ASTM D6812 tandard Practice for Ground-Based Octane Rating Procedures for Turbocharged/Supercharged Spark Ignition Aircraft Engines
1. Scope
1.1 This practice covers ground-based octane rating procedures for turbocharged/supercharged spark ignition aircraft engines. This practice has been developed to allow the widest range of applicability possible but may not be appropriate for all engine types. This practice is specifically directed to ground-based testing and actual in-flight octane ratings may produce significantly different results.
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.
2. Referenced Documents
2.1 ASTM Standards:
D2700 Test Method for Motor Octane Number of Spark-Ignition Engine Fuel
3. Terminology
3.1 Definitions:
3.1.1 amine number of reference fuels above 100, AN - determined in terms of the weight percent of 3-methylphenylamine in reference grade isooctane (2,2,4-trimethylpentane). For example, 5 % of 3-methylphenylamine in reference grade isooctane has an amine number if 105 (AN 105). No attempt has been made to correlate performance number of leaded reference fuels to the amine number of unleaded reference fuels, and none is implied.
3.1.2 engine octane requirement - one full number greater than the maximum number that results in knock (graphic knock level descriptions can be seen in Annex A1). For example, a test engine knocks on primary reference fuels with 98 and 99 motor octane numbers. The test engine does not knock on a primary reference fuel with a 100 motor octane number. The maximum motor octane number that results in knock is 99 so the motor octane requirement is 100. Ifa test engine knocks on a reference fuel with a 3-amine number and does not knock on a fuel with a 4-amine number, then the engine requirement is a 4-amine number.
3.1.3 full rich - condition where the mixture control is at the full-rich stop position with the fuel flow within the manufacturer's recommended settings.
3.1.4 house fuel, n - for engine operation, a fuel that does not contain metallic additives used for engine warm-up and all non-octane rating engine operation.
3.1.5 knock, n - in an aircraft spark ignition engine, abnormal combustion caused by autoignition of the air/fuel mixture.
3.1.6 knock condition, n - for octane rating, where the knock intensity in any cylinder is light knock or greater, as described in Annex A1.
3.1.7 knock number, n - for octane rating, a numerical quantification of knock intensity.
3.1.8 motor octane number of primary reference fuels from 0 to 100 - the volume % of isooctane (equals 100.0) in a blend with n-heptane (equals 0.0).
3.1.9 no-knock condition, n - for octane rating, where the knock intensity in all cylinders is less than light knock. Refer to Annex A1 for description of knock intensity.
3.1.10 peak EGT, n - for octane rating, as the mixture is manually leaned from a state rich of stoichiometric, the exhaust gas temperature will increase with the removal of excess fuel. As the mixture is continually leaned, a peak temperature will be attained, after which continued leaning will result in lower exhaust gas temperatures.
3.1.11 primary reference fuels, n - for octane rating, blended fuels of reference grade isooctane and n-heptane.
3.1.12 reference fuels above 100, n - for octane rating, blended fuels of reference grade isooctane and 3-methylphenylamine.
3.1.12.1 Discussion - This practice describes reference fuels above 100 MON in terms of isooctane/3-methylphenylamine. Alternate reference fuels may be used if appropriate, for example, MON in Test Method D2700, Section 8, mixtures of tetraethyl lead and reference grade isooctane. Care should be exercised to ensure the reference fuel does not adversely contaminate the engine and influence the results.
3.1.13 stable engine conditions, n - for octane rating, cylinder head temperatures change less than 5°C (9°F) during a 1-min period. Any changes or minor adjustments to throttle, mixture, or engine conditions mandate restarting the clock for determining stable conditions.
3.1.14 takeoff power, n - for octane rating, normal or maximum rated power with the engine speed at maximum rated.
3.1.15 turbocharged/supercharged aircraft engine, n - aircraft piston engine that breathes with forced means from either turbochargers or superchargers.
3.2 Acronyms:
3-MPA = 3-methylphenylamine
AN = amine number
CHT = cylinder head temperature
EGT = exhaust gas temperature
inHg = inches of mercury
MAP = manifold absolute pressure
MAT = manifold absolute temperature
mmHg = millimetres of mercury
MON = motor octane number
PRF = primary reference fuel
psig = pounds per square inch gage
RF = reference fuel above 100
rpm = revolutions per minute
TDC = top dead center
TIT = turbine inlet temperature
