
304 Oxygen-Enhanced Combustion
since the fuel is not fully combusted. At fuel-lean con-
ditions, NO increases, while CO decreases. Again, the
fuel efciency is reduced because the excess oxidizer
carries heat out of the process. In order to minimize
both CO and NO
x
, the combustion system should be
operated near stoichiometrically, which also maxi-
mizes fuel efciency.
Figure 13.4 shows a plot of the adiabatic equilibrium
ame temperature for an air/CH
4
ame and an O
2
/CH
4
ame, as functions of the ame stoichiometry. There
are several things to notice. The ame temperature
for the air/CH
4
ame is very dependent on the stoichi-
ometry. For the O