柴油机排气尾流中核模态颗粒数浓度和粒径分布变化特性

摘要

The dilution and change characteristics of diesel engine exhaust near tailpipe atmospheric environment were investigated based on two-stage diluter experiments.The purpose is to find the evolution characteristics of nucleation mode particles in the exhaust plume of diesel engines.It is shown that the changes of primary dilution parameters,such as primary dilution mixture gas temperature（PDT）,primary dilution mixture air humidity（PDH）,primary dilution ratio（PDR）,and primary residence time（PRT）,significantly affect the size distribution of nucleation mode particles（Dp50 nm） in the exhaust plume of diesel engines,further indicating that the nucleation mode particles are composed mainly of secondary particles based on gas-to-particle conversion during exhaust dilution and cooling.The decrease of PDT or the increase of PDH and PRT can significantly increase the number concentration of nucleation mode particles in the exhaust plume of diesel engines.With increasing PDR,the number concentration of nucleation mode particles exhibits a rise-decay trend,and after a peak point it steadily decreases.The measurement results were explained based on the aerosol dynamic theory.%通过将柴油机尾气引入两级稀释取样系统,模拟柴油机排气在近排气管大气环境中稀释变化特性,以期揭示大气稀释作用下柴油机排气尾流中核模态颗粒的形成和变化机制。实验发现：改变初级稀释通道内混合气温度（PDT）、湿度（PDH）、混合气停留时间（PRT）和稀释比例（PDR）等稀释参数会显著影响稀释混合气中核模态粒子（Dp〈50 nm）的数浓度和粒径分布,表明核模态粒子主要由排气稀释过程中气-粒转化作用产生的二次颗粒构成;随PDT的降低以及PDH、PRT的增加,排气尾流中核模态粒子数浓度显著增加,颗粒粒径向大粒子方向迁移;核模态粒子的数浓度随PDR增加呈先增加后减小趋势,采用气溶胶动力学变化理论对测试结果进行了讨论。