整车排气系统对汽油机动力性的影响

Influence of Vehicle Exhaust System on Torque Performance of a Gasoline Engine

基于一款自主开发的自然吸气直喷汽油机,通过台架试验,采用GT仿真的方法研究了整车排气系统对汽油机动力性的影响,并采用傅里叶频谱分析方法对排气波动进行傅里叶正变换及逆变换,实现波动信号在时域和频域的转换,进而分析了影响动力性的关键谐波成分,并确定了在整车排气系统中影响此谐波的反射源为前级消声器.结果表明:前级消声器在整车排气系统中的位置对某些转速的动力性影响显著,通过合理优化控制整车排气系统反射波的频率,使其波疏在排气结束时到达排气道口,可以明显降低缸内残余废气量,从而提升动力性.最后,探索了通过傅里叶频谱分析方法验证及优化整车排气系统以提高发动机低速动力性的方法.

The influence of vehicle exhaust system on the torque performance of a gasoline engine was investigated by engine bench test and GT simulation.Fourier spectrum analysis method was adopted to transform the pressure oscillation wave between time and frequency domains in order to determine the key harmonic component waves that affect the engine torque.The results show that among the reflection sources in the vehicle exhaust system,the front muffler exerts a main effect to the key harmonic waves.Its location in the vehicle exhaust system brings a significant influence to the torque performance for some certain engine speeds.The residual exhaust gas and therefore the engine torque performance can be improved by optimizing the pressure oscillation frequency introduced by the front muffler so that the rarefaction waves reach the exhaust runner port at the close time of the exhaust valve.Finally,the best location of the front muffler was determined and the low-end torque performance of the gasoline engine was confirmed by engine test.