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Show It should be also noted that most of N O x concentration measured in this study is expected to be N O because the furnace temperature was much higher for the formation of N 0 2 . In the oxy-fuel combustion, even though the net NOx emission decreases, the NOx concentration of the flue gas is sometimes quite high due to that the flue gas volume drastically decreases. The net N O x emission of 100 p p m for oxy-fuel combustion was equal to that of 12 p p m for conventional air-fuel combustion. In the experiments, the N O x emission was expressed by the concentration of dry flue gas and converted to the O 2 = 0 % basis. The estimated N O x emission equivalent to the air-fuel combustion is given in the figure in parentheses. 4. RESULTS 4.1 Radiation and NOx characteristics Figure 5 summarizes the characteristics of the tested three types of oxy-fuel burners in terms of averaged total radiative heat flux and N O x emission. High radiative heat flux and low N O x emission characteristics are preferred for glass melters. The generic oxy-fuel burner had high averaged total radiative heat flux with high N O x emission. The FDI oxy-fuel burner had low averaged total radiative heat flux with very low N O x emission. The FDI flat flame oxy-fuel burner accomplished both high averaged total radiative heat flux and low N O x emission. Figure 6 shows photographs of tested three types of flames. The flames were generated vertically in the open air. Note that the scale of the photographs are not identical. Figure 6(a) shows the flame of the generic oxy-fuel burner at V = 8 m/s. Luminous and long flame was observed. Flame was stabilized at the nozzle exit. Figure 6(b) shows the flame of the FDI oxy-fuel burner at V=35 m/s and L=100 m m . Lifted and long flame was observed. Figures 6(c) and (d) clearly show that the FDI flat flame oxy-fuel burner at V=35 m/s, L=100 m m and 0=10 degrees creates widely-spread flat flame suitable for glass melters. In the following section, the experimental results of the three types of burner are described in detail. 4.2 Generic oxy-fuel burner Figure 7 shows the effect of the injection velocity, V, on the total radiative heat flux. The velocity, V, was varied at 8, 30 and 60 m/s. High V (30 and 60 m/s) resulted in low total radiative heat flux with non-luminous flame and relatively flat total radiative heat flux distribution downstream of the burner center line. L o w V (8 m/s) resulted in high total 6 |