气门二次开启策略对柴油机性能及能量损失的影响

Influence of Valve Re-Opening Strategies on Performance and Energy Loss of a Diesel Engine

基于一台两级增压高压共轨柴油机,建立了整机一维热力学仿真模型,研究不同气门二次开启策略对柴油机燃烧特性、NO_x排放及能量分布的影响。研究结果表明:在相同气门升程时,随进气门、排气门二次开启时刻提前及进排气门同时二次开启时刻间隔增大,缸内压力和瞬时放热率峰值升高,燃烧重心前移,有效热效率升高,燃烧温度升高,NO_x排放升高。在相同气门二次开启时刻时,随气门升程增大,对发动机各项指标的影响增大。不同气门二次策略相比,进排气门同时二次开启对燃烧重心、排气损失、有效热效率及NO_x排放影响最大,排气门二次开启的影响最小。进气门二次开启策略的气门升程为2.4mm、二次开启时刻为上止点后210°时,能够较好改善有效燃油消耗率与NO_x排放之间的折中关系。

Based on a common-rail diesel engine equipped with two-stage turbocharger system,a onedimensional thermodynamic model was established to study the effects of different valve secondary opening strategies(intake valve re-opening,exhaust valve re-opening as well as intake and exhaust valves re-opening)on engine combustion,NO_x emissions and energy distribution.The results show that,at the same valve lift,with the advances of the intake valve re-opening timing and exhaust valve re-opening timing,and with the increase of interval between the timings of the intake valve re-opening and exhaust valve re-opening,the pressure in the cylinder and peak heat release rate increases,the crank angle corresponding to 50%of total heat release(CA50)advances,and the brake thermal efficiency,combustion temperature as well as NO_x emissions increases.At the same valve re-opening timing,the influence of increasing valve lift on the engine performance and emissions increases.The comparison of the different valve re-opening strategies shows that the re-opening of both intake and exhaust valves has the greatest impact on the CA50,exhaust energy loss,brake thermal efficiency and NO_x emissions,while the exhaust valve re-opening strategy has the least impact.The trade-off between the brake specific fuel consumption(BSFC)and NO_x emissions can be better improved by the intake valve re-opening strategy with the intake valve lift being 2.4 mm and the re-opening timing 30 degrees after bottom dead center.