颗粒物粒径对EGR冷却器沉积物及换热效率的影响

摘要

通过一台高压共轨涡轮增压柴油机,对4种相同规格、不同换热芯管长度(140、180、220和260 mm)的冷却器进行颗粒物沉积试验及换热效率测试,结果表明:连续运行240 min后,EGR气体中小粒径颗粒物(Dp≤5 nm)在4种不同长度换热芯管中的减少率均为100％,中等粒径颗粒物(5 nm＜Dp＜50 nm)减少率依次为:73％、54％、70％和71％,大粒径颗粒物(Dp≥ 50 nm)减少率依次为:-171％、-8％、-3％和11％;换热芯管长度为140mm的单位长度换热效率提高,而换热芯管长度为180、220和260 mm的单位长度换热效率基本保持不变.沉积物表面的扫描电子显微镜(SEM)扫描结果显示,同一换热芯管的上游到下游沉积层表面逐渐形成“沟壑”并不断扩大,且不同长度换热芯管随管长增加,其出口处沉积层表面的“沟壑”也逐渐增加.%In order to investigate characteristics of soot deposit on EGR cooler's interior surface and their effects on the heat transfer efficiency of a diesel engine EGR cooler,four different tube lengths (140,180,220 and 260 mm,respectively) with the same EGR cooler specification were tested on a high pressure common rail turbocharged diesel engine.Results show that all the elementary soot particles(Dp≤5 nm)deposit on the EGR cooler's interior surface when passing through the EGR cooler.The soot reduction rate for the primary soot particles (5 nm＜Dp＜50 nm)is 73％,54％,70％ and 71％ respectively for the four tube lengths.While,the soot reduction rate for the soot clusters (Dp ≥ 50 nm) is-171％ 、-8％、-3％ and 11％ respectively.The heat transfer efficiency of 40 mm length EGR cooler is improved but the heat transfer efficiency of other three length EGR coolers is nearly not changed.Scanning electron microscopy (SEM) test results show that the surface of particulate deposit gradually becomes rough from up stream to downstream in the same tube of the cooler.Even some ravines appear on the surface of the deposition.In addition,different tube lengths of the EGR cooler give different deposition surface patterns,and the longer is the tube,the more ravine patterns occur on the deposition surface.