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In this work a multilevel CFD analysis have been applied for the design of an intake air-box with improved characteristics of noise reduction and fluid dynamic response. The approaches developed and applied for the optimization process range from the 1D to fully 3D CFD simulation, exploring hybrid approaches based on the integration of a 1D model with quasi-3D and 3D tools. In particular, the quasi-3D strategy is exploited to investigate several configurations, tailoring the best trade-off between noise abatement at frequencies below 1000 Hz and optimization of engine performances. Once the best configuration has been defined, the 1D-3D approach has been adopted to confirm the prediction carried out by means of the simplified approach, studying also the impact of the new configuration on the engine performances.

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.

In the last decades numerical simulations have become reliable tools for the design and the optimization of silencers for internal combustion engines. Different approaches, ranging from simple 1D models to detailed 3D models, are nowadays commonly applied in the engine development process, with the aim to predict the acoustic behavior of intake and exhaust systems. However, the acoustic analysis is usually performed under the hypothesis of infinite stiffness of the silencer walls. This assumption, which can be regarded as reasonable for most of the applications, can lose validity if low wall thickness are considered. This consideration is even more significant if the recent trends in the automotive industry are taken into account: in fact, the increasing attention to the weight of the vehicle has lead to a general reduction of the thickness of the metal sheets, due also to the adoption of high-strength steels, making the vibration of the components a non negligible issue.

In this paper a three-dimensional time-domain CFD approach has been employed to predict and analyze the acoustic attenuation performance of complex perforated muffler geometries, where strong 3D effects limit the validity of the use of one-dimensional models. A pressure pulse has been imposed at the inlet to excite the wave motion, while unsteady flow computation have been performed to acquire the time histories of the pressures upstream and downstream of the silencer. Pressures in the time domain have been then transformed to acoustic pressures in the frequency domain, to predict the transmission loss.

Automotive exhaust systems give a major contribution to the sound quality of a vehicle and must be properly designed in order to produce acceptable acoustic performances. Obviously, noise attenuation is strictly related to the used materials and to its internal geometry. This last influences the wave propagation and the gas-dynamic field. The purpose of this paper is to describe advantages and disadvantages of different numerical approaches in evaluating the acoustic performance in terms of attenuation versus frequency (Transmission Loss) of a commercial two perforated tube muffler under different conditions. At first, a one-dimensional analysis is performed through the 1D GTPower® code, solving the nonlinear flow equations which characterize the wave propagation phenomena. The muffler is characterized as a network of properly connected pipes and volumes starting from 3D CAD information. Then, two different 3D analyses are performed within the commercial STS VNOISE® code.

The characteristics of the intake system affect both engine power output and gas-dynamic noise emissions. The latter is particularly true in downsized VVA engines, where a less effective attenuation of the pressure waves is realized, due to the intake line de-throttling at part-load. For this engine architecture, a refined air-box design is hence requested. In this work, the Transmission Loss (TL) of the intake air-box of a commercial VVA engine is numerically computed through a 3D FEM approach. Results are compared with experimental data, showing a very good correlation. The validated model is then coupled to an external optimizer (ModeFRONTIERTM) to increase the TL parameter in a prefixed frequency range. The improvement of the acoustic attenuation is attained through a shape deformation of the inner structure of the base device, taking into account constraints related to the device installation inside the engine bay.

For vibration and acoustics vehicle development, one of the main challenges is the identification and the analysis of the noise sources, which is required in order to increase the driving comfort and to meet the stringent legislative requirements for the vehicle noise emission. Transfer Path Analysis (TPA) is a fairly well established technique for estimating and ranking individual low-frequency noise or vibration contributions via the different transmission paths. This technique is commonly applied on test measurements, based on prototypes, at the end of the design process. In order to apply such methodology already within the design process, a contribution analysis method based on dynamic substructuring of a multibody system is proposed with the aim of improving the quality of the design process for vehicle NVH assessment and to shorten development time and cost.

The acoustic simulation of internal combustion engine exhaust systems is an important aspect to meet customer expectations and legislation targets. One dimensional gas dynamic simulation tools are used for the calculation of the exhaust orifice noise in the early stages of the engine development process. This includes the prediction of the acoustic performance of individual components in the exhaust line. One common element used in exhaust systems to increase the acoustic damping is the plug flow muffler. This study looks at the prediction of acoustic performance of various plug mufflers at different flow velocities. These include a single plug muffler, a double plug muffler and an eccentric plug muffler with different porosities for the perforated sections. To this purpose a generic 3D cell approach was developed and applied.

This paper describes the development, application and comparison of two different non-linear numerical codes, respectively based on a 1D and 3D schematization of the geometrical domain, for the prediction of the acoustic behavior of common silencing devices for i.c. engine pulse noise abatement. A white noise approach has been adopted and applied to predict the attenuation curves of silencers in the frequency domain, while a non-reflecting boundary condition was used to represent an anechoic termination. Expansion chambers, Helmholtz and column resonators, Herschel-Quincke tubes have been simulated by both the 1D and the 3D codes and the results compared to the available linear acoustic analytical solutions. Finally, a hybrid approach, in which the CFD code has been integrated with the 1D model, is described and applied to the simulation of a single cylinder engine. The computed results are compared to the measured pressure waves and emitted sound pressure level spectra.

In recent years, great interest on NVH characteristics of vehicles has been paid by all the big automotive manufacturers. Interior acoustic comfort is now one of the main key factors in vehicle development process, since it contributes to improved product overall quality. Therefore, in automotive industry advanced NVH refinement needs to work in synergy with all research activities. Assessing the level of experienced noise in interior cabin requires particular arrangements for ensuring adequate measurement accuracy (AC system off, closed window, etc.). The use of parameters such as the level of seat vibration, not affected by the acoustic field conditions inside the vehicle, could facilitate experiments in parallel with engine/vehicle calibration activities.

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.

This work presents the results of an experimental investigation on a GDI injector, in order to analyze fuel injection process and atomization phenomenon, correlating imaging and vibro-acoustic diagnostic techniques. A single-hole, axially-disposed, 0.200 mm diameter GDI injector was used to spray commercial gasoline in a test chamber at room temperature and atmospheric backpressure. The explored injection pressures were ranged from 5.0 to 20.0 MPa. Cycle-resolved acquisitions of the spray evolution were acquired by a high-speed camera. Simultaneously, the vibro-acoustic response of the injector was evaluated. More in detail, noise data acquired by a microphone sensor were analyzed for characterizing the acoustic emission of the injection, while a spherical loudspeaker was used to excite the spray injection at a proper distance detecting possible fuel spray resonance phenomena.