Environmental Engineering Reference
In-Depth Information
5mm
Test specimen
Z
Oxidizing gas flow
Nozzle
12.7mm
FIGURE 2.128 Combustion field in stagnation flow.
section first presents the results of the test utilizing room temperature airflow and
then discusses the results of the test using high temperature airflow.
2.5.4.3 Combustion Rate in Room Temperature Airflow
The relations between the surface temperature and combustion rate are shown in
Figure 2.129a a nd Figure 2.129b . 68 The parameter is velocity gradient. Data points
are based on the test results, and the solid line indicates the results of calculation.
With the velocity gradient at 200 and 640 s -1 , the combustion rate increased with
surface temperature. However, the combustion rate dropped sharply at a certain
temperature and thereafter it again increased. The sharp drop of the combustion rate
was closely associated with the formation of a CO flame above the surface. 66,67 With
the velocity gradient at 1300 s -1 , the combustion rate did not show a sharp drop;
however, the rate of increase in the combustion rate fluctuated at a certain temper-
ature. The discontinuity also resulted from the formation of a CO flame. When the
velocity gradient was further increased (Figure 2.129b), unlike in the case of Figure
2.129a, the combustion rate increased homogeneously and continuously with the
surface temperature, thus getting closer to a certain value (diffusion-dominated
combustion rate). The reason no discontinuous change occurred in this case was that
the formation of CO flame had been suppressed due to its high velocity gradient. 66,67
2.5.4.4 Combustion Rate in High Temperature Airflow
The relationship between the surface temperature and combustion rate in a test using
high temperature airflow (at the temperature of 1280 K and velocity gradient of
40,000 s -1 ) is shown in Figure 2.130 . In the same way as shown in Figure 2.129b,
a CO flame was not formed above the surface due to high velocity gradient and the
 
 
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