ASTM D6424-03
(Practice)Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines
Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines
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
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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An American National Standard
Designation: D 6424 – 03
Standard Practice for
Octane Rating Naturally Aspirated Spark Ignition Aircraft
1
Engines
This standard is issued under the fixed designation D 6424; 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 (e) 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.
D 2700 Test Method for Motor Octane Number of Spark-
3.1.8 motor octane number of primary reference fuels from
Ignition Engine Fuel
0to100—the volume % of isooctane (equals 100.0) in a blend
3. Terminology
with n-heptane (equals 0.0).
3.1.9 motor octane number of primary reference fuels above
3.1 Definitions:
100—determined in terms of the number of millilitres of
3.1.1 amine number of reference fuels above 100,
tetraethyl lead in isooctane.
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. No attempt
ton engine that breathes without forced means from either
has been made to correlate performance number of leaded
turbochargers or superchargers.
reference fuels to the amine number of unleaded reference
3.1.11 no-knock condition, n—for octane rating, when the
fuels, and none is implied.
combustion instability in all cylinders is less than light knock.
3.1.2 engine motor octane requirement—one full motor
Refer to Annex A1 for description of knock intensity.
octane number greater than the maximum motor octane num-
3.1.12 peak EGT, n—for octane rating, as the mixture is
ber that results in knock (graphic knock level descriptions can
manually leaned from a state rich of stoichiometric, the exhaust
be seen in Annex A1). For example, a test engine knocks on
gas temperature will increase with the removal of excess fuel.
primary reference fuels with 96 and 97 motor octane numbers.
As the mixture is continually leaned, a peak temperature will
The test engine does not knock on a primary reference fuel
be attained, after which continued leaning will result in lower
with a 98 motor octane number. The maximum motor octane
exhaust gas temperatures.
number that results in knock is 97, so the motor octane
3.1.13 primary reference fuels, n—for octane rating,
requirement is 98.
blended fuels of reference grade isooctane and n-heptane.
3.1.14 stable engine conditions, n—for octane rating, cyl-
inder head temperatures change less than 5°C (9°F) during a 1
1
This test method is under the jurisdiction of ASTM Committee D02 on
min period. Any changes or minor adjustments to throttle,
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
mixture, or engine conditions mandate restarting the clock for
D02.J0 on Aviation Fuels.
determining stable conditions.
Current edition approved Dec. 1, 2003. Published January 2004. Originally
approved in 1999. Last previous edition approved in 1999 as D 6424 – 99.
3.2 Symbols:
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.1 CHT—cylinder head temperature.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.2 EGT—exhaust gas temperature.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.2.3 inHg—inches of mercury.
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D6424–03
3.2.4 MAP—manifold absolute pressure. least 0.4° of crank shaft rotation. The encoder TDC pulse shall
3.
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