预混燃烧室的NO_x与CO排放性能研究

Experimental study on NO_x and CO emissions in premixed combustion system

建立了一套预混燃烧装置,进行了不同过量空气系数a、预混段长径比L/D、燃气平均速度v和旋流器旋流数Sn下的燃烧试验,研究了不同燃料-空气预混条件对燃烧尾气中污染物NOx与CO体积分数的影响。结果表明：当过量空气系数a〉1.1时,NOx与CO体积分数均呈下降趋势;预混长径比L/D在4~8时,增长预混长度可以减少污染物NOx的排放;减小燃气平均速度可以降低NOx体积分数,但CO体积分数略有增加;强旋流（Sn〉1.56）可以增强预混,降低NOx体积分数,但强旋流下CO体积分数增加迅速。

This paper is aimed at an analysis of the effects of the fuel-air premixed conditions on NOx and CO by doing the emissions experiments at different excess air coefficients （ a）, the aspect ratios of the premixed tubes （L/D）, the average gas velocities （v） and swirl numbers （Sn） in a premixed combustion system. The mentioned premixed combustor is composed of three parts ： the cylindrical premixing segment, the rectangular combustion chamber and the exhaust gather segments. Air was injected into the premixing tube through the swirler and uniformly mixed with propane in the premixing segment before entering the combustion chamber. For our research purpose, we have collected the flame temperature data by using the thermocouples and capture cards, in addition, we have measured the exhausted gas component concentrations by using the emissions analyzer. The results of our investigation can be stated as follows ： the range of the excess air coefficient has been worked out at 0.6 to 1.3. We have also measured and witnessed the four aspect ratios of the premixed tubes of 4, 5, 6 and 8 and five average gas velocities of 1.81 m/s, 2.13 m/s, 2.47 m/s, 3.05 m/s and 3.36 m/s. In addition, we have also designed two kinds of swirler, the swirl numbers of which were 1.56 and 0.9 respectively. The results show that the optimal excess air coefficient is 0. 9, in which the generations of fast-NOx and thermal-NOx were both less. When the gas velocity is low, the NOx emission tends to decrease with L/D increasing in the range of 4 - 8. The effect of the gas average speed on the emissions of pollutants NOx and CO can be potentially made to affect the uniformity of the fuel and air mixing in the premix tube. When the average speed of the gases is low, they would be mixed more uniformly through a longer process of mixer, as a result of which the pollutant emissions could be made reduced. However, the average gas speed might not be able to get lower than the flame propagation speed of the fuel-air combustion. Strong swirling （ Sn 〉 1.56） can help to enhance the mixture of the fuel and air, which may result in the decrease of NOx emission, but the emission of CO tends to increase significantly.