Environmental Engineering Reference
In-Depth Information
Table 2 Experimental parameters for air dilution
Case
Air (top) stream
Fuel (cross) stream
Overall
equivalence
ratio
Air
ow
(SLPM)
fl
CH
4
fl
ow
(SLPM)
Φ
Air
ow
(SLPM)
fl
CH
4
fl
ow
(SLPM)
Φ
Premixed
137
11.5
-
7.2
0.8
-
0.5
0.8
-
0.5
-
-
-
Non-premixed
137
11.5
-
7.2
0.8
-
0.5
-
-
-
-
Dilution
119.9
-
126.3
2.5
-
1.6
0.2
-
0.12
17.1
-
10.7
9
-
5.6
5
0.8
-
0.6
Fig. 10 NO emission for premixed, non-premixed, and air dilution case
Figure
10
shows the measured NO emissions for the premixed, non-premixed,
and dilution cases. Air dilution demonstrated favorable performance as NO emis-
sions were substantially lower than that from non-premixed combustion. For
instance, at an equivalence ratio of 0.6, NO emission for the dilution case was about
37 % that of the non-premixed case. This percentage changed between 33 and 60 %
depending on the equivalence ratio. Comparing these emissions to that of the
premixed case, NO emission was almost as low as the premixed case especially at
lower equivalence ratio, where NO emission was only 0.5 PPM higher than that of
the premixed case (at equivalence ratio 0.6). Previously, this air dilution case had
demonstrated emissions equal to those of premixed case (Khalil et al.
2013
).
However, due to the difference in the
fl
ow
field, the behavior is different. This
difference in the
field arises from the center exit tube which prevents the fuel
(cross jet) from further penetration into the combustor. CO emissions were also
reduced under the dilution scenario where the emissions were about 40 % of those
under non-premixed conditions. However, these emissions were slightly higher
than those of premixed combustion mode (
fl
ow
20 % higher)
To further examine the effect of air dilution, OH* chemiluminescence was used
to identify the reaction zone and determine any differences between traditional non-
premixed combustion and air dilution cases. The OH* intensity distribution is
*
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