ASTM D2699-24a

Standard Test Method for Research Octane Number of Spark-Ignition Engine Fuel

SIGNIFICANCE AND USE
5.1 Research O.N. correlates with commercial automotive spark-ignition engine antiknock performance under mild conditions of operation.  
5.2 Research O.N. is used by engine manufacturers, petroleum refiners and marketers, and in commerce as a primary specification measurement related to the matching of fuels and engines.  
5.2.1 Empirical correlations that permit calculation of automotive antiknock performance are based on the general equation:
Values of k1,  k2, and k3 vary with vehicles and vehicle populations and are based on road-O.N. determinations.  
5.2.2 Research O.N., in conjunction with Motor O.N., defines the antiknock index of automotive spark-ignition engine fuels, in accordance with Specification D4814. The antiknock index of a fuel approximates the Road octane ratings for many vehicles, is posted on retail dispensing pumps in the U.S., and is referred to in vehicle manuals.
This is more commonly presented as:
5.2.3 Research O.N. is also used either alone or in conjunction with other factors to define the Road O.N. capabilities of spark-ignition engine fuels for vehicles operating in areas of the world other than the United States.  
5.3 Research O.N. is used for measuring the antiknock performance of spark-ignition engine fuels that contain oxygenates.  
5.4 Research O.N. is important in relation to the specifications for spark-ignition engine fuels used in stationary and other nonautomotive engine applications.
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., including fuels that contain up to 25 % v/v of ethanol. However, this test method may not be applicable to fuel and fuel components that are primarily oxygenates.2 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 For purposes of determining conformance with all specified limits in this standard, an observed value or a calculated value shall be rounded “to the nearest unit” in the last right-hand digit used in expressing the specified limit, in accordance with the rounding method of Practice E29.  
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see Section 8, 14.4.1, 15.5.1, 16.6.1, Annex A1, A2.2.3.1, A2.2.3.3 (6) and (9), A2.3.5, X3.3.7, X4.2.3.1, X4.3.4.1, X4.3.9.3, X4.3.11.4, and X4.5.1.8.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Gu...

General Information

• Status: Published
• Publication Date: 30-Apr-2024
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.01 - Combustion Characteristics

Overview

ASTM D2699-24a, "Standard Test Method for Research Octane Number of Spark-Ignition Engine Fuel," is a key international standard developed by ASTM International. This standard provides a laboratory test method for quantitatively determining the research octane number (Research O.N.) of liquid spark-ignition engine fuels, including those with up to 25% ethanol content. The procedure involves testing the fuel in a standardized single-cylinder, four-stroke, variable compression ratio Cooperative Fuel Research (CFR) engine under controlled conditions and comparing its knock intensity to that of primary reference fuel blends.

The research octane number is a primary indicator for the antiknock quality of gasoline and is directly relevant to the performance, efficiency, and emissions of automotive spark-ignition engines.

Key Topics

• Research Octane Number (Research O.N.): This is a quantitative measure of a fuel's resistance to engine knock under mild operating conditions.
• Primary Reference Fuels (PRF): The octane number scale is established by volumetric blends of n-heptane and isooctane, the fundamental reference compounds used in the test method.
• Knock Measurement: The standard requires precise adjustment of the fuel-air ratio and engine compression to measure knock intensity, or abnormal combustion, compared to reference fuels.
• Test Method Range: The working range is from 40 to 120 Research O.N., covering typical commercial automotive fuels which usually rate between 88 and 101.
• Applicability: The method applies to most gasoline fuels, including those with oxygenates such as ethanol, though it may not be suitable for blends primarily composed of oxygenates.
• Quality Assurance: The standard emphasizes proper sample handling, storage, blending procedures, and instrumentation calibration to ensure accurate and repeatable results.
• Safety Considerations: Various safety, health, and environmental precautions are highlighted, including proper ventilation, handling of flammable liquids, and compliance with regulatory guidelines.

Applications

ASTM D2699-24a plays a crucial role in the fuel, automotive, and refining industries:

• Fuel Manufacturers: Determines the research octane number of gasoline, which is vital for product development, blending, and quality control.
• Engine Manufacturers: Utilizes octane ratings for engine design and to ensure compatibility between engines and available fuel grades.
• Fuel Marketers and Retailers: Relies on research octane number (combined with Motor O.N. per ASTM D2700) to derive the antiknock index, the fuel rating displayed at retail pumps in many regions, particularly the USA.
• Regulatory Compliance: Ensures fuels meet specifications such as ASTM D4814 for automotive spark-ignition engine fuel.
• International Use: Supports the matching of fuels to vehicles in markets worldwide and is referenced in manufacturer manuals and government regulations.
• Stationary & Nonautomotive Engines: Provides essential quality data for applications beyond automotive, such as industrial engines.

Related Standards

For consistent and reliable measurement of gasoline properties, ASTM D2699-24a is commonly used alongside several related standards, including:

• ASTM D2700 - Test Method for Motor Octane Number of Spark-Ignition Engine Fuel (companion test for more severe conditions)
• ASTM D4814 - Specification for Automotive Spark-Ignition Engine Fuel (defines fuel quality in North America)
• ASTM D4057 / D4177 - Practices for Manual and Automatic Sampling of Petroleum Products
• ASTM D2268 - Analysis of High-Purity n-Heptane and Isooctane
• ASTM D6299 - Statistical Quality Assurance for Analytical Measurement System Performance
• ANSI C-39.1 - Requirements for Electrical Analog Indicating Instruments
• Energy Institute IP 224/02 - For lead content analysis in light petroleum distillates

