ASTM D2700-24a

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

SIGNIFICANCE AND USE
5.1 Motor O.N. correlates with commercial automotive spark-ignition engine antiknock performance under severe conditions of operation.  
5.2 Motor 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-octane number determinations.  
5.2.2 Motor O.N., in conjunction with Research 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 United States, and is referred to in vehicle manuals.
This is more commonly presented as:
5.3 Motor O.N. is used for measuring the antiknock performance of spark-ignition engine fuels that contain oxygenates.  
5.4 Motor O.N. is important in relation to the specifications for spark-ignition engine fuels used in stationary and other nonautomotive engine applications.  
5.5 Motor O.N. is utilized to determine, by correlation equation, the Aviation method O.N. or performance number (lean-mixture aviation rating) of aviation spark-ignition engine fuel.7
SCOPE
1.1 This laboratory test method covers the quantitative determination of the knock rating of liquid spark-ignition engine fuel in terms of Motor octane number, 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 in a standardized single cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions. The octane number scale is defined by the volumetric composition of primary reference fuel blends. The sample fuel knock intensity is compared to that of one or more primary reference fuel blends. The octane number of the primary reference fuel blend that matches the knock intensity of the sample fuel establishes the Motor octane number.  
1.2 The octane number scale covers the range from 0 to 120 octane number, but this test method has a working range from 40 to 120 octane number. Typical commercial fuels produced for automotive spark-ignition engines rate in the 80 to 90 Motor octane number range. Typical commercial fuels produced for aviation spark-ignition engines rate in the 98 to 102 Motor octane number range. Testing of gasoline blend stocks or other process stream materials can produce ratings at various levels throughout the Motor octane number 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-pounds 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 more specific hazard 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, X4.3.12.4, and X4.5.1.8. ...

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 D2700-24a: Standard Test Method for Motor Octane Number of Spark-Ignition Engine Fuel establishes a laboratory method for determining the knock rating (motor octane number, or Motor O.N.) of liquid spark-ignition engine fuels. This standard test method, developed by ASTM, is a critical benchmark for engine and fuel manufacturers, ensuring fuel quality and performance in the context of severe engine operating conditions. It applies to conventional gasoline as well as blends containing up to 25% ethanol by volume.

The Motor O.N. measured under this standard correlates strongly with antiknock performance in commercial automotive engines operating under harsh conditions and is widely referenced in industry specifications, regulatory standards, and commercial transactions.

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Key Topics

• Motor Octane Number (Motor O.N.): A quantitative measure of a fuel’s resistance to engine knock under severe conditions, as determined by a standardized test protocol (using a CFR engine).
• Test Methodology: This laboratory procedure uses a single-cylinder, variable-compression engine (CFR engine) to compare the knock intensity of a sample fuel against primary reference fuels under controlled conditions.
• Sample Range: The method covers octane numbers from 40 to 120 for commercial and aviation spark-ignition engine fuels.
• Fuel Types: Applicable to gasoline and gasoline-ethanol blends, but not to fuels primarily composed of oxygenates.
• Primary Reference Fuels: Isooctane and n-heptane blends are used as standards to calibrate the octane scale.

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Applications

• Engine Design and Validation: Engine and vehicle manufacturers use Motor O.N. to match engines with fuels that provide optimal antiknock performance.
• Fuel Refining and Marketing: Petroleum refiners and marketers rely on Motor O.N. as a crucial specification for product quality and compliance with regulatory requirements.
• Commercial Transactions: In fuel commerce, Motor O.N. is a primary measurement for specifying and certifying product integrity.
• Retail Fuel Labelling: The antiknock index, defined as the average of Research Octane Number (RON, per ASTM D2699) and Motor O.N., is commonly displayed at retail pumps in the United States and cited in vehicle manuals.
• Aviation and Stationary Engines: The method is also utilized to estimate performance ratings for aviation spark-ignition engine fuels and nonautomotive engine applications.
• Quality Assurance: The standard’s repeatable procedures facilitate quality control within and across laboratories, improving fuel consistency and safety.
• Correlation Calculations: Empirical relationships involving Motor O.N. support calculations for road octane numbers and aviation performance numbers, contributing to broader industry practices.

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Related Standards

• ASTM D2699: Standard Test Method for Research Octane Number of Spark-Ignition Engine Fuel - a companion method conducted under less severe operating conditions.
• ASTM D4814: Specification for Automotive Spark-Ignition Engine Fuel, which references this test for compliance in automotive gasoline.
• ASTM D6299: Statistical Quality Assurance techniques for fuel test labs.
• ASTM D4057 & D4177: Sampling practices for petroleum products.
• ASTM E29: Practice for using significant digits in test data conformance.
• ASTM D1193: Specification for reagent water used in laboratory procedures.

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Conclusion

Compliance with ASTM D2700-24a is fundamental for maintaining high standards in fuel quality, engine performance, and safety. This standard supports a consistent approach to measuring the Motor Octane Number, which is indispensable for fuel formulation, regulatory compliance, engine design, and end-user satisfaction. By referencing primary related standards, industry stakeholders ensure comprehensive coverage of spark-ignition engine fuel properties, from lab testing to market delivery.

Keywords: ASTM D2700, motor octane number, spark-ignition engine fuel, antiknock performance, CFR engine, octane rating, fuel quality, gasoline testing, ASTM fuel standards.

