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How Can Active Exhaust Systems Contribute to the Reduction of CO2 Emission and Comply with Future Pass-by Noise Limits?

Eberspaecher Exhaust Technology GmbH-Jan Krueger, Peter Wink, Maike Werner
  • Technical Paper
  • 2020-01-1534
To be published on 2020-06-03 by SAE International in United States
The pass-by noise limits of passenger vehicles according to ISO 362 / R51.3 will be further reduced by 2 dB in 2024 in Europe. Since the pass-by noise is substantially influenced by exhaust noise, the effort for the exhaust system needs to be increased. This results in systems with larger mufflers or higher backpressure. However, the more stringent CO2-emission targets require ever more efficient powertrains, which calls for rather lower backpressure to optimize the engine design. This paper describes, how compact active exhaust lines can support a design for low backpressure and high acoustic attenuation at the same time. For two passenger vehicle with gasoline engines, active exhaust lines are investigated in detail and the results are compared to the series production exhaust lines. Thus, in one exemplary case, the pass-by noise of a limousine could be reduced from 70 dB(A) to 68 dB(A) without any change in the vehicle design except the improved exhaust system.
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Resabtors - Advanced Multi-Material Muffler Designs for Clean Air Applications

Umfotec GmbH-Ralf Buck, Ingo Krebs
  • Technical Paper
  • 2020-01-1554
To be published on 2020-06-03 by SAE International in United States
The development and production of resonators on the charged air side of combustion engines require profound base of knowledge in designing, simulating and the production of such parts in different materials (aluminum, copper, stainless steel and technical plastic). As combustion engines are under constant discussion, this existing knowledge base should be used for other applications within and outside the automotive industry. Very quickly it became apparent that new challenges often require completely new solutions, designs and materials to meet the requirements of flow noise reducing parts. For example, for clean air applications mufflers based on “special treated foams” and “meta-materials” can be introduced. These materials offer new potentials for tuning of the frequency range and allow improved broad banded flow noise attenuation. Such parts are named “Resabtors” in order to take respect of the different flow noise attenuation principles resonation and absorbing. Since in almost all applications the installation space is very limited, it was necessary to combine these two principles into one component. This results into significant challenges to identify the properties of the…
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Research on Measurement Method of Aerodynamic Noise of Reactive Muffler

Wuhan University of Technology-Liping Xie, Zhien Liu, Zhu Yawei, Kai Liu, Chenhui Ye
  • Technical Paper
  • 2020-01-0423
To be published on 2020-04-14 by SAE International in United States
The aerodynamic noise of the reactive muffler is generated inside the muffler and mixed with the noise of the muffler body, which is difficult to be measured in the exhaust system. Based on two-microphone transfer function method and transmission loss of mufflers in the absence of airflow, this paper proposes a method for measuring the aerodynamic noise of the muffler. On the built-in muffler aerodynamic noise test bench, a special sampling tube was designed to measure the aerodynamic noise of the muffler at different flow velocity. For the sound absorption end with large reflection coefficient, the test and simulation data have large error at low frequency, and a correction formula that can eliminate the reflection of sound waves at the end of the test pipeline and form multiple reflections in the upstream and downstream is derived. The test results of the muffler on the test bench show: The aerodynamic noise data obtained by the sampling pipe is basically consistent with the simulation results by means of leading out measurement, which realizes the measurement of high…
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Innovative Passive Exhaust Valve Improves Sound Quality and Reduces Muffler Volume without Backpressure Penalty

Tenneco, Inc.-Adam Kotrba, Stephen Thomas, Gabriel Ostromecki, Asela Benthara, Nicholas Morley
  • Technical Paper
  • 2020-01-0410
To be published on 2020-04-14 by SAE International in United States
Exhaust systems traditionally require a specific amount of muffler volume to reduce sound levels appropriately. However, as hybridization evolves, the packaging area becomes smaller, reducing available muffler space and requiring alternative solutions to attenuate exhaust sound with less volume. Passive exhaust valves are a key solution, leveraging the physics of the exhaust (flow, temperature, and pressure) to cycle the valve. Passive exhaust valves typically operate in a closed position under low-flow conditions (low engine speeds and loads), which helps to reduce low-frequency boom, moderately increasing backpressure when it is not detrimental to engine efficiency. Conversely, under higher engine speed and load operating conditions, when exhaust flow increases and backpressure is critical to achieve desired power output, the passive valve opens to reduce its impact. Such valves are often positioned within the muffler, fully immersed and exposed to exhaust heat, humidity, and corrosion, as well as vibrations from road and engine loads. A next-generation passive valve is detailed in this paper, highlighting its operating advantages, including compact size (fits inside mufflers), low mass (all sheet metal…
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Modelling for Collective Effect of Muffler Geometric Modifications and Blended Microalgae Fuel Use on Exhaust Performance of a Four-Stroke Diesel Engine: A Computational Fluid Dynamics Approach

Lovely Professional University-Sumit Kanchan, Rajesh Choudhary, Chavagani Brahmaiah
University of Kashmir-Shahid Qayoom
  • Technical Paper
  • 2019-28-2377
Published 2019-11-21 by SAE International in United States
Engine performance significantly depends on the effective exhaust of the combustion gases from the muffler. With stricter BSVI norms more efficient measures have to be adopted to reduce the levels of emissions from the exhaust to the atmosphere. Muffler along with reducing the engine noise is intended to control the back pressure as well. Back pressure change has a significant effect on muffler temperature distribution which affects the NOx emission from the exhaust. Many research communications have been made to reduce the exhaust emissions like HC, CO and CO2 from the exhaust by using different generation biofuels as an alternative fuel, yet they have confronted challenges in controlling the NOx content from the exhaust.This work presents the combined effect of Muffler geometry modifications and blended microalgal fuel on exhaust performance with an aim to reduce NOx emission form a four-stroke engine. In this exertion, the computational fluid dynamics model is developed to analyze the effect of muffler geometry modification on vital exhaust parameters of an engine. The engine is powered with a blend of chlorella…
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Design and Development of an Exhaust Muffler with Improved Transmission Loss for a Naturally Aspirated Diesel Engine

