Combustion Phenomena of High Temperature Air Combustion - High Temperature Air Combustion: From Energy Conservation to Pollution Reduction - page 42

in the vicinity of the burner. But, in the area between two fuel nozzles where the
preheated airflow and the fuel jet flow contacted each other, a spontaneous emission
light of a slightly blue color was observed, which was considered to be an incipient
decomposition of the fuel.
Furthermore, the NO x concentration in an y of the conditions (b) through (e) was
significantly lower, compared with the condition (a). But, the lowering of NO x is
affected more by both the airflow velocity and the fuel jet angle than the fuel jet
velocity, resulting in a maximum difference in NO x concentration of twice as much
depending on conditions. Figures 2.16a through c show the results of the distribution
of the in-furnace temperatures measured, when the maximum temperature was
1190˚C among the temperatures measured by an R-type thermocouple at 25 points
at a distance of 100 mm from the upper part of the in-furnace combustion chamber
for the cases of conditions (a), (d), and (e).
From these results, the deviation between the maximum temperature and the
minimum temperature at the 25 points measured is as follows:

condition(a) (117˚C) > condition(d) (96˚C) > condition(e) (69˚C)

This shows a correlation between the exhaust NO x concentration and the combustion
conditions. In the case of condition (a), the flame at large becomes a luminous flame
and its length is rather short, and further a steep section is observed in the temperature
distribution. As for the distributed flame — conditions (d) and (e) — condition (e)
gives a comparatively flat temperature distribution and none of the local portions at
a higher temperature was observed.

2.2.3.3 Optical Measurement Results

Under the conditions shown in Table 2.2 , LIF measurement was carried out in a
range (shown in Figure 2.17 ) of about 220 mm in distance on the left side of each
base portion of the burners. At the center of the base portion of the burners, holes
for jetting the preheated air are arranged and the fuel nozzles are set up at the top
and bottom portions of each hole. Here, the acetone steam was added only to the
fuel nozzles at the bottom part. Figure 2.18a shows the results of the OH distribution
for one laser pulse under the condition (a). As shown in the figure, the intensity of

In-furnace
temperature

In-furnace
temperature

In-furnace
temperature

1200 1200

1200

1100 1100

1100

1050 1050 1050

Fuel Fuel Fuel

(a) (b) (c)

FIGURE 2.16 In-furnace temperature distribution. Condition (a) T infmax = 1190˚C, ∆ T inf =
117˚C, Condition (b) T infmax = 1190˚C, ∆ T inf = 96˚C, Condition (c) T infmax = 1190˚C, ∆ T inf =
69˚C ( T infmax : maximum in-furnace temperature, ∆ T inf : temperature deviation).