Study On Design Technique Of Internal Combustion Engine Exhaust Muffler

As a effective way of controlling vehicles noise, muffler has been widely applied in exhaust system of engine. Current theoretical research of muffler is based on plane wave approximation, and the effect of flow induced noise is neglected. Actually muffler is working on a condition with flow, so the flow induced noise is exist in muffler, and sometimes the noise is quite strong. The sound propagation in the muffler becomes nonplanar wave model. These factors induce that the computational results are different from these in the engine real process. So, the design technique of muffler considering the flow induced noise is researched in this paper.As a foundation of researching flow induced noise, jet injection noise is researched using numerical and experimental methods. The velocity and turbulent kinetic energy distribution is calculated by computational fluid dynamics (CFD) method. The spectrum characteristic of flow induced noise is calculated by computational aero-acoustics (CAA) method. Sound power of district jet, liner increaser jet and round increaser jet is experimental measured using sound intensity method. The result shows that there is little difference among the jet injection noise sound power of three jets. But the directivity of noise radiation has significant difference, the jet injection noise induced by round increaser jet is easy to radiativing divergently. The Relation of jet injection noise intensity and distance from jet is researched, a result is summarized by combining with turbulent kinetic energy distribution, the result shows that jet injection noise is induced by turbulent flow in airflow mixing area shear layer around the potential core.Against the flow induced noise of muffler, the flow induced noise of various tube insertion styles at two flow speeds are experimental researched. The sound spectrums are analyzed, the results show that the frequency of peak of flow induced noise is increased gradually with the shortening distance between inlet and outlet tube. When the distance is much shorter and the velocity of flow is higher, there is a squeal generating in the muffler. The effect of insertion styles of tube to flow induced noise sound power is analyzed, the results show that the change trends of flow induced noise with insertion depth in different insertion styles. The sound power of flow induced noise at two flow speeds are researched, the results show that flow induced noise sound power of all insertion styles is increasing with the flow speed increased. The computational method of flow induced noise is preliminary studied on. Based on the aero-acoustics theory, the sound power of flow induced noise at muffler outlet is calculated, and the trend is agreed with the experimental measurement.At last, a multi-cavity muffler is selected as a subject investigated. The aerodynamic performances are researched. Against the design disadvantage, the structure of muffler is improved based on the results generalized in the flow induced noise researches. The results show that the improvement of muffler make the velocity, turbulent kinetic energy and pressure loss lower. And the power of flow induced noise is lower after improvement.