OCR Text |
Show Figure 1 shows a generic burner tested in the study. The burner consisted of an annular injector with a single-hole nozzle in the center and was mounted in the furnace wall. Several flames were generated with various momenta of gas and oxygen by widely varying the velocity . Table 1 lists the velocities of gas and oxygen tested, and the calculated momentum flux of gas and oxygen at the burner. Flames are categorized into three groups according to the combination of the velocity of gas and oxygen and the configuration of nozzles gas and oxygen. The first group (flames A-E) maintained the same velocity of gas and oxygen, with oxygen introduced into the annular injector and fuel gas into the single center nozzle. The velocity of gas and oxygen was varied widely from 6 to 130 m/s. The second group (flames F-I) generated relatively low momentum flames, with oxygen passed into the annular injector and fuel gas into the single hole center nozzle, as for the first group. The velocity of gas was different from that of oxygen. Both of the velocities were maintained low, with the gas velocity ranging from 6-30 mls and oxygen velocity almost identical at a low level of 3-4 m/s. The third group (flames J-M) also generated low momentum flames. In contrast to the second group, gas was introduced into the annular nozzle with oxygen injected through the center nozzle. Oxygen velocity ranged from 12-60 mls and gas velocity was maintained almost identical at a low level of 1-2 m/s. The FDI (fuel direct injection) flames(l)'(2) , already commercially utilized for ultra-low NOx emission from high temperature preheated air combustion, were tested as well. Figure 2 shows the concept of the FDI combustion. Gas and oxygen are directly and remotely injected into the furnace at high velocity. Injected gas and oxygen entrain a substantial amount of combustion products, creating an enhanced effect of self -induced exhaust gas recirculation (EGR). Since the self-induced EGR effect reduces flame peak temperature, NOx emission is reported to decrease drastically for high temperature preheated air combustion. Table 2 shows the |