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230 CHAPTER 10 THERMODYNAMICS OF COMBUSTION
FIGURE 10.9
Pressure, p 2 3
peV diagram for constant pressure combustion.
1
Volume, V
The stoichiometric chemical equation is
C 6 H 6 þ 7:5ðO 2 þ 3:76N 2 Þ/6CO 2 þ 3H 2 O þ 23:5N 2 : (10.35)
The rich mixture equation is
7:5
C 6 H 6 þ O 2 þ 3:76N 2 /aCO 2 þ bCO þ 3H 2 O þ 23:5N 2 : (10.36)
1:2
a þ b ¼ 6
a ¼ 3:5; b ¼ 2:5
2a þ b þ 3 ¼ 12:5
Hence
C 6 H 6 þ 6:25ðO 2 þ 3:76N 2 Þ / 3:5CO 2 þ 2:5CO þ 3H 2 O þ 23:5N 2 (10.37)
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n R ¼30:75 n P ¼32:5
The energy equation, for constant pressure combustion is
H P ðT P Þ¼ Q p þ½H R ðT R Þ H R ðT s Þ þ H P ðT s Þ: (10.38)
s
Reactants energy [H R (T R ) H R (T s )]
Constituent C 6 H 6 O 2 N 2
39,936.1 27,230.9 26,342.1
h 880
8201.8 8509.7 8503.4
h 298
Difference 31,734.4 18,721.2 17,838.7
n 1 6.25 23.5
nh 31,734.4 117,007.5 419,209.3
½H R ðT R Þ H R ðT s Þ ¼ 567951:2kJ:
