柴油/甲醇双燃料发动机耦合后处理系统的排放性能研究

Experimental Study on Emission Characteristics of Diesel/Methanol Dual-Fuel Engine Coupled with an After-Treatment System

为了实现压燃式发动机污染物的超低排放,在一台高压共轨柴油机上进行柴油/甲醇双燃料燃烧模式耦合后处理系统的排放特性研究。通过调节不同负荷下进气预混甲醇比例,分析了氧化催化转化器(DOC)、催化型颗粒物捕集器(CDPF)和选择性催化还原催化器(SCR)对柴油/甲醇双燃料发动机污染物排放的影响规律。结果表明:双燃料模式的排气温度降低,有效热效率在中低负荷时降低,在高负荷时增加;随着甲醇比例的增加,排气中CO、HC、NO_(2)和HCHO的体积分数增加,n(NO_(2))/n(NO_(x))显著提高,NO_(x)和碳烟的排放量明显降低。后处理系统工作特性受发动机负荷影响较大:在中低负荷时排气温度低,后处理系统对CO、HC和HCHO转换效率较低;在高负荷时排气温度高,系统催化活性增强,各种排放物转换效率也大幅提高。双燃料模式下,DOC后端氧化升温明显,n(NO_(2))/n(NO_(x))经DOC后显著降低,而纯柴油模式下则呈相反趋势。在不同负荷下:CDPF对碳烟的平均捕集效率超过90%;SCR催化反应降低NO_(x)的同时会导致N 2O排放增加,甲醇的加入可在一定程度上减少N_(2)O生成。研究结果可为实现双燃料燃烧模式的排放控制提供基础数据。

This paper investigates the emission characteristics of a high-pressure common-rail diesel engine coupled with an aftertreatment system in the diesel/methanol dual-fuel combustion mode,aiming to achieve ultra-low emissions of compression-ignition engines.The effects of the diesel oxidation catalyst(DOC),catalytic diesel particulate filter(CDPF)and selective catalytic reduction(SCR)on pollutant emissions of the diesel/methanol dual-fuel engine are studied by adjusting the ratio of inlet premixed methanol under different loads.According to the results,the exhaust temperature drops in the dual-fuel mode and the effective thermal efficiency decreases under low and medium loads and increases under high loads.With the increase of methanol ratio,the volume fractions of CO,HC,NO_(2)and HCHO in exhaust gas increases together with the n(NO_(2))/n(NO_(x)) ratio while NO_(x) and soot emissions significantly decrease.The after-treatment system is greatly affected by engine loads:Under low and medium loads,the exhaust temperature is low so is the efficiency in the conversion of CO,HC and HCHO;under high loads,the exhaust temperature increases and the catalytic activity in the system is enhanced,leading to remarkable increase in the conversion efficiency of various emissions.In the diesel/methanol dual-fuel combustion mode,there is significant temperature increase at the back end of the DOC and a remarkable drop of the n(NO_(2))/n(NO_(x))ratio.However,the opposite trend was observed in the diesel combustion mode.The average soot capture efficiency of CDPF is higher than 90%under different loads.The catalytic reaction of SCR leads to the decrease in NO_(x) and increase in N_(2)O emissions.However,adding methanol can reduce the formation of N_(2)O to a certain extent.The research results may provide useful data for realizing emission control in the dual-fuel combustion mode.