Characteristic Analysis Of The Exhaust System Of An Automobile's Engine

It is an important topic to design exhaust mufflers that have good attenuation performance and low pressure loss in the field of automobile's noise control. Most of the exhaust system design methods developed earlier have dealt primarily with one-dimension-plane wave theory. But the theory is hard to provide accurate analysis result because of the effect of the three dimensional wave and some other actual factors. The three dimension numerical method such as the finite element method can simulate the exhaust system's characteristic accurately and take the influence of several outside factors into account. So it is an effective method to predict exhaust system's performance and have an improved design. The flow and attenuation performance of an engine's exhaust system is simulated applying the three dimension numerical method, which is basing on the studying of the attenuation performance and rules of basic muffler elements Distribution of velocity, temperature and pressure in the muffler is achieved by analyzing the flow performance. The results indicate that: Pressure loss in the muffler is high and velocity in every chamber change complexly. Though temperature distributes equably, the difference between every chamber is large. All these could have effect on the attenuation performance. The finite element method is applied to analyze the attenuation performance, which is basing on that porous clapboard, porous pipes and absorbent are accurately modeled and the influence of temperature, velocity and tail reflection is taken into account. The results indicate that: Attenuation performance of the exhaust system in low and high frequencies isn't good and the magnitude is obvious insufficient. But when temperature rises, the spectrum moves toward higher frequency, which makes the attenuation performance in high frequencies better and that in middle frequencies worse. Tail pipe's reflection has good effect on the attenuation performance in low frequencies. The flow of air reduces the attenuation. As a result, these outside factors can't be ignored when analyzing the attenuation performance and redesigning the exhaust system. In order to improve the original exhaust system's aerodynamic quality and attenuation performance in low and high frequencies, the inside structure is primarily redesigned after studying the attenuation performance of every muffler element. We can see from the numerical results of the improved exhaust system in acoustic and fluid fields that: the improved design succeeds in increasing the attenuation performance and reducing the pressure loss and meliorating the aerodynamic quality. The numerical simulation in this paper can provide powerful guidance for the test. What's more, some improved experiences and improved methods are accumulated, which will be the important reference for the redesign of exhaust system in future. In conclusion, a new modern design method for the characteristic's prediction and redesign of the engine's exhaust system is developed in this paper.