Browse Topic: Mufflers

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Numerical Modeling of Internal Helmholtz Resonators Created by Punching Small Holes on a Thin-Walled Tube2019-01-14866/5/2019
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 length commonly used in an analytical solution. The effect of changing the locations of the holes is also investigated.
Zhou, Hao, Wu, T. W.
Engine Exhaust Noise Optimization Using Sobol DoE Sequence and NSGA-II Algorithms2019-01-14836/5/2019
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 to notable productivity improvement.
Sethi, Ishwinder Pal Singh, Nene, Devendra, Shivajirao Patil, Anand
Development of a Muffler Insertion Loss Flow Rig2019-01-14826/5/2019
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.
Chen, Jonathan, Herrin, D. W.
Multi-Physics and CFD Analysis of an Enclosed Coaxial Carbon Nanotube Speaker for Automotive Exhaust Noise Cancellation2019-01-15696/5/2019
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 flow analysis would help understand any flow penetration into the speaker as well as the effect of heat transfer due to the flow. The model is validated by comparing the experimental results with the simulation results. Along with multi-physics simulation, CFD analysis of the coaxial speaker is also studied in this paper. The CFD analysis is focused on the backpressure generated by the speaker and the flow path of the exhaust gases inside the CNT speaker.
Prabhu, Suraj Madhav, Barnard, Andrew, Senczyszyn, Steven
Modelling and Optimization of Plug Flow Mufflers in Emission Control Systems2017-01-17826/5/2017
Large-scale emergency or off-grid power generation is typically achieved through diesel or natural gas generators. To meet governmental emission requirements, emission control systems (ECS) are required. In operation, effective control over the generator’s acoustic emission is also necessary, and can be accomplished within the ECS system. Plug flow mufflers are commonly used, as they provide a sufficient level of noise attenuation in a compact structure. The key design parameter is the transmission loss of the muffler, as this dictates the level of attenuation at a given frequency. This work implements an analytically decoupled solution, using multiple perforate impedance models, through the transfer matrix method (TMM) to predict the transmission loss based on the muffler geometry. An equivalent finite element model is implemented for numerical simulation. The analytical results and numerical results are then evaluated against experimental data from literature. The transmission loss required in each application of the ECS system will vary depending on the noise profile of the generator in question; therefore, it is necessary to have an effective method of redesigning the muffler to meet the design requirements. Prior work on TMM-based muffler shape optimization utilized complex algorithms such as neural networks and simulated annealing. The present study simplifies the process by using the bounded, limited-memory implementation of the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm in a multi-start framework for shape optimization to achieve the desired transmission loss. By constraining the multi-start method with appropriate design limits, the algorithm is initialized at multiple random points within the design space, ensuring that the solution approaches the global optimum when using a sufficiently large number of initializations.
Puthuparampil, Jobin, Pong, Henry, Sullivan, Pierre
Measurement of Flow-Generated Noise inside Mufflers2017-01-17956/5/2017
Flow-generated noise has recently received a lot of attention within the process of designing exhaust and intake systems. Flow-generated noise can limit the amount of sound reduction a muffler can introduce inside ducts. This is more important in the modern system design where mufflers are compact and the flow speeds become higher in different sections inside the muffler. In this paper, three measurement techniques are used to measure the flow-generated noise from a duct element. The first is based on calculating the sound power levels inside a reverberation room according to ISO 3741. The radiated noise is measured from the muffler body as a source of noise, then from the tail pipe as an active one-port source. The second is based on sound power measurements inside the ducts using the active two-port theory. The third is measuring the sound pressure radiation inside an anechoic room. There has been a lot of work done to calculate the flow generated noise from simple duct elements but little has been published on full mufflers. In this paper, a compact muffler was studied. A 1D model based on the two-port theory was built for this muffler and whereas the flow-generation mechanisms were included in the active two-port formulation, and calculated using different scaling laws from literature for different duct elements such as orifices, pipes and open ends. Comparisons between simulations and measurements were performed to prove the reliability of the flow noise simulation technique.
Abosrea, Ahmad, Elnady, Tamer
Active Cancellation of Exhaust Noise over Broad RPM Range with Simultaneous Exhaust Sound Enhancement2017-01-17536/5/2017
Demands for engines to operate at low-frequency firing order are increasing in the automotive market. This requirement is driven by consumer and regulatory demand for vehicles which are more efficient in the use of fuel. As a result, engine and transmission technologies have been developed which permit operation of engines with fewer cylinders at increasingly low RPM’s. The resulting low frequency exhaust noise is more difficult to attenuate than in vehicles in years past. At the same time, vehicles often have less packaging space for mufflers, when larger volume would otherwise be needed to attenuate at lower frequencies. A further challenge is the demand for increasingly refined performance sounds from the exhaust systems of premium cars despite the technical obstacles involved in even maintaining sound quality. Finally, legally permissible sound levels are decreasing in some markets. These market and regulatory demands require new solutions. Technology has been demonstrated using an ANC system. The system uses the operating principle of ANC, using a feed-forward control mechanism. This system has now been demonstrated to attenuate multiple firing orders by sound cancellation down to 1000 RPM on a 4 cylinder gasoline turbocharged engine. It has also been demonstrated to simultaneously attenuate undesirable orders and accentuate desirable orders. This has been demonstrated in a vehicle with a 4 cylinder TC engine and also in a V8 application operating in 4 cylinder mode, where such desired engine order sounds could not be expected typically.
