A Comparison Between External and Internal Resonators Employment to Reduce the Gas-Dynamic Noise of a SI Engine 2014-01-2864

This paper reports 1D and 3D CFD analyses aiming to improve the gas-dynamic noise emission of a downsized turbocharged VVA engine through the re-design of the intake air-box device, consisting in the introduction of external or internal resonators.

Nowadays, modern spark-ignition (SI) engines show more and more complex architectures that, while improving the brake specific fuel consumption (BSFC), may be responsible for the increased noise radiation at the engine intake mouth. In particular VVA systems allow for the actuation of advanced valve strategies that provide a reduction in the BSFC at part load operations thanks to the intake line de-throttling. In these conditions, due to a less effective attenuation of the pressure waves that travel along the intake system, VVA engines produce higher gas-dynamic noise levels. The worsening of the engine gas-dynamic performance can be compensated with a partial re-design of the air-box device, without significantly penalizing the engine power output. In order to find new design configurations of the air-box device capable of improving the noise levels, different numerical models can be successfully employed.

In the present work, a detailed 1D engine model is firstly developed and validated against the experimental data at full load operations. 1D model is realized within GT-Power™ software and it utilizes proper user routines for the modeling of the turbulence and combustion process and for the handling of different intake valve strategies. The 1D engine model also includes a refined user model of the turbocharger able to better describe the acoustic behavior of the device.

The engine model allows for the prediction of the main overall engine performances and the gas-dynamic noise with good accuracy. It also provides a first estimation of the gas-dynamic noise and gives reliable boundary conditions for the subsequent unsteady 3D CFD analyses, allowing to obtain a more accurate noise prediction.

A proper Helmholtz resonator is designed and virtually installed along the inlet pipe of the air-box device. An additional geometrical configuration of the air-filter box, that includes an internal resonator, obtained through the insertion of inner walls, is considered, too. The effectiveness of the redesigned air-box configurations, are firstly tested in terms of Transmission Loss characteristics, and in terms of gasdynamic noise abatement, as well.