ASTM D6424-04a

Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines

SIGNIFICANCE AND USE
This practice is used as a basis for determining the minimum motor octane requirement of naturally aspirated aircraft engines by use of PRFs.
Results from standardized octane ratings will play an important role in defining the actual octane requirement of a given aircraft engine, which can be applied in an effort to determine a fleet requirement.
SCOPE
1.1 This practice covers ground based octane rating procedures for naturally aspirated spark ignition aircraft engines using primary reference fuels.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Oct-2004
• ICS: 75.160.20 - Liquid fuels
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.J0.01 - Jet Fuel Specifications

Relations

• Replaces: ASTM D6424-04 - Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines
• Effective Date: 01-Nov-2004
• Replaced By: ASTM D6424-04a(2010) - Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines
• Effective Date: 01-Jul-2010
• Referred By: ASTM D7826-23a - Standard Guide for Evaluation of New Aviation Gasolines and New Aviation Gasoline Additives
• Effective Date: 01-Nov-2004

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation:D6424–04a
Standard Practice for
Octane Rating Naturally Aspirated Spark Ignition Aircraft
1
Engines
This standard is issued under the fixed designation D6424; 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.
1. Scope* 3.1.3 full rich—condition in which the mixture control is at
the full stop position with the fuel flow within manufacturer’s
1.1 This practice covers ground based octane rating proce-
recommended settings.
dures for naturally aspirated spark ignition aircraft engines
3.1.4 house fuel, n—for octane rating, an unleaded, straight
using primary reference fuels.
hydrocarbon fuel used for engine warm-up and all non-octane
1.2 This standard does not purport to address all of the
rating testing.
safety concerns, if any, associated with its use. It is the
3.1.5 knock, n—in an aircraft spark ignition engine, abnor-
responsibility of the user of this standard to establish appro-
mal combustion caused by autoignition of the air/fuel mixture.
priate safety and health practices and determine the applica-
3.1.6 knock condition, n—for octane rating, when the
bility of regulatory limitations prior to use.
knock intensity in any cylinder is light knock or greater as
2. Referenced Documents
described in Annex A1.
2
3.1.7 knock number, n—for octane rating, a numerical
2.1 ASTM Standards:
quantification of knock intensity.
D2700 Test Method for Motor Octane Number of Spark-
3.1.8 motor octane number of primary reference fuels above
Ignition Engine Fuel
100—determined in terms of the number of millilitres of
3. Terminology
tetraethyl lead in isooctane.
3.1.9 motor octane number of primary reference fuels from
3.1 Definitions:
0to100—the volume % of isooctane (equals 100.0) in a blend
3.1.1 amine number of reference fuels above 100, AN,
with n-heptane (equals 0.0).
n—determined in terms of the weight percent of
3.1.10 naturally aspirated aircraft engine, n—aircraft pis-
3-methylphenylamine in reference grade isooctane (2,2,4–tri-
ton engine that breathes without forced means from either
methylpentane). For example, 5 % of 3–methylphenylamine in
turbochargers or superchargers.
reference grade isooctane has an amine number of 105 (AN
3.1.11 no-knock condition, n—for octane rating, when the
105). No attempt has been made to correlate performance
combustion instability in all cylinders is less than light knock.
number of leaded reference fuels to the amine number of
Refer to Annex A1 for description of knock intensity.
unleaded reference fuels, and none is implied.
3.1.12 peak EGT, n—for octane rating, as the mixture is
3.1.2 engine motor octane requirement—one full motor
manuallyleanedfromastaterichofstoichiometric,theexhaust
octane number greater than the maximum motor octane num-
gas temperature will increase with the removal of excess fuel.
ber that results in knock (graphic knock level descriptions can
As the mixture is continually leaned, a peak temperature will
be seen in Annex A1). For example, a test engine knocks on
be attained, after which continued leaning will result in lower
primary reference fuels with 96 and 97 motor octane numbers.
exhaust gas temperatures.
The test engine does not knock on a primary reference fuel
3.1.13 primary reference fuels, n—for octane rating,
with a 98 motor octane number. The maximum motor octane
blended fuels of reference grade isooctane and n-heptane.
number that results in knock is 97, so the motor octane
3.1.14 stable engine conditions, n—for octane rating, cyl-
requirement is 98.
inder head temperatures change less than 5°C (9°F) during a
1-min period. Any changes or minor adjustments to throttle,
1
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
mixture, or engine conditions mandate restarting the clock for
Products and Lubricants and is the direct responsibility of Subcommittee D02.J0.02
determining stable conditions.
on Aviation Gasoline.
Current edition approved Nov. 1, 2004. Published November 2004. Originally
3.2 Acronyms:
approved in 1999. Last previous edition approved in 2004 as D6424–04. DOI:
3.2.1 CHT—cylinder head temperature.
10.1520/D6424-04A.
2 3.2.2 EGT—exhaust gas temperature.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.3 inHg—inches of mercury.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
3.2.4 MAP—manifold absolute pressure.
the ASTM website.
*A Summary of Changes section appears at the end of this standard.
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