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Show 4 The pressures and teInperatures were continuously recorded and the concentrations of produced gases were analyzed by two kinds of gascronlatographs and NOx rneter. 3-2. RESULTS AND DISCUSSION Prior to the experiments, chemical equilibriunl was theoretically calculated by using CHEMKIN code developed in Santiago National laboratory)). This code is based on 54 chemical species and 234 elenlentary reaction Inechanisms. Figure 4 shows a typical example of the relationship between the equivalence ratio and the calculated equilibriurn concentrations of product gases at 0.5 MPa. The concentration of 02 decreases with increase of the equivalence ratio and leads to allno t zero over <1>= 1.1. On the other hand, CO and H2 generate above q>= 1.0 and increase drastically with increasing the equivalence ratio. Figure 5 concerns the flammability limits that were measured in the present cOInbustor. As can see from this figure, lower (lean) limit for the stable cOlnbustion does not depend on the methane flow rate and is constant while the upper (rich) limit extends with increase of the equivalence ratio. This result suggests that the stable combustor of methane/air system can be easily realized rather in fuel-rich condition than in fuel-lean one. The measured results for concentrations of product gases under various equivalence ratios are plotted in Figure 6. COlllpared to the equilibrium calculation results (Figure 4), the measured C02 concentrations were a little higher than those of the calculation results. The concentrations of CO, however, were lower than those of the calculation results. This n1ay be because the amount of heat release from the wall of the combustor would not be neglected and because the calculation was not taken the effect of fluid rnixing into consideration. Negligible small amount of 02 was detected under more than q>= 1.1 in spite of 02 free in the calculation. Methane was also detected even in fuel-lean combustion region. It was found from these results that much better mixing of methane and air would be necessary to realize better combustion state. Swirling or improvement of the injector may be effective to solve this problem. Figure 7 shows the relationship between NOx emission and the equivalence ratio that were obtained by both the equilibrium calculation and the experiments. It was seen from this figure that pressurization can control the NOx emissions particularly in fuel-rich side. The equilibrium concentrations of NOx are theoretically below 10 ppm under the conditions of q> > 1.25. Although it was well-known that prompt NOx is mainly contributed to total NOx emissions in fuel-rich hydrocarbon combustion, the measured NOx emissions decreased with increasing the equivalence ratio as mentioned above. As can understand from Figure 7, the NOx emissions can be also controlled In fuel-lean combustion condition. However, the produced gas from fuel-rich con1bustion contains not only low-concentration of NOx but also H2 and CO that can generate heat at the second combustor as mentioned above. Therefore, the proposed combined cycle systeln based on the combination of |
