Combustion Phenomena of High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 114

2.4.1.3 Experimental Results

2.4.1.3.1 Temperature of Blowout
It could be observed that the flame in the case of the spray combustion in the high
temperature preheated diluted air differed clearly from the flame in the air at ordinary
temperature. Investigation was carried out on how the range, where the diffused
flame could be steadily combusted, was affected by both the temperature of the high
temperature preheated diluted air and its oxygen content. The results of the exper-
iment are shown in Figure 2.77 , in which the broken line shows the results obtained
when LPG with none of the evaporating process was burned. Under the conditions
of the experiment, i.e., in high temperature preheated and diluted air, the flame
formed a lifted flame, and it was curtailed as the in-furnace temperature went down,
resulting in blowing out. Further, the blowout of the flame occurred at a higher
temperature, as the air dilution rate was greater.

1400

Flammable Region

1200

LPG

1000

Kerosene

800

600

400

20 15 10 5 0

Oxygen Contents of Air, %

FIGURE 2.77 Relationship between the oxygen content and the flame blowoff temperature.

In the case of using kerosene and under the conditions that the oxygen content
was 15%, the flame blowout temperature could not be measured in the temperature
range below 250˚C. However, it is considered that the curves shown in Figure 2.77
would vary depending on a flame to be formed and the structure of the combustion
device. If the temperature of autoignition, which is a specific characteristic of the
fuel itself, can be decided according to the air dilution rate, it could be considered
that these curves are to be dependent on only the fuel itself.
Photographs of the states of spray flame combustion in the high temperature
preheated diluted air, when the oxygen content is changed, were taken with the
digital camera. The photographs are shown in Figures 2.78 through 2.81 . It was
observed that the more red the color is, the higher the temperature, and the bluer