By adhering to ASTM D2699-24a, stakeholders ensure compatibility, safety, and efficiency in the global supply and utilization of spark-ignition engine fuels. This standard is essential for anyone involved in the testing, production, regulation, or sale of gasoline and related fuels.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2699 − 24a
Standard Test Method for
Research Octane Number of Spark-Ignition Engine Fuel
This standard is issued under the fixed designation D2699; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This laboratory test method covers the quantitative
responsibility of the user of this standard to establish appro-
determination of the knock rating of liquid spark-ignition
priate safety, health, and environmental practices and deter-
engine fuel in terms of Research O.N., including fuels that
mine the applicability of regulatory limitations prior to use.
contain up to 25 % v/v of ethanol. However, this test method
For specific warning statements, see Section 8, 14.4.1, 15.5.1,
may not be applicable to fuel and fuel components that are
2 16.6.1, Annex A1, A2.2.3.1, A2.2.3.3 (6) and (9), A2.3.5,
primarily oxygenates. The sample fuel is tested using a
X3.3.7, X4.2.3.1, X4.3.4.1, X4.3.9.3, X4.3.11.4, and X4.5.1.8.
standardized single cylinder, four-stroke cycle, variable com-
1.6 This international standard was developed in accor-
pression ratio, carbureted, CFR engine run in accordance with
dance with internationally recognized principles on standard-
a defined set of operating conditions. The O.N. scale is defined
ization established in the Decision on Principles for the
by the volumetric composition of PRF blends. The sample fuel
Development of International Standards, Guides and Recom-
knock intensity is compared to that of one or more PRF blends.
mendations issued by the World Trade Organization Technical
The O.N. of the PRF blend that matches the K.I. of the sample
Barriers to Trade (TBT) Committee.
fuel establishes the Research O.N.
1.2 The O.N. scale covers the range from 0 to 120 octane
2. Referenced Documents
number but this test method has a working range from 40 to
2.1 ASTM Standards:
120 Research O.N. Typical commercial fuels produced for
D1193 Specification for Reagent Water
spark-ignition engines rate in the 88 to 101 Research O.N.
D2268 Test Method for Analysis of High-Purity n-Heptane
range. Testing of gasoline blend stocks or other process stream
and Isooctane by Capillary Gas Chromatography
materials can produce ratings at various levels throughout the
D2700 Test Method for Motor Octane Number of Spark-
Research O.N. range.
Ignition Engine Fuel
1.3 The values of operating conditions are stated in SI units
D2885 Test Method for Determination of Octane Number of
and are considered standard. The values in parentheses are the
Spark-Ignition Engine Fuels by On-Line Direct Compari-
historical inch-pound units. The standardized CFR engine
son Technique
measurements continue to be in inch-pound units only because
D3703 Test Method for Hydroperoxide Number of Aviation
of the extensive and expensive tooling that has been created for
Turbine Fuels, Gasoline and Diesel Fuels
this equipment.
D4057 Practice for Manual Sampling of Petroleum and
Petroleum Products
1.4 For purposes of determining conformance with all
specified limits in this standard, an observed value or a D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
calculated value shall be rounded “to the nearest unit” in the
last right-hand digit used in expressing the specified limit, in D4177 Practice for Automatic Sampling of Petroleum and
Petroleum Products
accordance with the rounding method of Practice E29.
D4814 Specification for Automotive Spark-Ignition Engine
Fuel
D5842 Practice for Sampling and Handling of Fuels for
This test method is under the jurisdiction of ASTM Committee D02 on
Volatility Measurement
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.01 on Combustion Characteristics.
Current edition approved May 1, 2024. Published May 2024. Originally
approved in 1968. Last previous edition approved in 2024 as D2699 – 24. DOI:
10.1520/D2699-24A. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Motor O.N., determined using Test Method D2700, is a companion method to contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
provide a similar but typically lower octane rating under more severe operating Standards volume information, refer to the standard’s Document Summary page on
conditions. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2699 − 24a
D6299 Practice for Applying Statistical Quality Assurance 3.1.3 cylinder height, n—for the CFR engine, the relative
and Control Charting Techniques to Evaluate Analytical vertical position of the engine cylinder with respect to the
Measurement System Performance piston at top dead center (tdc) or the top machined surface of
D6300 Practice for Determination of Precision and Bias the crankcase.
Data for Use in Test Methods for Petroleum Products, 3.1.3.1 digital counter reading, n—for the CFR engine, a
Liquid Fuels, and Lubricants numerical indication of cylinder height, indexed to a basic
D6304 Test Method for Determination of Water in Petro- setting at a prescribed compression pressure when the engine is
leum Products, Lubricating Oils, and Additives by Cou- motored.
lometric Karl Fischer Titration 3.1.3.2 dial indicator reading, n—for the CFR engine, a
D6708 Practice for Statistical Assessment and Improvement numerical indication of cylinder height, in thousandths of an
of Expected Agreement Between Two Test Methods that inch, indexed to a basic setting at a prescribed compression
Purport to Measure the Same Property of a Material pressure when the engine is motored.
D7504 Test Method for Trace Impurities in Monocyclic 3.1.4 detonation meter, analog, n—for knock testing, the
Aromatic Hydrocarbons by Gas Chromatography and signal conditioning instrumentation that accepts the electrical
Effective Carbon Number signal from the detonation pickup and provides an analog
E29 Practice for Using Significant Digits in Test Data to output signal to the analog knockmeter.
Determine Conformance with Specifications
3.1.4.1 Discussion—In the context of this test method, three
E344 Terminology Relating to Thermometry and Hydrom-
contemporary generations of apparatus have been developed as
etry
detonation meters. These are (year of introduction in parenthe-
E456 Terminology Relating to Quality and Statistics
sis): the 501T Detonation Meter (1969), the 501C Detonation
E542 Practice for Gravimetric Calibration of Laboratory
Meter (1979), and the SSD7000 Detonation Meter (2017).
Volumetric Instruments
3.1.5 detonation meter, digital, n—for knock testing, the
E1064 Test Method for Water in Organic Liquids by Coulo-
digital signal conditioning instrumentation that accepts the
metric Karl Fischer Titration
electrical signal from the detonation pickup and provides a
2.2 ANSI Standard:
digital output for display.
C-39.1 Requirements for Electrical Analog Indicating In-
3.1.6 detonation pickup, n—for knock testing, a
struments
magnetostrictive-type transducer that threads into the engine
2.3 Energy Institute Standard:
cylinder and is exposed to combustion chamber pressure to
IP 224/02 Determination of Low Lead Content of Light
provide an electrical signal that is proportional to the rate-of-
Petroleum Distillates by Dithizone Extraction and Colo-
change of cylinder pressure.
rimetric Method
3.1.7 dynamic fuel level, n—for knock testing, test proce-
dure in which the fuel-air ratio for maximum knock intensity
3. Terminology
for sample and reference fuels is determined using the falling
3.1 Definitions:
level technique that changes carburetor fuel level from a high
3.1.1 accepted reference value, n—a value that serves as an
or rich mixture condition to a low or lean mixture condition, at
agreed-upon reference for comparison, and which is derived
a constant rate, causing knock intensity to rise to a maximum
as: (1) a theoretical or established value, based on scientific
and then decrease, thus permitting observation of the maxi-
principles, (2) an assigned or certified value, based on experi-
mum knockmeter reading.
mental work of some national or international organization, or
3.1.8 equilibrium fuel level, n—for knock testing, test pro-
(3) a consensus or certified value, based on collaborative
cedure in which the fuel-air ratio for maximum knock intensity
experimental work under the auspices of a scientific or
for sample and reference fuels is determined by making
engineering group. E456
incremental step changes in fuel-air ratio, observing the equi-
3.1.1.1 Discussion—In the context of this test method,
librium knock intensity for each step, and selecting the level
accepted reference value is understood to apply to the Research
that produces the highest knock intensity reading.
octane number of specific reference materials determined
3.1.9 firing, n—for the CFR engine, operation of the CFR
empirically under reproducibility conditions by the National
engine with fuel and ignition.
Exchange Group or another recognized exchange testing orga-
3.1.10 fuel-air ratio for maximum knock intensity, n—for
nization.
knock testing, that proportion of fuel to air that produces the
3.1.2 Check Fuel, n—for quality control testing, a spark-
highest knock intensity for each fuel in the knock testing unit,
ignition engine fuels of selected characteristics having an
provided this occurs within specified carburetor fuel level
octane number accepted reference value (O.N. ) determined
ARV
limits.
by round-robin testing under reproducibility conditions.
3.1.11 guide tables, n—for knock testing, the specific rela-
tionship between cylinder height (compression ratio) and
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. Supporting data have been filed at ASTM International Headquarters and may
Available from Energy Institute, 61 New Cavendish St., London, W1G 7AR, be obtained by requesting Research Report RR:D02-1870. Contact ASTM Customer
U.K., http://www.energyinst.org. Service at [e-mail].
D2699 − 24a
octane number at standard knock intensity for specific primary per octane number. (This feature is not a necessary adjustment
reference fuel blends tested at standard or other specified in the digital detonation meter.)
barometric pressure.
3.1.25 standard knock intensity, n—for knock testing, that
3.1.12 knock, n—in a spark-ignition engine, abnormal level of knock established when a primary reference fuel blend
combustion, often producing audible sound, caused by autoi- of specific octane number is used in the knock testing unit at
gnition of the air/fuel mixture. D4175 maximum knock intensity fuel-air ratio, with the cylinder
height (dial indicator or digital counter reading) set to the
3.1.13 knock intensity, n—for knock testing, a measure of
prescribed guide table value.
the level of knock.
3.1.26 toluene standardization fuels, n—for knock testing,
3.1.14 knockmeter, analog, n—for knock testing, the 0 to
those volumetrically proportioned blends of two or more of the
100 division analog indicating meter that displays the knock
following: reference fuel grade toluene, n-heptane, and isooc-
intensity signal from the analog detonation meter.
