空燃比波动对压缩天然气发动机TWC甲烷起燃特性的影响

Effect of A/F ratio fluctuation on light-off performance of methane of TWC for CNG engine

针对压缩天然气(Compressed natural gas,CNG)发动机专用三元催化器(Three way catalyst,TWC)中空燃比波动影响甲烷起燃特性的重要因素,以小样试验为基础建立数值模型,考虑空燃比波动对甲烷起燃特性进行仿真计算,探究空燃比波动的振幅、浓燃占空比和波动中心的影响因素及规律。结果表明:在空燃比波动的一定范围内,空燃比波动振幅的增大会降低甲烷的起燃温度(T_(50))和完全转化温度(T_(90));空燃比波动的浓燃占空比越大,会使催化器内部的载体轴向平均温度升高,有利于甲烷水蒸气重整反应,相对降低甲烷的T_(50)和T_(90);空燃比波动的中心由偏稀变为偏浓,可以促进甲烷起燃;CNG发动机专用TWC工作在微浓的进气条件下有助于甲烷的起燃。

The light-off performance of methane of special Three-Way Catalytic converter(TWC)for Compressed Natural Gas(CNG)engine is significantly impacted by the A/F ratio fluctuation.Based on sample test data,a TWC model is established considering the A/F ratio.The effects of the amplitude,duty cycle and fluctuation center of A/F ratio on the light-off performance of methane are analyzed.The results show that greater amplitude would reduce the light-off temperature(T50)and complete conversion temperature(T90)of methane.Longer duty cycle of rich gas composition would cause smaller T50 and T90 because of higher mean axial temperature of substrate,which could promote the methane steam reforming and reaction.The fluctuation center from lean to rich would promote thelight-off performance of methane,and the greater the amplitude the stronger this effect.The rich gas composition could contribute to the light-off performance of methane based on the results of the duty cycle and the fluctuation center.