1 consider an isentropic combustion system with a

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Unformatted text preview: Þ ma 1 À1 ¼ 100 À 1 ¼ 100 %EA ¼ 100 mas f mas Global equation for lean combustion fb1   1 bg a þ À ðO2 þ 3:76N2 Þ Ca Hb Og þ f 42      b 3:76 bg bg 1 a þ À N2 þ a þ À À 1 O2 ! aCO2 þ H2 O þ 2 f 42 42f in terms of l   bg Ca Hb Og þ l a þ À ðO2 þ 3:76N2 Þ 42     b bg bg ! aCO2 þ H2 O þ 3:76 l Á a þ À N2 þ ðl À 1Þ a þ À O2 2 42 42 Global equation for rich combustion f>1with the assumption that products contain unburned fuel   1 bg a þ À ðO2 þ 3:76N2 Þ Ca Hb Og þ f 42     a b 3:76 bg 1 H2 O þ a þ À N2 þ 1 À ! CO2 þ Ca Hb Og f 2f f 42 f Enthalpy of formation (heat of formation) determined by bomb calorimeter ^ Q0 ;v þ DN Á Ru T0 rxn Ni;P X X bg DN ¼ Ni;P À Ni;R ¼ þ À 1 42 i i ^ D ho ¼ i 2.5 Chapter Summary 43 where Q0 ;v is the heat released from a constant-volume reactor where the rxn products and reactants are at STP. Heating values at STP (T0) from a constant-volume reactor P HHV ¼ i ^o Ni;R Dhi;R À P i ^o Ni;P Dhi;P þ  P i Ni;p À P i  ^ Ni;R Ru T0 ðMJ=kgÞ Nfuel Mfuel LHV ¼ HHV À NH2O;P MH2O hfg ; hfg ¼ 2;440kJ =kg Nfuel Mfuel Heating values at STP (T0) determined from a constant-pressure reactor P HHV ¼ i ^ Ni;R Dhi;R À o P i ^ Ni;P Dhi;P o Nfuel Mfuel Adiabatic flame temperature for reactants at standard conditions ^ Method 1: Estimate based on average cp values P ^ Nfuel Mfuel LHV þ Ni;R hsi;R ðTR Þ i P TP ¼ T0 þ ^ Ni;P cpi i TP % TR þ Nfuel Mfuel LHV P ^ Ni;P cpi i or if mixture is not stoichiometric: mass-base analysis using LHV and f f b 1 TP ¼ TR þ f Á LHV f Á fs Á LHV ¼ TR þ   ð1 þ f Þcp ð1 þ f Á fs Þcp f > 1 TP ¼ T R þ fs Á LHV fs Á LHV ¼ TR þ   ð1 þ f Þcp ð1 þ f Á fs Þcp Method 2: Enthalpy Balance HP ðTP Þ ¼ HR ðTR Þ X X ^ ^ ^ Ni;P hi;P ¼ Ni;P ½Dho;P þ hsi;P ðTP ފ HP ðTP Þ ¼ i i i Trial and error of TP such that HP(TP) matches HR(TR) 44 2 Thermodynamics of Combustion Exercises 2.1 Consider an isentropic combustion system with a total of K species. Assuming constant specific heats, show that the mixture temperature and pressure at two different states are related to the resp...
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This document was uploaded on 01/20/2014.

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