tane that have prescribed rating tolerances for O.N. deter-
ARV
3.1.15 knockmeter, digital, n—for knock testing, the 0 to 999
mined by round-robin testing under reproducibility conditions.
division digital indicating meter that displays the knock inten-
3.2 Definitions of Terms Specific to This Standard:
sity from the digital detonation meter.
3.2.1 primary reference fuels, n—for knock testing,
3.1.16 motoring, n—for the CFR engine, operation of the
isooctane, n-heptane, volumetrically proportioned mixtures of
CFR engine without fuel and with the ignition shut off.
isooctane with n-heptane, or blends of tetraethyllead in isooc-
3.1.17 octane number, n—for spark-ignition engine fuel,
tane that define the octane number scale.
any one of several numerical indicators of resistance to knock
3.2.2 repeatability conditions NEG, n—replicate testing
obtained by comparison with reference fuels in standardized
conditions employed by the National Exchange Group in
engine or vehicle tests. D4175
which a single operator tests two specimens taken from a single
3.1.17.1 research octane number, n—for spark-ignition en-
sample container with at least one other sample being tested
gine fuel, the numerical rating of knock resistance obtained by
between the two specimens.
comparison of its knock intensity with that of primary refer-
3.3 Abbreviations:
ence fuel blends when both are tested in a standardized CFR
3.3.1 ARV = accepted reference value
engine operating under the conditions specified in this test
3.3.2 CFR = Cooperative Fuel Research
method.
3.3.3 C.R. = compression ratio
3.1.18 oxygenate, n—an oxygen-containing organic
3.3.4 IAT = intake air temperature
compound, which may be used as a fuel or fuel supplement, for
3.3.5 K.I. = knock intensity
example, various alcohols and ethers. D4175
3.3.6 NEG = National Exchange Group
3.1.19 primary reference fuel blends above 100 octane,
3.3.7 OA = Octane Analyzer
n—the millilitres per U.S. gallon of tetraethyllead in isooctane 3.3.8 O.N. = octane number
that define octane numbers above 100 in accordance with an 3.3.9 PRF = primary reference fuel
empirically determined relationship. 3.3.10 r = repeatability conditions NEG
NEG
3.3.11 RTD = resistance thermometer device (E344) plati-
3.1.20 primary reference fuel blends below 100 octane,
num type
n—the volume % of isooctane in a blend with n-heptane that
3.3.12 TSF = toluene standardization fuel
defines the octane number of the blend, isooctane being
assigned as 100 and n-heptane as 0 octane number.
4. Summary of Test Method
3.1.21 quality control (QC) sample, n—for use in quality
4.1 The Research O.N. of a spark-ignition engine fuel is
assurance programs to determine and monitor the precision and
determined using a standard test engine and operating condi-
stability of a measurement system, a stable and homogeneous
tions to compare its knock characteristic with those of PRF
material having physical or chemical properties, or both,
blends of known O.N. Compression ratio and fuel-air ratio are
similar to those of typical samples tested by the analytical
adjusted to produce standard K.I. for the sample fuel, as
measurement system. The material is properly stored to ensure
measured by a specific electronic detonation measurement
sample integrity, and is available in sufficient quantity for
system. A standard K.I. guide table relates engine C.R. to O.N.
repeated, long term testing. D6299
level for this specific method. The fuel-air ratio for the sample
3.1.22 repeatability conditions, n—conditions where inde-
fuel and each of the primary reference fuel blends is adjusted
pendent test results are obtained with the same method on
to maximize K.I. for each fuel.
identical test items in the same laboratory by the same operator
4.1.1 The fuel-air ratio for maximum K.I. may be obtained
using the same equipment within short intervals of time. E456
(1) by making incremental step changes in mixture strength,
3.1.23 reproducibility conditions, n—conditions where test observing the equilibrium K.I. value for each step, and then
selecting the condition that maximizes the reading or (2) by
results are obtained with the same method on identical test
items in different laboratories with different operators using picking the maximum K.I. as the mixture strength is changed
from either rich-to-lean or lean-to-rich at a constant rate.
different equipment. E456
3.1.24 spread, n—in knock measurement, the sensitivity of 4.2 Bracketing Procedures—The engine is calibrated to
the analog detonation meter expressed in knockmeter divisions operate at standard K.I. in accordance with the guide table. The
D2699 − 24a
fuel-air ratio of the sample fuel is adjusted to maximize the spark-ignition engine fuels for vehicles operating in areas of
K.I., and then the cylinder height is adjusted so that standard the world other than the United States.
K.I. is achieved. Without changing cylinder height, two PRF
5.3 Research O.N. is used for measuring the antiknock
blends are selected such that, at their fuel-air ratio for maxi-
performance of spark-ignition engine fuels that contain oxy-
mum K.I., one knocks harder (higher K.I.) and the other softer
genates.
(lower K.I.) than the sample fuel. A second set of K.I.
5.4 Research O.N. is important in relation to the specifica-
measurements for sample fuel and PRF blends is required, and
tions for spark-ignition engine fuels used in stationary and
the sample fuel octane number is calculated by interpolation in
other nonautomotive engine applications.
proportion to the differences in average K.I. readings. A final
condition requires that the cylinder height used shall be within
6. Interferences
prescribed limits around the guide table value for the calculated
6.1 Precaution—Avoid exposure of sample fuels to sunlight
O.N. Bracketing procedure ratings may be determined using
or fluorescent lamp UV emissions to minimize induced chemi-
either the equilibrium or dynamic fuel-air ratio approach.
cal reactions that can affect octane number ratings.
4.3 C.R. Procedure—A calibration is performed to establish
6.1.1 Exposure of these fuels to UV wavelengths shorter
standard K.I. using the cylinder height specified by the guide
than 550 nm for a short period of time may significantly affect
table for the O.N. of the selected PRF. The fuel-air ratio of the
octane number ratings.
sample fuel is adjusted to maximize the K.I. under equilibrium
6.2 Certain gases and fumes that can be present in the area
conditions; the cylinder height is adjusted so that standard K.I.
where the knock testing unit is located may have a measurable
is achieved. The calibration is reconfirmed and the sample fuel
effect on the Research O.N. test result.
rating is repeated to establish the proper conditions a second
6.2.1 Halogenated refrigerant used in air conditioning and
time. The average cylinder height reading for the sample fuel,
refrigeration equipment can promote knock. Halogenated sol-
compensated for barometric pressure, is converted directly to
vents can have the same effect. If vapors from these materials
O.N., using the guide table. A final condition for the rating
enter the combustion chamber of the CFR engine, the Research
requires that the sample fuel O.N. be within prescribed limits
O.N. obtained for sample fuels can be depreciated.
around that of the O.N. of the single PRF blend used to
calibrate the engine to the guide table standard K.I. condition. 6.3 Electrical power subject to transient voltage or fre-
quency surges or distortion can alter CFR engine operating
5. Significance and Use conditions or knock measuring instrumentation performance
and thus affect the Research O.N. obtained for sample fuels.
5.1 Research O.N. correlates with commercial automotive
6.3.1 Electromagnetic emissions can cause interference
spark-ignition engine antiknock performance under mild con-
with the analog knock meter and thus affect the Research O.N.
ditions of operation.
obtained for sample fuels.
5.2 Research O.N. is used by engine manufacturers, petro-
7. Apparatus
leum refiners and marketers, and in commerce as a primary
specification measurement related to the matching of fuels and
7.1 Engine Equipment —This test method uses a single
engines.
cylinder, CFR F-1 test engine for the determination of O.N.
5.2.1 Empirical correlations that permit calculation of auto- that consists of standard components as follows: crankcase, a
motive antiknock performance are based on the general equa- cylinder/clamping sleeve assembly to provide continuously
tion: variable compression ratio adjustable with the engine
operating, a thermal syphon recirculating jacket coolant
Road O.N. 5 k × Research O.N. 1 k × Motor O.N. 1 k
~ ! ~ !
1 2 3
system, a multiple fuel tank system with selector valving to
(1)
deliver fuel through a single jet passage and carburetor venturi,
an intake air system with controlled temperature and humidity
Values of k , k , and k vary with vehicles and vehicle
1 2 3
populations and are based on road-O.N. determinations. equipment, electrical controls, and a suitable exhaust pipe. The
engine flywheel is belt connected to a special electric power-
5.2.2 Research O.N., in conjunction with Motor O.N.,
absorption motor utilized to both start the engine and as a
defines the antiknock index of automotive spark-ignition en-
means to absorb power at constant speed when combustion is
gine fuels, in accordance with Specification D4814. The
occurring (engine firing). See Fig. 1. The intensity of combus-
antiknock index of a fuel approximates the Road octane ratings
tion knock is measured by electronic detonation sensing and
for many vehicles, is posted on retail dispensing pumps in the
metering instrumentation. See Fig. 1 and Table 1.
U.S., and is referred to in vehicle manuals.
Antiknock index = 0.5 Research O.N. + 0.5 Motor O.N. + 0 (2)
Supporting data have been filed at ASTM International Headquarters and may
This is more commonly presented as:
be obtained by requesting Research Report RR:D02-1502. Contact ASTM Customer
Service at [e-mail].
R 1 M
~ !
The sole source of supply of the new complete engine known to the committee
Antiknock Index = (3)
at this time is CFR Engines Inc., N8 W22577 Johnson Drive, Pewaukee, WI 53186.
If you are aware of alternative suppliers, please provide this information to ASTM
5.2.3 Research O.N. is also used either alone or in conjunc-
International Headquarters. Your comments will receive careful consideration at a
tion with other factors to define the Road O.N. capabilities of meeting of the responsible technical committee, which you may attend.
D2699 − 24a
A—Air humidifier tube G—Oil Filter
B—Intake air heater H—Ignition Detonation meter
C—Coolant condenser J—Analog Knockmeter
D—Four bowl carburetor K—C.R. digital counter
E—C.R. change motor L—Digital Detonation Meter
F—CFR-48 crankcase
FIG. 1 Research Method Test Engine Assembly
D2699 − 24a
TABLE 1 General Rating Unit Characteristics and Information
Item Description
Test Engine CFR F-1 Research Method Octane Rating Unit with
cast iron, box type crankcase with flywheel
connected by V-belts to power absorption
electrical motor for constant speed operation
Cylinder type Cast iron with flat combustion surface and integral
coolant jacket
Compression ratio Adjustable 4:1 to 18:1 by cranked worm shaft and
