Environmental Engineering Reference
In-Depth Information
3500
Temperature of
mixture
3000
300 K
400
500
600
700
800
900
1000
1100
1200
1300
1400
2500
2000
1500
1000
500
0
0
500
1000
1500
2000
2500
3000
3500
Theoretical flame temperature, K
(a) Lean fuel mixture
3500
Temperature of
mixture
3000
300 K
400
500
600
700
800
900
1000
1100
1200
1300
1400
2500
2000
1500
1000
500
0
0
500
1000
1500
2000
2500
3000
3500
Theoretical flame temperature, K
(b) Rich fuel mixture
FIGURE 3.5
Relation between theoretical complete combustion temperature and chemical
equilibrium temperature.
specific heat taking account of thermal dissociation can compensate for the tem-
perature overshoot resulting from the complete combustion in the fuel-lean mix-
tures if the global one-step reaction model is adopted. The other is that the global
one-step reaction model is not appropriate to be applied to fuel-rich mixtures, and
we need to use combustion models predicting, at least, CO and H
2
concentrations.
When an elementary reaction including forward and reverse reactions is at
chemical equilibrium, the ratio of forward and reverse reaction rates is equal to the
equilibrium constant, and it looks as if the reaction is staying on hold. But, since
the reduced reaction mechanisms, including several reaction steps, used in the
simulations are not the real elementary reactions, they do not necessarily include
reverse reactions. If the following two reactions, for example, that do not include
reverse reactions, are included in the reaction mechanism used in a simulation:
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