Riddle, Jack Hall, Bemman, Ya-Juan, Frei, Tom, Wu, Sihui, Padalkar, Ishang
Modeling the Sound Pressure Loss of an Electromechanical Active Helmholtz Resonator2017-01-18276/5/2017
A muffler attached to an engine attenuates sound over a dedicated frequency range. This research involves the development of an active muffler that is keyed to the revolutions per minute (rpm) of the engine and suppresses the fundamental frequency being exhausted through the tailpipe. The active muffler consists of a tracking side-branch resonator terminated with a composite piezoelectric transducer. The use of an exponential horn as a resonating cavity and terminated with a composite piezoelectric transducer is presented. This would create Electromechanical Active Helmholtz Resonator (EMAHR) creates a notch that can be moved between 200-1000 Hz. The use of acoustical-to-mechanical, mechanical-to-electrical, and analog-to-digital transformations to develop a system model for the active muffler are presented. These transforms will be presented as two-port network parameters. The use of two-port networks to model the electroacoustic system are a defining factor in the analysis. The two-port network parameters for the pipe, horn and piezoelectric transducer are discussed. Using the developed electroacoustic model in simulation the system can be further developed, specifically the load on the composite piezoelectric transducer. The load can be produced with analog-to-digital, digital, and digital-to-analog circuitry. A microcontroller can be used to perform filtering to produce the desired current from the voltage input, or response of an electrical impedance. This impedance generation with a microcontroller is briefly discussed. The sound pressure level results of the modeling are shown over the frequency range of 200-1000 Hz. The maximum sound pressure loss at these frequencies is characterized by the model for the EMAHR.
Santora, Michael J., Ige, Cyril Gbenga, Otto, Jeff, Egolf, David
A 3D Linear Acoustic Network Representation of Mufflers with Perforated Elements and Sound Absorptive Material2017-01-17896/5/2017
The acoustics of automotive intake and exhaust systems is typically modeled using linear acoustics or gas-dynamics simulation. These approaches are preferred during basic sound design in the early development stages due to their computational efficiency compared to complex 3D CFD and FEM solutions. The linear acoustic method reduces the component being modelled to an equivalent acoustic two-port transfer matrix which describes the acoustic characteristic of the muffler. Recently this method was used to create more detailed and more accurate models based on a network of 3D cells. As the typical automotive muffler includes perforated elements and sound absorptive material, this paper demonstrates the extension of the 3D linear acoustic network description of a muffler to include the aforementioned elements. The proposed method was then validated against experimental results from muffler systems with perforated elements and sound absorptive material.
Veloso, Rafael, Fairbrother, Robert, Elnemr, Yasser
Acoustic Analysis of a Tractor Muffler2017-01-17916/5/2017
Parametric model of a production hybrid (made up of reactive and dissipative elements) muffler for tractor engine is developed to compute the acoustic Transmission Loss (TL). The objective is to simplify complex muffler acoustic simulations without any loss of accuracy, robustness and usability so that it is accessible to all product development engineers and designers. The parametric model is a 3D Finite Element Method (FEM) based built in COMSOL model builder which is then converted into a user-friendly application (App) using COMSOL App builder. The uniqueness of the App lies in its ability to handle not only wide range of parametric variations but also variations in the physics and boundary conditions. This enables designers to explore various design options in the early design phase without the need to have deep expertise in a specific simulation tool nor in numerical acoustic modeling. The accuracy of the model is firstly verified with the results obtained from published literature. The validated models are then extended to the current application. Finally, parametric studies are conducted to obtain the effect of various design parameters and the results are presented as design guidelines which enables efficient and cost effective design of mufflers for tractor engines.
Neihguk, David, Fulkar, Shreyas
Computational Aeroacoustics of Mufflers for Exhaust Air Rush Prediction and Experimental Validation2017-01-13113/28/2017
Air rush noise is exhaust gas driven flow-induced noise in the frequency range of 500-6500 Hz. It is essential to understand the flow physics of exhaust gases within the mufflers in order to identify any counter measures that can attenuate this error state. This study is aimed at predicting the flow physics and air rush noise of exhaust mufflers in the aforementioned frequency range at a typical exhaust flow rate and temperature. The study is performed on two different muffler designs which show a significant air rush noise level difference when tested on the vehicle. The transient computational study was performed using DES with 2nd order spatial discretization and 2nd order implicit scheme for temporal discretization in StarCCM+. To compare with test data, a special flow test stand is designed so that all high and low frequency contents emanating from the engine are attenuated before the flow enters the test part. Also, the flow pulsation is dampened before entering the test parts to agree closely with CFD boundary conditions. The predicted air rush noise from CFD study exhibited good agreement with the experimental results.
