OCR Text |
Show stoichiometry was held constant at 1.2. Load was fixed at 55,000 Btu/hr. Fuel-staging results with injector locations F and J (see figure 3 for definition) are shown in figures 4 and 5. For comparison purposes, classical-staging results taken with the same combustor are also presented in figure 5. In this fuel-staging case, 50 percent of the fuel was injected at the second-stage entrance (fuel fraction of f = 1, ratio of first- to second-stage fuel flowrate). As with classical staging, the NO at the exit decreases with decreasing SR^ and SR2. However, there are some important differences. For fuel staging, the injection of fuel in the second stage allows a much wider range of operating first- and second-stage stoichiometries to achieve the same NO level. For example, with fuel staging, the first stage can be run fuel lean, while the second stage remains fuel rich, a situation not possible with air staging. These conditions are highlighted by dashed lines in figure 5. As can be seen in figure 5, NO levels are fairly insensitive to SR^, and are particularly insensitive in those regions where the second stage is fuel rich (i.e., SR2 <^ 1.0). This can also be seen in figure 4, where the variation of NO for different SRj's is much smaller than the variation of NO with SR2. Thus, very significant NO reductions, over 60 percent relative to baseline levels, can be achieved while maintaining the first stage fuel lean. Under fuel-rich first-stage conditions, a maximum reduction of about 75 percent can be achieved. Comparing the classical-staging results in figure 5 with the fuel staging results In figure 4 at equivalent fuel-rich-stage stoichiometry, it appears that the NO level is dominated by the richest point in the combustion system. Comparing fuel-staging results to classical-staging results as a function of SR| in figure 5, fuel staging with SR2 £ 0.8 gives 8-11 |