ASTM D6424-04a(2019)
(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
5.1 This practice is used as a basis for determining the minimum motor octane requirement of naturally aspirated aircraft engines by use of PRFs.
5.2 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.3 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.
General Information
Relations
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: D6424 − 04a (Reapproved 2019)
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 ber that results in knock (graphic knock level descriptions can
be seen in Annex A1). For example, a test engine knocks on
1.1 This practice covers ground based octane rating proce-
primary reference fuels with 96 and 97 motor octane numbers.
dures for naturally aspirated spark ignition aircraft engines
The test engine does not knock on a primary reference fuel
using primary reference fuels.
with a 98 motor octane number. The maximum motor octane
1.2 This standard does not purport to address all of the
number that results in knock is 97, so the motor octane
safety concerns, if any, associated with its use. It is the
requirement is 98.
responsibility of the user of this standard to establish appro-
3.1.3 full rich—condition in which the mixture control is at
priate safety, health, and environmental practices and deter-
the full stop position with the fuel flow within manufacturer’s
mine the applicability of regulatory limitations prior to use.
recommended settings.
1.3 This international standard was developed in accor-
3.1.4 house fuel, n—for octane rating, an unleaded, straight
dance with internationally recognized principles on standard-
hydrocarbon fuel used for engine warm-up and all non-octane
ization established in the Decision on Principles for the
rating testing.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
3.1.5 knock, n—in an aircraft spark ignition engine, abnor-
Barriers to Trade (TBT) Committee.
mal combustion caused by autoignition of the air/fuel mixture.
3.1.6 knock condition, n—for octane rating,whentheknock
2. Referenced Documents
intensity in any cylinder is light knock or greater as described
2.1 ASTM Standards:
in Annex A1.
D2700 Test Method for Motor Octane Number of Spark-
3.1.7 knock number, n—for octane rating, a numerical
Ignition Engine Fuel
quantification of knock intensity.
3. Terminology
3.1.8 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, AN,
tetraethyl lead in isooctane.
n—determined in terms of the weight percent of
3.1.9 motor octane number of primary reference fuels from
3-methylphenylamine in reference grade isooctane (2,2,
0 to 100—the volume % of isooctane (equals 100.0) in a blend
4–trimethylpentane). For example, 5 % of 3–methylphenylam-
with n-heptane (equals 0.0).
ine in reference grade isooctane has an amine number of 105
3.1.10 naturally aspirated aircraft engine, n—aircraftpiston
(AN 105). No attempt has been made to correlate performance
engine that breathes without forced means from either turbo-
number of leaded reference fuels to the amine number of
chargers or superchargers.
unleaded reference fuels, and none is implied.
3.1.11 no-knock condition, n—for octane rating, when the
3.1.2 engine motor octane requirement—one full motor
combustion instability in all cylinders is less than light knock.
octane number greater than the maximum motor octane num-
Refer to Annex A1 for description of knock intensity.
1 3.1.12 peak EGT, n—for octane rating, as the mixture is
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom- manuallyleanedfromastaterichofstoichiometric,theexhaust
mittee D02.J0.02 on Aviation Piston Engine Fuels.
gas temperature will increase with the removal of excess fuel.
Current edition approved May 1, 2019. Published June 2019. Originally
As the mixture is continually leaned, a peak temperature will
approved in 1999. Last previous edition approved in 2014 as D6424 – 04a (2014).
be attained, after which continued leaning will result in lower
DOI: 10.1520/D6424-04AR19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
exhaust gas temperatures.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.1.13 primary reference fuels, n—for octane rating,
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. blended fuels of reference grade isooctane and n-heptane.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6424 − 04a (2019)
3.1.14 stable engine conditions, n—for octane rating, cyl- fied location. Manifold pressures shall be measured with an
inder head temperatures change less than 5 °C (9 °F) during a accuracy of less than 2.5 mmHg and recorded to ensure proper
1 min period. Any changes or minor adjustments to throttle, engine behavior and repeatability.
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
least 0.4° of crank shaft rotation. The encoder TDC pulse shall
3.2.5 mmHg—millimetres of mercury.
be aligned with the TDC of cylinder number one prior to
3.2.6 MON—motor octane number.
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-
couplesshallconformtotheenginemanufacturer’srecommen-
3.2.9 r/min—revolutions per minute.
dations. The CHT measurements shall be accurate to within
3.2.10 TDC—top dead center.
1 % of full scale.
