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1、1.ReasonsforleanburnenginesLegalregulationslimittheemissionofpollutantssuchasNOx,COandHCwhichareformed,amongothers,bythecombustionofnaturalgasininternalcombustionengines.Thelimitscanbemetifsuitabletechnicalmeasuresaretaken.Themeasuresconsistofeithercleaningtheexhaustgasesdownstrea
2、mbyacatalyticconverterorrearrangingtheinternalcombustionprocessinsuchawaythatthepollutingconstituentscannotbeformedtoanappreciableamount.Thislowemissionenergyconversionprocesscanberealizedinaleanburngasengine.Acharacteristicfeaturetherebyisacertainamountofexcessairinthenaturalgasa
3、irmixturewhichlowersthecombustiontemperatureandtherebyfreezesthechemicalreactionfortheformationofNOx.Thepenalityforthisisthatthecombustionisaffected,tooandtheunburnedconstituentssuchasCOandHCareincreased.Finally,theproblemsofleanburnenginescanbemasteredbytheuseofexhaustturbocharge
4、rs,highpowerignitionsystems,specialsparkplugdesign,favourablecombustionchamberdesignandairfuelratiocontrolling,tonamebutafew.Inthiswayareliableoperationoftheenginewithemissionssignificantlylowerthanlegalstandardsisachievedwithoutanylossofengineefficiency.Thus,leanburnenginesoffert
5、hesimplestwaytorealizetheobjectivesofecologyandeconomyfortheconversionofenergyunderfavourableexpendítures.Returntotopofpage2.ProblemsofignitionThehighvoltagecreatedbytheignitionsystemwhichcandelivervaluesmorethan30KVatamaximumcausesthesparktojumpacrossthesparkgapandignitesthegasai
6、rmixture.Therequirementofignitionvoltageislowest(around10KV)atasmallgapofabout0,35mmandairfuelratios(AFR)=1,0---1,3.Itincreaseswithleanermixturestoabout15----20KVatAFR=1,6whennewstandardsparkplugsareused.Awearoftheelectrodeswhichincreasesthesparkgapforonly0,2mmelevatesthevoltagere
7、quirementclearlyabove20KV.Iftheignitionsystemdoesnotprovidethisrequirement,thenmisfiringoccursandfinallyadowntimeoftheenginewillhappen.Withstandardsparkplugsthispointisalreadyreachedafter700---1500hoursofservice.Thenofcoursethereisthepossibilityofreducingthegapdistancebybendingthe
8、electrodesbackagainandresumingope