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: D2700 − 24a
Standard Test Method for
Motor Octane Number of Spark-Ignition Engine Fuel
This standard is issued under the fixed designation D2700; 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* calculated value shall be rounded “to the nearest unit” in the
last right-hand digit used in expressing the specified limit, in
1.1 This laboratory test method covers the quantitative
accordance with the rounding method of Practice E29.
determination of the knock rating of liquid spark-ignition
1.5 This standard does not purport to address all of the
engine fuel in terms of Motor octane number, including fuels
safety concerns, if any, associated with its use. It is the
that contain up to 25 % v/v of ethanol. However, this test
responsibility of the user of this standard to establish appro-
method may not be applicable to fuel and fuel components that
priate safety, health, and environmental practices and deter-
are primarily oxygenates. The sample fuel is tested in a
mine the applicability of regulatory limitations prior to use.
standardized single cylinder, four-stroke cycle, variable com-
For more specific hazard statements, see Section 8, 14.4.1,
pression ratio, carbureted, CFR engine run in accordance with
15.5.1, 16.6.1, Annex A1, A2.2.3.1, A2.2.3.3(6) and (9),
a defined set of operating conditions. The octane number scale
A2.3.5, X3.3.7, X4.2.3.1, X4.3.4.1, X4.3.9.3, X4.3.12.4, and
is defined by the volumetric composition of primary reference
X4.5.1.8.
fuel blends. The sample fuel knock intensity is compared to
1.6 This international standard was developed in accor-
that of one or more primary reference fuel blends. The octane
dance with internationally recognized principles on standard-
number of the primary reference fuel blend that matches the
ization established in the Decision on Principles for the
knock intensity of the sample fuel establishes the Motor octane
Development of International Standards, Guides and Recom-
number.
mendations issued by the World Trade Organization Technical
1.2 The octane number scale covers the range from 0 to 120
Barriers to Trade (TBT) Committee.
octane number, but this test method has a working range from
40 to 120 octane number. Typical commercial fuels produced
2. Referenced Documents
for automotive spark-ignition engines rate in the 80 to 90
2.1 ASTM Standards:
Motor octane number range. Typical commercial fuels pro-
D1193 Specification for Reagent Water
duced for aviation spark-ignition engines rate in the 98 to 102
D2268 Test Method for Analysis of High-Purity n-Heptane
Motor octane number range. Testing of gasoline blend stocks
and Isooctane by Capillary Gas Chromatography
or other process stream materials can produce ratings at various
D2699 Test Method for Research Octane Number of Spark-
levels throughout the Motor octane number 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-pounds 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
1.4 For purposes of determining conformance with all
Petroleum Products
specified limits in this standard, an observed value or a
D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
1 D4177 Practice for Automatic Sampling of Petroleum and
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Petroleum Products
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 D2700 – 24. DOI:
10.1520/D2700-24A. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Research octane number, determined using Test Method D2699, is a companion contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
method to provide a similar but typically higher octane rating under milder Standards volume information, refer to the standard’s Document Summary page on
operating 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
D2700 − 24a
D4814 Specification for Automotive Spark-Ignition Engine number accepted reference value (O.N. ) determined by
ARV
Fuel round-robin testing under reproducibility conditions.
D5842 Practice for Sampling and Handling of Fuels for
3.1.3 cylinder height, n—for the CFR engine, the relative
Volatility Measurement
vertical position of the engine cylinder with respect to the
D6299 Practice for Applying Statistical Quality Assurance
piston at top dead center (tdc) or the top machined surface of
and Control Charting Techniques to Evaluate Analytical
the crankcase.
Measurement System Performance
3.1.4 detonation meter, analog, n—for knock testing, the
D6300 Practice for Determination of Precision and Bias
signal conditioning instrumentation that accepts the electrical
Data for Use in Test Methods for Petroleum Products,
signal from the detonation pickup and provides an analog
Liquid Fuels, and Lubricants
output signal to the analog knockmeter.
D6304 Test Method for Determination of Water in Petro-
leum Products, Lubricating Oils, and Additives by Cou-
3.1.4.1 Discussion—In the context of this test method, three
lometric Karl Fischer Titration
contemporary generations of apparatus have been developed as
D6708 Practice for Statistical Assessment and Improvement
detonation meters. These are (year of introduction in parenthe-
of Expected Agreement Between Two Test Methods that
sis): the 501T Detonation Meter (1969), the 501C Detonation
Purport to Measure the Same Property of a Material 6
Meter (1979), and the SSD7000 Detonation Meter (2017).
D7504 Test Method for Trace Impurities in Monocyclic
3.1.5 detonation meter, digital, n—for knock testing, the
Aromatic Hydrocarbons by Gas Chromatography and
digital signal conditioning instrumentation that accepts the
Effective Carbon Number
electrical signal from the detonation pickup and provides a
E29 Practice for Using Significant Digits in Test Data to
digital output signal for display.
Determine Conformance with Specifications
3.1.6 detonation pickup, n—for knock testing, a
E344 Terminology Relating to Thermometry and Hydrom-
magnetostrictive-type transducer that threads into the engine
etry
cylinder and is exposed to combustion chamber pressure to
E456 Terminology Relating to Quality and Statistics
provide an electrical signal that is proportional to the rate-of-
E542 Practice for Gravimetric Calibration of Laboratory
change of cylinder pressure.
Volumetric Instruments
E1064 Test Method for Water in Organic Liquids by Coulo-
3.1.7 dial indicator reading, n—for the CFR engine, a
metric Karl Fischer Titration
numerical indication of cylinder height, in thousandths of an
2.2 ANSI Standard:
inch, indexed to a basic setting at a prescribed compression
C-39.1 Requirements for Electrical Analog Indicating In-
pressure when the engine is motored.
struments
3.1.8 digital counter reading, n—for the CFR engine, a
2.3 Energy Institute Standard:
numerical indication of cylinder height, indexed to a basic
IP 224/02 Determination of Low Lead Content of Light
setting at a prescribed compression pressure when the engine is
Petroleum Distillates by Dithizone Extraction and Colo-
motored.
rimetric Method
3.1.9 dynamic fuel level, n—for knock testing, test proce-
3. Terminology
dure in which the fuel-air ratio for maximum knock intensity
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) a consensus or certified value, based on collaborative
3.1.10 equilibrium fuel level, n—for knock testing, test
experimental work under the auspices of a scientific or
procedure in which the fuel-air ratio for maximum knock
engineering group. E456
intensity for sample and reference fuels is determined by
3.1.1.1 Discussion—In the context of this test method,
making incremental step changes in fuel-air ratio, observing
accepted reference value is understood to apply to the Motor
the equilibrium knock intensity for each step, and selecting the
octane number of specific reference materials determined
level that produces the highest knock intensity reading.
empirically under reproducibility conditions by the National
