Designation:D4737−21StandardTestMethodforCalculatedCetaneIndexbyFourVariableEquation1ThisstandardisissuedunderthefixeddesignationD4737;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope*1.1ThecalculatedCetaneIndexbyFourVariableEquationprovidesameansforestimatingtheASTMcetanenumber(TestMethodD613)ofdistillatefuelsfromdensityanddistillationrecoverytemperaturemeasurements.ThevaluecomputedfromtheequationistermedtheCalculatedCetaneIndexbyFourVariableEquation.1.2TheCalculatedCetaneIndexbyFourVariableEquationisnotanoptionalmethodforexpressingASTMcetanenumber.ItisasupplementarytoolforestimatingcetanenumberwhenaresultbyTestMethodD613isnotavailableandifcetaneimproverisnotused.Asasupplementarytool,theCalculatedCetaneIndexbyFourVariableequationmustbeusedwithdueregardforitslimitations.1.3ProcedureAistobeusedforSpecificationD975,GradesNo.1–DS15,No.1–DS500,No.1–DS5000,No.2–DS15,No.2–DS5000,andNo.4–D.ThismethodforestimatingcetanenumberwasdevelopedbyChevronResearchCo.2ProcedureAisbasedonadatasetincludingarelativelysmallnumberofNo.1–Dfuels.TestMethodD4737ProcedureAmaybelessapplicabletoNo.1–DS15,No.1–DS500,andNo.1–DS5000thantoNo.2–DgradeS5000ortoNo.4–Dfuels.1.3.1ProcedureAhasbeenverifiedasapplicabletoGradeNo.2–DS15dieselfuels.31.4ProcedureBistobeusedforSpecificationD975,GradeNo.2–DS500.1.5Thetestmethod“CalculatedCetaneIndexbyFourVariableEquation”isparticularlyapplicabletoGrade1–DS5000,GradeNo.1–DS500,GradeNo.2–DS5000andGradeNo.2–DS500dieselfueloilscontainingstraight-runandcrackedstocks,andtheirblends.Itcanalsobeusedforheavierfuelswith90%recoverypointslessthan382°Candforfuelscontainingderivativesfromoilsandsandoilshale.NOTE1—Sxxisthedesignationformaximumsulfurlevelspecifiedforthegrade.Forexample,S500gradesarethosewithamaximumsulfurlimitof500ppm(µg/g...
