Designation:D6424−04a(Reapproved2014)AnAmericanNationalStandardStandardPracticeforOctaneRatingNaturallyAspiratedSparkIgnitionAircraftEngines1ThisstandardisissuedunderthefixeddesignationD6424;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thispracticecoversgroundbasedoctaneratingproce-duresfornaturallyaspiratedsparkignitionaircraftenginesusingprimaryreferencefuels.1.2Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.ReferencedDocuments2.1ASTMStandards:2D2700TestMethodforMotorOctaneNumberofSpark-IgnitionEngineFuel3.Terminology3.1Definitions:3.1.1aminenumberofreferencefuelsabove100,AN,n—determinedintermsoftheweightpercentof3-methylphenylamineinreferencegradeisooctane(2,2,4–trimethylpentane).Forexample,5%of3–methylphenylam-ineinreferencegradeisooctanehasanaminenumberof105(AN105).Noattempthasbeenmadetocorrelateperformancenumberofleadedreferencefuelstotheaminenumberofunleadedreferencefuels,andnoneisimplied.3.1.2enginemotoroctanerequirement—onefullmotoroctanenumbergreaterthanthemaximummotoroctanenum-berthatresultsinknock(graphicknockleveldescriptionscanbeseeninAnnexA1).Forexample,atestengineknocksonprimaryreferencefuelswith96and97motoroctanenumbers.Thetestenginedoesnotknockonaprimaryreferencefuelwitha98motoroctanenumber.Themaximummotoroctanenumberthatresultsinknockis97,sothemotoroctanerequirementis98.3.1.3fullrich—conditioninwhichthemixturecontrolisatthefullstoppositionwiththefuelflowwithinmanufacturer’srecommendedsettings.3.1.4housefuel,n—foroctanerating,anunleaded,straighthydrocarbonfuelusedforenginewarm-upandallnon-octaneratingtesting.3.1.5knock,n—inanair...