Mishra, Suman, Gummadi, Nagesh, Bozzi, Lloyd, Vaughn, Neil, Higley, Rob
Experimental Acoustic Analysis of a Motorcycle Dissipative Muffler in Presence of Mean Flow2016-32-003911/8/2016
In recent years, the motorcycle muffler design is moving to dissipative silencer architectures. Due to the increased of restrictions on noise emissions, both dissipative and coupled reactive-dissipative mufflers have substituted the most widely used reactive silencers. This led to higher noise efficiency of the muffler and size reduction. A dissipative muffler is composed by a perforated pipe that crosses a cavity volume filled by a fibrous porous material. The acoustic performance of this kind of muffler are strictly dependent on the porosity of the perforated pipe and the flow resistivity characteristic of the porous material. However, while the acoustic performance of a reactive muffler is almost independent from the presence of a mean flow for typical Mach numbers of exhaust gases, in a dissipative muffler the acoustic behaviour is strictly linked to the mass flow rate intensity. In this paper, an experimental analysis on a commercial dissipative muffler for motorcycles is presented. More in details, the acoustic performance of the silencer is determined by using a test rig that is based on the multi-microphone technique and the two source method. The acoustic test rig used allows carrying out the measurements in presence of mean flow in order to evaluate the influence of the mean flow on the muffler acoustic performance. The possibility to study the muffler behaviour in presence of mean flow makes the experimental conditions closer to the real operating ones. The aim of the present work is to determine how the acoustic response of a dissipative muffler is influenced by the fluid-dynamic interaction between the mean flow and the flow resistivity chamber.
Fioravanti, Andrea, Vichi, Giovanni, Stiaccini, Isacco, Ferrara, Giovanni, Ferrari, Lorenzo
Research on Integration of Automotive Exhaust-Based Thermoelectric Generator with Front Muffler2016-01-02034/5/2016
In order to make full use of engine exhaust heat, the thermoelectric module been used to contribute to thermoelectric power generation in the automotive. At present, the thermoelectric generators (TEGs) have been developing with continuously advances in thermoelectric technology. And almost all of the existing thermoelectric technologies are adding a gas tank to the vehicle exhaust system which increases the exhaust back pressure and occupying excessive space of the vehicle chassis. In this study, a new TEG integrated with a front silencer muffler (FMTEG) is proposed. The muffler is reshaped as the heat exchanger which has a hexagon cross-section. The water tank and clamping mechanism have been redesigned for the new heat exchanger. The FMTEG system’s dimensions are small that can well meet the installation requirements and has a good compatibility with the vehicle exhaust system. The multi-dimensional computational fluid dynamics (CFD) models have been built to simulate the transmission loss (TL) of the noise, thermal field, pressure field of the integrated heat exchanger. The maximum output power has been calculated. The simulation and calculation results show that FMTEG have a better thermal performance and output power performance than the hollow structure. It has a lower back pressure about 250pa. Meanwhile, the average transmission loss of the FMTEG is about 15dB. The FMTEG’s acoustic performance has been proved that it can meet the requirements of the vehicle. Consequently, the use of the FMTEG with better performance could be effectively achieved.
Deng, Yadong, Liu, Chunhua, Chu, Panqi
Determination of Transmission and Insertion Loss for the General Multi-Inlet Multi-Outlet Case2016-01-13104/5/2016
Prior research on assessing multiple inlet and outlet mufflers is limited, and only recently have researchers begun to consider suitable metrics for multiple inlet and outlet mufflers. In this paper, transmission loss and insertion loss are defined for multiple inlet and outlet mufflers using a superposition method that can be extended to any m-inlet n-outlet muffler. Transmission loss is determined assuming that the sources and terminations are anechoic. On the other hand, insertion loss considers reflections. For both metrics, the amplitude and phase relationship between the sources should be known a priori. This paper explains both metrics, and measurement of transmission and insertion loss are demonstrated for a 2-inlet 2-outlet muffler with good agreement.
Zhang, Yitian, Herrin, David W., Wu, T., Hua, Xin
Research on Acoustic Performance of Automotive Exhaust Thermoelectric Generator2016-01-02204/5/2016
With great development of thermoelectric exhaust heat recovery technology, more and more attention has been paid to optimization of automotive thermoelectric generators (ATEGs). A lot of work has been done on optimization of flow field and thermal analysis. However, investigation on acoustic optimization is rather limited. In this paper, efforts have been paid to study the acoustic performance of a flat-plate TEG, and the feasibility of integration of automotive exhaust thermoelectric generator with muffler was discussed. The internal configuration of heat exchanger looks like “fishbone”. Four factors have been taken into consideration: the spacing of two fins, angle of the fins, the diameter of inlet and outlet of exchanger; and filling sound absorbing material in heat exchanger chamber. Based on these four factors, acoustic analysis was carried out. LMS Virtual.Lab was used to compute the acoustic performance of exhaust-based heat exchanger, and transmission loss (TL) is regarded as the evaluation index for acoustic performance. GT-Suite simulations were used to obtain the pressure drop of TEGs. Results indicate that changing the spacing of two fins and angle of fins have a negligible effect on improving the overall TL of a heat exchanger, decreasing the diameter of inlet and outlet of heat exchanger and filling up the heat exchanger chamber with sound absorbing material improves overall acoustic performance.
