EGR冷却器积碳研究综述

A Review of EGR Intercooler Soot Deposition

废气再循环(exhaust gas recirculation,EGR)技术是解决柴油机氮氧化物(NO_x)排放的有效措施之一,尤其是经中冷后的EGR在NO_x、颗粒物(particulate matter,PM)的排放以及经济性方面能够实现更好的折衷。在冷却EGR时,排气中所含的干碳烟(soot)和碳氢(carbureted hydrogens,HCs)在热泳力、静电、扩散和凝结等作用下沉积到EGR冷却器的换热元件表面而形成积碳,达到稳定状态的积碳导致EGR中冷换热效率下降达20%~30%,背压达无积碳状态的2倍,由此导致发动机NO_x、PM的排放以及经济性变差。研究表明,温度、soot的粒径分布、HCs的浓度是影响积碳的主要因素,同时EGR冷却器的结构、燃料等也会造成一定的影响。通过对各影响因素的优化可以延缓积碳的形成过程,目前实现EGR冷却器再生的有效手段尚处于研究阶段,可能有效的再生措施有高速气流冲刷表面疏松的soot、蒸发积碳当中的HCs、高温氧化soot以及利用水或酸等弱化积碳的黏附力而自然脱落。

The exhaust gas recirculation （EGR） is an effective method for reduction of NOx emission from diesel engine. Especial-ly the cooled EGR can get better trade off among NOx, PM and brake specific fuel consumption （ BSFC）. Soot and HCs within the ex-haust gas deposit onto the wall of heat exchanger when the exhaust gas flow through the intercooler and cooled down. The thermophore-sis is the main mechanism of deposition, and diffusion, static charge and condensation are also affecting the deposition. The deposition in EGR intercoolers may causes the degradation in heat exchange efficiency on the order of 20% - 30% , which may affect the NOx and PM emission. The deposition also increases the back pressure of the EGR intercooler and thus adversely affects the BSFC. The back pressure of fouled intercooler may be as twice as the back pressure of fresh intercooler. Temperature, soot diameter distribution and HCs concentration are main factors that affect the deposit formation process, and it is also affected by the structure, fuel and after treat-ment et al. Mitigation of the deposit can be achieved by controlling these factors that affect the deposit formation process. There is no effective method to remove the deposit of EGR intercooler because the deposit removal mechanisms is not fully understood. But here have some potential method for EGR intercooler regeneration based on results from some published literatures as follow： using high speed flow to blow out loose soot, HCs evaporation, soot burning, and cracking and/or flaking for water and acids condensation.