排气系统对VVT发动机性能影响的研究

Research on Effects of Exhaust System on VVT Engine Performance

某款VVT汽油发动机开发过程中发现匹配新状态的排气系统后,发动机低速充气效率降低,性能不如匹配旧状态的排气系统的发动机。为了分析原因,使用一维仿真软件建立了该款发动机的详细模型,对比老状态和新状态的排气系统,并且设计试验方案进行验证排气系统对其性能的影响。计算结果表明:匹配老状态排气系统的发动机排气门处在气门重叠早期出现压力低谷,有利于增加充气效率。根据计算结果优化新状态排气系统并且测试发动机低速外特性,结果表明:匹配根据优化结果改造的排气系统,能够提升发动机低速扭矩。

In the development of a gasoline engine equipped variable valve timing technology,it is found that the engine charging efficiency at low speed is reduced after being matched with a new state of exhaust system,and its performance is no better than the engine with the old exhaust system. To make it clear,a specific model of the engine is established to compare the old exhaust system with the new system by 1D simulation,and a test scheme is designed to testify the effects of the exhaust system on VVT engine performance. The calculation results show that a low pressure appears at the exhaust valve of the engine being matched with a old exhaust system in the early of valve overlap angle,and that it is beneficial for increasing the engine charging efficiency. The new exhaust system was optimized and the torque at low speed was measured. The test results of optimizing a new exhaust system and measuring a torque at low speed according to the calculation findings indicates that the torque at low speed is increased after the engine is matched with the optimized exhaust system.