2.1 ARV = accepted reference value

3.2.2 C.R. = compression ratio

3.2.3 IAT = intake air temperature

3.2.4 K.I. = knock intensity

3.2.5 O.N. = octane number

3.2.6 PRF = primary reference fuel

3.2.7 TSF = toluene standardization fuel