3.1.11 firing, n—for the CFR engine, operation of the CFR
Exchange Group or another recognized exchange testing orga-
engine with fuel and ignition.
nization.
3.1.12 fuel-air ratio for maximum knock intensity, n—for
3.1.2 Check Fuel, n—for quality control testing, a spark-
knock testing, that proportion of fuel to air that produces the
ignition engine fuel of selected characteristics having an octane
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, WIG 7AR, be obtained by requesting Research Report RR:D02-1870. Contact ASTM Customer
U.K., http://www.energyinst.org.uk. Service at [e-mail].
D2700 − 24a
highest knock intensity for each fuel in the knock testing unit, items in different laboratories with different operators using
provided this occurs within specified carburetor fuel level different equipment. E456
limits.
3.1.27 spread, n—in knock measurement, the sensitivity of
3.1.13 guide tables, n—for knock testing, the specific rela- the analog detonation meter expressed in knockmeter divisions
tionship between cylinder height (compression ratio) and per octane number. (This feature is not a necessary adjustment
octane number at standard knock intensity for specific primary in the digital detonation meter.)
reference fuel blends tested at standard or other specified
3.1.28 standard knock intensity, n—for knock testing, that
barometric pressure.
level of knock established when a primary reference fuel blend
3.1.14 knock, n—in a spark-ignition engine, abnormal of specific octane number is used in the knock testing unit at
combustion, often producing audible sound, caused by autoi- maximum knock intensity fuel-air ratio, with the cylinder
gnition of the air/fuel mixture. D4175 height (dial indicator or digital counter reading) set to the
prescribed guide table value.
3.1.15 knock intensity, n—for knock testing, a measure of
the level of knock. 3.1.29 toluene standardization fuels, n—for knock testing,
those volumetrically proportioned blends of two or more of the
3.1.16 knockmeter, analog, n—for knock testing, the 0 to
following: reference fuel grade toluene, n-heptane, and isooc-
100 division analog indicating meter that displays the knock
tane that have prescribed rating tolerances for O.N. deter-
ARV
intensity signal from the analog detonation meter.
mined by round-robin testing under reproducibility conditions.
3.1.17 knockmeter, digital, n—for knock testing, the 0 to 999
3.2 Definitions of Terms Specific to This Standard:
division digital indicating software meter that displays the
3.2.1 primary reference fuels, n—for knock testing,
knock intensity from the digital detonation meter.
isooctane, n-heptane, volumetrically proportioned mixtures of
3.1.18 motoring, n—for the CFR engine, operation of the
isooctane with n-heptane, or blends of tetraetyllead in isooc-
CFR engine without fuel and with the ignition shut off.
tane that define the octane number scale.
3.1.19 motor octane number, n—for spark-ignition engine
3.2.2 repeatability conditions NEG, n—replicate testing
fuel, the numerical rating of knock resistance obtained by
conditions employed by the National Exchange Group in
comparison of its knock intensity with that of primary refer-
which a single operator tests two specimens taken from a single
ence fuels when both are tested in a standardized CFR engine
sample container with at least one other sample being tested
operating under the conditions specified in this test method.
between the two specimens.
3.1.20 octane number, n—for spark-ignition engine fuel,
3.3 Abbreviations:
any one of several numerical indicators of resistance to knock
3.3.1 ARV—accepted reference value
obtained by comparison with reference fuels in standardized
3.3.2 CFR—Cooperative Fuel Research
engine or vehicle tests. D4175
3.3.3 C.R.—compression ratio
3.1.21 oxygenate, n—an oxygen-containing organic
compound, which may be used as a fuel or fuel supplement, for
3.3.4 IAT—intake air temperature
example, various alcohols and ethers. D4175
3.3.5 K.I.—knock intensity
3.1.22 primary reference fuel blends above 100 octane,
3.3.6 MIXT—mixture temperature
n—the millilitres per U.S. gallon of tetraethyllead in isooctane
3.3.7 NEG—National Exchange Group
that define octane numbers above 100 in accordance with an
3.3.8 OA—octane analyzer
empirically determined relationship.
3.3.9 O.N.—octane number
3.1.23 primary reference fuel blends below 100 octane,
n—the volume percent of isooctane in a blend with n-heptane
3.3.10 PRF—primary reference fuel
that defines the octane number of the blend, isooctane being
3.3.11 r —repeatability conditions NEG
NEG
assigned as 100 and n-heptane as zero octane number.
3.3.12 RTD—resistance thermometer device (Terminology
3.1.24 quality control (QC) sample, n—for use in quality
E344), platinum type
assurance programs to determine and monitor the precision and
3.3.13 TSF—toluene standardization fuel
stability of a measurement system, a stable and homogeneous
material having physical or chemical properties, or both,
4. Summary of Test Method
similar to those of typical samples tested by the analytical
4.1 The Motor O.N. of a spark-ignition engine fuel is
measurement system; the material is properly stored to ensure
determined using a standard test engine and operating condi-
sample integrity, and is available in sufficient quantity for
tions to compare its knock characteristic with those of PRF
repeated, long term testing. D6299
blends of known O.N. Compression ratio and fuel-air ratio are
3.1.25 repeatability conditions, n—conditions where inde-
adjusted to produce standard K.I. for the sample fuel, as
pendent test results are obtained with the same method on
measured by a specific electronic detonation measurement
identical test items in the same laboratory by the same operator
system. A standard K.I. guide table relates engine C.R. to O.N.
using the same equipment within short intervals of time. E456
level for this specific method. The fuel-air ratio for the sample
3.1.26 reproducibility conditions, n—conditions where test fuel and each of the PRF blends is adjusted to maximize K.I.
results are obtained with the same method on identical test for each fuel.
D2700 − 24a
4.1.1 The fuel-air ratio for maximum K.I. may be obtained for many vehicles, is posted on retail dispensing pumps in the
(1) by making incremental step changes in mixture strength, United States, and is referred to in vehicle manuals.
observing the equilibrium K.I. value for each step, and then
Antiknock index = 0.5 Research O.N. + 0.5 Motor O.N. + 0 (2)
selecting the condition which maximizes the reading or (2) by
This is more commonly presented as:
picking the maximum K.I. as the mixture strength is changed
from either rich-to-lean or lean-to-rich at a constant rate.
R 1 M
~ !
Antiknock Index = (3)
4.2 Bracketing Procedures—The engine is calibrated to
operate at standard K.I. in accordance with the guide table. The
5.3 Motor O.N. is used for measuring the antiknock perfor-
fuel-air ratio of the sample fuel is adjusted to maximize the mance of spark-ignition engine fuels that contain oxygenates.
K.I., and then the cylinder height is adjusted so that standard
5.4 Motor O.N. is important in relation to the specifications
K.I. is achieved. Without changing cylinder height, two PRFs
for spark-ignition engine fuels used in stationary and other
are selected such that, at their fuel-air ratio for maximum K.I.,
nonautomotive engine applications.
one knocks harder (higher K.I.) and the other softer (lower
5.5 Motor O.N. is utilized to determine, by correlation
K.I.) than the sample fuel. A second set of K.I. measurements
equation, the Aviation method O.N. or performance number
for sample fuel and reference fuels is required, and the sample
(lean-mixture aviation rating) of aviation spark-ignition engine
fuel O.N. is calculated by interpolation in proportion to the
fuel.
differences in average K.I. readings. A final condition requires
