Hans Rämmal

Investigations of Automotive Turbocharger Acoustics

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 turbocharge ...

Acoustical Methods for Investigating Turbocharger Flow Instabilities

In order to increase the internal combustion engine efficiency turbocharging is today widely used. The trend, in modern engine technology, is towards higher boost pressures while keeping the combus ...

Experimental determination of sound transmission in turbo-compressors

In this paper experimental procedures to determine the sound transmission through automotive turbo-charger compressors are described. An overview of a unique turbocharger testing facility establish ...

Sound reflection at an open end of a circular duct exhausting hot gas.

Sound reflection from hot flow duct openings is a classical problem in acoustics. In practice this is important for effective modelling and prediction off noise radiation from engine exhaust system ...

Experimental Facility for the Complete Determination of Sound Transmission in Turbochargers

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.

Sound transmission in automotive turbochargers

In search for quieter engines there is a need for a better understanding of the acoustic properties of engine intake and exhaust system components. Besides mufflers which have the purpose of reducing pressure pulses originating from the internal combustion (IC) engine, there are many components in a modern car exhaust and intake system, e.g., air-filters, coolers, catalytic converters, particulate filters - all having an effect on the pressure pulses or sound field in the system. In this work the focus is on the turbocharged IC-engine where both, sound scattering (reflection and transmission) and sound generation from automotive turbochargers are studied. In addition, sound reflection from an open ended pipe, such as the tailpipe of an IC-engine exhaust is investigated. Accurate and efficient methods to fully characterize turbochargers by measuring the acoustic two-port have been developed. Compared to earlier work, a number of modifications are suggested for improving the quality of the results. A study on three different automotive turbochargers is also presented, including data for sound scattering for both the compressor and turbine. The results for the transmission of sound, which is of interest for the ability of a turbocharger to reduce noise coming from the engine, is plotted for all tested cases against a dimensionless frequency scale (Helmholtz-number). This makes it possible to generalize the result in order to draw conclusions about the behavior for any turbocharger. The sound generation was also studied and three different methods to estimate the sound power are suggested. The methods were used to investigate sound generation at different operating points and identify source mechanisms for a turbocharger compressor. An accurate method for measuring the reflection of plane acoustic waves from a pipe termination in a duct with hot gas flow has been developed and tested. Representing the acoustical conditions at an exhaust tail-pipe, the data obtained is important for effective modeling of exhaust systems. The experimental results of the reflection coefficient were compared with Munt`s theory on flow duct openings. The measurements were carried out for air jet velocities up to Mach 0.4 and for flow temperatures up to 100°C in order to study temperature effects on the reflection properties. It was concluded, that the experimental results agree well with the Munt theory.

Testrig for Characterization of Turbo-compressor Acoustic Properties

The aim of this paper is to present a description of a novel experimental facility designed for the acoustical characterization of turbochargers. The facility is created to determine both the passive (scattering) and active (source) acoustic properties of automotive turbochargers. In this paper the experimental procedures for the determination of the scattering data for automotive turbo-chargers at realistic operating conditions will be described. The first experimental results obtained for a Volvo passenger car turbo-compressor are presented for several operating conditions.

A Novel Design for Cruiser Type Motorcycle Silencer Based on Micro-Perforated Elements

Regulations stipulating the design of motorcycle silencers are strict, especially when the unit incorporates fibrous absorbing materials. Therefore, innovative designs substituting such materials while still preserving acceptable level of characteristic sound are currently of interest. Micro perforated elements are innovative acoustic solutions, which silencing effect is based on the dissipation of the acoustic wave energy in a pattern of sub-millimeter apertures. Similarly to fibrous materials the micro-perforated materials have been proved to provide effective sound absorption in a wide frequency range. Additionally, the silencer is designed as a two-stage system that provides an optimal solution for a variety of exploitation conditions. In this paper a novel design for a cruiser type motorcycle silencer, based on micro-perforated elements, is presented. It has been demonstrated that the micro-perforated elements can successfully be used to achieve high attenuation of IC-engine noise in strictly limited circumstances. A technical description of the design and manufacturing of the prototype silencer is given and technological issues are discussed. The acoustical and aerodynamical performance of the silencer is characterized by transmission loss and pressure drop data. The influence of the two-stage system valve operation has been analyzed by studying the acoustics data and engine output characteristics. In addition to the experimental investigations, numerical 1-D models were developed for the optimization of the silencer geometry and the results are compared in a number of operating conditions. The studies have resulted in development of a silencer system for a small series cruiser type motorcycle. The first silencer prototypes have been tested on the motorcycle. While maintaining acceptable pressure drop characteristics, it has proven to comply with standard noise criteria without incorporating fibrous materials. The radiated motorcycle sound, as one of the key features of successful design, has been evaluated. The sound design has been recognized as well suitable for the product.

Test-rig for Complete Acoustic Characterization of Turbochargers

The aim of this paper is to present description of a novel experimental facility designed and set up in KTH Cicero Centre for complete acoustic characterization of turbochargers. The facility is created to determine both the passive (scattering) and active (source) acoustic properties of automotive turbochargers. In this paper the currently most accurate experimental technique to determine the passive acoustic effect of the turbocharger is described. A detailed overview of the test-rig is given together with the mathematical procedures followed to obtain the acoustic 2-port data for turbochargers. The results, including transmission loss and scattering matrix elements, are presented for the compressor and turbine side of a typical automotive turbocharger working in a number of different operating conditions. The influence of the operating conditions on the passive acoustic effect of the device is studied and summarized.