Optimization Design And Applicable Analysis On Engine Exhaust System

At present, installing appropriate exhaust muffler in exhaust system which is the most effective^simple and the widespread used method for automobile exhaust noise controlling both domestic and overseas. In the work of the air temperature and pressure environment, a good muffler is supposed to having greater sound deadening capacity in a certain range of frequency and lower pressure loss. With the auto market increased competition and customer awareness of product improvement, NVH performance of vehicles particular acoustic noise inside vehicle have attracted people's attention increasingly. The design of exhaust system is a step of critical importance in product development, which conforms to the noise level legislations and backpressure requirement and also has good sound quality inside the car. Centring on two exhaust system—A type and B type mated on a certain engine, this paper accomplishes the optimization design using a approach to combination of test, simulation and test, which presents application of numerical simulation in auto exhaust system design.Another catalyst is adding to A type exhaust system, it needs optimize and design the exhaust system structural for the purpose of reducing the backpressure of exhaust cold part. First, GT-Power is used to build pressure loss simulation model, simulation results are in good agreement with the experimental results, which verifies the correctness of simulation model, and then we analyze the contribution ratio of each part to the entire backpressure. Study on the parameters, such as exhaust bend pipe's bend angle and diameter, inserted pipe and perforated pipe inside muffler, how they influent the backpressure. Based on the study, three optimizing plan are raised. The test results show that the backpressure on cold side is reduced about9to10kPa compared to initial exhaust system, the simulation results show a good agreement, the error between them is about4%.For B type exhaust system, it comes abnormal interior noise during engine idling and rapid acceleration, optimization of exhaust system is required to solve the poor vehicle riding comfortability problem. First of all, such phenomenon is mainly caused by the high sound level of second order exhaust noise and resonance of exhaust system during engine idling. The insertion loss test without airflow comes to the conclusion that the attenuation performance of the present exhaust muffler in low frequencies especially100Hz is insufficient. Two improved design are raised. A resonant chamber is introduced to reduce the exhaust sound level of second order and noise due to resonance. The high frequency flow noise is lowered by a pinch-can structure. Also the addition of tailpipe's diameter is employed to reduce backpressure. A simulation model is built to calculate the transient tailpipe noise when car is accelerating and analyze the acoustic and aerodynamic performance of improving plan. The test results show that the maximum of transient tailpipe noise during idling and acceleration of improved exhaust system drops up obviously, there is also a and acceleration of improved exhaust system decreases10dB(A) and8dB(A) respectively, at the same time, the sound quality inside car improves obviously.Using Numerical simulation software to guide the design of exhaust system has remarkable practical results, and it can shorten development circles, which has great significance for the exhaust system's design.