that the cylinder height used shall be within prescribed limits
6. Interferences
around the guide table value for the calculated O.N. Bracketing
procedure ratings may be determined using either the equilib- 6.1 Precaution—Avoid exposure of sample fuels to sunlight
or fluorescent lamp UV emissions to minimize induced chemi-
rium 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 to 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, which can be present in the
conditions; the cylinder height is adjusted so that standard K.I.
area where the knock testing unit is located, may have a
is achieved. The calibration is reconfirmed and the sample fuel
measurable effect on the Motor 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 Motor
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 primary reference blend
used to calibrate the engine to the guide table standard K.I.
6.3 Electrical power subject to transient voltage or fre-
condition.
quency surges or distortion can alter CFR engine operating
conditions or knock measuring instrumentation performance
5. Significance and Use
and thus affect the Motor O.N. obtained for sample fuels.
6.3.1 Electromagnetic emissions can cause interference
5.1 Motor O.N. correlates with commercial automotive
with the analog knock meter and thus affect the Motor O.N.
spark-ignition engine antiknock performance under severe
obtained for sample fuels.
conditions of operation.
5.2 Motor O.N. is used by engine manufacturers, petroleum
7. Apparatus
refiners and marketers, and in commerce as a primary specifi-
7.1 Engine Equipment —This test method uses a single
cation measurement related to the matching of fuels and
cylinder, CFR F-2 test engine for the determination of O.N.
engines.
that consists of standard components as follows: crankcase, a
5.2.1 Empirical correlations that permit calculation of auto-
cylinder/clamping sleeve assembly to provide continuously
motive antiknock performance are based on the general equa-
tion:
Road O.N. 5 ~k × Research O.N. !1~k × Motor O.N.! 1 k
Correlation information is given in ASTM research report RR:D02–69,
1 2 3
Aviation Gasoline Antiknock Quality by ASTM Methods D614 and D357. (Re-
(1)
placed by Test Method D2700.) Refer to the Report Section, in this test method, for
application of the correlation relationship.
Values of k , k , and k vary with vehicles and vehicle
1 2 3
Supporting data have been filed at ASTM International Headquarters and may
populations and are based on road-octane number determina-
be obtained by requesting Research Report RR:D02-1502. Contact ASTM Customer
tions.
Service at [e-mail].
The sole source of supply of the new complete engine known to the committee
5.2.2 Motor O.N., in conjunction with Research O.N.,
at this time is CFR Engines Inc., N8 W22577 Johnson Drive, Pewaukee, WI 53186.
defines the antiknock index of automotive spark-ignition en-
If you are aware of alternative suppliers, please provide this information to ASTM
gine fuels, in accordance with Specification D4814. The
International Headquarters. Your comments will receive careful consideration at a
antiknock index of a fuel approximates the road octane ratings meeting of the responsible technical committee, which you may attend.
D2700 − 24a
variable C.R. adjustable with the engine operating, a thermal 7.3.2 Volumetric Blending of Tetraethyllead—A calibrated
syphon recirculating jacket coolant system, a multiple fuel tank buret, pipette assembly, or other liquid dispensing apparatus
system with selector valving to deliver fuel through a single jet having a capacity of not more than 4.0 mL and a critically
passage and carburetor venturi, an intake air system with controlled volumetric tolerance shall be used for dispensing
controlled temperature and humidity equipment, electrical dilute tetraethyllead into 400 mL batches of isooctane. Cali-
controls, and a suitable exhaust pipe. The engine flywheel is bration of the dispensing apparatus shall be verified in accor-
belt connected to a special electric power-absorption motor dance with Practice E542.
utilized to both start the engine and as a means to absorb power 7.3.3 Gravimetric Blending of Reference Fuels—Use of
at constant speed when combustion is occurring (engine firing). blending systems that allow preparation of the volumetrically-
The intensity of combustion knock is measured by electronic defined blends by gravimetric (mass) measurements based on
detonation sensing and metering instrumentation. See Fig. 1 the density of the individual components is also permitted,
and Table 1. provided the system meets the requirement for maximum
0.2 % blending tolerance limits.
7.2 Auxiliary Equipment—A number of components and
7.3.3.1 Calculate the mass equivalents of the
devices have been developed to integrate the basic engine
volumetrically-defined blend components from the densities of
equipment into complete laboratory or on-line octane measure-
the individual components at 15.56 °C (60 °F).
ment systems. These include computer interface and software
7.4 Auxiliary Apparatus:
systems, as well as common hardware, tubing, fasteners,
7.4.1 Special Maintenance Tools—A number of specialty
electrical and electronic items. Appendix X1 contains a listing
tools and measuring instruments should be utilized for easy,
of such items, many of which are potentially available from
convenient, and effective maintenance of the engine and testing
multiple sources. In some cases, selection of specific dimen-
equipment. Lists and descriptions of these tools and instru-
sions or specification criteria are important to achieve proper
ments are available from the manufacturer of the engine
conditions for the knock testing unit, and these are included in
equipment and those organizations offering engineering and
Appendix X1 when applicable.
service support for this test method.
7.3 Reference and Standardization Fuel Dispensing
7.4.2 Ventilation Hoods—Handling of reference and stan-
Equipment—This test method requires repeated blending of
dardization fuels, dilute tetraethyllead, and sample fuels having
reference fuels and TSF materials in volumetric proportions. In
various hydrocarbon compositions is best conducted in a well
addition, blending of dilute tetraethyllead in isooctane may be
ventilated space or in a laboratory hood where air movement
performed on-site for making rating determinations above
across the area is sufficient to prevent operator inhalation of
100 O.N. Blending shall be performed accurately because
vapors.
rating error is proportional to blending error.
7.4.2.1 General purpose laboratory hoods are typically ef-
7.3.1 Volumetric Blending of Reference Fuels—Volumetric
fective for handling hydrocarbon fuel blending.
blending has historically been employed to prepare the re-
7.4.2.2 A blending hood meeting the requirements for dis-
quired blends of reference fuels and TSF materials. For
pensing toxic material shall be utilized in testing laboratories
volumetric blending, a set of burets, or accurate volumetric
that choose to prepare leaded isooctane PRF blends on-site.
apparatus, shall be used and the desired batch quantity shall be
7.4.3 Barometer—A pressure measurement device capable
collected in an appropriate container and thoroughly mixed
of measuring the absolute value of air pressure in the room
before being introduced to the engine fuel system.
where the testing apparatus is located with a resolution of at
7.3.1.1 For manual preparation of reference and standard-
least 0.34 kPa (0.1 in. Hg) and a suggested range of 71 kPa to
ization fuel blends, calibrated burets or volumetric apparatus
105 kPa (21 in. Hg to 31 in. Hg).
having a capacity of 200 mL to 500 mL and a maximum
8. Reagents and Reference Materials
volumetric tolerance of 60.2 % shall be used. Calibration shall
be verified in accordance with Practice E542.
8.1 Cylinder Jacket Coolant—Water shall be used in the