Gu, Ban, Yuan, Xiaohong
Coupled CFD and Vibro-Acoustic Modeling of Complex-Shaped Mufflers Accounting for Non-Uniform Mean Flow Effects2015-01-23136/15/2015
Flow strongly affects the propagation of acoustics wave transmission within a duct and this must be addressed by the vibro-acoustic modelling of duct systems subject to non-uniform flow. Flow impacts both the effective sound propagation speed in a duct and refracts the sound towards or away from the duct walls depending on whether the acoustic waves are propagating in the direction of the flow or against the flow. Accurate modeling of the acoustic propagation within a duct is crucial for design and “tuning” of muffler systems that need to strongly attenuate narrowband acoustic sources from the engine. Muffler systems that may avoid matching acoustic resonances to engine narrowband sources when no flow is present may experience shifting of resonances to frequencies that match engine sources and cause problems when the flow during a real operating condition is present. Therefore accounting for detailed flow effects on the acoustic propagation and the modal characteristics of the muffler system is essential for effective design. However, for real-life, complex geometries, flow patterns have no analytical solution and have to be determined by means of computational fluid dynamics (CFD). This paper describes an automated process for coupling acoustic finite element (FE) muffler vibro-acoustic design to an open source computational fluid dynamics (CFD) solver whose predicted results are automatically returned and used to generate muffler noise attenuation predictions accounting for flow effects. A validation case study showing the ability for a non-CFD expert modeler to obtain accurate muffler predictions for cases of non-uniform flow is presented. This approach can support a broad range of muffler designs and can represent a significant savings of testing and development time. Limitations and future steps for this modeling approach are discussed.
Gardner, Bryce, Mejdi, Abderrazak, Musser, Chadwyck, Chaigne, Sébastien, De Campos Macarios, Tiago
A Comparison of the Transfer and Scattering Matrix Approaches for Determining Muffler Transmission Loss using the Two Load Method2015-01-23086/15/2015
The two-load method is commonly applied to determine the transmission loss for a muffler especially if an impedance tube rig is used. Although one procedure and algorithm is detailed in ASTM E2611, the quality of the transmission loss curve is dependent on several factors that are not discussed in detail in the standard. In this paper, several practical concerns are investigated including (1) the number of channels used in the measurement, (2) the selection of the reference channel, and (3) the choice of data processing algorithm (transfer or scattering matrix). Results are compared for a simple expansion chamber first, then for mufflers of other types. Recommendations are made for obtaining smoother transmission loss curves for various measurement methods.
Zhang, Yitian, Herrin, David W.
Pressure Drop Characteristics of Perforated Pipes with Particular Application to the Concentric Tube Resonator2015-01-23096/15/2015
The bias flow in Concentric Tube Resonator (CTR) is a flow-induced phenomenon in which the pressure gradient along the radial direction is produced by the kinetic energy of the flow. As a result, the flow dynamics in CTR is characterized by bias flow into the annular cavity in the upstream and outflow from the annular cavity in the downstream of the flow. This is due to the change in direction of the radial component of the bias flow at a point called the point of recovery, as a consequence of mass conservation. The pressure drop of CTR is a complex function of the momentum flux and other geometric parameters such as porosity, open area ratio, discharge coefficient of the perforated holes, bias inflow, bias outflow, grazing flow and length. In this study, numerical experiments are conducted to obtain an empirical formula for the friction factor of perforated pipes which are extensively used in automotive mufflers. The finite element based numerical results are validated with test results reported in the literature and are found to be in good agreement.
Neihguk, David, Munjal, M.L., Prasad, Abhinav
Development of Alternate Split Cat-Con - Muffler Configuration Solution for Front Engine Low Floor Bus2015-01-23116/15/2015
Development of split Catalytic Converter (Cat-Con)-Muffler system was done to be used in front engine low floor (FELF) Bus from perspective of cost saving, modularity and reduction in complexity. This system is developed as an alternate to an existing solution of integrated Cat-Con and muffler. The paper describes the development of a split Cat-Con and muffler exhaust system for a FELF Bus, so as to meet cost and time considerations. The development also had to achieve a feasible solution, which could be installed within the packaging volume of the existing configuration of FELF while meeting the regulatory requirements [1] for Pass by noise (PBN), and at the same time conforming to backpressure limits set for optimum engine performance. Multiple design - prototypes - test iterations were carried out to meet the PBN and back pressure target for FELF Bus. The final solution was developed which achieved both the requirements within the specified space constraints. Solution is based on configuration used in Front Engine Semi Low Floor (FESLF) Bus where a split Cat-Con configuration was already used as it had higher scope for volume where PBN and back pressure conflict didn't rise.
Palsule, Aditya, Budama, Arun, Somasundaraeswer, Nandakumar
The Effect of Phase Difference between Inputs on Insertion Loss for a Two-Inlet Muffler2015-01-23056/15/2015
A recently developed superposition approach for determining the insertion loss of a two-inlet muffler is reviewed. To validate the approach, calculated and measured insertion losses are compared for a small engine muffler with two inlets and one outlet. After which, the phasing between the two inputs is varied and the insertion loss is evaluated. Results show that the insertion loss is strongly affected by the phasing between sources at low frequencies while phasing between sources has a lesser impact at high frequencies. At the conclusion of the paper, the theory for applying the superposition approach to transmission loss is reviewed.
