EGR对生物柴油颗粒物氧化活性及微观结构的影响

Influence of EGR and Diesel-Biodiesel Blend on Oxidation Reactivity and Nanostructure of Particulate Matter in Diesel Engine

为研究废气再循环(EGR)及燃用调合生物柴油(B0,B20)对柴油机排放颗粒物(PM)氧化活性与微观结构的影响,通过一台4缸共轨柴油机进行试验,并采集燃烧颗粒物,使用热重分析仪(TGA)、高倍透射电镜(HRTEM)和拉曼光谱(RS)对颗粒物进行研究.结果表明:燃用同种燃料时,随着EGR率增加,颗粒中干碳烟含量增加,起始氧化温度T_(i)上升,表观氧化活化能E逐渐增强,氧化活性降低;相比B0颗粒,B20颗粒中干碳烟含量略有减少,起始氧化温度T_(i)略有下降,E减弱,氧化活性增加.随着EGR率增加,颗粒物核-壳结构更为明显,当EGR率从0增至25%时,B0和B20颗粒初级碳粒子的平均微晶尺寸分别增加20%和25%,平均微晶曲率分别降低10%和7%,平均碳层间距分别降低5.8%和6.0%.同时,B0和B20颗粒的I_(G)/I_(D)增加,石墨化程度提高.

Combined effects of exhaust gas recirculation(EGR)rate and biodiesel blends(B0,B20)on oxidation reactivity and nanostructure of particular matters(PM)were collected and investigated experimentally on a fourcylinder common rail diesel engine by using thermogravimetric analyzer(TGA),high resolution transmission electron microscopy(HRTEM)and Raman spectroscopy(RS)to study burning particulate matter.The results show that when the same fuel is used,as the EGR rate increases,the dry soot content in the particles increases,the initial oxidation temperature T_(i)increases,the apparent oxidation activation energy gradually increases,and the oxidation reactivity decreases;compared with the B0 particles,the dry soot content in the B20 particles slightly decreases,the initial oxidation temperature T_(i)decreases,the apparent activation energy decreases,and the oxidation reactivity increases.With the increase of EGR rate,the core-shell structure of the particulate matters is more obvious.When the EGR rate increases from 0 to 25%,the average fringe length of the primary particles from B0 particles and B20 particles increases by 20%and 25%,respectively.The average fringe tortuosity reduces by 10%and 7%and the average fringe separation distance reduces by 5.8%and 6.0%.Also,with the increase of EGR rate,the I_(G)/I_(D)of B0 particles and B20 particles are increased,and the degree of graphitization is increased gradually.