ASTM D6424-04a(2010)
(Practice)Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines
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
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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D6424 − 04a(Reapproved 2010) An American National Standard
Standard Practice for
Octane Rating Naturally Aspirated Spark Ignition Aircraft
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* with a 98 motor octane number. The maximum motor octane
number that results in knock is 97, so the motor octane
1.1 This practice covers ground based octane rating proce-
requirement is 98.
dures for naturally aspirated spark ignition aircraft engines
using primary reference fuels. 3.1.3 full rich—condition in which the mixture control is at
the full stop position with the fuel flow within manufacturer’s
1.2 This standard does not purport to address all of the
recommended settings.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.1.4 house fuel, n—for octane rating, an unleaded, straight
priate safety and health practices and determine the applica-
hydrocarbon fuel used for engine warm-up and all non-octane
bility of regulatory limitations prior to use. rating testing.
3.1.5 knock, n—in an aircraft spark ignition engine, abnor-
2. Referenced Documents
mal combustion caused by autoignition of the air/fuel mixture.
2.1 ASTM Standards:
3.1.6 knock condition, n—for octane rating,whentheknock
D2700 Test Method for Motor Octane Number of Spark-
intensity in any cylinder is light knock or greater as described
Ignition Engine Fuel
in Annex A1.
3.1.7 knock number, n— for octane rating, a numerical
3. Terminology
quantification of knock intensity.
3.1 Definitions:
3.1.8 motor octane number of primary reference fuels above
3.1.1 amine number of reference fuels above 100, AN,
100—determined in terms of the number of millilitres of
n—determined in terms of the weight percent of
tetraethyl lead in isooctane.
3-methylphenylamine in reference grade isooctane (2,2,
4–trimethylpentane). For example, 5 % of 3–methylphenylam- 3.1.9 motor octane number of primary reference fuels from
0 to 100—the volume % of isooctane (equals 100.0) in a blend
ine in reference grade isooctane has an amine number of 105
(AN 105). No attempt has been made to correlate performance with n-heptane (equals 0.0).
number of leaded reference fuels to the amine number of
3.1.10 naturally aspirated aircraft engine, n—aircraftpiston
unleaded reference fuels, and none is implied.
engine that breathes without forced means from either turbo-
3.1.2 engine motor octane requirement—one full motor
chargers or superchargers.
octane number greater than the maximum motor octane num-
3.1.11 no-knock condition, n—for octane rating, when the
ber that results in knock (graphic knock level descriptions can
combustion instability in all cylinders is less than light knock.
be seen in Annex A1). For example, a test engine knocks on
Refer to Annex A1 for description of knock intensity.
primary reference fuels with 96 and 97 motor octane numbers.
3.1.12 peak EGT, n—for octane rating, as the mixture is
The test engine does not knock on a primary reference fuel
manuallyleanedfromastaterichofstoichiometric,theexhaust
gas temperature will increase with the removal of excess fuel.
As the mixture is continually leaned, a peak temperature will
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
be attained, after which continued leaning will result in lower
Products and Lubricants and is the direct responsibility of Subcommittee D02.J0.02
exhaust gas temperatures.
on Aviation Gasoline.
Current edition approved July 1, 2010. Published July 2010. Originally approved
3.1.13 primary reference fuels, n—for octane rating,
in 1999. Last previous edition approved in 2004 as D6424–04a. DOI: 10.1520/
blended fuels of reference grade isooctane and n-heptane.
D6424-04AR10.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.14 stable engine conditions, n—for octane rating, cyl-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
inder head temperatures change less than 5°C (9°F) during a
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 1-min period. Any changes or minor adjustments to throttle,
*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
D6424 − 04a (2010)
mixture, or engine conditions mandate restarting the clock for 6.1.1.2 Cooling Air Pressure Transducer, located so as to
determining stable conditions. determine the pressure within the cowling.
6.1.1.3 Cooling Air Temperature Sensor, located either
3.2 Acronyms:
within the cowling or at the entrance to the cowling. If a
3.2.1 CHT—cylinder head temperature.
thermocouple is utilized, it should extend at least a third of the
3.2.2 EGT—exhaust gas temperature.
way across the measured area.
3.2.3 inHg—inches of mercury.
6.1.1.4 Crankshaft Angle Encoder, if required for knock
3.2.4 MAP—manifold absolute pressure.
detection. The encoder shall have a sample resolution of at
3.2.5 mmHg—millimetres of mercury.
least 0.4° of crank shaft rotation. The encoder TDC pulse shall
3.2.6 MON—motor octane number. be aligned with the TDC of cylinder number one prior to
octane rating.