Hua, Xin, Herrin, David W., Zhang, Yitian
Measurement and Simulation of Two-Inlet Single-Outlet Mufflers2015-01-23166/15/2015
In several applications, two-inlet single-outlet mufflers are possible to encounter in exhaust systems. They are usually used to merge two exhaust streams from two similar engines or from two sides of an engine. They have an advantage of reducing the back pressure on the engine(s). There is a lot of published research on the analysis of single-inlet single-outlet mufflers acting as a two-port. On the other hand, there are a few publications on the analysis of two-inlet single-outlet mufflers due to their complexity representing a three-port. A three-port is characterized by a 3×3 Scattering Matrix. The nine elements of this matrix represent the 3 reflection coefficients at each port, and the 6 transmission coefficients between the 3 ports in both directions. In this work, a two-inlet single-outlet muffler is studied. The elements of the scattering matrix were measured using the two-source two-microphone technique with and without flow. These elements were also calculated from 1D simulation using a set of two-port elements representing the internal dimensions of the muffler, and compared to those obtained from the measurement. A similar 1D simulation was performed using Flow two-ports in order to analyze the flow distribution inside the muffler and the pressure drop across both flow paths. The flow distribution is crucial to obtain accurate acoustic predictions. For all cases, there was a very good agreement between the measurement and the simulations.
Elsahar, Weam, Elnady, Tamer
Numerical Determination of Transfer Impedance for Perforates2015-01-23126/15/2015
A simplified method to model perforated tubes in mufflers is the equivalent transfer impedance approach. Various empirical formulas that consider the porosity, hole diameter, wall thickness, and flow type have been proposed to date. They normally work very well under the conditions that the formulas are intended for. However, there are situations that the empirical formulas may not be able to cover. In this paper, we propose a simple BEM-based numerical procedure to determine the transfer impedance from a small perforate sample, and then send the transfer impedance to the muffler BEM model for analysis purposes. Numerical results are verified in three test cases.
Wang, P., Li, J., Wu, T. W.
Exhaust and Muffler Aeroacoustics Predictions using Lattice Boltzmann Method2015-01-23146/15/2015
Exhaust and muffler noise is a challenging problem in the transport industry. While the main purpose of the system is to reduce the intensity of the acoustic pulses originating from the engine exhaust valves, the back pressure induced by these systems must be kept to a minimum to guarantee maximum performance of the engine. Emitted noise levels have to ensure comfort of the passengers and must respect community noise regulations. In addition, the exhaust noise plays an important role in the brand image of vehicles, especially with sports car where it must be tuned to be “musical”. However, to achieve such performances, muffler and exhaust designs have become quite complex, often leading to the rise of undesired self-induced noise. Traditional purely acoustic solvers, like Boundary Element Methods (BEM), have been applied quite successfully to achieve the required acoustic tuning. However, they fail at predicting all of flow-induced noise, as well as non-linear noise dissipation mechanisms. A natural candidate for this type of problem is the use of a Lattice-Boltzmann Method (LBM) solver as a CFD tool. It has already been successfully applied and validated to quantify self-induced noise of mufflers as well as complex acoustic devices performance like acoustic liners. In this paper, a muffler baseline geometry self-induced noise is assessed using the commercial LBM solver PowerFLOW. Noise generation mechanisms are identified and design modifications are proposed to atone it. The given baseline and iterations designs noise mechanisms are analyzed and the obtained noise reductions are compared and discussed.
Mann, Adrien, Kim, Min-Suk, Neuhierl, Barbara, Perot, Franck, Powell, Robert, Rose, Thomas, Krueger, Jan
Experimental Acoustic Characterization of Double-Inlet and Single-Outlet Muffler2015-01-23156/15/2015
The acoustic performance of mufflers with single-inlet and single-outlet are well described using Insertion Loss (IL) and Transmission Loss (TL). These parameters represent the acoustic damping on the engine emission and on the incident pressure wave respectively. However, for mufflers with multi-inlet these parameters depend also on the sources characteristics, as consequence their use is quite difficult. In the present work the acoustic performance of a double-inlet and single-outlet muffler are experimentally evaluated in terms of reflection and transmission coefficients of each port of the muffler itself. These coefficients are used to evaluate the Insertion Loss of the manifold muffler taking into account specific sources on the inlets. The characteristic coefficients are also used to predict the acoustic emission of the manifold muffler using a known engine source on the two inlets. The resulting acoustic emission is compared with the measured one on the corresponding experimental test. Therefore, in the present work, the experimental procedure and test rig adopted to estimate the acoustic characteristic coefficients are shown.
Lenzi, Giulio, Ferrara, Giovanni, Fioravanti, Andrea
Modular Exhaust Design and Manufacturing Techniques for Build-to-Order Muffler SystemsTBMG-222156/1/2015
Managing the acoustic signature of military vehicles can play a critical role in the safety of soldiers. Low-frequency sounds propagate through the atmosphere, resulting in unacceptable acoustic vehicle detection ranges, requiring relatively large silencer structures to mitigate. Currently, these requirements are met by using a custom muffler that is hand-assembled using low-volume prototyping manufacturing techniques. This method results in significant engineering and manufacturing time.
