Optimal design of compact multi-partition MPP silencers for IC engines noise control

Abstract

Engine exhaust noise is always characterized as the major source of automotive noise especially in the urban areas which can be reduced using the passive mufflers. Muffler performance is controlled by using complex geometries or by adding porous materials inside the chamber. However, when a clean absorbent system is desirable or when the muffler must support high air flux, it is not possible to add fibrous materials. The use of micro-perforated panels (MPP) as another alternative to improve the acoustic performance becomes important. Different constraints such as muffler size and cost as well as back pressure present the major challenge in muffler design. The purpose of this work is to optimize the acoustic performance of low-cost simple geometry mufflers using MPP and to find the best shape design under a limited space constraint aiming at improving the acoustic performance of automotive engines. On the basis of linear plane wave theory, the four-pole matrix for two wave guides coupled via an MPP tube is derived and used to compute the transmission loss. Two different procedures to optimize the muffler performance, the internal design and wall damping methods, are used. The muffler internal structure is firstly chosen using the acoustically based method and then numerically optimized by maximizing its transmission loss. Different methods to improve the MPP wall impedance via its geometry and the back cavity dimension are also presented and compared using the 3-D FEM. A new optimized muffler is proposed and experimentally used to study the acoustic performance of a four-cylinder diesel engine and its performance compared to the existing straight through resonator muffler. It is shown that the new optimized muffler reduces the A-weighted engine noise by 5 dB and also reduces the brake specific fuel consumption by 6% at the same operating conditions. (C) 2016 Institute of Noise Control Engineering.