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다음과 같다.(1) 과잉공기비를 증가시키면 Prompt NOx는 감소되며 연소영역의 온도는 저하되지만, N2와 O2의 농도 증가로 Thermal NOx의 발생량은 증가하였고 NOx의 총 발생량도 증가하였다. (2) 3단 공기 공급단의 선회수가 증가할수록 연료로의 원활한 공급이 어려워 Thermal NOx의 발생은 억제되며 Prompt NOx는 발생 영역은 증가한다.(3) 공기 다단 연소기를 이용한 LPG 연소시 과잉 공기비를 증가시키면 NOx의 발생이 증가하지만 3단 공기 공급단의 선회강도를 증가하는 경우 약 10% 정도의 NOx가 저감됨을 알 수 있었다.


Experimental and numerical studies have been done to examine the effects of excess air ratio and tertiary air swirl number on the formation characteristics of NOx in a pilot scale combustor adopting a multi-air staged burner. In numerical calculation the mathematical models for turbulence, radiation and nitric oxide chemistry were taken into account. The radiative transfer equation was solved using the discrete ordinates method with the weighted sum of gray gases model. In the NOx chemistry model, the chemical reaction rates for thermal and prompt NOx were statistically averaged using a probability density function. The results were validated by comparison with measurements. For the experiment, a 0.2 MW pilot multi-staged air burner has been designed and fabricated. Using the numerical simulation developed here, a variation of thermal and prompt NOx formation was predicted by changing the excess air ratio and tertiary air swirl number. As the excess air ratio increased up to 1.9, the formation of the total as well as thermal NOx at exit increased while the prompt NOx decreased. The formation of thermal NOx was more affected by concentration of O2 and N2 than gas temperature. When the tertiary air swirl number increased, the formation of the total as well as the prompt NOx slightly decreased.