Application of the Fourier Amplitude Sensitivity Test (FAST) to Analyze Thermal Performance of Vehicle Underbody Components2015-01-04384/14/2015
This paper describes the application of the Fourier Amplitude Sensitivity Test (FAST) method [1] to investigate the effect of uncertainty in design parameters on the thermal system performance of vehicle underbody components. The results from this study will pinpoint the design parameters which offer the greatest opportunity for improvement of thermal system performance and reliability. In turn, this method can save engineering time and resources. An analytical model was developed for a vehicle underbody system consisting of a muffler, heat shield, and spare tire tub. The output from this model was defined as the temperature of the spare tire tub. The majority of the input parameters in this model deviate from their nominal values due to environmental factors, wear and ageing, and/or variation in the manufacturing process. Using MATLAB software package, the model was simulated with input parameters which were simultaneously and sinusoidally varied at distinct frequencies over their respective uncertainty ranges. Finally, the Fourier transform was applied to the output of the model to convert the response into the frequency domain to allow the amplitude of each of the distinct frequencies to be recognized. The amplitude of each frequency was used as an indication of the effect of the corresponding parameter's variation on the temperature of the spare tire tub. Reducing the amount of variation in the most influential parameters and/or reducing the system sensitivity to these parameters will have the greatest improvement on the overall thermal performance of the system.
Lehman, Ashley, Stoilov, Vesselin, Sobiesiak, Andrzej
Assessment and Experimental Validation of a 3D Acoustic Model of a Motorcycle Muffler2014-32-012211/11/2014
The intake and exhaust lines provide the main abatement of the acoustic emissions of an Internal Combustion Engine (ICE). Many different numerical approaches can be used to evaluate the acoustic attenuation, which is commonly expressed by the Transmission Loss. One-dimensional (1D) and three-dimensional (3D) simulations are conventionally carried out only considering the acoustic domain of the muffler or of the air-box. The walls of the acoustic filter are considered fully rigid and the interaction between the acoustic waves and the structure is consequently negligible. Moreover, the effect of the manufacturing characteristics and the attenuation of the acoustic waves due to the fluid viscous-thermal effects are also commonly disregarded in the numerical analysis of the filters. In addition, the presence of a catalytic converter or a filter cartridge may have an influence on the numerical results. All these aspects, however, can remarkably affect the matching between simulations and experiments both at high frequencies and at medium-low ones. In the present study, the effect of the aforementioned issues on the prediction capabilities of a 3D FEM model are analysed, with particular attention to the prediction of the acoustic attenuation of a commercial muffler. In detail, simplified models were developed in order to include the manufacturing features into acoustic simulations with almost negligible increase of the computational time. Numerical models were applied to a commercial motorcycle muffler featuring three chambers and a catalytic converter, and then validated by means of a specific experimental campaign that was carried out on an acoustic test rig. The tests were run at ambient temperature and no-flow conditions, obtaining good agreement between theory and experiments.
Fioravanti, Andrea, Lenzi, Giulio, Vichi, Giovanni, Ferrara, Giovanni, Ricci, Stefano, Bagnoli, Leonardo
Commercial Vehicles Muffler Volume Optimization using CFD Simulation2014-01-24409/30/2014
In today's competitive world, vehicle with light weighting is the most focused area. Vehicle light weighting can be done either by using light weight materials or by reducing the size of the existing components. In present paper later approach of vehicle light weighting is followed. It will help in design lay outing and reduce weight will add benefit to Fuel Efficiency (FE) too. Scope for light weighting is identified in exhaust system where muffler volume is optimized using Computational Fluid Dynamics (CFD) commercial tool FLUENT™. The back pressure, exhaust gas temperature, sound noise level & sound quality are chosen as design verification parameters. The muffler volume is reduced by 14.1%; resultant system become 14.1% compact with 2% lighter weight. Initially CFD analysis is performed on existing muffler and correlated with available test results. Accordingly parameters like pressure drop and flow induced noise are set as target values for new design. Same CFD analysis process is used to find the optimum solution among the series of options available. Optimized design took the shape of proto sample and test results found very well correlation between CFD and physical test results.
Patidar, Ashok, Prasad, Shivdayal, Gupta, Umashanker, Subbarao, Mohan
Systematic Optimization of an Exhaust System to Meet Noise Radiation Criteria at Idle2014-01-00064/1/2014
Exhaust noise is a major contributor to the radiated noise level of a vehicle, especially at idle. The radiated noise level has to meet a certain criteria based on regulation and consumer demand. In many cases, the problem appears after the vehicle is manufactured and the tailpipe noise measurement is performed indicating a high noise level that needs to be reduced. This paper describes one of those cases where the radiated noise level of a certain passenger car at idle was required to be reduced by 6 dB(A). The exhaust system consists of one main muffler and one auxiliary muffler. A 1D two-port model of the exhaust system including the two mufflers was built using commercial software. This model was validated against the measurement of the two-port matrix of both mufflers. The model was then used together with tailpipe noise measurements to estimate the characteristics of the source strength and impedance. Using a 1D model of the complete system, it was possible to propose several modifications for the vehicle manufacturer to choose from. A systematic optimization approach is presented in this paper describing several suggestions to reduce the radiated tailpipe noise.