worm wheel drive assembly in cylinder clamping
sleeve
Cylinder bore (diameter), 3.250 (standard)
in.
Stroke, in. 4.50
Displacement, cu in. 37.33
Valve mechanism Open rocker assembly with linkage for constant
valve clearance as C.R. changes
Intake valve Stellite faced, with 180° shroud
Exhaust valve Stellite faced, plain type without shroud
Piston Cast iron, flat top
Piston rings
Top compression ring 1 chrome plated or ferrous, straight sided
Other compression 3 ferrous, straight sided
rings
Oil control 1 cast iron, one piece, slotted (Type 85)
Camshaft overlap, ° 5
Fuel system
Carburetor Single vertical jet and fuel flow control to permit
adjustment of fuel-air ratio
Venturi throat ⁄16 for all altitudes
diameter, in.
Ignition Electronically triggered condenser discharge
through coil to spark plug
Ignition timing, ° Constant 13 btdc
Intake air humidity Controlled within specified limited range
7.2 Instrumentation—Auxiliary Equipment—A number of volumetric tolerance of 60.2 % shall be used. Calibration shall
components and devices have been developed to integrate the be verified in accordance with Practice E542.
basic engine equipment into complete laboratory or on-line
7.3.1.2 Calibrated burets shall be outfitted with a dispensing
octane measurement systems. These include computer inter- valve and delivery tip to accurately control dispensed volume.
face and software systems, as well as common hardware,
The delivery tip shall be of such design that shut-off tip
tubing, fasteners, electrical and electronic items. Appendix X1 discharge does not exceed 0.5 mL.
contains a listing of such items, many of which are potentially
7.3.1.3 The rate of delivery from the dispensing system
available from multiple sources. In some cases, selection of
shall not exceed 400 mL per 60 s.
specific dimensions or specification criteria are important to
7.3.1.4 The set of burets for the reference and standardiza-
achieve proper conditions for the knock testing unit, and these
tion fuels shall be installed in such a manner and be supplied
are included in Appendix X1 when applicable.
with fluids such that all components of each batch or blend are
dispensed at the same temperature.
7.3 Reference and Standardization Fuel Dispensing
7.3.1.5 See Appendix X2 for volumetric reference fuel
Equipment—This test method requires repeated blending of
dispensing system information.
reference fuels and TSF materials in volumetric proportions. In
7.3.1.6 Automated volumetric blending apparatus may be
addition, blending of dilute tetraethyllead in isooctane may be
used providing the system achieves a maximum volumetric
performed on-site for making rating determinations above 100
blending tolerance limit of 60.2 %.
O.N. Blending shall be performed accurately because rating
error is proportional to blending error. 7.3.2 Volumetric Blending of Tetraethyllead—A calibrated
buret, pipette assembly, or other liquid dispensing apparatus
7.3.1 Volumetric Blending of Reference Fuels—Volumetric
blending has historically been employed to prepare the re- having a capacity of not more than 4.0 mL and a critically
controlled volumetric tolerance shall be used for dispensing
quired blends of reference fuels and TSF materials. For
volumetric blending, a set of burets, or accurate volumetric dilute tetraethyllead into 400 mL batches of isooctane. Cali-
bration of the dispensing apparatus shall be verified in accor-
apparatus, shall be used and the desired batch quantity shall be
collected in an appropriate container and thoroughly mixed dance with Practice E542.
before being introduced to the engine fuel system. 7.3.3 Gravimetric Blending of Reference Fuels—Use of
7.3.1.1 For manual preparation of reference and standard- blending systems that allow preparation of the volumetrically-
ization fuel blends, calibrated burets or volumetric apparatus defined blends by gravimetric (mass) measurements based on
having a capacity of 200 mL to 500 mL and a maximum the density of the individual components is also permitted,
D2699 − 24a
provided the system meets the requirement for maximum spark-ignition engines shall be used. It shall contain a detergent
0.2 % blending tolerance limits. additive and have a kinematic viscosity of 9.3 mm to
TABLE 2 Specifications for Primary Reference Fuels
Property Isooctane n-heptane 80 PRF Test Method
Purity, vol %, min 99.75 99.75 ASTM D2268
n-heptane, vol % 0.10 max 19.9 – 20.1 ASTM D2268
Isooctane, vol % 0.10 max 79.9 – 80.1 ASTM D2268
Lead, max 0.5 mg/L 0.5 mg/L 0.5 mg/L
IP 224/02
(0.002 g/U.S. gal) (0.002 g/U.S. gal) (0.002 g/U.S. gal)
7.3.3.1 Calculate the mass equivalents of the 12.5 mm per s (cSt) at 100 °C (212 °F) and a viscosity index
volumetrically-defined blend components from the densities of of not less than 85. Oils containing viscosity index improvers
the individual components at 15.56 °C (60 °F). shall not be used. Multigraded oils shall not be used.
(Warning—Lubricating oil is combustible and its vapor is
7.4 Auxiliary Apparatus:
harmful. See Annex A1.)
7.4.1 Special Maintenance Tools—A number of specialty
tools and measuring instruments should be utilized for easy,
8.3 PRF, isooctane, 80-octane, and normal heptane classi-
convenient, and effective maintenance of the engine and testing
fied as reference fuel grade and meeting the specifications that
equipment. Lists and descriptions of these tools and instru-
follow: (Warning—Primary reference fuel is flammable and
ments are available from the manufacturer of the engine
its vapors are harmful. Vapors may cause flash fire. See Annex
equipment and those organizations offering engineering and
A1.)
service support for this test method.
8.3.1 Isooctane (2,2,4-trimethylpentane) shall meet the
7.4.2 Ventilation Hoods—Handling of reference and stan-
specifications in Table 2. (Warning—Isooctane is flammable
dardization fuels, dilute tetraethyllead, and test samples having
and its vapors are harmful. Vapors may cause flash fire. See
various hydrocarbon compositions is best conducted in a well
Annex A1.)
ventilated space or in a laboratory hood where air movement
8.3.2 n-heptane shall meet the specifications in Table 2.
across the area is sufficient to prevent operator inhalation of
(Warning—n-heptane is flammable and its vapors are harmful.
vapors.
Vapors may cause flash fire. See Annex A1.)
7.4.2.1 General purpose laboratory hoods are typically ef-
8.3.3 80 octane PRF blend, prepared using reference fuel
fective for handling hydrocarbon fuel blending.
grade isooctane and n-heptane shall meet the specifications in
7.4.2.2 A blending hood meeting the requirements for dis-
Table 2. (Warning—80 octane PRF is flammable and its
pensing toxic material shall be utilized in testing laboratories
vapors are harmful. Vapors may cause flash fire. See Annex
that choose to prepare leaded isooctane PRF blends on-site.
A1.)
7.4.3 Barometer—A pressure measurement device capable
8.3.4 Refer to Annex A3 for octane numbers of various
of measuring the absolute value of air pressure in the room
blends of 80 octane PRF and either n-heptane (Table A3.1) or
where the testing apparatus is located. With a resolution of at
isooctane (Table A3.2).
least 0.34 kPa (0.1 in. Hg) and a suggested range of 71 kPa to
8.4 Dilute Tetraethyllead (Commonly referred to as TEL
105 kPa (21 in. Hg to 31 in. Hg).
Dilute Volume Basis) is a prepared solution of aviation mix
8. Reagents and Reference Materials
tetraethyllead antiknock compound in a hydrocarbon diluent of
70 % (V/V) xylene, 30 % (V/V) n-heptane. (Warning—Dilute
8.1 Cylinder Jacket Coolant—Water shall be used in the
tetraethyllead is poisonous and flammable. It may be harmful
cylinder jacket for laboratory locations where the resultant
or fatal if inhaled, swallowed, or absorbed through the skin.
boiling temperature shall be 100 °C 6 1.5 °C (212 °F 6 3 °F).
May cause flash fire. See Annex A1.)
Water with commercial glycol-based antifreeze added in suf-
8.4.1 The fluid shall contain 18.23 % 6 0.05 % (m/m)
ficient quantity to meet the boiling temperature requirement
tetraethyllead and have a relative density 15.6/15.6 °C (60/
shall be used when laboratory altitude dictates. A commercial
60 °F) of 0.957 to 0.967. The typical composition of the fluid,
multifunctional water treatment material should be used in the
excluding the tetraethyllead, is as follows:
coolant to minimize corrosion and mineral scale that can alter
Typical Concentration,
heat transfer and rating results. (Warning—Ethylene glycol
Ingredient
% (m/m)
based antifreeze is poisonous and may be harmful or fatal if
Ethylene dibromide (scavenger) 10.6
inhaled or swallowed. See Annex A1.)
Diluent:
xylene 52.5
8.1.1 Water shall be understood to mean reagent water
n-heptane 17.8
conforming to Type IV, of Specification D1193.
Dye, antioxidant and inerts 0.87
8.2 Engine Crankcase Lubricating Oil—An SAE 30 viscos-
ity grade oil meeting the current API service classification for
Dilute tetraethyllead is available from Ethyl Corporation, 330 South Fourth
Refer to Industrial Ventilation Manual, published by the American Conference Street, Richmond, VA 23219-4304; or from The Associated Octel Company, Ltd., 23
of Governmental Industrial Hygienists, Cincinnati, OH. Berkeley Square, London, England W1X 6DT.
D2699 − 24a
8.4.2 Add dilute tetraethyllead, in millilitre quantities, to a 10.1.1 Proper operation of the CFR engine requires assem-
400 mL volume of isooctane to prepare PRF blends used for bly of a number of engine components and adjustment of a
ratings over 100 O.N. The composition of the dilute fluid is
series of engine variables to prescribed specifications. Some of
such that when 2.0 mL are added to 400 mL of isooctane, the these settings are established by component specifications,
blend shall contain the equivalent of 2.0 mL of lead/U.S. gal
others are established at the time of engine assembly or after
(0.56 g of lead/L).
overhaul, and still others are engine running conditions that
8.4.3 Refer to Annex A3 for octane numbers of blends of
must be observed or determined by the operator during the
tetraethyllead and isooctane (see Table A3.3).
testing process.
8.4.4 An alternative to blending with dilute tetraethyllead is
10.2 Conditions Based on Component Specifications:
to prepare leaded PRF from isooctane + 6.0 mL TEL per U.S.
10.2.1 Engine Speed—600 r ⁄min 6 6 r ⁄min when the en-
gallon and isooctane (see Table A3.4).
gine is firing, with a maximum variation of 6 r ⁄min occurring
8.5 Toluene, Reference Fuel Grade shall meet the specifi-
during a rating. Engine speed, while firing, shall not be more
cations in Table 3. Toluene purity is determined by subtracting
than 3 r ⁄min greater than when it is motoring without combus-
the sum of the hydrocarbon impurities and water content from
tion.
100 %. (Warning—Toluene is flammable and its vapors are
10.2.2 Indexing Flywheel to Top-Dead-Center (tdc)—With
harmful. Vapors may cause flash fire. See Annex A1.)
the piston at the highest point of travel in the cylinder, set the
NOTE 1—Experience has shown that Toluene exposed to atmospheric
flywheel pointer mark in alignment with the 0° mark on the
moisture (humidity) can absorb water. Options to help manage or control
flywheel in accordance with the instructions of the manufac-
