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In an Internal Combustion Engine, the design of the intake system is a very critical aspect since it affects both the engine power output and noise emissions at the intake side. In particular, downsized VVA engines typically produce higher gas-dynamic noise levels since, due to the intake line de-throttling at part-load, a less effective attenuation of the pressure waves is realized. In this work, the acoustic performance of the intake air filter of a commercial VVA engine is numerically and experimentally analyzed. In particular, a FEM model of the system is realized in order to compute the Transmission Loss (TL) parameter of the base device. The numerical analysis accounts of fluid-structure interaction, which gives the possibility to determine the effect of structure participation on the TL profile. Contemporarily, the experimental tests are performed on an acoustic test bench based on the multi-microphone technique for the evaluation of the acoustic parameters.

The acoustic performance of mufflers with single-inlet and single-outlet are well described using Insertion Loss (IL) and Transmission Loss (TL). These parameters represent the acoustic damping on the engine emission and on the incident pressure wave respectively. However, for mufflers with multi-inlet these parameters depend also on the sources characteristics, as consequence their use is quite difficult. In the present work the acoustic performance of a double-inlet and single-outlet muffler are experimentally evaluated in terms of reflection and transmission coefficients of each port of the muffler itself. These coefficients are used to evaluate the Insertion Loss of the manifold muffler taking into account specific sources on the inlets. The characteristic coefficients are also used to predict the acoustic emission of the manifold muffler using a known engine source on the two inlets.