Combustion Phenomena of High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 45

1100 C

1000 C

900 C

One-shot image Ten-shot averaged image

FIGURE 2.19 Results of simultaneous measuring of the combustion reaction domain (OH)
and acetone (fuel distributed domain).

of hydrocarbon, the intensity of a CH radical or a C 2 radical, which is an intermediate
product of combustion, varies according to the air ratio, 1,2 and the emission from the
C 2 is made more intense at the visible side as the ratio of the combustible gas is
higher. 1,2 Also, as for the diffused flame which is formed when LPG is used as the
fuel in a high temperature airflow at 1100˚C, the spectrum intensity of a C 2 Swan band
(516.5 nm) against the intensity of CH A-X(0,0), 431.5 nm in the spontaneous emission
spectrum of the flame increases when the oxygen concentration is decreased. This fact
has been reported by the Basic Research Working Group, based on results obtained
from the following experiment. When methane, a main component of city gas, is used
in the experiment, the amount of change in the emission spectrum according to an
equivalence ratio of the methane is small. 3 Therefore, LPG was applied as the fuel in
the experiment, and the spontaneous emission of the flame was measured under the
combustion conditions where the NO x concentration differed. However, under condi-
tion (a) for the usual flame that makes the NO x concentration maximum, the flame
became luminous at its downstream portion, resulting in making the background larger
due to black body radiation even in the case of the distributed flame. Three spectra
were compared, which were measured at three points from the base portion of the
flame contacting with the airflow at the central portion extending to the downstream
portion of flame just before the luminous flame.
In the experiment, images of the flame were formed on the end face of an optical
fiber of the spectrometer (Hamamatsu Photonics C7473) at the magnification of 1 to
1, using a spherical lens with a focal length of 200 mm, and the spectra were obtained.
The measurement was carried out at an in-furnace temperature of 1100˚C, the air ratio
1.2, and under the same combustion conditions as conditions (d) and (e) shown in
Table 2.2 . In this case, the exhaust NO x concentration was 153 ppm (the conversion
rate of O 2 = 11%) under condition (d), and 60 ppm under condition (e). The measured
results of the spontaneous emission spectra are shown in Figure 2.20 . No significant