the Toluene moisture levels include installing an inline air filter/dryer on
turer.
the drum vent, installing a nitrogen purge on the drum, and the use of
dryer desiccant beads, etc.
10.2.3 Valve Timing—The engine uses a four-stroke cycle
8.5.1 Antioxidant shall be added by the supplier at a treat
with two crankshaft revolutions for each complete combustion
rate suitable for good long term stability as empirically cycle. The two critical valve events are those that occur near
determined with the assistance of the antioxidant supplier.
tdc; intake valve opening and exhaust valve closing. See
Annex A2 for camshaft timing and valve lift measurement
8.6 Check Fuels are in-house typical spark-ignition engine
procedures.
fuels having selected octane numbers, low volatility, and good
10.2.3.1 Intake valve opening shall occur 10.0° 6 2.5°
long term stability. (Warning—Check Fuel is flammable and
its vapors are harmful. Vapors may cause flash fire. See Annex after-top-dead-center (atdc) with closing at 34° after-bottom-
dead-center (abdc) on one revolution of the crankshaft and
A1.)
flywheel.
9. Sampling
10.2.3.2 Exhaust valve opening shall occur 40° before-
9.1 Collect samples in accordance with Practices D4057,
bottom-dead-center (bbdc) on the second revolution of the
D4177, or D5842.
crankshaft and flywheel, with closing at 15.0° 6 2.5° atdc on
the next revolution of the crankshaft and flywheel.
9.2 Sample Temperature—Samples shall be cooled to a
temperature of 2 °C to 10 °C (35 °F to 50 °F), in the container 10.2.4 Valve Lift—Intake and exhaust cam lobe contours,
in which they are received, before the container is opened. while different in shape, shall have a contour rise of 0.246 in.
to 0.250 in. (6.248 mm to 6.350 mm) from the base circle to
9.3 Protection from Light—Collect and store sample fuels in
the top of the lobe. The resulting valve lift shall be 0.238 in. 6
an opaque container, such as a dark brown glass bottle, metal
0.002 in. (6.045 mm 6 0.05 mm). See Annex A2 for camshaft
can, or a minimally reactive plastic container to minimize
timing and valve lift measurement procedure.
exposure to UV emissions from sources such as sunlight or
10.2.5 Intake Valve Shroud—The intake valve has a 180°
fluorescent lamps.
shroud or protrusion just inside the valve face to direct the
10. Basic Engine and Instrument Settings and Standard
incoming fuel-air charge and increase the turbulence within the
Operating Conditions
combustion chamber. This valve stem is drilled for a pin, which
is restrained in a valve guide slot, to prevent the valve from
10.1 Installation of Engine Equipment and
Instrumentation—Installation of the engine and instrumenta- rotating and thus maintain the direction of swirl. The valve
shall be assembled in the cylinder, with the pin aligned in the
tion requires placement of the engine on a suitable foundation
and hook-up of all utilities. Engineering and technical support valve guide, so that the shroud is toward the spark plug side of
the combustion chamber and the swirl is directed in a coun-
for this function is required, and the user shall be responsible
to comply with all local and national codes and installation terclockwise direction if it could be observed from the top of
requirements. the cylinder.
TABLE 3 Specifications for Toluene
Property Toluene Test Method
Purity, vol %, minimum 99.5 ASTM D7504
Water, ppm, max 200 ASTM D6304 or E1064
Hydroperoxide number, mg/kg as O, max 5 ASTM D3703
D2699 − 24a
controlling engine running and hot operating level.
10.2.6 Carburetor Venturi—A ⁄16 in. (14.3 mm) venturi
throat size shall be used regardless of ambient barometric
10.3.9 Engine Crankcase Lubricating Oil Level:
pressure.
10.3.9.1 Engine Running and Hot—Oil shall be added to the
crankcase so that the level is approximately mid-position in the
10.3 Assembly Settings and Operating Conditions:
crankcase oil sight glass.
10.3.1 Direction of Engine Rotation—Clockwise rotation of
the crankshaft when observed from the front of the engine.
NOTE 4—When stopped and cold, oil added to the crankcase so that the
10.3.2 Valve Clearances:
level is near the top of the sight glass will typically provide the engine
running and hot operating level.
10.3.2.1 Engine Running and Hot—The clearance for both
intake and exhaust valves shall be set to 0.008 in. 6 0.001 in.
10.3.10 Crankcase Internal Pressure—As measured by a
(0.20 mm 6 0.025 mm), measured under standard operating
gage, pressure sensor, or manometer connected to an opening
conditions with the engine running at equilibrium conditions
to the inside of the crankcase through a snubber orifice to
on a 90 O.N. PRF blend.
minimize pulsations, the pressure shall be less than zero (a
10.3.3 Oil Pressure—172 kPa to 207 kPa (25 psi to 30 psi).
vacuum) and is typically from 25 mm to 150 mm (1 in. to 6 in.)
See Annex A2 for the procedure to adjust crankcase lubricating
of water less than atmospheric pressure. Vacuum shall not
oil pressure.
exceed 255 mm (10 in.) of water.
10.3.4 Oil Temperature—57 °C 6 8 °C (135 °F 6 15 °F).
10.3.11 Exhaust Back Pressure—As measured by a gage or
10.3.5 Cylinder Jacket Coolant Temperature—100 °C 6
manometer connected to an opening in the exhaust surge tank
1.5 °C (212 °F 6 3 °F) constant within 60.5 °C (61 °F) when
or main exhaust stack through a snubber orifice to minimize
CR or KI results used for octane determination on each fuel are
pulsations, the static pressure should be as low as possible, but
recorded.
shall not create a vacuum nor exceed 255 mm (10 in.) of water
10.3.6 Intake Air Temperature—52 °C 6 1 °C (125 °F 6
differential in excess of atmospheric pressure.
2 °F) is specified for operation at standard barometric pressure
10.3.12 Exhaust and Crankcase Breather System
of 101.0 kPa (29.92 in. Hg). IATs for other prevailing baromet-
Resonance—The exhaust and crankcase breather piping sys-
ric pressure conditions are listed in Annex A4 (see Tables A4.4
tems shall have internal volumes and be of such length that gas
and A4.5). If IAT tuning is used to qualify the engine as
resonance does not result. See Appendix X3 for a suitable
fit-for-use, the temperature selected shall be within 622 °C
procedure to determine if resonance exists.
(640 °F) of the temperature listed in Annex A4 (Tables A4.4
10.3.13 Belt Tension—The belts connecting the flywheel to
and A4.5) for the prevailing barometric pressure and this
the absorption motor shall be tightened, after an initial break-
temperature shall then be maintained within 61 °C (62 °F)
in, so that with the engine stopped, a 2.25 kg (5 lb) weight
when CR or KI results used for octane determination on each
suspended from one belt halfway between the flywheel and
fuel are recorded.
motor pulley shall depress the belt approximately 12.5 mm
10.3.6.1 The IAT required to qualify the engine in each TSF
(0.5 in.).
blend O.N. range shall also be used for rating all sample fuels
10.3.14 Basic Rocker Arm Carrier Adjustment:
in that O.N. range during an operating period.
10.3.14.1 Basic Rocker Arm Carrier Support Setting—For
10.3.6.2 Temperature measurement systems used to estab-
exposed valve train applications, each rocker arm carrier
lish the Intake Air Temperature in this test method shall exhibit
support shall be threaded into the cylinder so that the distance
the same temperature indicating characteristics and accuracy as
between the machined surface of the cylinder and the underside
the relevant ASTM Type 83C (83F) or 135C (135F) thermom-
of the fork is 31 mm (1 ⁄32 in.). For enclosed valve train
eter installed at the orifice provided using the manufacturer’s
applications, each rocker arm carrier support shall be threaded
prescribed fitting.
into the cylinder so that the distance between the top machined
10.3.6.3 To ensure the correct temperature is indicated, the
surface of the valve tray and the underside of the fork is 19 mm
temperature measurement system shall be installed in accor-
( ⁄4 in.).
dance with the instructions provided for this specific applica-
10.3.14.2 Basic Rocker Arm Carrier Setting—With the cyl-
tion.
inder positioned so that the distance between the underside of
10.3.7 Intake Air Humidity—0.00356 kg to 0.00712 kg wa-
the cylinder and the top of the clamping sleeve is approxi-
ter per kg (25 to 50 grains of water per lb) of dry air. 5
mately 16 mm ( ⁄8 in.), the rocker arm carrier shall be set
horizontal before tightening the bolts that fasten the long
NOTE 2—The humidity specification is based upon the original ice
carrier support to the clamping sleeve.
tower. If air conditioning equipment is used it may not supply air within
the specification if the ambient relative humidity is excessively high or too
10.3.14.3 Basic Rocker Arm Setting—With the engine on
low. The equipment manufacturers should be consulted to verify the
tdc on the compression stroke, and the rocker arm carrier set at
effective working range.
the basic setting, set the valve adjusting screw to approxi-
10.3.8 Cylinder Jacket Coolant Level:
mately the mid-position in each rocker arm. Then adjust the
10.3.8.1 Engine Running and Hot—Treated water/coolant
length of the push rods so that the rocker arms shall be in the
shall be added to the cooling condenser-cylinder jacket so that
horizontal position.
the level in the condenser sight glass shall be within 61 cm
10.3.15 Basic Spark Setting—13° btdc regardless of cylin-
(60.4 in.) of the LEVEL HOT mark on the coolant condenser.
der height.
10.3.15.1 The digital timing indicator currently supplied
NOTE 3—When stopped and cold, a coolant level that is just observable
in the bottom of the condenser sight glass will typically provide the with CFR engine units, or the graduated spark quadrant
D2699 − 24a
FIG. 2 Actual Compression Pressure for Setting Cylinder Height
formerly supplied, sha
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D2699 − 24 D2699 − 24a
Standard Test Method for
Research Octane Number of Spark-Ignition Engine Fuel
This standard is issued under the fixed designation D2699; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
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., including fuels that contain up to 25 % v/v of ethanol. However, 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 For purposes of determining conformance with all specified limits in this standard, an observed value or a calculated value
shall be rounded “to the nearest unit” in the last right-hand digit used in expressing the specified limit, in accordance with the
rounding method of Practice E29.
1.5 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. For specific warning statements, see Section 8, 14.4.1, 15.5.1, 16.6.1, Annex A1, A2.2.3.1,
A2.2.3.3 (6) and (9), A2.3.5, X3.3.7, X4.2.3.1, X4.3.4.1, X4.3.9.3, X4.3.11.4, and X4.5.1.8.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.01 on Combustion Characteristics.
Current edition approved March 1, 2024May 1, 2024. Published April 2024May 2024. Originally approved in 1968. Last previous edition approved in 20232024 as
D2699 – 23b.D2699 – 24. DOI: 10.1520/D2699-24.10.1520/D2699-24A.
Motor O.N., determined using Test Method D2700, is a companion method to provide a similar but typically lower octane rating under more severe operating conditions.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2699 − 24a
