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Regulations stipulating the design of motorcycle silencers are strict, especially when the unit incorporates fibrous absorbing materials. Therefore, innovative designs substituting such materials while still preserving acceptable level of characteristic sound are currently of interest. Micro perforated elements are innovative acoustic solutions, which silencing effect is based on the dissipation of the acoustic wave energy in a pattern of sub-millimeter apertures. Similarly to fibrous materials the micro-perforated materials have been proved to provide effective sound absorption in a wide frequency range. Additionally, the silencer is designed as a two-stage system that provides an optimal solution for a variety of exploitation conditions. In this paper a novel design for a cruiser type motorcycle silencer, based on micro-perforated elements, is presented.

In this paper the acoustic performance of silencers has been investigated. The experimental techniques to study the attenuation of a silencer are in focus. A novel test procedure has been described and used to determine the sound transmission through the silencers in hot mean flow conditions. The experiments have been carried out on two motorcycle engine silencers with different design. The results analyzed and discussed clearly present the influence of the induct flow conditions on the sound transmission loss of the silencer.

As a suitable replacement for prevalent but environmentally hazardous fibrous materials used in exhaust system silencers, innovative micro-perforated (MP) elements have been progressively implemented for internal combustion engine noise control during the past decades. Although MP elements are already massproduced for IC engine noise control, surprisingly few scientific publications can still be found on the endurance of these MP elements. Recently the reliability of MP element was studied by the authors for a small four-stroke petrol engine silencer application. The results clearly demonstrated that the performance of the micro-perforated elements is influenced by the contamination of residual combustion products of the exhaust gas. In this paper the endurance of MP element tested in small industrial diesel engine application of a novel unmanned ground vehicle (UGV) has been treated.