Elnady, Tamer, Abom, Mats, Yang, Yong
The Proper Use of Plane Wave Models for Muffler Design2014-01-00164/1/2014
In many industries, muffler and silencer design is primarily accomplished via trial and error. Prototypes are developed and tested, or numerical simulation (finite or boundary element analysis) is used to assess the performance. While these approaches reliably determine the transmission loss, designers often do not understand why their changes improve or degrade the muffler performance. Analyses are time consuming and models cannot be changed without some effort. The intent of the current work is to demonstrate how plane wave muffler models can be used in industry. It is first demonstrated that plane wave models can reliably determine the transmission loss for complicated mufflers below the cutoff frequency. Some tips for developing dependable plane wave models are summarized. Moreover, it is shown that plane wave models used correctly help designers develop intuition and a better understanding of the effect of their design changes.
Herrin, David W., Hua, Xin, Zhang, Yitian, Elnady, Tamer
Using the Reciprocal Work Identity to Evaluate the Transmission Loss of Mufflers2013-01-18885/13/2013
Transmission loss (TL) is a good performance measure of mufflers since it represents the muffler's inherent capability of sound attenuation. There are several existing numerical methods, which have been widely used to calculate the TL from numerical simulation results, such as the four-pole and three-point methods. In this paper, a new approach is proposed to evaluate the transmission loss based on the reciprocal work identity. The proposed method does not assume plane wave propagation in the inlet and outlet ducts, and more importantly, does not explicitly apply the anechoic termination impedance at the outlet. As a result, it has the potential of extending TL computation above the plane wave cut-off frequency.
Zhou, L., Herrin, D. W., Wu, T. W.
Adding Bypass Ducts to Enhance Muffler Performance without Increasing Size2013-01-18825/13/2013
It was demonstrated that a bypass duct similar to a Herschel- Quincke tube could be used to increase the transmission loss of mufflers at selected frequencies. In many cases, the duct can be short and thought of as a leak. It was shown that the optimal length and cross-sectional area could be determined by using a simple optimization technique known as the Vincent Circle. Most importantly, it was demonstrated that the attenuation at low frequencies could be improved by as much as 15 dB. To prove the concept, a muffler was designed and optimized using transfer matrix theory. Then, the optimized muffler was constructed and the transmission loss measured using the two-load method. The measured results compared well with prediction from transfer matrix theory. Boundary element simulation was then used to further study the attenuation mechanism.
Zhang, Y., Herrin, D. W., Wu, T. W.
Investigation of the Urea Evaporation and Mixing with Various Temperatures and Injector and Injection Angles in the Catalytic Muffler2013-01-10784/8/2013
Diesel engine is being used widely in many industrial fields, as it provides merits in the aspects of higher thermal efficiency and less CO₂ emission. However, NOx regulations for diesel engines are being strengthened and it is impossible to meet the emission standard without aftertreatment systems such as SCR (Selective catalytic reduction), LNC (Lean NOx catalyst), and LNT (Lean NOx trap). Among the NOx reduction aftertreatments, Urea-SCR system is known as the most stable and efficient method to solve the problem of NOx emission. But this device has some issues associated with the ammonia slip phenomenon which is occurred by shortage of evaporation and thermolysis time, and that makes it difficult to achieve uniform distribution of the injected urea. Therefore, this study has focused on the mixing enhancement between urea and exhaust gases to enhance the efficiency of the SCR equipped in catalytic muffler by changing injector angle to improve the spray uniformity of the urea water solution. Finally, it can be found that various parameters such as the injector and injection angles and an exhaust gas temperature significantly affect the urea evaporation and mixing with exhaust gases, and therefore, optimization of these parameters are required.
An, Tae Hyun, Kim, Man Young, Jung, Hak Sup, Kim, Hongsuk, Cho, Gyubaek
Reduction of Exhaust Noise by Means of Thermal Acoustics2012-01-08044/16/2012
It is well known that mufflers attenuate the engine noise essentially through dissipative and reflective effects. There is however another alternative technique for noise attenuation that has not been deeply explored, i.e. thermal acoustics. In fact the temperature of the gas influences the acoustic behaviour of the exhaust system; reducing the exhaust gas temperature, the sound pressure of the acoustic waves is reduced. This phenomenum could be used to improve the sound attenuation. We propose an experimental study of this phenomenum and of how it could be used to reduce the exhaust noise. We measured that, using in underfloor position passive heat exchangers like corrugated pipes, the exhaust gas quickly exchanges heat with the external environment and arrives to the rear muffler significantly colder. We observe about 2 dB decrease of the OA dB value when the gas temperature decreases of about 100°C. With colder exhaust gas the noise can be heavily reduced; in particular the flow noise improves the sound attenuation at high engine speed.
