Effects of exhaust manifold with different structures on sound order distribution in exhaust system of four-cylinder engine

Abstract

This paper analyses the effects of an exhaust manifold with different structures on the sound order distribution of exhaust noise based on the one-dimensional plane wave theory. The theoretical analysis shows that the isometric exhaustmanifold retains the firing-order and harmonic-firing-order components of the exhaust noise while suppressing its half-order and the integer-order components. Concurrently, the symmetric isometric manifold merely suppresses the half-order components of the exhaust noise. Finally, the non-isometric exhaust manifold increases the half-order and integer-order components of the exhaust noise. To verify the theoretical analysis, dynamometer experiments under full-load condition are conducted on a four-cylinder naturally aspirated gasoline engine with the aforementioned three typical structures of an exhaust manifold. The results show that for the isometric and symmetric isometric manifolds, the half-order components of the exhaust noise are rather weak. In addition, for the former, the integer-order components of the exhaust noise are sufficiently low to be neglected. Therefore, the theoretical analysis and experimental results are basically consistent, indicating that this study is beneficial for estimating the sound order distribution during the predesign stage.