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rises only by about 300 K if the preheated air temperature is raised from 300 to
1000 K. In the high temperature range, endothermic dissociation reactions become
predominant. Consequently, the adiabatic flame temperature is not much affected
by a rise in the preheated air temperature. For the Arrhenius plot, it is necessary to
express the chemical reaction rate in the form of a function of flame temperature.
As stated before, the critical velocity gradient can be used as a measure of the overall
chemical reaction rate of propane.
Figure 2.45
is an Arrhenius plot of the data obtained in the present study. The
axis of ordinate ln (2
V
/
R
)
c
is a measure of the overall chemical reaction rate and the
axis of abscissa is the reciprocal of adiabatic flame temperature. The highly linear
gradient shows that the overall chemical reaction rate of propane can be expressed
in the form of the Arrhenius plot. From this gradient, activation energy is calculated
to be 380 kJ/kmol. It is understood from this that the oxidizing reaction of propane
is strongly dependent on temperature and that NO
x
production by the Zel'dovich
mechanism is predominant.
2.3.1.7
Summary
In this study high-temperature air as combustion air is used for the purpose of
investigations on extinction limit and NO
x
formation in laminar diffusion flames. As
a result, the mechanism of NO
x
formation and NO
x
reduction under the conditions
of high temperature air combustion has been clarified.
8.5
8
7.5
7
6.5
0.40
0.42
0.44
1000/T
ad
1/K
FIGURE 2.45
Arrhenius plot of data.
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