| OCR Text |
Show 9 appears to decrease. 3.3 Concentration and Temperature Profiles Figure 6 shows tne temperature, NO, NO2, N 0 X (= NO + NO2), O2, CO, and CO2 profiles in the flame along the stagnation stream line at the typical flow field and temperature conditions (1100 K-preheat, 3000 1/sec-strain rate). Under this condition, the diffusion flame is extremely stable. Therefore, in the present study, these conditions were assumed to be the reference condition. Figure 7 shows also the concentration profiles of same species at the state of near extinction, including the temperature profile (1100 K-preheat, 6000 1/sec-strain rate). Note that the vertical axes are same with each other, but the horizontal axes are different, because the distance between flame and cylinder surface is larger for the reference states, Figure 6, than that for the case of high strain rate, Figure 7. From the temperature profiles, we can see that the thermal diffusive layer for high strain case is narrower than the reference states case. Because the size of the water-cooled-probe diameter was large, concentration measurements can be done between the center of the flame and air side, and inner side (fuel side) of the flame zone cannot be measured. The maximum temperature for the high strain rate is lower than the reference states. N 0 X is generated mainly in the flame zone in this particular burner system. In the practical furnaces, the residence time is much longer and N 0 X should generate much more. The maximum N 0 X concentration in the flame increases with the increasing of preheating, because the thermal N 0 X originating from the Zel'dovich mechanism increases. Comparing these two figures, we can find that the N0X concentration in the flame zone under the reference states, Figure 6, is larger than that for the high strain rate, Figure 7. NO and NO2 concentrations are also lower for the high strain case. For both cases, NO2 concentration exceeds the NO concentration. In the present study, NO and |
