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Increased demands for reduction of fuel consumption and CO2 emissions are driven by the global warming. To meet these challenges with respect to the passenger car segment the strategy of utilizing IC-engine downsizing has shown to be effective. In order to additionally meet requirements for high power and torque output supercharging is required. This can be realized using e.g. turbo-chargers, roots blowers or a combination of several such devices for the highest specific power segment. Both turbo-chargers and roots blowers can be strong sources of sound depending on the operating conditions and extensive NVH abatements such as resonators and encapsulation might be required to achieve superior vehicle NVH. For an efficient resonator tuning process in-duct acoustic source data is required. No published studies exists that describe how the gas exchange process for roots blowers can be described by acoustic sources in the frequency domain.

Air pollution caused by exhaust particulate matter (PM) from vehicular traffic is a major health issue. Increasingly strict regulations of vehicle emission have been introduced and efforts have been put on both the suppression of particulate formation inside the engine cylinders and the development of after-treatment technologies such as filters. With modern direct injected engines that produce a large number of really small sub-micron particles, the focus has increased even further and now also includes a number count. The problem of calculating particle trajectories in flow ducts like vehicle exhaust systems is challenging but important to further improve the technology. The interaction between particles and oscillating flows may lead to the formation of particle groups (regions where the particle concentration is increased), yielding a possibility of realizing particle agglomeration.

The paper gives an overview of techniques used for characterization of IC-engines as acoustic sources of exhaust and intake system noise. Some recent advances regarding nonlinear source models are introduced and discussed. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is often the linear time invariant one-port model. The acoustic source data is obtained from experimental tests or from 1-D CFD codes describing the engine gas exchange process. The IC-engine is a high level acoustic source and in most cases not completely linear. It is therefore of interest to have models taking weak non-linearity into account while still maintaining a simple method for interfacing the source model with a linear frequency domain model for the attached exhaust or intake system.

The paper gives an overview of techniques used for characterization of IC-engines as acoustic sources of exhaust and intake system noise. Some recent advances are introduced and discussed. Linear frequency domain prediction codes are frequently used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust and intake systems, even though nonlinear time domain models are also developing fast. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is often the linear time invariant one-port model. The acoustic source data is obtained from experimental tests or from 1-D CFD codes describing the engine gas exchange process. Multi-load methods and especially the two-load method are most commonly used to extract the source data. The IC-engine is a high level acoustic source and in most cases not completely linear.

Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the present work is to develop acoustic models for these resonators where relevant effects such as the effect of a realistic mean flow on losses and 3D effects are considered. An experimental campaign has been performed where the two-port matrices and transmission loss of sample resonators have been measured without flow and for two different mean flow speeds. Models for two resonators have been developed using 1D linear acoustic theory and a FEM code (COMSOL Multi-physics). For some resonators a separate linear 1D Matlab code has also been developed.

In this paper an overview of recent experimental studies performed at KTH on the sound transmission and sound generation in turbochargers is presented. The compressor and turbine of the turbochargers are treated as acoustic active 2-ports and characterized using the unique experimental test facility established at KTH. The 2-port model is limited to the plane wave range so for higher frequencies the propagating acoustic power is estimated using an average based on pressure cross-spectra. A number of automotive turbochargers have been studied for a variety of operating conditions systematically selected from the compressor and turbine charts. The paper discusses the experimental procedures including special techniques implemented to improve the quality of the data. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are presented.

Analysis of pressure pulsations in ducts is an active research field within the automotive industry. The fluid dynamics and the wave transmission properties of internal combustion (IC) engine intake and exhaust systems contribute to the energy efficiency of the engines and are hence important for the final amount of CO₂ that is emitted from the vehicles. Sound waves, originating from the pressure pulses caused by the in- and outflow at the engine valves, are transmitted through the intake and exhaust system and are an important cause of noise pollution from road traffic at low speeds. Reliable prediction methods are of major importance to enable effective optimization of gas exchange systems. The use of nonlinear one-dimensional (1D) gas dynamics simulation software packages is widespread within the automotive industry. These time-domain codes are mainly used to predict engine performance parameters such as output torque and power but can also give estimates of radiated orifice noise.

Turbochargers are common parts of a modern automotive engine. This paper presents an overview of the recent studies performed in the competence center for gas exchange studies at KTH on the sound transmission in turbochargers. The compressor and turbine of the turbochargers are treated as acoustic 2-ports and the scattering matrix for these devices are determined. A unique experimental facility established in the competence center for gas exchange research at KTH has been utilized to study the turbochargers at a variety of operating conditions systematically selected from compressor and turbine charts. A description of the experimental procedures to determine the acoustic 2-port data including techniques implemented to improve the quality of the results is presented. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are included.

In this paper a unique experimental facility designed for a complete determination of the sound transmission in turbochargers is introduced. The facility can be used to characterize the passive acoustic effect for turbocharger compressors and turbines working in realistic operating conditions by extracting the acoustic two-port data. The acoustic pressure transmission loss results for a passenger car turbocharger compressor and turbine measured in up- and downstream directions regarding the mean flow are presented. The data are obtained for various operating points of the turbocharger and the influence of operating conditions on the sound transmission is discussed.

Non-linear 1-D CFD time domain prediction codes are used to calculate the performance of the gas exchange process for IC-engines. These softwares give time-varying pressures and velocities in the exhaust and intake systems. They could therefore in principle be used to predict radiated orifice noise. However, the accuracy is not sufficient for them to be used as a virtual design tool. More accurate results might be provided by dividing the problem into a source domain and a transmission domain and use linear 3-D frequency domain codes to describe the transmission part. Radiated shell noise and frequency dependent damping could also be included in the frequency domain models. The simplest source model used in the low frequency plane wave range for simulation of dominating engine harmonics is the linear time invariant 1-port model. This acoustic source data is usually obtained from experimental tests where the multi-load methods and especially the two-load method are most commonly used.

Both linear (frequency domain) and non-linear (time domain) prediction codes are used for the simulation of duct acoustics in exhaust systems. Each approach has its own set of advantages and disadvantages. One disadvantage of the linear method is that information about the engine as an acoustic source is needed in order to calculate the insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. This source characterization data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These measurements are time consuming and expensive. However, this data can also be extracted from an existing 1-D non-linear CFD code describing the engine gas exchange process.