集成排气歧管对汽油机动力性能影响的研究

Effect of Integrated Exhaust Manifold on Dynamic Performance for a Gasoline Engine

以一台国五发动机为基础设计了4-1和4-2-1两款集成排气歧管,通过一维仿真的方式探究两种形式的集成排气歧管对发动机动力性能的影响。结果表明:采用了集成排气歧管后,转速大于1600 r/min时转矩变化不明显,与原机转矩有2%的波动;但转速低于1600 r/min时,转矩下降较多,其中4-1方案低速下转矩下降更加明显,1200 r/min时转矩下降11.1 N·m,比原机下降5.9%。继而以1200 r/min为例探究了低速情况下,采用集成排气歧管造成转矩下降的原因。结果表明,采用了4-2-1与4-1集成排气歧管后,涡轮增压器前压力状态产生差异,影响了增压器效率;气门叠开期期间,由于排气背压增大,导致废气回流增加和缸内残余废气量增加,降低了充量系数。最后通过试验验证,采用了4-1集成排气歧管后的低速转矩确实低于原机,验证了仿真的准确性。

Based on a CNⅤgasoline engine,two integrated exhaust manifolds of Type 4-1 and 4-2-1 were designed,and the effect of these two different structures on engine dynamics was studied by one dimensional simulation.Results show that with the integrated exhaust manifold,the engine torque does not change obviously at the speed greater than 1600 r/min,with a fluctuation of 2%relative to the original exhaust manifold.However,at the speed less than 1600 r/min,the engine torque drops significantly.Especially for the use of Type 4-1 exhaust manifold,the engine torque drops by 11.1 N·m at the speed of 1200 r/min,which is more than 6%torque of using original exhaust manifold.Therefore,the reason for the reduction of low speed torque caused by the integrated exhaust manifold was studied at the speed of 1200 r/min.Results show that the use of integrated exhaust manifold changes the intake pressure before the turbocharger,which affects the turbocharger efficiency.At the same time,an increase in the exhaust back pressure during the overlap of intake and exhaust valves causes an increase in the exhaust reflux and residual gas in the cylinder,thus reducing the inflation coefficient of the engine.The final test indicates that the use of Type 4-1 integrated exhaust manifold is indeed to make the low speed torque lower than with the original exhaust manifold,which verifies the accuracy of the simulation calculation.