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D2268 Test Method for Analysis of High-Purity n-Heptane and Isooctane by Capillary 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 Hydroperoxide Number of Aviation Turbine Fuels, Gasoline and Diesel Fuels
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, 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 Measurement
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
D6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and
Lubricants
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl
Fischer Titration
D6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport
to Measure the Same Property of a Material
D7504 Test Method for Trace Impurities in Monocyclic Aromatic Hydrocarbons by Gas Chromatography and Effective Carbon
Number
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E344 Terminology Relating to Thermometry and Hydrometry
E456 Terminology Relating to Quality and Statistics
E542 Practice for Gravimetric Calibration of Laboratory Volumetric Instruments
E1064 Test Method for Water in Organic Liquids by Coulometric Karl Fischer Titration
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. E456
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. ) determined by round-robin testing under reproducibility conditions.
ARV
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.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from Energy Institute, 61 New Cavendish St., London, W1G 7AR, U.K., http://www.energyinst.org.
D2699 − 24a
3.1.3.1 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.
3.1.3.2 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.
3.1.4 detonation meter, analog, n—for knock testing, the signal conditioning instrumentation that accepts the electrical signal from
the detonation pickup and provides an analog output signal to the analog knockmeter.
3.1.4.1 Discussion—
In the context of this test method, three contemporary generations of apparatus have been developed as detonation meters. These
are (year of introduction in parenthesis): the 501T Detonation Meter (1969), the 501C Detonation Meter (1979), and the SSD7000
Detonation Meter (2017).
3.1.5 detonation meter, digital, n—for knock testing, the digital signal conditioning instrumentation that accepts the electrical
signal from the detonation pickup and provides a digital output for display.
3.1.6 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.
3.1.7 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.
3.1.8 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 fuel-air ratio, observing the equilibrium knock
intensity for each step, and selecting the level that produces the highest knock intensity reading.
3.1.9 firing, n—for the CFR engine, operation of the CFR engine with fuel and ignition.
3.1.10 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.
3.1.11 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.
3.1.12 knock, n—in a spark-ignition engine, abnormal combustion, often producing audible sound, caused by autoignition of the
air/fuel mixture. D4175
3.1.13 knock intensity, n—for knock testing, a measure of the level of knock.
3.1.14 knockmeter, analog, n—for knock testing, the 0 to 100 division analog indicating meter that displays the knock intensity
signal from the analog detonation meter.
3.1.15 knockmeter, digital, n—for knock testing, the 0 to 999 division digital indicating meter that displays the knock intensity
from the digital detonation meter.
3.1.16 motoring, n—for the CFR engine, operation of the CFR engine without fuel and with the ignition shut off.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1870. Contact ASTM Customer
Service at [e-mail].
D2699 − 24a
3.1.17 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. D4175
3.1.17.1 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.
3.1.18 oxygenate, n—an oxygen-containing organic compound, which may be used as a fuel or fuel supplement, for example,
various alcohols and ethers. D4175
3.1.19 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.
3.1.20 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.
3.1.21 quality control (QC) sample, n—for use in quality assurance programs to determine and monitor the precision and stability
of a measurement system, a stable and homogeneous material having physical or chemical properties, or both, similar to those of
typical samples tested by the analytical measurement system. The material is properly stored to ensure sample integrity, and is
available in sufficient quantity for repeated, long term testing. D6299
3.1.22 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. E456
3.1.23 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. E456
3.1.24 spread, n—in knock measurement, the sensitivity of the analog detonation meter expressed in knockmeter divisions per
octane number. (This feature is not a necessary adjustment in the digital detonation meter.)
3.1.25 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.
3.1.26 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. determined
ARV
by round-robin testing under reproducibility conditions.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 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.
3.2.2 repeatability conditions NEG, n—replicate testing conditions employed by the National Exchange Group in which a single
operator tests two specimens taken from a single sample container with at least one other sample being tested between the two
specimens.
3.3 Abbreviations:
3.3.1 ARV = accepted reference value
3.3.2 CFR = Cooperative Fuel Research
3.3.3 C.R. = compression ratio
3.3.4 IAT = intake air temperature
D2699 − 24a
3.3.5 K.I. = knock intensity
3.3.6 NEG = National Exchange Group
3.3.7 OA = Octane Analyzer
3.3.8 O.N. = octane number
3.3.9 PRF = primary reference fuel
3.3.10 r = repeatability conditions NEG
NEG
3.3.11 RTD = resistance thermometer device (E344) platinum type
3.3.12 TSF = toluene standardization fuel
4. Summary of Test Method
4.1 The Research O.N. of a spark-ignition engine fuel is determined using a standard test engine and operating conditions to
compare its knock characteristic with those of PRF blends of known O.N. Compression ratio and fuel-air ratio are adjusted to
produce standard K.I. for the sample fuel, as measured by a specific electronic detonation measurement system. A standard K.I.
guide table relates engine C.R. to O.N. level for this specific method. The fuel-air ratio for the sample fuel and each of the primary
reference fuel blends is adjusted to maximize K.I. for each fuel.
4.1.1 The fuel-air ratio for maximum K.I. may be obtained (1) by making incremental step changes in mixture strength, observing
the equilibrium K.I. value for each step, and then selecting the condition that maximizes the reading or (2) by picking the maximum
K.I. as the mixture strength is changed from either rich-to-lean or lean-to-rich at a constant rate.
4.2 Bracketing Procedures—The engine is calibrated to operate at standard K.I. in accordance with the guide table. The fuel-air
ratio of the sample fuel is adjusted to maximize the K.I., and then the cylinder height is adjusted so that standard K.I. is achieved.
Without changing cylinder height, two PRF blends are selected such that, at their fuel-air ratio for maximum K.I., one knocks
harder (higher K.I.) and the other softer (lower K.I.) than the sample fuel. A second set of K.I. measurements for sample fuel and
PRF blends is required, and the sample fuel octane number is calculated by interpolation in proportion to the differences in average
K.I. readings. A final condition requires that the cylinder height used shall be within prescribed limits around the guide table value
for the calculated O.N. Bracketing procedure ratings may be determined using either the equilibrium or dynamic fuel-air ratio
approach.
4.3 C.R. Procedure—A calibration is performed to establish standard K.I. using the cylinder height specified by the guide table
for the O.N. of the selected PRF. The fuel-air ratio of the sample fuel is adjusted to maximize the K.I. under equilibrium conditions;
the cylinder height is adjusted so that standard K.I. is achieved. The calibration is reconfirmed and the sample fuel rating is repeated
to establish the proper conditions a second time. The average cylinder height reading for the sample fuel, compensated for
barometric pressure, is converted directly to O.N., using the guide table. A final condition for the rating requires that the sample
fuel O.N. be within prescribed limits around that of the O.N. of the single PRF blend used to calibrate the engine to the guide table
standard K.I. condition.
5. Significance and Use
5.1 Research O.N. correlates with commercial automotive spark-ignition engine antiknock performance under mild conditions of
operation.
5.2 Research O.N. is used by engine manufacturers, petroleum refiners and marketers, and in commerce as a primary specification
measurement related to the matching of fuels and engines.
5.2.1 Empirical correlations that permit calculation of automotive antiknock performance are based on the general equation:
Road O.N. 5 k × Research O.N. 1 k × Motor O.N. 1k (1)
~ ! ~ !
1 2 3
Values of k , k , and k vary with vehicles and vehicle populations and are based on road-O.N. determinations.
1 2 3
D2699 − 24a
5.2.2 Research O.N., in conjunction with Motor O.N., defines the antiknock index of automotive spark-ignition engine fuels, in
accordance with Specification D4814. The antiknock index of a fuel approximates the Road octane ratings for many vehicles, is
posted on retail dispensing pumps in the U.S., and is referred to in vehicle manuals.
Antiknock index = 0.5 Research O.N. + 0.5 Motor O.N. + 0 (2)
This is more commonly presented as:
R 1 M
~ !
Antiknock Index = (3)
5.2.3 Research O.N. is also used either alone or in conjunction with other factors to define the Road O.N. capabilities of
spark-ignition engine fuels for vehicles operating in areas of the world other than the United States.
5.3 Research O.N. is used for measuring the antiknock performance of spark-ignition engine fuels that contain oxygenates.
5.4 Research O.N. is important in relation to the specifications for spark-ignition engine fuels used in stationary and other
nonautomotive engine applications.
6. Interferences
6.1 Precaution—Avoid exposure of sample fuels to sunlight or fluorescent lamp UV emissions to minimize induced chemical
reactions that can affect octane number ratings.
6.1.1 Exposure of these fuels to UV wavelengths shorter than 550 nm for a short period of time may significantly affect octane
number ratings.
6.2 Certain gases and fumes that can be present in the area where the knock testing unit is located may have a measurable effect
on the Research O.N. test result.
6.2.1 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 Research O.N. obtained
for sample fuels can be depreciated.
6.3 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 Research O.N. obtained for sample fuels.
6.3.1 Electromagnetic emissions can cause interference with the analog knock meter and thus affect the Research O.N. obtained
for sample fuels.
7. Apparatus
