中文摘要：

在一台加装独立的甲醇供给系统的自然吸气柴油机上,采用柴油甲醇组合燃烧模式（DMCC）进行台架试验.利用气相色谱仪分析技术,全面研究并总结了甲醛在不同的发动机工况如转速、负荷、排气温度（改变柴油氧化催化转化器DOC位置）和不同甲醇替代率的情况下的排放规律以及甲醛和未燃碳氢（HC）之间的相互关系.研究结果显示,DMCC模式下的甲醛排放主要受到负荷、甲醇替代率、排气温度3方面的共同影响.在中等负荷排温在240～380℃之间时,DOC促进甲醛的生成;在高负荷排温在400℃以上时,DOC减少甲醛排放.在同样工况下将DOC位置移近排气歧管对减少甲醛排放有显著的作用.在此情况下,当排气温度超过400℃,DOC后的甲醛排放体积分数降低到（10～15）×10^-6左右,与燃用纯柴油的甲醛浓度相近.另外,未燃碳氢和甲醛的转化效率的规律有一定的关联.当排温高于320℃以后,尽管HC迅速下降到比原机还低的水平,但甲醛排放浓度却比较高.当排气温度超过380℃并将DOC位置移近排气歧管,此时,HC与甲醛的排放将同步减少直至接近零排放水平.

英文摘要：

A naturally aspirated diesel engine equipped with an independent methanol supply system is operated to investigate the effect of the oxidation catalyst on formaldehyde emission from the engine running in Diesel/Methanol Compound Combustion mode.The influence of speed,load,the position of the DOC （diesel oxidation catalyst） from the exhaust manifold,as well as the proportion of methanol in the fuel on the formaldehyde emission is studied.The relationship of formaldehyde and hydrocarbon （HC） emissions is also analyzed.Gas chromatography is applied to measure the concentration of formaldehyde.The test results showed that the formaldehyde emission is mainly influenced by the load,exhaust temperature and proportion of methanol.The DOC increased the formaldehyde emission at medium load in which the exhaust temperature ranges from 240℃ to 380℃,while at heavy load the DOC reduced formaldehyde emission and even eliminated it completely when the exhaust temperature exceeded 400℃.Changing the position of the DOC to the exhaust manifold of the engine has a significant impact on formaldehyde emissions because of the exhaust temperature.If the DOC is placed close to the exhaust manifold,where the temperature is up to 400℃ the concentration of formaldehyde can be reduced to as low as （10～15）×10^-6,which is comparable with those from the basic diesel engine,（5～10）×10^-6.In addition,there is some relationship between formaldehyde and HC emissions.At temperatures up to 320℃,HC emission is remarkably reduced even lower than the diesel engine but formaldehyde remained almost the same.The HC and formaldehyde emission can be reduced together only if the DOC is positioned close to exhaust manifold and the temperature is higher than 380℃.