OCR Text |
Show emission is sirnilar to what has been observed with the air-fuel FDI combustion technique (15). Higher V is believed to promote the self-induced E G R (exhaust gas recirculation), thereby reducing peak flame temperature to reduce N O x emission. Enhancement of self-induced exhaust gas recirculation appears to play a major role to reduce N O x emission. Figure 14 shows the effect of L on NOx emission. Three levels of L (100, 200 and 300 m m ) were tested with V set at 35 and 70 m/s. Figure 14 includes two N O x levels for the generic burner, which could represent N O x levels at L=0. N O x emission decreased with the increase in L. The lowest N O x emission was less than 9 p p m (estimated N O x emission equivalent to air fuel combustion is 1 ppm) at V=35 m/s and L=300 m m . The very low N O x emission characteristics of the FDI oxy-fuel burner were thus demonstrated. The effect of L on N O x is similar, if not identical, to that of V shown in Figure 13. Lager L delays the mixing between the fuel gas and the oxygen, allowing higher degree of the self-induced E G R before the combustion initiates. Larger L therefore reduces the peak flame temperature to reduce NOx . If the effect of L on the distribution of total radiative heat flux in Figure 12 is reviewed, lager L resulted in relatively lower heat flux neat the burner, suggesting that lager L reduces flame temperature with presumably longer flame. Figure 15 shows the effect of nitrogen in the oxidant on NOx emission. Figure 15 shows the highest and lowest cases of N O x emission in the experiment. N O x emission increased with the increase in the nitrogen content in the oxidant at low V and small L. N O x emission was kept low with 5 % of nitrogen contained in the oxidant at high V and wide L. N O x emission at 5 % of nitrogen involved in the oxidant was 1500 p p m (estimated N O x emission equivalent to air fuel combustion is 180 ppm) at V=35 m/s and L=100 m m , and 20 p p m (estimated N O x emission equivalent to air fuel combustion is 2 ppm) at V = 7 0 m/s and L=300 mm. Figure 16 shows the effect of nitrogen content in the fuel on N O x emission. Figure 16 shows the highest and lowest cases of N O x emission in the experiment. At low V and small L, N O x emission drastically increased as the nitrogen content in the fuel increased. N O x emission was kept low at high V and wide L. The results for the FDI oxy-fuel burner showed that there was litde difference in total radiative heat flux when V and L were varied. The total radiative heat flux was relatively low and in the same level as that of the generic oxy-fuel burner at V = 3 0 and 60 m/s. N O x emission was very low at higher V and wider L. The low N O x emission characteristics was satisfactory but total radiative heat flux characteristics needed to be improved. The flame stability was high enough and the emission of unburned hydrocarbons was not 9 |