3.2.7 PRF—primary reference fuel.
6.1.1.5 Cylinder Head Temperature Sensors, installed in
3.2.8 psig—pounds per square inch gauge.
each cylinder. The sensing locations and types of thermo-
3.2.9 rpm—revolutions per minute.
couplesshallconformtotheenginemanufacturer’srecommen-
3.2.10 TDC—top dead center.
dations. The CHT measurements shall be accurate to within
1 % of full scale.
4. Summary of Practice
6.1.1.6 Exhaust Gas Temperature Sensors, on all cylinders.
4.1 A recently overhauled, remanufactured, or new, natu-
Installation shall conform with manufacturer’s recommended
rally aspirated aircraft engine is octane rated, using PRFs, to
location and proper material selection. EGT probes are usually
determine the minimum motor octane requirement. Minimum
installed within 5 cm (2 in.) of the exhaust stack flange. The
motor octane requirement is defined as one number above the
EGT probes shall be accurate to within 1 % of full scale.
highest MON in which knock was detected. The engine is
6.1.1.7 Engine Speed Sensor—The dynamometer or propel-
tested at three or more of the worst power points subject to
ler stand shall measure the engine shaft speed to determine
detonation behavior. These points usually involve high mani-
power development. The engine speed sensor shall be accurate
fold pressures. At the very least, takeoff power, a maximum
to within 65 rpm.
continuous or climb power, and a cruise configuration shall be
tested. Takeoff power and climb power are tested under full
6.1.1.8 Fuel Flow Meter—If the device is calibrated for a
rich mixture conditions, and cruise power is tested under full
particular fuel, then the device shall be recalibrated for each
rich and lean mixture configurations in 5 % increment reduc-
different and subsequent fuel. Data should be reported in mass
tions from full rich fuel flow. Engine operating temperatures
flow units.
and oil temperatures are kept at maximum allowable limits,
6.1.1.9 Fuel Pressure Transducers—Locations of fuel pres-
while induction and cooling air temperatures are maintained at
sure transducers shall conform with those recommended by the
extreme hot day conditions for severe case testing.
engine manufacturer. One transducer is required for the me-
4.2 Octane ratings are determined under stable engine
tered fuel pressure, if necessary, and another is required for the
conditions using PRFs of known MON.
pump pressure. The fuel inlet pressure shall not fall below the
4.3 Knock sensor installation and knock quantification are minimum specified by the engine manufacturer during the
described in Annex A1. rating process.
6.1.1.10 Induction Air Pressure Transducer, located so as to
5. Significance and Use
measure the pressure of the induction stream prior to the
5.1 This practice is used as a basis for determining the
throttle plate.
minimum motor octane requirement of naturally aspirated
6.1.1.11 Induction Air Temperature Sensor, located so as to
aircraft engines by use of PRFs.
measure the temperature of the induction stream prior to the
5.2 Results from standardized octane ratings will play an
throttle plate.
important role in defining the actual octane requirement of a
6.1.1.12 Knock Sensors—The referee method for knock
given aircraft engine, which can be applied in an effort to
detection is described in AnnexA1.This method requires flush
determine a fleet requirement.
mounting piezoelectric transducers. At the very least, the four
cylinders with the highest CHTs shall be monitored. These
6. Apparatus
transducers are connected to charge amplifiers and shall be
6.1 Instrumentation:
capable of measuring combustion pressures under a high
6.1.1 The engine shall be equipped with the following
temperature environment.
instrumentation, which shall be accurate within 62 % of full
6.1.1.13 Oil Pressure Transducer—Location of pressure
scale unless noted otherwise.
measurement shall conform to engine manufacturer’s specified
6.1.1.1 Absolute Manifold Pressure Transducer—Location
location.
of MAP sensor shall conform to engine manufacturer’s speci-
fied location. Manifold pressures shall be measured with an 6.1.1.14 Oil Temperature Sensor—Location of temperature
measurement shall conform with manufacturer’s specified
accuracy of less than 2.5 mmHg and recorded to ensure proper
engine behavior and repeatability. location.
D6424 − 04a (2010)
6.1.1.15 Torque Meter—The dynamometer or propeller 7.1.3 Asampleshallbetakenofeachprimaryreferencefuel
stand shall measure the torque to determine power develop- and subjected to Test Method D2700 for motor octane verifi-
ment. The torque measurement shall be accurate to within 1 % cation.
of full scale.
