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1、Chapter10ExamplesofSprayCombustionModeling10.1DieselspraycombustionmodelingWiththeadventofsupercomputinghardwareandmatureCFDsoftwareitisnowbecomingincreasinglyfeasibletoanalyzenumericallycomplex,multi-phaseinjector/combustorowsatconditionsrelevanttocontemporarypropulsio
2、nandpowergeneratingsystems.10.1.1Modulatedkinetics(MK)combustionmodelingThe”ModulatedKinetics”(MK)system,developedbyNissan,incorporatesinaregularDIcompessionignitionengineusingdieselfuel.Atlightload,theengineoperateswithhighswirl,highEGR,andretardedinjectiontiming.Undert
3、heseconditions,thetimerequiredtoachievenearlycompletemixingisshorterthanthetimerequiredforfuelautoignition.Thus,MKregimeisbasedonlow-temperaturepre-mixedcombustionforthesimultaneousreductionofNOxandparticulatematterwithoutearlyinjection.FortheNOxreduction,thecombustionFi
4、gure10.1:Theconceptualpatternofthedieselspraycombustion.69(a)(b)Figure10.2:Comparisonofa)conventionaldieselspraycombustionandb)dieselHCCIcombustionpatterns.(Caterpillarresearch)temperatureisdecreasedandEGRisusedtolowertheoxygenconcentrationoftheintakegas.Tocombattheincre
5、aseinsmoke,theinjectiontimingisretarded,theignitiondelayisextended,andthepremixedcombustionratioisincreased.This,incombinationwiththeoptimizationofthecombustionsystem(gasow,pistonconguration,etc.),lowersthefuelconsumptionandandunburnthydrocarbons(UHC).TheMKconceptwasus
6、edinsinglecylinderenginesandthenmultiple-cylinderengines.NOxandsmokereductionresultedfromtheloweroxygenconcentrationintheintakegasandtheretardedfuelinjection.Withtheuseofhighspeedphotography,lowtemperaturepre-mixedcombustionwasconrmed.HighEGR,retardedinjectionandalarged
7、iametertoroidalcombustionchamberreducedNOxandsmokewithoutincreasingfuelconsumption.Butinthehighloadregion,thehightemperatureintakegasshortenedtheignitiondelay,socoolingoftheintakegaswasnecessaryforthelowtemperaturepre-mixedcombustiontooccur.Intheirmorerecentresearch,they
8、triedtoextendtherangefortheMKcombustionoperationbyvaryingintakegastemperature,theexcessairratioandtheco