7.3.1.2 Calibrated burets shall be outfitted with a dispensing
cylinder jacket for laboratory locations where the resultant
valve and delivery tip to accurately control dispensed volume.
boiling temperature shall be 100 °C 6 1.5 °C (212 °F 6 3 °F).
The delivery tip shall be of such design that shut-off tip
Water with commercial glycol-based antifreeze added in suf-
discharge does not exceed 0.5 mL.
ficient quantity to meet the boiling temperature requirement
7.3.1.3 The rate of delivery from the dispensing system shall be used when laboratory altitude dictates. A commercial
shall not exceed 400 mL per 60 s.
multifunctional water treatment material should be used in the
coolant to minimize corrosion and mineral scale that can alter
7.3.1.4 The set of burets for the reference and standardiza-
heat transfer and rating results.
tion fuels shall be installed in such a manner and be supplied
8.1.1 Water shall be understood to mean reagent water
with fluids such that all components of each batch or blend are
conforming to Type IV, Specification D1193. (Warning—
dispensed at the same temperature.
Ethylene glycol based antifreeze is poisonous and may be
7.3.1.5 See Appendix X2 for volumetric reference fuel
harmful or fatal if inhaled or swallowed. See Annex A1.)
dispensing system information.
7.3.1.6 Automated volumetric blending apparatus may be
used providing the system achieves a maximum volumetric
Refer to Industrial Ventilation Manual, published by the American Conference
blending tolerance limit of 60.2 %. of Governmental Industrial Hygienists, Cincinnati, OH.
D2700 − 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 Motor Method Test Engine Assembly
D2700 − 24a
TABLE 1 General Rating Unit Characteristics and Information
Item Description
Test Engine CFR F-2 Motor 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), in. 3.250 (Standard)
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 Rings 3 ferrous, straight sided
Oil Control 1 cast iron, one piece, slotted (Type 85)
Camshaft Overlap, degrees 5
Fuel System
Carburetor Single vertical jet and fuel flow control to
permit adjustment of fuel-air ratio
Venturi Throat Diameter, in. Dependent on installation altitude
⁄16 ; sea level to 500 m (1600 ft)
⁄32 ; 500 m to 1000 m (3300 ft)
⁄4 ; over 1000 m (3300 ft)
Ignition Electronically triggered condenser discharge
through coil to spark plug
Ignition Timing Variable as cylinder height (C.R.) is changed
Intake Air Humidity Controlled within specified limited range
Knock Measurement System
Detonation Pickup Pressure-sensitive, magnetostrictive core rod
and coil
Detonation meter Integrated electronic filter with adjustable gain
and zero offset
8.2 Engine Crankcase Lubricating Oil—An SAE 30 viscos- 8.3.2 n-heptane shall meet the specifications in Table 2.
ity grade oil meeting the current API service classification for (Warning—n-heptane is flammable and its vapors are harmful.
spark-ignition engines shall be used. It shall contain a detergent Vapors may cause flash fire. See Annex A1.)
additive and have a kinematic viscosity from 8.3.3 80 octane PRF blend prepared using reference fuel
2 2
9.3 mm per s (cSt) to 12.5 mm per s (cSt) at 100 °C (212 °F) grade isooctane and n-heptane shall meet the specifications in
and a viscosity index of not less than 85. Oils containing Table 2. (Warning—80 octane PRF is flammable and its
viscosity index improvers shall not be used. Multigraded oils vapors are harmful. Vapors may cause flash fire. See Annex
shall not be used. (Warning—Lubricating oil is combustible A1.)
and its vapor is harmful. See Annex A1.) 8.3.4 Refer to Annex A3 for octane numbers of various
blends of 80 octane PRF and either n-heptane (see Table A3.1)
8.3 PRF, isooctane, 80-octane, and normal heptane classi-
or isooctane (see Table A3.2).
fied as reference fuel grade shall meet the specifications that
follow: (Warning—PRF is flammable and its vapors are 8.4 Dilute Tetraethyllead, (commonly referred to as TEL
harmful. Vapors may cause flash fire. See Annex A1.) Dilute Volume Basis) is a prepared solution of aviation mix
8.3.1 Isooctane (2,2,4-trimethylpentane) shall meet the
specifications in Table 2. (Warning—Isooctane is flammable
Dilute tetraethyllead is available from Ethyl Corporation, 330 S. Fourth St.,
and its vapors are harmful. Vapors may cause flash fire. See
Richmond, VA 23219-4304; or from The Associated Octel Company, Ltd., 23
Annex A1.) Berkeley Square, London, England W1X 6DT.
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)
D2700 − 24a
tetraethyllead antiknock compound in a hydrocarbon diluent of 9.2 Sample Temperature—Samples shall be cooled to a
70 % (V/V) xylene, 30 % (V/V) n-heptane. (Warning—Dilute temperature of 2 °C to 10 °C (35 °F to 50 °F), in the container
tetraethyllead is poisonous and flammable. It may be harmful in which they are received, before the container is opened.
or fatal if inhaled, swallowed, or absorbed through the skin.
9.3 Protection from Light—Collect and store sample fuels in
May cause flash fire. See Annex A1.)
an opaque container, such as a dark brown glass bottle, metal
8.4.1 The fluid shall contain 18.23% 6 0.05 % (m/m)
can, or a minimally reactive plastic container to minimize
tetraethyllead and have a relative density 15.6/15.6 °C (60/
exposure to UV emissions from sources such as sunlight or
60 °F) of 0.957 to 0.967. The typical composition of the fluid,
fluorescent lamps.
excluding the tetraethyllead, is as follows:
Typical Concentration,
10. Basic Engine and Instrument Settings and Standard
Ingredient % (m/m)
Operating Conditions
Ethylene dibromide (scavenger) 10.6
10.1 Installation of Engine Equipment and
Diluent:
xylene 52.5 Instrumentation—Installation of the engine and instrumenta-
n-heptane 17.8
tion requires placement of the engine on a suitable foundation
Dye, antioxidant and inerts 0.87
and hook-up of all utilities. Engineering and technical support
8.4.2 Add dilute tetraethyllead, in mL quantities, to a
for this function is required, and the user shall be responsible
400 mL volume of isooctane to prepare PRF blends used for
to comply with all local and national codes and installation
ratings over 100 O.N. The composition of the dilute fluid is
requirements.
such that when 2.0 mL are added to 400 mL of isooctane, the
10.1.1 Proper operation of the CFR engine requires assem-
blend shall contain the equivalent of 2.0 mL of lead/U.S. gal
bly of a number of engine components and adjustment of a
(0.56 g of lead/L).
series of engine variables to prescribed specifications. Some of
8.4.3 Refer to Annex A3 for octane numbers of blends of
these settings are established by component specifications,
tetraethyllead isooctane (see Table A3.3).
others are established at the time of engine assembly or after
8.4.4 An alternative to blending with dilute tetraethyllead is
overhaul, and still others are engine running conditions that
to prepare leaded PRF from isooctane + 6.0 mL TEL per U. S.
must be observed or determined by the operator during the
gallon and isooctane (see Table A3.4).
testing process.
8.5 Toluene, Reference Fuel Grade shall meet the require-
10.2 Conditions Based on Component Specifications:
ments in Table 3. Toluene purity is determined by subtracting
10.2.1 Engine Speed—900 r ⁄min 6 9 r ⁄min, when the en-
the sum of the hydrocarbon impurities and water content from
gine is firing, with a maximum variation of 9 r/min occurring
100 %. (Warning—Toluene is flammable and its vapors are
during a rating. Engine speed, while firing, shall not be more
harmful. Vapors may cause flash fire. See Annex A1.)
than 3 r/min greater than when it is motoring without combus-
NOTE 1—Experience has shown that Toluene exposed to atmospheric tion.
moisture (humidity) can absorb water. Test Methods D6304 or E1064 may
10.2.2 Indexing Flywheel to Top-Dead-Center (tdc)—With
be utilized to measure the water content of the Toluene. Options to help