7.1 Engine Equipment —This test method uses a single cylinder, CFR F-1 test engine for the determination of O.N. that consists
of standard components as follows: crankcase, a cylinder/clamping sleeve assembly to provide continuously variable compression
ratio adjustable with the engine operating, a thermal syphon recirculating jacket coolant system, a multiple fuel tank system with
selector valving to deliver fuel through a single jet passage and carburetor venturi, an intake air system with controlled temperature
and humidity equipment, electrical controls, and a suitable exhaust pipe. The engine flywheel is belt connected to a special electric
power-absorption motor utilized to both start the engine and as a means to absorb power at constant speed when combustion is
occurring (engine firing). See Fig. 1. The intensity of combustion knock is measured by electronic detonation sensing and metering
instrumentation. See Fig. 1 and Table 1.
7.2 Instrumentation—Auxiliary Equipment—A number of components and devices have been developed to integrate the basic
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1502. Contact ASTM Customer
Service at [e-mail].
The sole source of supply of the new complete engine known to the committee at this time is CFR Engines Inc., N8 W22577 Johnson Drive, Pewaukee, WI 53186. If
you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting
of the responsible technical committee, which you may attend.
D2699 − 24a
A—Air humidifier tube G—Oil Filter
B—Intake air heater H—Ignition Detonation meter
C—Coolant condenser J—Analog Knockmeter
D—Four bowl carburetor K—C.R. digital counter
E—C.R. change motor L—Digital Detonation Meter
F—CFR-48 crankcase
D2699 − 24a
FIG. 1 Research Method Test Engine Assembly
TABLE 1 General Rating Unit Characteristics and Information
Item Description
Test Engine CFR F-1 Research Method Octane Rating Unit with
cast iron, box type crankcase with flywheel
connected by V-belts to power absorption
electrical motor for constant speed operation
Cylinder type Cast iron with flat combustion surface and integral
coolant jacket
Compression ratio Adjustable 4:1 to 18:1 by cranked worm shaft and
worm wheel drive assembly in cylinder clamping
sleeve
Cylinder bore (diameter), 3.250 (standard)
in.
Stroke, in. 4.50
Displacement, cu in. 37.33
Valve mechanism Open rocker assembly with linkage for constant
valve clearance as C.R. changes
Intake valve Stellite faced, with 180° shroud
Exhaust valve Stellite faced, plain type without shroud
Piston Cast iron, flat top
Piston rings
Top compression ring 1 chrome plated or ferrous, straight sided
Other compression 3 ferrous, straight sided
rings
Oil control 1 cast iron, one piece, slotted (Type 85)
Camshaft overlap, ° 5
Fuel system
Carburetor Single vertical jet and fuel flow control to permit
adjustment of fuel-air ratio
Venturi throat ⁄16 for all altitudes
diameter, in.
Ignition Electronically triggered condenser discharge
through coil to spark plug
Ignition timing, ° Constant 13 btdc
Intake air humidity Controlled within specified limited range
engine equipment into complete laboratory or on-line octane measurement systems. These include computer interface and software
systems, as well as common hardware, tubing, fasteners, electrical and electronic items. Appendix X1 contains a listing of such
items, many of which are potentially available from multiple sources. In some cases, selection of specific dimensions or
specification criteria are important to achieve proper conditions for the knock testing unit, and these are included in Appendix X1
when applicable.
7.3 Reference and Standardization Fuel Dispensing Equipment—This test method requires repeated blending of reference fuels
and TSF materials in volumetric proportions. In addition, blending of dilute tetraethyllead in isooctane may be performed on-site
for making rating determinations above 100 O.N. Blending shall be performed accurately because rating error is proportional to
blending error.
7.3.1 Volumetric Blending of Reference Fuels—Volumetric blending has historically been employed to prepare the required blends
of reference fuels and TSF materials. For volumetric blending, a set of burets, or accurate volumetric apparatus, shall be used and
the desired batch quantity shall be collected in an appropriate container and thoroughly mixed before being introduced to the
engine fuel system.
7.3.1.1 For manual preparation of reference and standardization fuel blends, calibrated burets or volumetric apparatus having a
capacity of 200 mL to 500 mL and a maximum volumetric tolerance of 60.2 % shall be used. Calibration shall be verified in
accordance with Practice E542.
7.3.1.2 Calibrated burets shall be outfitted with a dispensing valve and delivery tip to accurately control dispensed volume. The
delivery tip shall be of such design that shut-off tip discharge does not exceed 0.5 mL.
7.3.1.3 The rate of delivery from the dispensing system shall not exceed 400 mL per 60 s.
7.3.1.4 The set of burets for the reference and standardization fuels shall be installed in such a manner and be supplied with fluids
such that all components of each batch or blend are dispensed at the same temperature.
D2699 − 24a
7.3.1.5 See Appendix X2 for volumetric reference fuel dispensing system information.
7.3.1.6 Automated volumetric blending apparatus may be used providing the system achieves a maximum volumetric blending
tolerance limit of 60.2 %.
7.3.2 Volumetric Blending of Tetraethyllead—A calibrated buret, pipette assembly, or other liquid dispensing apparatus having a
capacity of not more than 4.0 mL and a critically controlled volumetric tolerance shall be used for dispensing dilute tetraethyllead
into 400 mL batches of isooctane. Calibration of the dispensing apparatus shall be verified in accordance with Practice E542.
7.3.3 Gravimetric Blending of Reference Fuels—Use of blending systems that allow preparation of the volumetrically-defined
blends by gravimetric (mass) measurements based on the density of the individual components is also permitted, provided the
system meets the requirement for maximum 0.2 % blending tolerance limits.
TABLE 2 Specifications for Primary Reference Fuels
Property Isooctane n-heptane 80 PRF Test Method
Purity, vol %, min 99.75 99.75 ASTM D2268
n-heptane, vol % 0.10 max 19.9 – 20.1 ASTM D2268
Isooctane, vol % 0.10 max 79.9 – 80.1 ASTM D2268
Lead, max 0.5 mg/L 0.5 mg/L 0.5 mg/L
IP 224/02
(0.002 g/U.S. gal) (0.002 g/U.S. gal) (0.002 g/U.S. gal)
7.3.3.1 Calculate the mass equivalents of the volumetrically-defined blend components from the densities of the individual
components at 15.56 °C (60 °F).
7.4 Auxiliary Apparatus:
7.4.1 Special Maintenance Tools—A number of specialty tools and measuring instruments should be utilized for easy, convenient,
and effective maintenance of the engine and testing equipment. Lists and descriptions of these tools and instruments are available
from the manufacturer of the engine equipment and those organizations offering engineering and service support for this test
method.
7.4.2 Ventilation Hoods—Handling of reference and standardization fuels, dilute tetraethyllead, and test samples having various
hydrocarbon compositions is best conducted in a well ventilated space or in a laboratory hood where air movement across the area
is sufficient to prevent operator inhalation of vapors.
7.4.2.1 General purpose laboratory hoods are typically effective for handling hydrocarbon fuel blending.
7.4.2.2 A blending hood meeting the requirements for dispensing toxic material shall be utilized in testing laboratories that choose
to prepare leaded isooctane PRF blends on-site.
7.4.3 Barometer—A pressure measurement device capable of measuring the absolute value of air pressure in the room where the
testing apparatus is located. With a resolution of at least 0.34 kPa (0.1 in. Hg) and a suggested range of 71 kPa to 105 kPa (21 in.
Hg to 31 in. Hg).
8. Reagents and Reference Materials
8.1 Cylinder Jacket Coolant—Water shall be used in the cylinder jacket for laboratory locations where the resultant boiling
temperature shall be 100 °C 6 1.5 °C (212 °F 6 3 °F). Water with commercial glycol-based antifreeze added in sufficient quantity
to meet the boiling temperature requirement shall be used when laboratory altitude dictates. A commercial multifunctional water
treatment material should be used in the coolant to minimize corrosion and mineral scale that can alter heat transfer and rating
results. (Warning—Ethylene glycol based antifreeze is poisonous and may be harmful or fatal if inhaled or swallowed. See Annex
A1.)
8.1.1 Water shall be understood to mean reagent water conforming to Type IV, of Specification D1193.
Refer to Industrial Ventilation Manual, published by the American Conference of Governmental Industrial Hygienists, Cincinnati, OH.
D2699 − 24a
8.2 Engine Crankcase Lubricating Oil—An SAE 30 viscosity grade oil meeting the current API service classification for
2 2
spark-ignition engines shall be used. It shall contain a detergent additive and have a kinematic viscosity of 9.3 mm to 12.5 mm
per s (cSt) at 100 °C (212 °F) and a viscosity index of not less than 85. Oils containing viscosity index improvers shall not be used.
Multigraded oils shall not be used. (Warning—Lubricating oil is combustible and its vapor is harmful. See Annex A1.)
8.3 PRF, isooctane, 80-octane, and normal heptane classified as reference fuel grade and meeting the specifications that follow:
(Warning—Primary reference fuel is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.)
8.3.1 Isooctane (2,2,4-trimethylpentane) shall meet the specifications in Table 2. (Warning—Isooctane is flammable and its
vapors are harmful. Vapors may cause flash fire. See Annex A1.)
8.3.2 n-heptane shall meet the specifications in Table 2. (Warning—n-heptane is flammable and its vapors are harmful. Vapors
may cause flash fire. See Annex A1.)
8.3.3 80 octane PRF blend, prepared using reference fuel grade isooctane and n-heptane shall meet the specifications in Table 2.
(Warning—80 octane PRF is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.)
8.3.4 Refer to Annex A3 for octane numbers of various blends of 80 octane PRF and either n-heptane (Table A3.1) or isooctane
(Table A3.2).
8.4 Dilute Tetraethyllead (Commonly referred to as TEL Dilute Volume Basis) is a prepared solution of aviation mix
tetraethyllead antiknock compound in a hydrocarbon diluent of 70 % (V/V) xylene, 30 % (V/V) n-heptane. (Warning—Dilute
tetraethyllead is poisonous and flammable. It may be harmful or fatal if inhaled, swallowed, or absorbed through the skin. May
cause flash fire. See Annex A1.)
8.4.1 The fluid shall contain 18.23 % 6 0.05 % (m/m) tetraethyllead and have a relative density 15.6/15.6 °C (60/60 °F) of 0.957
to 0.967. The typical composition of the fluid, excluding the tetraethyllead, is as follows:
Typical Concentration,
Ingredient
% (m/m)
Ethylene dibromide (scavenger) 10.6
Diluent:
xylene 52.5
n-heptane 17.8
Dye, antioxidant and inerts 0.87
8.4.2 Add dilute tetraethyllead, in millilitre quantities, to a 400 mL volume of isooctane to prepare PRF blends used for ratings
over 100 O.N. The composition of the dilute fluid is such that when 2.0 mL are added to 400 mL of isooctane, the blend shall
