Environmental Engineering Reference
In-Depth Information
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(a) Nozzle 1
(b) Nozzle 2
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(c) Nozzle 3
(d) Nozzle 4
FIGURE 2.55
Influence of combustion air temperature and global excess air ratio on emis-
sion of nitric oxides.
It is thought that the flame structure or combustion regime was affected by the
change of fuel nozzle location. Thus, the difference was in the mixing process of
fuel in the combustor, because other experimental parameters, such as global excess
air ratio and combustion air temperature, were kept the same.
A typical jet flame emitting intense radiation was observed for cases with high
nitric oxides emission. The typical features of the flame for low nitric oxides were
vague, with weak flames like a fog spreading everywhere, probably the “flameless
oxidation” named byWunning and Wunning.
24
Judging from the intensity of radiative
emission, the maximum temperature level was relatively low because the flame never
emitted bright emission. Therefore, we measured fluctuating temperatures with a
fine thermocouple of 25 µm (Pt/Pt-Rh13%) coated with SiO
2
, whose time constant
of frequency response was electrically compensated.
The distributions of time-averaged temperature in the combustion chamber are
shown in
Figure 2.56
.
The maximum temperature appeared around the center of the
recirculation zone for fuel injection nozzles 1 and 2. This fact agrees with the visual
observation of flames mentioned above. The maximum temperatures were 1770 and
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