the piston at the highest point of travel in the cylinder, set the
manage or control the Toluene moisture levels include installing an inline
flywheel pointer mark in alignment with the 0° mark on the
air filter/dryer on the drum vent, installing a nitrogen purge on the drum,
flywheel in accordance with the instructions of the manufac-
and the use of dryer desiccant beads, etc.
turer.
8.5.1 Antioxidant shall be added by the supplier at a treat
10.2.3 Valve Timing—The engine uses a four-stroke cycle
rate suitable for good long term stability as empirically
with two crankshaft revolutions for each complete combustion
determined with the assistance of the antioxidant supplier.
cycle. The two critical valve events are those that occur near
8.6 Check Fuels are in-house typical spark-ignition engine
tdc; intake valve opening and exhaust valve closing. See
fuels having selected O.N. values, low volatility, and good long
Annex A2 for camshaft timing and valve lift measurement
term stability. (Warning—Check Fuel is flammable and its
procedures.
vapors are harmful. Vapors may cause flash fire. See Annex
10.2.3.1 Intake valve opening shall occur 10.0° 6 2.5°
A1.)
after-top-dead-center (atdc) with closing at 34° after-bottom-
dead-center (abdc) on one revolution of the crankshaft and
9. Sampling
flywheel.
9.1 Samples shall be collected in accordance with Practices 10.2.3.2 Exhaust valve opening shall occur 40° before-
D4057, D4177, and D5842. bottom-dead-center (bbdc) on the second revolution of the
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
D2700 − 24a
crankshaft or flywheel, with closing at 15.0° 6 2.5° atdc on the the ASTM Type 83C (83F) thermometer installed at the orifice
next revolution of the crankshaft and flywheel. provided using the manufacturer’s prescribed fitting.
10.2.4 Valve Lift—Intake and exhaust cam lobe contours, 10.3.6.2 To ensure the correct temperature is indicated the
while different in shape, shall have a contour rise of 6.248 mm temperature measurement system shall be installed in accor-
to 6.350 mm (0.246 in. to 0.250 in.) from the base circle to the dance with the instructions provided for this specific applica-
top of the lobe. The resulting valve lift shall be tion.
6.045 mm 6 0.05 mm (0.238 in. 6 0.002 in.). See Annex A2 10.3.7 Intake Mixture Temperature—149 °C (300 °F) main-
for camshaft timing and valve lift measurement procedures. tained within 61 °C (62 °F) when CR or KI results used for
10.2.5 Intake Valve Shroud—The intake valve has a 180° octane determination on each fuel are collected. If intake
shroud or protrusion just inside the valve face to direct the MIXT tuning is used to qualify the engine as fit-for-use, the
incoming fuel-air charge and increase the turbulence within the temperature selected shall be between 141 °C (285 °F) and
combustion chamber. This valve stem is drilled for a pin, which 163 °C (325 °F) and this temperature shall then be maintained
is restrained in a valve guide slot, to prevent the valve from within 61 °C (62 °F) when the CR or KI results used for
rotating and thus maintain the direction of swirl. The valve octane determination on each fuel are recorded.
shall be assembled in the cylinder, with the pin aligned in the 10.3.7.1 The intake MIXT required to qualify the engine in
valve guide, so that the shroud is toward the spark plug side of
each TSF blend O.N. range shall also be used for rating all
the combustion chamber and the swirl is directed in a coun- sample fuels in that O.N. range during an operating period.
terclockwise direction if it could be observed from the top of
10.3.7.2 Temperature measurement systems used to estab-
the cylinder. lish the Intake Mixture Temperature in this test method shall
10.2.6 Carburetor Venturi—The venturi throat size is de-
exhibit the same temperature indicating characteristics and
pendent on the altitude of the location where the CFR engine accuracy as the ASTM 86C (86F) thermometer installed at the
is installed. Select the proper venturi in accordance with Table
orifice provided using the manufacturer’s prescribed fitting.
4. 10.3.7.3 To ensure the correct temperature is indicated the
10.2.6.1 For CFR engines located at altitudes close to where
temperature measurement system shall be installed in accor-
venturi size is designated to change, select whichever venturi dance with the instructions provided for this specific applica-
size results in minimum bias when rating TSF blends in
tion.
accordance with the requirements of Section 12. 10.3.8 Intake Air Humidity—0.00356 kg to 0.00712 kg wa-
ter per kg (25 grains to 50 grains of water per lb) of dry air.
10.3 Assembly Settings and Operating Conditions:
10.3.1 Direction of Engine Rotation—Clockwise rotation of
NOTE 2—The humidity specification is based upon the original ice
the crankshaft when observed from the front of the engine. 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
10.3.2 Valve Clearances:
low. The equipment manufacturers should be consulted to verify the
10.3.2.1 Engine Running and Hot—The clearance for both
effective working range.
intake and exhaust valves shall be set to 0.20 mm 6 0.025 mm
10.3.9 Cylinder Jacket Coolant Level:
(0.008 in. 6 0.001 in.), measured under standard operating
10.3.9.1 Engine Running and Hot—Treated water/coolant
conditions with the engine running at equilibrium conditions
shall be added to the cooling condenser-cylinder jacket so that
on a 90 O.N. PRF blend.
the level in the condenser sight glass shall be within 61 cm
10.3.3 Oil Pressure—172 kPa to 207 kPa (25 psi to 30 psi).
(60.4 in.) of the LEVEL HOT mark on the coolant condenser.
See Annex A2, for the procedure to adjust crankcase lubricat-
ing oil pressure.
NOTE 3—When stopped and cold, a coolant level that is just observable
10.3.4 Oil Temperature—57 °C 6 8 °C (135 °F 6 15 °F). in the bottom of the condenser sight glass will typically provide the
controlling engine running and hot operating level.
10.3.5 Cylinder Jacket Coolant Temperature—
100 °C 6 1.5 °C (212 °F 6 3 °F) constant within 60.5 °C
10.3.10 Engine Crankcase Lubricating Oil Level:
(61 °F) when CR or KI results used for octane determination
10.3.10.1 Engine Running and Hot—Oil level shall be
on each fuel are recorded.
approximately mid-position in the crankcase oil sight glass.
10.3.6 Intake Air Temperature—38 °C 6 2.8 °C
NOTE 4—When stopped and cold, oil added to the crankcase so that the
(100 °F 6 5 °F).
level is near the top of the sight glass will typically provide the engine
10.3.6.1 Temperature measurement systems used to estab-
running and hot operating level.
lish the Intake Air Temperature in this test method shall exhibit
10.3.11 Crankcase Internal Pressure—As measured by a
the same temperature indicating characteristics and accuracy as
gauge, 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
TABLE 4 Carburetor Venturi Size for Various Laboratory
vacuum) and is typically from 25 mm to 150 mm (1 in. to 6 in.)
Elevations
of water less than atmospheric pressure. Vacuum shall not
Venturi Throat
Altitude at Engine Location, Typical Barometric Pressure
Diameter, exceed 255 mm (10 in.) of water.
ft (m) Range, in. Hg (kPa)
in. (mm)
10.3.12 Exhaust Back Pressure—As measured by a gauge or
Sea level to 1600 (500) ⁄16 (14.3) 31.0 to 28.0 (105.0 to 94.8)
manometer connected to an opening in the exhaust surge tank
1600 to 3300 (500 to 1000) ⁄32 (15.1) 29.0 to 26.0 (98.2 to 88.0)
or main exhaust stack through a snubber orifice to minimize
Higher than 3300 (1000) ⁄4 (19.1) 27.0 and less (91.4 and less)
pulsations, the static pressure should be as low as possible, but
D2700 − 24a
shall not create a vacuum nor exceed 255 mm (10 in.) of water the spark timing is automatically changed and shall provide the
differential in excess of atmospheric pressure. characteristic given in Table 5.
10.3.17 Spark Plug—Champion D16, or equivalent.
10.3.13 Exhaust and Crankcase Breather System
10.3.17.1
...

