| OCR Text |
Show 9 only the location of fuel injection nozzle, in spite other experimental parameters, such as global excess air ratio and inlet air temperature were kept unchanged. Therefore, it is considered that the flame structure or combustion regime was probably affected by the change of fuel nozzle location, and what we can point out for that reason was the difference in the mixing process of fuel in the combustor, because other experimental parameters, such as global excess air ratio and combustion air temperature were kept the same. In order to simulate the concentration distribution of the injected fuel, we injected carbon dioxide instead of the fuel which produced noncombusting mixing field, although the same preheated air as combusting conditions was used. Since the heat release due to combustion was not included in this procedure, the actual local concentrations of fuel cannot be simulated precisely by the method. However, the qualitative discussion on the mixing processes in the combustor is expected to some extent. Figure 5 demonstrates examples of concentration distribution of carbon dioxide for various locations of the fuel injection nozzle. As was suggested in the previous section, a large fraction of the injected carbon dioxide was caught by the recirculating flow for the injection nozzle 1. This fact coincides with that a block of flames was formed at the center of the recirculation zone. Therefore, the local mixture seems considerably richer than the global excess air ratio and most of nitric oxides are thought to be formed in this region. For fuel injection nozzle 2, the high concentration of carbon dioxide was observed in the right hand side corners as well as the center of the recirculating flow. The mixing was seemed worse than the case for fuel injection nozzle 1, which is probably the reason why considerable amounts of nitric oxides were emitted because the production of nitric oxides depends on the residence time of burned gas in high temperature region. For fuel injection nozzle 3, the high concentration of carbon dioxide appeared near the entrance of the combustor which probably resulted in the combustion with the incoming preheated air in this region, although this high concentration region disappeared as the inlet air velocity was increased. For fuel injection nozzle 4, almost uniform distribution of carbon dioxide was observed except in the vicinity of the combustor exit. This distribution |
