高原环境压缩比及EGR耦合LIVC对柴油机性能影响

本文基于某两级增压柴油机,建立一维热力学模型,研究高原环境压缩比、EGR耦合LIVC对柴油机性能和NO_x排放的影响。结果表明:同压缩比,4 km海拔,随晚关角度增大,热效率及扭矩增大,NO_x排放大幅降低;在相同晚关角度下,随压缩比增大,热效率及扭矩增大,NO_x排放略有增加。高压缩比,引入EGR率相同且小于15%时,增大晚关角度使扭矩、热效率增大,BFSC与NO_x排放降低;引入EGR率相同且大于15%时,增大晚关角度导致扭矩、热效率降低;当NO_x原始排放较高时(大于2.0 g·kW^-1·h^-1,国V法规ESC限值),随晚关角度增大,等NO_x条件下BSFC降低,采用LIVC策略有利于改善NO_x-BSFC之间的trade-off关系;但随NO_x的进一步降低(尤其小于0.4 g·kW^-1·h^-1,国Ⅵ法规WHSC限值),采用LIVC策略会导致NO_x-BSFC之间的Trade-off关系显著变差。

Effects of Compression Ratio and EGR Coupled LIVC on the Performance of Diesel Engine

Based on a diesel engine equipped with two-stage turbocharging systems,a one-dimensional thermodynamic model was established.The effects of compression ratio,EGR and late inlet valve closing(LIVC)on the performance and the specific NO_xemission of diesel engine were studied at high altitude.The results show that,when compression ratio were the same,the break thermal efficiency and torque increased significantly and the specific NO_x emission decreased rapidly with the increasing of the angle of LIVC at the altitude of 4 km.When the angle of LIVC were the same,the break thermal eficiency and torque increased significantly and the specific NO_x emission increased slightly with the increasing of compression ratio.When the compression ratio is high and the EGR rate is less than 15%,the torque and the break thermal efficiency increased with the increasing of the angle for LIVC,while the brake specific fuel consumption(BSFC)and the specific NO_x emission decreased.When the compression ratio is high and the EGR rate is more than 15%,the increasing of the angle of LIVC would cause that the torque and break thermal decreased.When the original NO_x emission is high(greater than 2.0 g·kW^-1·h^-1,ESC limit of national V regulation),the BSFC decreased under the condition of equal NO_x with the increasing of the angle for LIVC.The adoption of LIVC strategy is conducive to improving the trade-off relationship between NO_x-BSFC.However,with the further reduction of NO_x(especially less than 0.4 g·kW^-1·h^-1,WHSC limit of national VI regulation),the adoption of LIVC strategy will lead to a significant decline in the trade-off relationship between NO_x-BSFC.