6.1.1.6 Exhaust Gas Temperature Sensors, on all cylinders.
4. Summary of Practice
Installation shall conform with manufacturer’s recommended
4.1 A recently overhauled, remanufactured, or new, natu-
location and proper material selection. EGT probes are usually
rally aspirated aircraft engine is octane rated, using PRFs, to
installed within 5 cm (2 in.) of the exhaust stack flange. The
determine the minimum motor octane requirement. Minimum
EGT probes shall be accurate to within 1 % of full scale.
motor octane requirement is defined as one number above the
6.1.1.7 Engine Speed Sensor—The dynamometer or propel-
highest MON in which knock was detected. The engine is
ler stand shall measure the engine shaft speed to determine
tested at three or more of the worst power points subject to
power development. The engine speed sensor shall be accurate
detonation behavior. These points usually involve high mani-
to within 65 r⁄min.
fold pressures. At the very least, takeoff power, a maximum
6.1.1.8 Fuel Flow Meter—If the device is calibrated for a
continuous or climb power, and a cruise configuration shall be
particular fuel, then the device shall be recalibrated for each
tested. Takeoff power and climb power are tested under full
different and subsequent fuel. Data should be reported in mass
rich mixture conditions, and cruise power is tested under full
flow units.
rich and lean mixture configurations in 5 % increment reduc-
6.1.1.9 Fuel Pressure Transducers—Locations of fuel pres-
tions from full rich fuel flow. Engine operating temperatures
sure transducers shall conform with those recommended by the
and oil temperatures are kept at maximum allowable limits,
engine manufacturer. One transducer is required for the me-
while induction and cooling air temperatures are maintained at
tered fuel pressure, if necessary, and another is required for the
extreme hot day conditions for severe case testing.
pump pressure. The fuel inlet pressure shall not fall below the
4.2 Octane ratings are determined under stable engine
minimum specified by the engine manufacturer during the
conditions using PRFs of known MON.
rating process.
4.3 Knock sensor installation and knock quantification are
6.1.1.10 Induction Air Pressure Transducer, located so as to
described in Annex A1.
measure the pressure of the induction stream prior to the
throttle plate.
5. Significance and Use
6.1.1.11 Induction Air Temperature Sensor, located so as to
5.1 This practice is used as a basis for determining the
measure the temperature of the induction stream prior to the
minimum motor octane requirement of naturally aspirated
throttle plate.
aircraft engines by use of PRFs.
6.1.1.12 Knock Sensors—The referee method for knock
detection is described in AnnexA1.This method requires flush
5.2 Results from standardized octane ratings will play an
mounting piezoelectric transducers. At the very least, the four
important role in defining the actual octane requirement of a
cylinders with the highest CHTs shall be monitored. These
given aircraft engine, which can be applied in an effort to
transducers are connected to charge amplifiers and shall be
determine a fleet requirement.
capable of measuring combustion pressures under a high
6. Apparatus
temperature environment.
6.1.1.13 Oil Pressure Transducer—Location of pressure
6.1 Instrumentation:
measurement shall conform to engine manufacturer’s specified
6.1.1 The engine shall be equipped with the following
location.
instrumentation, which shall be accurate within 62 % of full
scale unless noted otherwise. 6.1.1.14 Oil Temperature Sensor—Location of temperature
6.1.1.1 Absolute Manifold Pressure Transducer—Location measurement shall conform with manufacturer’s specified
of MAP sensor shall conform to engine manufacturer’s speci- location.
D6424 − 04a (2019)
6.1.1.15 Torque Meter—The dynamometer or propeller 7.1.3 Asample shall be taken of each primary reference fuel
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.
6.1.2.3 Outside Air Temperature Sensor, capable of measur- 7.4 All engine operations, other than during the break-in
period, shall be performed with an oil approved by the engine
ing both the ambient wet bulb and the dry bulb temperatures
prior to any engine testing. manufacturer. (Warning—Lubricating oil is combustible, and
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
at least 1800 samples per pressure cycle per cylinder.
8.2 Only the engine accessories required to operate the
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
test stand that shall be capable of maintaining a constant speed
8.3 The exhaust system employed shall not induce a back
to within 610 r⁄min.
pressure greater than the back pressure called for in the engine
manufacturer’s specifications.
6.4 Fuel System:
6.4.1 The fuel supply shall have a disposable or cleanable
8.4 If the test engine’s fuel system is designed to recirculate
filter. The filter shall allow the proper minimum fuel flow.
fuel to the tank, provisions shall be made to ensure that no fuel
6.4.2 The fuel selection valve shall be capable of selecting
is recirculated to the containers with the PRFs.
at least two different fuel sources without the possibility of
8.5 The idle mixture setting and full rich fuel flow rate shall
cross contamination of either source.
be set in accordance with the engine manufacturer’s recom-
6.4.3 The fuel supply system must comply with federal,
mendations.
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-
D2700. All fuels used for the initial engine octane ratings are
sion test shall be performed on all cylinders and the results
PRFs that consist of blends of reference grade isooctane and
recorded.
n-heptane. The PRFs will be prepared in increments of one
MON.(Warning—PRFisflammable,anditsvaporisharmful.
8.8 Prior to testing, the integrity of the fuel selection system
Vapors may cause flash fire.)
shall be confirmed and the system flushed. The engine fuel
7.1.1 Isooctane (2,2,4-trimethylpentane) shall be no less
selector apparatus shall b
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