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CombustionGasesinReciprocatingGasEngines
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investigationsofsimilarcasesofheatexchangepresentedintheliterature.
Theformulaearepresentedasfunctionscorrelatedtoprobabilityvaluesused
todescribetheflowofpostflamegases
Nu=f(RelPrlGr……)
whereReisReynolds,Pr:ν/aPandtlandGr-Grashofnumbersrespectively.
Lastoneisimportantinfreeconvectionparticularlyinbigcombustioncham-
berswherewallsareevenaseveralmetershigh.
Convectiveheatexchangeisthebasicformofheatflowatlowtempera-
tures.Incombustionchambersofsteamboilersandinindustrialfurnaces,such
asforgingfurnaces,ceramicfurnacesandmostofallglassbaths,thedominant
formofheatexchangeisradiation.
Thestreamofheatflowingfromahightemperaturegaslayertothe
chamberwallstakestheformofradiationmainly(upto90%).Itcanbede-
scribedasacorrelation
Q
-
rad
=
Q
-
g
–
s
=Aεg-s(Cc[(Tg/100)
4–(Ts/100)4]
whereCcisconstant:Cc:5,67Wm
2K-4.Theεg-srepresentsemissivitycoeffi-
cientbetweenthegasandthewallthatcanbedefinedasafunctionofthegas
emissivitycoefficient,emissivitycoefficientofthewall,andacoefficientof
configurationorthemutualplacementofradiationenergyexchangingsur-
faces.
Thewholestreamofheatwillbethesumoftheconvectionandradiation
streams
Qc=Qk+Qr
Tosimplifythecalculationsformulaeareoftenusedinwhichthetotalheat
exchangecoefficientisassumedtobethesumofconvectionandradiation
coefficients.
αc=αk+αr
Thisapproachallowstocalculatethetotalstreamofheatasasimplecorrela-
tion:
Qc=Aαc(Tsp-Ts).
Ascanbeseen,thecrucialpointoftheabovediscussionistodetermine
thecoefficientofemissivityofgases.Thisstudypresentscalculationsandin-
vestigationsofflamesandpostflamegasesoflowcalorificnaturalgases.Thus
