Transmission loss and gas-dynamic noise analyses of a downsized spark ignition engine

Experimental and numerical analyses of a turbocharged spark-ignition engine, aiming to characterize the gas-dynamic noise radiated at the intake mouth of the engine, are presented. The radiated noise level is measured on the production engine, during a dedicated experimental campaign. The analysis of the measured frequency spectra allows to identify the frequency range where most of the acoustic energy is contained, and gives the possibility to select the design modifications required to improve the acoustic performance of the component under investigation. A Helmholtz resonator of proper resonance frequency is installed upstream the original air-box. A three-dimensional finite element method approach computes the transmission loss parameter for the original and the modified designs, as well. A more refined transmission loss analysis is carried out to take into account the effects exerted by the structural participation. A onedimensional model of the original propulsion system allows to forecast the engine performance data and the in-cylinder pressure cycles. In addition, it provides a preliminary evaluation of the radiated noise and gives boundary conditions for unsteady three-dimensional computational fluid dynamics simulations. The latter is utilized to obtain a reduction in terms of gas-dynamic noise through the introduction of the Helmholtz resonator.