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: D2700 − 24 D2700 − 24a
Standard Test Method for
Motor Octane Number of Spark-Ignition Engine Fuel
This standard is issued under the fixed designation D2700; 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 Motor octane number, 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 in a standardized single cylinder,
four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions.
The octane number scale is defined by the volumetric composition of primary reference fuel blends. The sample fuel knock
intensity is compared to that of one or more primary reference fuel blends. The octane number of the primary reference fuel blend
that matches the knock intensity of the sample fuel establishes the Motor octane number.
1.2 The octane number scale covers the range from 0 to 120 octane number, but this test method has a working range from 40
to 120 octane number. Typical commercial fuels produced for automotive spark-ignition engines rate in the 80 to 90 Motor octane
number range. Typical commercial fuels produced for aviation spark-ignition engines rate in the 98 to 102 Motor octane number
range. Testing of gasoline blend stocks or other process stream materials can produce ratings at various levels throughout the Motor
octane number 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-pounds 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 more specific hazard 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, X4.3.12.4, 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
D2700 – 23b.D2700 – 24. DOI: 10.1520/D2700-24.10.1520/D2700-24A.
Research octane number, determined using Test Method D2699, is a companion method to provide a similar but typically higher octane rating under milder 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
D2700 − 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
D2699 Test Method for Research 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 Motor 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 fuel 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, WIG 7AR, U.K., http://www.energyinst.org.uk.
D2700 − 24a
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 signal 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 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.
3.1.8 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.
3.1.9 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.
3.1.10 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.
3.1.11 firing, n—for the CFR engine, operation of the CFR engine with fuel and ignition.
3.1.12 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.
3.1.13 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.
3.1.14 knock, n—in a spark-ignition engine, abnormal combustion, often producing audible sound, caused by autoignition of the
air/fuel mixture. D4175
3.1.15 knock intensity, n—for knock testing, a measure of the level of knock.
3.1.16 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.
3.1.17 knockmeter, digital, n—for knock testing, the 0 to 999 division digital indicating software meter that displays the knock
intensity from the digital detonation meter.
3.1.18 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].
D2700 − 24a
3.1.19 motor 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 fuels when both are tested in a standardized CFR engine operating under the
conditions specified in this test method.
3.1.20 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
3.1.21 oxygenate, n—an oxygen-containing organic compound, which may be used as a fuel or fuel supplement, for example,
various alcohols and ethers. D4175
3.1.22 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.
3.1.23 primary reference fuel blends below 100 octane, n—the volume percent 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 zero octane number.
3.1.24 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
3.1.25 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
3.1.26 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
3.1.27 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.)
3.1.28 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.
3.1.29 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 tetraetyllead 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
D2700 − 24a
3.3.4 IAT—intake air temperature
3.3.5 K.I.—knock intensity
3.3.6 MIXT—mixture temperature
3.3.7 NEG—National Exchange Group
3.3.8 OA—octane analyzer
3.3.9 O.N.—octane number
3.3.10 PRF—primary reference fuel
3.3.11 r —repeatability conditions NEG
NEG
3.3.12 RTD—resistance thermometer device (Terminology E344), platinum type
3.3.13 TSF—toluene standardization fuel
4. Summary of Test Method
4.1 The Motor 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 PRF 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 which 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 PRFs 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 reference
fuels is required, and the sample fuel O.N. 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 primary reference blend used to calibrate the engine to
the guide table standard K.I. condition.
5. Significance and Use
5.1 Motor O.N. correlates with commercial automotive spark-ignition engine antiknock performance under severe conditions of
operation.
D2700 − 24a
5.2 Motor 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-octane number determinations.
1 2 3
5.2.2 Motor O.N., in conjunction with Research 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 United States, 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)
5.3 Motor O.N. is used for measuring the antiknock performance of spark-ignition engine fuels that contain oxygenates.
5.4 Motor O.N. is important in relation to the specifications for spark-ignition engine fuels used in stationary and other
nonautomotive engine applications.
5.5 Motor O.N. is utilized to determine, by correlation equation, the Aviation method O.N. or performance number (lean-mixture
aviation rating) of aviation spark-ignition engine fuel.
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 to 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, which can be present in the area where the knock testing unit is located, may have a measurable effect
on the Motor 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 Motor 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 Motor O.N. obtained for sample fuels.
6.3.1 Electromagnetic emissions can cause interference with the analog knock meter and thus affect the Motor O.N. obtained for
sample fuels.
Correlation information is given in ASTM research report RR:D02–69, Aviation Gasoline Antiknock Quality by ASTM Methods D614 and D357. (Replaced by Test
Method D2700.) Refer to the Report Section, in this test method, for application of the correlation relationship.
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].
D2700 − 24a
7. Apparatus
7.1 Engine Equipment —This test method uses a single cylinder, CFR F-2 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 C.R.
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). The intensity of combustion knock is measured by electronic detonation sensing and metering
