Charpter 2 Combustion Fundamentals

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1、2CombustionFundamentals2.1IntroductionThesubjectofcombustionembracesawidevarietyofprocessesandphenomena.Evenabriefsummaryofthevastamountofmaterialthathasbeenpublishedoncombustionscienceandtechnologywouldbewellbeyondthescopeandintentionofthischapter.Instead,attentionisfocusedonafewkeyaspectsofc

2、ombustionthatareconsideredtobemostrelevanttothegasturbineandarenotcoveredintheremainingchaptersofthisbook.Combustionisperhapsdescribedmostsimplyasanexothermicreactionofafuelandanoxidant.Ingasturbineapplications,thefuelmaybegaseousorliquid,buttheoxidantisalwaysair.Combustionoccursinmanyforms,no

3、tallofwhichareaccompaniedbyflameorluminescence.Twoimportantregimesofcombustioncanbedistinguished[1].2.1.1DeflagrationThisisafastprocessthatrequireslessthan1msfor80%completion.Itischar-acterizedbythepresenceofaflamethatpropagatesthroughtheunburnedmixture.Aflamemaybedefinedasarapidchemicalchange

4、occurringinaverythinfluidlayer,involvingsteepgradientsoftemperatureandspe-ciesconcentrations,andaccompaniedbyluminescence.Fromamacroscopicviewpoint,theflamefrontcanbeviewedasaninterfacebetweentheburnedgasesandtheunburnedmixture.Comparedwiththeunburnedmixture,theburnedgasesaremuchhigherinvolume

5、andtemperature,andmuchlowerindensity.Deflagrationwavesinhydrocarbonfuel-airmixturesnor-mallypropagateatvelocitiesbelow1m/s.Alltheflameprocessesthatoccuringasturbinecombustorsfallwithinthiscategory.2.1.2DetonationThecharacteristicfeatureofdetonationisashockwavethatisconnectedwithandsupportedbya

6、zoneofchemicalreaction.Detonationwavesproceedatsupersonicvelocities,rangingfrom1to4km/s.Theycannotoccurinthe3536GasTurbineCombustion:AlternativeFuelsandEmissions,ThirdEditionconventionalfuel–airmixturesemployedingasturbinecombustors,butthepossibilitycouldariseinsituationswhereoxygeninjectionis

7、employedtofacilitateignitionandengineacceleration.Currently,pulsedetonationenginesareofinteresttothemilitaryandtheseenginecombustorsemploydetonationwaves.2.2ClassificationofFlamesMostfundamentalstudiesofflamecombustionareperformedusingg