Prince Shri Venkateshwara Engg. College-Edison Rajasingh
SRM Institute of Science and Technology-Sundararaj Senthilkumar
Published 2019-10-11 by SAE International in United States
In the last two decades, most of the advances in exhaust systems such as acoustic filters and mufflers had been developed to attenuate noise levels and emissions as per environment norms. The purpose of this research work is to design, analyze and test an exhaust muffler in order to determine the pressure drop and noise reduction in the exhaust system. Computational Fluid Dynamic simulations were performed using ANSYS Fluent 16.2. The muffler diameter and length were chosen where as perforations and baffles were also considered so as to have the maximum pressure drop and noise reduction. This study is aimed at investigating a reactive perforated muffler. Several designs were considered for maximum pressure drop and the best was finally selected for manufacturing. Experimental testing was carried out with the finalized muffler prototype. Further the validation was done on a muffler in which the inlet pressure was found lower than that of the simulated results but the experimental outlet pressure was found higher than the simulated results. The backpressure was found to be less due to…
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Development of a Muffler Insertion Loss Flow Rig

University of Kentucky-Jonathan Chen, D. W. Herrin
Published 2019-06-05 by SAE International in United States
Bench tests are an important step to developing mufflers that perform adequately with acceptable pressure drop. Though the transmission loss of a muffler without flow is relatively simple to obtain using the two-load method, the presence of mean flow modifies the muffler behavior. The development of an insertion loss test rig is detailed. A blower produces the flow, and a silencer quiets the flow. Acoustic excitation is provided by a loudspeaker cluster right before the test muffler. The measurement platform allows for the measurement of flow-induced noise in the muffler. Also, the insertion loss of the muffler can be determined, and this capability was validated by comparison to a one-dimensional plane wave model.
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Numerical Modeling of Internal Helmholtz Resonators Created by Punching Small Holes on a Thin-Walled Tube

University of Kentucky-Hao Zhou, T. W. Wu
Published 2019-06-05 by SAE International in United States
Helmholtz resonators are normally an afterthought in the design of mufflers to target a very specific low frequency, usually the fundamental firing frequency of the engine. Due to space limitations in a complex muffler design, a resonator may have to be built by punching a few small holes on a thin-walled tube to create a neck passage into a small, enclosed volume outside the tube. The short neck passage created by punching a few small holes on a thin-walled tube can pose a great challenge in numerical modeling, especially when the boundary element method (BEM) is used. In this paper, a few different BEM modeling approaches are compared to one another and to the finite element method (FEM). These include the multi-domain BEM implemented in a substructure BEM framework, modeling both sides of the thin-walled tube and the details of each small hole using the Helmholtz integral equation and the hypersingular integral equation, and modeling just the mid surface of the thin-walled tube. The FEM and BEM solutions are used to estimate the effective neck…
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Multi-Physics and CFD Analysis of an Enclosed Coaxial Carbon Nanotube Speaker for Automotive Exhaust Noise Cancellation

SAE International Journal of Advances and Current Practices in Mobility

Michigan Technological University-Suraj Madhav Prabhu, Andrew Barnard, Steven Senczyszyn
  • Journal Article
  • 2019-01-1569
Published 2019-06-05 by SAE International in United States
Automotive exhaust noise is one of the major sources of noise pollution and it is controlled by passive control system (mufflers) and active control system (loudspeakers and active control algorithm). Mufflers are heavy, bulky and large in size while loudspeakers have a working temperature limitation. Carbon nanotube (CNT) speakers generate sound due to the thermoacoustic effect. CNT speakers are also lightweight, flexible, have acoustic and light transparency as well as high operating temperature. These properties make them ideal to overcome the limitations of the current exhaust noise control systems. An enclosed, coaxial CNT speaker is designed for exhaust noise cancellation application. The development of a 3D multi-physics (coupling of electrical, thermal and acoustical domains) model, for the coaxial speaker is discussed in this paper. The model is used to simulate the sound pressure level, input power versus ambient temperature and efficiency. The 3D model provides accurate results of the temperature profile and heat flow as compared to a 2D model. Also, the flow of exhaust gases can be efficiently modeled using a 3D model. The…
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Engine Exhaust Noise Optimization Using Sobol DoE Sequence and NSGA-II Algorithms

Tafe Motors and Tractors Limited-Ishwinder Pal Singh Sethi, Devendra Nene, Anand Shivajirao Patil
Published 2019-06-05 by SAE International in United States
Exhaust muffler is one of the most important component for overall vehicle noise signature. Optimized design of exhaust system plays a vital role in engine performance as well as auditory comfort. Exhaust orifice noise reduction is often contradicted by increased back pressure and packaging space. The process of arriving at exhaust design, which meets packaging space, back pressure and orifice noise requirements, is often manual and time consuming. Therefore, an automated numerical technique is needed for this multi-objective optimization.In current case study, a tractor exhaust system has been subjected to Design of Experiments (DoE) using Sobol sequencing algorithm and optimized using NSGA-II algorithm. Target design space of the exhaust muffler is identified and modeled considering available packaging constrain. Various exhaust design parameters like; length of internal pipes, location of baffles and perforation etc. are defined as input variables. Performance objective of back pressure and sound pressure level has also been defined in simulations workflow.Exhaust orifice noise has been reduced with significant reduction in overall simulations time. The optimal design is achieved satisfying all constrains leading…
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