喷油策略耦合EGR对不同燃料柴油机性能影响
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摘要
以高压共轨柴油机为研究机型,运用AVL Fire构建其燃用纯柴油(B0)、纯生物柴油(B100)和B70N30(体积70%生物柴油+30%正丁醇)的三维CFD模型并进行验证。利用该模型模拟研究不同EGR率和喷油定时条件下三种燃料对发动机排放特性的影响。研究表明:同一EGR率下,与B0相比,B100和B70N30燃空当量比减小,缸内活性基(OH、O)浓度升高,NOx排放增大而碳烟(Soot)和CO排放降低;与B100相比,B70N30含氧量增加,滞燃期延长,导致Soot和CO排放降低。在相同喷油时刻下,相比B0和B100,燃用B70N30时局部高燃空当量比区域减少,CO与Soot生成降低,NOx排放高于B0;随喷油时刻过度提前至24°CA BTDC时,三种燃料的理化特性对Soot排放影响较小。
In the present work, high pressure common rail diesel engine was used as the research model, and 3 D model of CFD was established and validated by using AVL Fire, with the mode burning pure diesel(B0), pure biodiesel B100 and B70 N30(70% B100 + 30% n-Butanol). The effect of three kinds of fuel on engine emission characteristics under different EGR rate and fuel injection timing were simulated by using this model. The results indicated that under the same EGR rate, combustion space of B100 and B70 N30 were lower than that of B0, while the concentration of active group in cylinder(e.g. OH., O.) and NOx emission were increased, and meanwhile carbon Soot and CO emission were reduced. Furthermore, oxygen content of B70 N30 was increased when compared with B100, and the ignition period was delayed, thus resulting in the reduction of Soot and CO emissions. Besides, it was shown that under the same injection time, the local combustion space of B70 N30 was lower than that of area combustion space, when compared with B0 and B100, while the formation of CO and Soot formation were decreased, and the NOx emissions of B70 N30 was higher than that of B0. When the fuel injection time was earlier than 24 ° CA BTDC, the physical and chemical properties of Soot emissions of three kinds of fuel exhibited small effect on soot emission.
In the present work, high pressure common rail diesel engine was used as the research model, and 3 D model of CFD was established and validated by using AVL Fire, with the mode burning pure diesel(B0), pure biodiesel B100 and B70 N30(70% B100 + 30% n-Butanol). The effect of three kinds of fuel on engine emission characteristics under different EGR rate and fuel injection timing were simulated by using this model. The results indicated that under the same EGR rate, combustion space of B100 and B70 N30 were lower than that of B0, while the concentration of active group in cylinder(e.g. OH., O.) and NOx emission were increased, and meanwhile carbon Soot and CO emission were reduced. Furthermore, oxygen content of B70 N30 was increased when compared with B100, and the ignition period was delayed, thus resulting in the reduction of Soot and CO emissions. Besides, it was shown that under the same injection time, the local combustion space of B70 N30 was lower than that of area combustion space, when compared with B0 and B100, while the formation of CO and Soot formation were decreased, and the NOx emissions of B70 N30 was higher than that of B0. When the fuel injection time was earlier than 24 ° CA BTDC, the physical and chemical properties of Soot emissions of three kinds of fuel exhibited small effect on soot emission.
引文
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[4]Pickett L M,Kook S,Williams T C.Transient liquid penetration of early-injection diesel sprays[J].SAE International Journal of Engines,2009,2(1):785-804.
[5]Valentino G,Corcione F E,Iannuzzi S E,et al.Experimental study on performance and emissions of a high speed diesel engine fuelled with n-butanol diesel blends under premixed low temperature combustion[J].Fuel,2012,92(1):295-307.
[6]Song J,Alam M,Boehman A L,et al.Examination of the oxidation behavior of biodiesel soot[J].Combustion and flame,2006,146(4):589-604.
[7]Wang H,Reitz R D,Yao M F,et al.Development of an n-heptane-n-butanol-PAH mechanism and its application for combustion and soot prediction[J].Combustion and Flame,2013,160(3):504-519.
[8]Chen G S,Shen Y G,Zhang Q C,et al.Experimental study on combustion and emission characteristics of a diesel engine fueled with 2,5-dimethylfurane-diesel,n-butanol-diesel and gasolinediesel blends[J].Energy,2013,54:333-342.
[9]Yao M F,Zhang Q C,Liu H F,et al.Diesel engine combustion control:medium or heavy EGR[C].SAE Paper 2010-01-1125,2010.