contain the equivalent of 2.0 mL of lead/U.S. gal (0.56 g of lead/L).
8.4.3 Refer to Annex A3 for octane numbers of blends of tetraethyllead and isooctane (see Table A3.3).
8.4.4 An alternative to blending with dilute tetraethyllead is to prepare leaded PRF from isooctane+6.0octane + 6.0 mL TEL per
U. S. U.S. gallon and isooctane (see Table A3.4).
8.5 Toluene, Reference Fuel Grade shall meet the specifications in Table 3. Toluene purity is determined by subtracting the sum
TABLE 3 Specifications for Toluene
Property Toluene Test Method
Purity, vol %, minimum 99.5 ASTM D7504
Water, ppm, max 200 ASTM D6304 or E1064
Hydroperoxide number, mg/kg as O, max 5 ASTM D3703
Dilute tetraethyllead is available from Ethyl Corporation, 330 South Fourth Street, Richmond, VA 23219-4304; or from The Associated Octel Company, Ltd., 23
Berkeley Square, London, England W1X 6DT.
D2699 − 24a
of the hydrocarbon impurities and water content from 100 %. (Warning—Toluene is flammable and its vapors are harmful. Vapors
may cause flash fire. See Annex A1.)
NOTE 1—Experience has shown that Toluene exposed to atmospheric moisture (humidity) can absorb water. Options to help manage or control the Toluene
moisture levels include installing an inline air filter/dryer on the drum vent, installing a nitrogen purge on the drum, and the use of dryer desiccant beads,
etc.
8.5.1 Antioxidant shall be added by the supplier at a treat rate suitable for good long term stability as empirically determined with
the assistance of the antioxidant supplier.
8.6 Check Fuels are in-house typical spark-ignition engine fuels having selected octane numbers, low volatility, and good long
term stability. (Warning—Check Fuel is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.)
9. Sampling
9.1 Collect samples in accordance with Practices D4057, D4177, or D5842.
9.2 Sample Temperature—Samples shall be cooled to a temperature of 2 °C to 10 °C (35 °F to 50 °F), in the container in which
they are received, before the container is opened.
9.3 Protection from Light—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.
10. Basic Engine and Instrument Settings and Standard Operating Conditions
10.1 Installation of Engine Equipment and Instrumentation—Installation of the engine and instrumentation requires placement of
the engine on a suitable foundation and hook-up of all utilities. Engineering and technical support for this function is required, and
the user shall be responsible to comply with all local and national codes and installation requirements.
10.1.1 Proper operation of the CFR engine requires assembly of a number of engine components and adjustment of a series of
engine variables to prescribed specifications. Some of these settings are established by component specifications, others are
established at the time of engine assembly or after overhaul, and still others are engine running conditions that must be observed
or determined by the operator during the testing process.
10.2 Conditions Based on Component Specifications:
10.2.1 Engine Speed—600 r ⁄min 6 6 r ⁄min when the engine is firing, with a maximum variation of 6 r ⁄min occurring during a
rating. Engine speed, while firing, shall not be more than 3 r ⁄min greater than when it is motoring without combustion.
10.2.2 Indexing Flywheel to Top-Dead-Center (tdc)—With the piston at the highest point of travel in the cylinder, set the flywheel
pointer mark in alignment with the 0° mark on the flywheel in accordance with the instructions of the manufacturer.
10.2.3 Valve Timing—The engine uses a four-stroke cycle with two crankshaft revolutions for each complete combustion cycle.
The two critical valve events are those that occur near tdc; intake valve opening and exhaust valve closing. See Annex A2 for
camshaft timing and valve lift measurement procedures.
10.2.3.1 Intake valve opening shall occur 10.0° 6 2.5° after-top-dead-center (atdc) with closing at 34° after-bottom-dead-center
(abdc) on one revolution of the crankshaft and flywheel.
10.2.3.2 Exhaust valve opening shall occur 40° before-bottom-dead-center (bbdc) on the second revolution of the crankshaft and
flywheel, with closing at 15.0° 6 2.5° atdc on the next revolution of the crankshaft and flywheel.
10.2.4 Valve Lift—Intake and exhaust cam lobe contours, while different in shape, shall have a contour rise of 0.246 in. to 0.250 in.
(6.248 mm to 6.350 mm) from the base circle to the top of the lobe. The resulting valve lift shall be 0.238 in. 6 0.002 in.
(6.045 mm 6 0.05 mm). See Annex A2 for camshaft timing and valve lift measurement procedure.
10.2.5 Intake Valve Shroud—The intake valve has a 180° shroud or protrusion just inside the valve face to direct the incoming
D2699 − 24a
fuel-air charge and increase the turbulence within the combustion chamber. This valve stem is drilled for a pin, which is restrained
in a valve guide slot, to prevent the valve from rotating and thus maintain the direction of swirl. The valve shall be assembled in
the cylinder, with the pin aligned in the valve guide, so that the shroud is toward the spark plug side of the combustion chamber
and the swirl is directed in a counterclockwise direction if it could be observed from the top of the cylinder.
10.2.6 Carburetor Venturi—A ⁄16 in. (14.3 mm) venturi throat size shall be used regardless of ambient barometric pressure.
10.3 Assembly Settings and Operating Conditions:
10.3.1 Direction of Engine Rotation—Clockwise rotation of the crankshaft when observed from the front of the engine.
10.3.2 Valve Clearances:
10.3.2.1 Engine Running and Hot—The clearance for both intake and exhaust valves shall be set to 0.008 in. 6 0.001 in. (0.20 mm
6 0.025 mm), measured under standard operating conditions with the engine running at equilibrium conditions on a 90 O.N. PRF
blend.
10.3.3 Oil Pressure—172 kPa to 207 kPa (25 psi to 30 psi). See Annex A2 for the procedure to adjust crankcase lubricating oil
pressure.
10.3.4 Oil Temperature—57 °C 6 8 °C (135 °F 6 15 °F).
10.3.5 Cylinder Jacket Coolant Temperature—100 °C 6 1.5 °C (212 °F 6 3 °F) constant within 60.5 °C (61 °F) when CR or KI
results used for octane determination on each fuel are recorded.
10.3.6 Intake Air Temperature—52 °C 6 1 °C (125 °F 6 2 °F) is specified for operation at standard barometric pressure of
101.0 kPa (29.92 in. Hg). IATs for other prevailing barometric pressure conditions are listed in Annex A4 (see Tables A4.4 and
A4.5). If IAT tuning is used to qualify the engine as fit-for-use, the temperature selected shall be within 622 °C (640 °F) of the
temperature listed in Annex A4 (Tables A4.4 and A4.5) for the prevailing barometric pressure and this temperature shall then be
maintained within 61 °C (62 °F) when CR or KI results used for octane determination on each fuel are recorded.
10.3.6.1 The IAT required to qualify the engine in each TSF blend O.N. range shall also be used for rating all sample fuels in that
O.N. range during an operating period.
10.3.6.2 Temperature measurement systems used to establish the Intake Air Temperature in this test method shall exhibit the same
temperature indicating characteristics and accuracy as the relevant ASTM Type 83C (83F) or 135C (135F) thermometer installed
at the orifice provided using the manufacturer’s prescribed fitting.
10.3.6.3 To ensure the correct temperature is indicated, the temperature measurement system shall be installed in accordance with
the instructions provided for this specific application.
10.3.7 Intake Air Humidity—0.00356 kg to 0.00712 kg water per kg (25 to 50 grains of water per lb) of dry air.
NOTE 2—The humidity specification is based upon the original ice tower. If air conditioning equipment is used it may not supply air within the
specification if the ambient relative humidity is excessively high or too low. The equipment manufacturers should be consulted to verify the effective
working range.
10.3.8 Cylinder Jacket Coolant Level:
10.3.8.1 Engine Running and Hot—Treated water/coolant shall be added to the cooling condenser-cylinder jacket so that the level
in the condenser sight glass shall be within 61 cm (60.4 in.) of the LEVEL HOT mark on the coolant condenser.
NOTE 3—When stopped and cold, a coolant level that is just observable in the bottom of the condenser sight glass will typically provide the controlling
engine running and hot operating level.
10.3.9 Engine Crankcase Lubricating Oil Level:
D2699 − 24a
10.3.9.1 Engine Running and Hot—Oil shall be added to the crankcase so that the level is approximately mid-position in the
crankcase oil sight glass.
NOTE 4—When stopped and cold, oil added to the crankcase so that the level is near the top of the sight glass will typically provide the engine running
and hot operating level.
10.3.10 Crankcase Internal Pressure—As measured by a gage, pressure sensor, or manometer connected to an opening to the
inside of the crankcase through a snubber orifice to minimize pulsations, the pressure shall be less than zero (a vacuum) and is
typically from 25 mm to 150 mm (1 in. to 6 in.) of water less than atmospheric pressure. Vacuum shall not exceed 255 mm (10 in.)
of water.
10.3.11 Exhaust Back Pressure—As measured by a gage or manometer connected to an opening in the exhaust surge tank or main
exhaust stack through a snubber orifice to minimize pulsations, the static pressure should be as low as possible, but shall not create
a vacuum nor exceed 255 mm (10 in.) of water differential in excess of atmospheric pressure.
10.3.12 Exhaust and Crankcase Breather System Resonance—The exhaust and crankcase breather piping systems shall have
internal volumes and be of such length that gas resonance does not result. See Appendix X3 for a suitable procedure to determine
if resonance exists.
10.3.13 Belt Tension—The belts connecting the flywheel to the absorption motor shall be tightened, after an initial break-in, so
that with the engine stopped, a 2.25 kg (5 lb) weight suspended from one belt halfway between the flywheel and motor pulley shall
depress the belt approximately 12.5 mm (0.5 in.).
10.3.14 Basic Rocker Arm Carrier Adjustment:
10.3.14.1 Basic Rocker Arm Carrier Support Setting—For exposed valve train applications, each rocker arm carrier support shall
be threaded into the cylinder so that the distance between the machined surface of the cylinder and the underside of the fork is
31 mm (1 ⁄32 in.). For enclosed valve train applications, each rocker arm carrier support shall be threaded into the cylinder so that
the distance between the top machined surface of the valve tray and the underside of the fork is 19 mm ( ⁄4 in.).
10.3.14.2 Basic Rocker Arm Carrier Setting—With the cylinder positioned so that the distance between the underside of the
cylinder and the top of the clamping sleeve is approximately 16 mm ( ⁄8 in.), the rocker arm carrier shall be set horizontal before
tightening the bolts that fasten the long carrier support to the clamping sleeve.
10.3.14.3 Basic Rocker Arm Setting—With the engine on tdc on the compression stroke, and the rocker arm carrier set at the basic
setting, set the valve adjusting screw to approximately the mid-position in each rocker arm. Then adjust the length of the push rods
so that the rocker arms shall be in the horizontal posi
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