Methods to Mitigate Tail Pipe Noise in Passenger Vehicles 2018-01-1280

The cold end of an exhaust system plays an important role in today’s passenger cars by reducing the engine noise and thus keeping a pleasant cabin room for optimum passenger comfort. However, due to vehicle layout constraints, it may be difficult to achieve a Muffler design which fulfills the required noise attenuation requirement. It becomes imperative to have an understanding of the different parameters that affect the overall tail pipe noise.

In an automobile exhaust system, Exhaust Mufflers play a major role in noise reduction by helping in the attenuation of undesirable noises from the engine. The overall content of the tail pipe noise of an IC engine can be segregated into two categories - Order noise and Flow noise. Order noises are low frequency pressure pulses generated during the exhaust valve opening and closing in the engine combustion cycle. Flow noises are high frequency noises which are generated due to the flow of the exhaust gas and primarily depends on gas velocity, temperature and flow path. Hence for good Muffler performance, it is necessary to understand the various parameters that have an impact on both these components of the overall noise. This paper analyses various parameters which influence the order noise and flow noise characteristics for an Exhaust Muffler design. Based on 1D flow simulation and actual test measurements of Tail pipe noise in a vehicle with a 1L NA petrol engine, the effects of the different parameters on Tail pipe order noise and flow noise have been studied. The results show the importance of the size of a muffler and its position in the Exhaust line in determining the level of the overall noise at the end of the tail pipe. In cases where a favorable position and size for an Exhaust muffler is not practical, other measures such as usage of absorptive material to attenuate high frequency noise can help in reducing the overall content of the tail pipe noise.