instrumentation. See Fig. 1 and Table 1.
7.2 Auxiliary Equipment—A number of components and devices have been developed to integrate the basic 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.
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.
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).
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.
D2700 − 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
D2700 − 24a
FIG. 1 Motor Method Test Engine Assembly
TABLE 1 General Rating Unit Characteristics and Information
Item Description
Test Engine CFR F-2 Motor 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), in. 3.250 (Standard)
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 Rings 3 ferrous, straight sided
Oil Control 1 cast iron, one piece, slotted (Type 85)
Camshaft Overlap, degrees 5
Fuel System
Carburetor Single vertical jet and fuel flow control to
permit adjustment of fuel-air ratio
Venturi Throat Diameter, in. Dependent on installation altitude
⁄16 ; sea level to 500 m (1600 ft)
⁄32 ; 500 m to 1000 m (3300 ft)
⁄4 ; over 1000 m (3300 ft)
Ignition Electronically triggered condenser discharge
through coil to spark plug
Ignition Timing Variable as cylinder height (C.R.) is changed
Intake Air Humidity Controlled within specified limited range
Knock Measurement System
Detonation Pickup Pressure-sensitive, magnetostrictive core rod
and coil
Detonation meter Integrated electronic filter with adjustable gain
and zero offset
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 sample fuels 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).
Refer to Industrial Ventilation Manual, published by the American Conference of Governmental Industrial Hygienists, Cincinnati, OH.
D2700 − 24a
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.
8.1.1 Water shall be understood to mean reagent water conforming to Type IV, Specification D1193. (Warning—Ethylene glycol
based antifreeze is poisonous and may be harmful or fatal if inhaled or swallowed. See Annex A1.)
8.2 Engine Crankcase Lubricating Oil—An SAE 30 viscosity grade oil meeting the current API service classification for
spark-ignition engines shall be used. It shall contain a detergent additive and have a kinematic viscosity from
2 2
9.3 mm per s (cSt) 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 shall meet the specifications that follow:
(Warning—PRF 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 (see Table A3.1) or isooctane
(see 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
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)
Dilute tetraethyllead is available from Ethyl Corporation, 330 S. Fourth St., Richmond, VA 23219-4304; or from The Associated Octel Company, Ltd., 23 Berkeley
Square, London, England W1X 6DT.
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8.4.2 Add dilute tetraethyllead, in mL 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 isooctane (see Table A3.3).
8.4.4 An alternative to blending with dilute tetraethyllead is to prepare leaded PRF from isooctane+6.0 mL octane + 6.0 mL TEL
per U. S. gallon and isooctane (see Table A3.4).
8.5 Toluene, Reference Fuel Grade shall meet the requirements in Table 3. Toluene purity is determined by subtracting the sum
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. Test Methods D6304 or E1064 may be
utilized to measure the water content of the Toluene. 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 O.N. values, 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 Samples shall be collected in accordance with Practices D4057, D4177, and 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—900 r ⁄min 6 9 r ⁄min, when the engine is firing, with a maximum variation of 9 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.
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
D2700 − 24a
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 or
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 6.248 mm to 6.350
mm (0.246 in. to 0.250 in.) from the base circle to the top of the lobe. The resulting valve lift shall be 6.045 mm 6 0.05 mm
(0.238 in. 6 0.002 in.). See Annex A2 for camshaft timing and valve lift measurement procedures.
10.2.5 Intake Valve Shroud—The intake valve has a 180° shroud or protrusion just inside the valve face to direct the incoming
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—The venturi throat size is dependent on the altitude of the location where the CFR engine is installed.
Select the proper venturi in accordance with Table 4.
10.2.6.1 For CFR engines located at altitudes close to where venturi size is designated to change, select whichever venturi size
results in minimum bias when rating TSF blends in accordance with the requirements of Section 12.
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 0.20 mm 6 0.025 mm
(0.008 in. 6 0.001 in.), 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—38 °C 6 2.8 °C (100 °F 6 5 °F).
TABLE 4 Carburetor Venturi Size for Various Laboratory
Elevations
Venturi Throat
Altitude at Engine Location, Typical Barometric Pressure
Diameter,
ft (m) Range, in. Hg (kPa)
in. (mm)
Sea level to 1600 (500) ⁄16 (14.3) 31.0 to 28.0 (105.0 to 94.8)
1600 to 3300 (500 to 1000) ⁄32 (15.1) 29.0 to 26.0 (98.2 to 88.0)
Higher than 3300 (1000) ⁄4 (19.1) 27.0 and less (91.4 and less)
D2700 − 24a
10.3.6.1 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 ASTM Type 83C (83F) thermometer installed at the orifice provided
using the manufacturer’s prescribed fitting.
10.3.6.2 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 Mixture Temperature—149 °C (300 °F) maintained within 61 °C (62 °F) when CR or KI results used for octane
determination on each fuel are collected. If intake MIXT tuning is used to qualify the engine as fit-for-use, the temperature selected
shall be between 141 °C (285 °F) and 163 °C (325 °F) and this temperature shall then be maintained within 61 °C (62 °F) when
the CR or KI results used for octane determination on each fuel are recorded.
10.3.7.1 The intake MIXT 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.
10.3.7.2 Temperature measurement systems used to establish the Intake Mixture Temperature in this test method shall exhibit the
same temperature indicating characteristics and accuracy as the ASTM 86C (86F) thermometer installed at the orifice provided
using the manufacturer’s prescribed fitting.
10.3.7.3 To ensure the correct temperature is indicated the temperature measurement system shall be installed in accordance with
the instructions provided for this specific application.
10.3.8 Intake Air Humidity—0.00356 kg to 0.00712 kg water per kg (25 grains 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.
10.3.9 Cylinder Jacket Coolant Level:
10.3.9.1 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.
10.3.10 Engine Crankcase Lubricating Oil Level:
10.3.10.1 Engine Running and Hot—Oil level shall be 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.
10.3.11 Crankcase Internal Pressure—As measured by a gauge, 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.
10.3.12 Exhaust Back Pressure—As measured by a gauge 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 vacuu
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