An experimental study was made to investigate the mixing and NO
x formation in a swirlstabilized, diffusion-type flame in a model combustor operating at lean fuel/air ratios. The city gas was injected from a fuel injector into an air flow passed through a swirler. The temperature, stable species and NO
x concentration profiles in the combustor were measured over a range of air flow velocities through the swirler from 5 to 20m/s, fuel injection velocities from 36.4 to 145.4m/s, overall equivalence ratios Φ from 0.2 to 0.8 and nominal fuel injection angles from 60° to 180°. The effects of these parameters on NO
x concentration in the flame zone and the emission level of NO
x from the combustor were discussed. The effects of mixing rates were also estimated by examination of the local equivalence ratio profiles across the flame zone.
In general, the flame clearly showed the characteristics of a fuel jet flame near the fuel injector. The temperature and the concentration profiles across the main flame zone and the recirculation zone change considerably with change in Φ. In the case of comparatively low value of Φ, it was shown that the high mixing rate had the effect of lowering the local equivalence ratio in the flame zone and the combustion gas temperature early in the post-flame zone. Then, the emission levels of NO
x can be reduced by achieving high mixing rate due to the increase of air flow velocity and the variation of the fuel injection angle, at the expense of slight increase of the emission levels of CO.
The minimum emission level of NO
x obtained is 0.23g NO
2/kg fuel at Φ of 0.2. Although the emission levels of NO
x from the present combustor are still higher than those from lean premixed system, they were found to be much lower than those from conventional diffusion flame combustor.
抄録全体を表示