Measurements and Simulations of Acoustical Performance of Plastic Air Intake Manifolds for Internal Combustion Engines

Automotive engine manufacturers are focusing increasingly their attention on noise generated by air intake systems. In particular in recent years the increased usage of plastics for air intake manifold (AIM) production, in place of metallic materials, made the NVH optimization more complicated. In this framework, it is very important not only the minimization of the noise generated via fluid propagation (orifice-noise from inlets) but also of the noise radiated via the coupled fluid-structure interaction. In this work acoustical performance of an AIM prototype has been experimentally and numerically investigated. From the experimental point of view, the acoustic analysis was performed by means of acoustic intensity measurements around the body. In order to minimize the noise contribution from all the other sources of an operating engine, the AIM was assembled on an engine head which was mounted on a dynamic flow test bench, where the intake valve-train was driven by an electrical motor. The intake orifice noise was differently treated, both leaving the orifice open and employing a dissipative muffler. Simulations through a coupled fluid-structure approach were performed. The normal modes of the structure were previously calculated on a fully-detailed FEM model and checked through accelerometric data; material properties could then be properly chosen. Measured data of the pressure pulsations at the inlet valves was used as excitation and applied to a coarsened acoustic Indirect-BEM model of the AIM coupled with a structural FEM one. Tuning of experimental and numerical acoustic data was useful for defining a practical analysis procedure for NVH design of plastic AIMs.