柴油机SCR系统尿素水溶液的喷雾特性

Spray characteristics of UWS for SCR system in diesel engine

通过建立柴油机SCR后处理系统的UWS喷射雾化模型,综合考虑UWS液滴在排气管道中的湍流扰动、变形、破碎、碰撞聚合和碰壁反弹等一系列理化过程,研究UWS的喷雾雾化分解特性,分析了喷嘴喷射压力、喷孔喷射角度α、喷雾锥角β、喷嘴偏置角度θ和排气管径长比对UWS液滴分解的影响.结果表明:喷射压力过小时,UWS液滴将呈液柱或大液滴状,喷射雾化效果差,NH_3平均体积分数随喷射压力的增大呈线性增大;α对UWS分解有显著影响,随着α的增加,NH_3平均体积分数升高;β对NH_3均匀性系数影响显著,随着β的增大,排气管内壁面附近NH_3的分布更加均匀;随着θ的增大,NH_3平均体积分数不断增大,但其均匀性系数急剧下降;NH_3平均体积分数随排气管直径的增大而减小,后逐渐趋于平缓.

Establishing the urea water solution (UWS) spray atomization model for selective catalytic reduction (SCR) aftertreatment system in diesel engine,the physical processes of UWS droplets of turbulence disturbance,distortion,breakup,collision-merging and wall-impingement bounce in exhaust pipe were investigated comprehensively. The effects of nozzle injection pressure,nozzle injection angle of α,spray cone angle of β,nozzle offset angle of θ and diameter-to-length ratio of exhaust pipe on the decomposition of UWS droplets were analyzed. The results show that when the injection pressure is too small,the UWS spray tends to be liquid column or large droplets with poor spray atomization ability of UWS,and the NH3 average volume fraction is increased linearly with the increasing of injection pressure. The value of α has significant effect on UWS decomposition,and the NH3 average volume fraction is increased with the increasing of α. The value of β has significant effect on NH3 uniformity coefficient,and the distribution of NH3 tends to be uniform with the increasing of β.With the increasing of θ,the average volume fraction of NH3 is increased,while the uniformity coefficient is decreased sharply. With the increasing of exhaust pipe diameter,the average volume fraction of NH3 is first decreased with latter gradually gentle decreasing.