7.2 Fuels used for operations other than octane rating (for
6.1.2 The engine should be equipped with the following
example,warm-up)shallconsistofunleadedhydrocarbonsand
instrumentation, which shall be accurate within 62 % of full
should be capable of satisfying the test engine’s octane
scale unless noted otherwise.
requirement under the conditions for the fuel to be used.
6.1.2.1 Induction Air Flow Meter—Data should be pre-
(Warning—These fuels are flammable, and their vapor is
sented in mass flow units.
harmful. Vapors may cause flash fire.)
6.1.2.2 Induction Air Humidity Sensor, located in either the
7.3 Engine break-in oil shall be one approved by the engine
induction air plenum or induction air duct. Data should be
manufacturer.
presented in absolute, rather than relative, quantities.
7.4 All engine operations, other than during the break-in
6.1.2.3 Outside Air Temperature Sensor, capable of measur-
period, shall be performed with an oil approved by the engine
ing both the ambient wet bulb and the dry bulb temperatures
manufacturer. (Warning—Lubricating oil is combustible, and
prior to any engine testing.
its vapor is harmful.)
6.2 Data Acquisition:
6.2.1 The instrumentation listed in 6.1 shall be scanned and
8. Preparation of Apparatus
the data recorded at least once every 15 s by an automatic data
8.1 The history and condition of each test engine should be
acquisition system. The data shall be stored in a universal
known and documented by means of engine log books, test run
format (for example, comma separated values (CSV) for IBM
sheets, and any other documentation issued by the original
compatible machines) that can be retrieved at a later date.
equipment manufacturers or repair overhaul shops before any
6.2.2 If in-cylinder pressures are recorded to determine
octane rating tests are performed.
knock intensity, the pressure data shall be sampled at a rate of
8.2 Only the engine accessories required to operate the
at least 1800 samples per pressure cycle per cylinder.
engineshallbeinstalledonthetestenginewhenconductingthe
6.3 Power Absorption—The testing is to be performed in a
octane ratings.
ground based test cell using either a dynamometer or propeller
8.3 The exhaust system employed shall not induce a back
test stand that shall be capable of maintaining a constant speed
pressure greater than the back pressure called for in the engine
to within 610 rpm.
manufacturer’s specifications.
6.4 Fuel System:
8.4 If the test engine’s fuel system is designed to recirculate
6.4.1 The fuel supply shall have a disposable or cleanable
fuel to the tank, provisions shall be made to ensure that no fuel
filter. The filter shall allow the proper minimum fuel flow.
is recirculated to the containers with the PRFs.
6.4.2 The fuel selection valve shall be capable of selecting
8.5 The idle mixture setting and full rich fuel flow rate shall
at least two different fuel sources without the possibility of
be set in accordance with the engine manufacturer’s recom-
cross contamination of either source.
mendations.
6.4.3 The fuel supply system must comply with federal,
state, and local regulations related to fire, hazards, and health
8.6 The idle stop and full throttle throw positions shall be
issues.
set in accordance with the engine manufacturer’s recommen-
dations.
7. Reagents and Materials
8.7 Before any octane rating, and after all break-in and
7.1 The MON of PRFs is confirmed by using Test Method power baseline runs have been performed, a cylinder compres-
sion test shall be performed on all cylinders and the results
D2700. All fuels used for the initial engine octane ratings are
PRFs that consist of blends of reference grade isooctane and recorded.
n-heptane. The PRFs will be prepared in increments of one
8.8 Prior to testing, the integrity of the fuel selection system
MON.(Warning—PRFisflammable,anditsvaporisharmful.
shall be confirmed and the system flushed. The engine fuel
Vapors may cause flash fire.)
selector apparatus shall be checked to ensure no leakage.
7.1.1 Isooctane (2,2,4-trimethylpentane) shall be no less
8.9 All engine settings shall be checked after the break-in
than 99.75 % by volume pure, contain no more than 0.10 % by
period and before any octane rating. As a minimum, this shall
volume n-heptane, and contain no more than 0.5 mg/L (0.002
include fuel pressures, oil pressure, fuel flow, and magneto
g/U.S.gal)oflead.(Warning—Isooctaneisflammable,andits
timing.
vapor is harmful. Vapors may cause flash fire.)
7.1.2 n-Heptane s
...
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