Environmental Engineering Reference
In-Depth Information
NO
x
formation in rich-dome combustors of propulsion engines can be described
reasonably well by assuming that it is represented well by an extended Zeldovich
mechanism (Gupta et al.
1991
):
N
2
þ
O
,
NO
þ
N
;
ð
1
Þ
N
þ
O
2
,
NO
þ
O
;
ð
2
Þ
OH
þ
N
,
NO
þ
H
ð
3
Þ
d
d
t
¼
Assume
0
;
then generalized rate of NO formation rate is given by:
(
)
2
dNO
½
1
NO
½
=
K
C
O
2
½
N
2
½
¼
2K
1
O
½
½
N
2
ð
4
'Þ
dt
1
þ
K
1
NO
½
=
K
2
O
2
½
þ
K
3
OH
½
Combining reactions
1
and
2
leads to an expression for K
C
given in above
equations, namely: N
2
þ
K
1
K
2
K
1
K
2
.
The next step of assumption (viz. O is in equilibrium with O
2
) can generally be
considered over simpli
O
2
,
2NO with equilibrium constant K
C
as K
C
¼
cation. But if it were true, it leads to the rate of NO
x
formation being proportional to p
0.5
because the generalized equation reduces to:
dNO
½
1
=
2
¼
2K
1
K
C5
N
2
½
½
O
2
;
ð
4
Þ
dt
here, K
C5
is chemical equilibrium constant of
1
2
O
2
,
O
:
ð
5
Þ
flame front, better agreement with data has been
achieved by making the super O equilibrium assumption which is achieved by
assuming that the radicals can be calculated by regarding reactions (
6
,
7
and
8
)as
fast reactions in addition to CO reaction (
9
) being equilibrated. This process leads to
the two expressions for [O] (viz. Equations
10
and
11
) in terms of equilibrium
constants of reactions
6
In the regions close to the
fl
-
9
, namely K
C6
, K
C7
, K
C8
, and K
C9
. Either of these equa-
tions can be used for plugging [O] in Eq.
4
′
to calculate the rate of formation of
[NO] under super-equilibrium O condition.
H
þ
O
2
,
OH
þ
O
ð
6
Þ
;
H
2
þ
O
,
OH
þ
H
ð
7
Þ
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