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Show 1. ABSTRACT 1 Effect of Premixing of Fuel and Air on NOx Formation K.Hase and V.Kon Energy Technology Research Institute, Tokyo Gas Co., Ltd., 1-16-25, Shibaura, Minate>-ku, Tokyo, 105 , JAPAN The relationship between air ratio fluctuations and NOx formation was investigated in a combustor with a multi-port burner. By using a laser absorption method, the air ratio fluctuations were measured under two mixing conditions, perfect and partial mixing. The fluctuations of the burned gas temperature were also measured by a fine thermocouple. From the measured fluctuations of the air ratio, the probability density distribution of the air ratio was obtained to quantify the degree of fluctuation. Using the model proposed by Heywood et aI., the effect of the air ratio fluctuations on NOx formation was investigated by numerical simulation. The simulation results using the measured probability density distribution of the air ratio give a reasonable prediction of the effect of the fluctuations on NOx formation. 2. INTRODUCTION Driven by the growing concern for environmental protection, combustion systems must operate with greatly reduced emission levels of nitrogen oxides (NOx), carbon monoxide and hydrocarbons. At present, emission levels of carbon monoxides and hydrocarbons from most combustion systems using city gas as a fuel are kept within satisfactory levels, however, the NOx emission has yet to be reduced to a satisfactory level. One promising method for reducing the NOx emission is a lean premixed combustion, and this appears to be very attractive and has already been employed in some combustion systems. However, it is well known that if the fuel and air are not sufficiently mixed, the NOx emission level is not as low as expected, despite lean premixed combustion. The effect of mixing fuel and air on NOx formation has been investigated by several researchers (Pompei and Heywood (1972), Appleton and Heywood (1973), Anderson (1973), Semerjian et al. (1978), Lyons (1982)). In recent work on the effect of mixing on NOx formation in a premixed combustor, Lyons concluded that in lean premixed combustors, highly uniform spatial fuel-air distribution was necessary to achieve a low NOx emission. However, no mention was made by Lyons on the effects of temporal fluctua- |