Environmental Engineering Reference
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Fig. 7 Variation of CO
concentration with premixing
equivalence ratio
3.5
Normalized CO
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1
2
3
4
5
6
7
8
9
Φ
p
Fig. 8 Variation of UHC
concentration with premixing
equivalence ratio
Normalized UHCs
2.0
1.5
1.0
0.5
0.0
1
2
3
4
5
6
7
8
9
Φ
p
height decreases with a decrease in
Φ
p implying better combustion and hence a
reduction in CO. It seems that the effect of reduction in
fl
flame height that dominates
at lower values of
Φ
p = 3.32.
As the premixing air is increased, leaner conditions prevail in the combustion
zone leading to a drop in both the thermal NO
x
and prompt NO
x
and, hence, the
overall NO
x
concentration decreases with respect to that produced in a diffusion
fl
Φ
p causes a drop in CO concentration below
flame as seen in Fig.
9
. Improvement in mixing and combustion leads to higher
temperature in the vicinity of
Φ
p = 3.0 results in an increase in temperature (Fig.
6
)
and, hence, an increase in NO
x
as well. On the other hand, adding premixing air
causes an increase in the concentration of soot in the exhaust as compared to that of
a pure diffusion
flame as seen in Fig.
10
. In the presence of premixing air, excess
oxygen molecules become available resulting in the increase of local concentration
of certain radials, which act as precursors to soot formation. Partial premixing also
alters the chemistry of intermediate hydrocarbons, which can account for the
fl
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