Analysis and Design of an Intake Filter Box for a Downsized VVA Engine

The present paper reports 1D and 3D CFD analyses of the air-filter box of a turbocharged VVA engine, aiming to predict and improve the gas-dynamic noise emissions through a partial re-design of the device. First of all, the gas-dynamic noise at the intake mouth is measured during a dedicated experimental campaign. The developed 1D and 3D models are then validated at full load operation, based on experimental data. In particular, 1D model provides a preliminary evaluation of the radiated noise and simultaneously gives reliable boundary conditions for the unsteady 3D CFD simulations. The latter indeed allow to better take into account the geometrical details of the air-filter and guarantee a more accurate gas-dynamic noise prediction. 3D CFD analyses put in evidence that sound emission mainly occur within a frequency range of 350 to 450 Hz. Starting from the above result, the original air-box design is modified through the installation of a single Helmholtz resonator, taking into account layout constraints and the influence on engine performance, as well. First, the isolated air-box is studied through a 3D FEM approach to compute the Transmission Loss (TL) parameter both for the original and the modified design. This analysis is employed to verify the noise abatement in the frequency range of interest, for a zero-mean flow. Then, the new intake system configuration is investigated under actual engine operation, through unsteady 3D CFD simulations. The resulting reduction in the gas-dynamic noise is verified both in terms of overall radiated SPL and frequency spectrum at full and part load operating conditions, as well. The proposed integrated 1D-3D approach demonstrated to be a useful tool for the design and the analysis of new geometrical intake system configurations, aiming to improve the engine acoustic performance without significant penalties on the delivered power and fuel consumption.