Milani, Emanuele, Paze, Costanza, Ambrosino, Massimo, Pagliano, Pierangelo
Improving the Simulation of the Acoustic Performance of Complex Silencers for ICE by a Multi-Dimensional Non-Linear Approach2012-01-08284/16/2012
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. In order to achieve reliable predictions of the acoustic attenuation, especially above the plane wave cut-off frequency, an advanced non-reflecting boundary condition to model the anechoic termination, based on the NSCBC characteristic theory, has been implemented in a multidimensional open-source CFD code and it has been used together with a time dependent compressible Navier Stokes equation solver. The original local one dimensional inviscid relations (LODI) in Cartesian coordinates presented in [1] have been extended to local coordinates and have been applied for unsteady calculations in a multistage time stepping scheme. Numerical results show that the agreement between simulations and experiments strongly improves at high frequency when the novel boundary condition is applied. A comparative study with a 1D non-linear model for unsteady compressible flows is shown on four different configuration of reverse flow chambers and on a single-plug perforated muffler for internal combustion engine applications. Advantages and drawbacks of the proposed approach are discussed.
Piscaglia, Federico, Montorfano, Andrea, Onorati, Angelo
Acoustic Characterization of Automotive Mufflers - Part I: Test Rig Design and Evaluation of Acoustic Properties2012-01-08004/16/2012
In current automotive research, increasing attention is being paid to the design of mufflers due to the lower noise levels which have been established by the acoustic international standards. The traditional design approaches are no longer sufficient to meet the standards and more refined techniques are necessary. Within this context, a specific test rig was built at the Energy Engineering Department of the University of Florence to analyze the acoustic characteristics of both industrial mufflers and simplified models. In particular, the latter is commonly used to investigate in detail the physical phenomena connected to the acoustic response of these disposals and to calibrate numerical models. The test rig operates at ambient condition with no flow. Instead of the widely used Four Microphones Technique, the test rig was designed considering the Multi-Microphone Technique, which guarantees a wider reliable frequency range of analysis and lower errors in the evaluation of the acoustic properties of mufflers. In this paper the details of the criteria adopted in the design and the characterization of the test rig will be discussed in depth.
Ferrara, Giovanni, ferrari, Lorenzo, Vichi, Giovanni, Lenzi, Giulio, Biliotti, Davide
Acoustic Characterization of Automotive Mufflers - Part II: Validation of the Numerical Models by Means of Experimental Data2012-01-08014/16/2012
Increasing interest is being paid to noise pollution of internal combustion engines and as a result, recent international standards imposed more severe limitations to acoustic emissions on engine manufacturers. In particular, the noise coming from gas-dynamic interactions has an important influence in determining the final noise level of the engine; as a consequence, the muffler design is currently being considered as one of the most important research threads for engine companies. Within this context, the 1D approach to numerical simulations, which has been successfully applied by industrial designers to the fluid-dynamic design of the engine, is considered to be inaccurate in the evaluation of the acoustic behavior of the muffler for medium-high frequencies. On the other hand, an extension of the applicability of these codes in the medium-high frequencies would be desirable. The direct advantage would be the use of the same software for the simulation of both the fluid-dynamic and acoustic performance of the engine. On these bases, a commercial 1D numerical code was primarily analyzed in terms of accuracy, computational cost and modeling capability of mufflers from the acoustic point of view. As a second step, two non-conventional approaches were developed in order to improve the prediction capabilities of the 1D code and to widen its frequency range of validity, as well. The base scheme of these new approaches was to extend the application of the traditional 1D nonlinear equations not only in the axial direction but also in perpendicular directions within the cross-section of the muffler, achieving a simplified description of the acoustic phenomena in the whole volume. The 1D predictions using these new approaches were compared both with several sets of experimental data collected on a purposefully developed test rig and specific 3D simulations; as a result, their limits in terms of accuracy were highlighted. Moreover, the introduction of the new sub-models increased the accuracy of the simulations and the frequency range of validity, leading to notable results with respect to traditional formulations of the problem.
Ferrara, Giovanni, ferrari, Lorenzo, Vichi, Giovanni, Lenzi, Giulio, Biliotti, Davide
Muffler Design, Development and Validation for Acoustic Advantages on Automotive Vehicles2011-01-22159/13/2011
Noise pollution has become one of the major environmental concerns in present era. With the ever tightening laws and increasingly straight regulations for controlling noise pollution of automotive vehicles, mufflers are important part of engine system and commonly used in exhaust system to minimize noise caused by exhaust gases. Design of mufflers is a complex function that affects the noise characteristics and fuel efficiency of the vehicle. Traditionally, muffler design has been an iterative process by trial and error method. However theories and science that has undergone development in recent years has given a way for an engineer to cut short number of iterations. In today's competitive world market, it is important for a company to shorten product development cycle time and thereby cost. The objective of this paper is to propose a practical approach to design, develop and validate muffler practically which will give advantage over conventional method. This paper also emphasis on how modern CAE tools could be leveraged for optimizing overall system design balancing conflicts like noise and back pressure. The project is considered for validation plan on real time vehicle application to realize objective of design as future scope of work.
Ramesh Shah, Shitalkumar, GS, Gangadhar
Steady-State and Transient Motor Vehicle Exhaust System Temperatures2009-01-00134/20/2009
One of the known causes of motor vehicle fires is hot surface ignition of combustible material that contacts engine exhaust system components. While ignition is a complicated phenomenon, the temperature of the surface is known to be an important parameter. However, little data is available in the literature concerning exhaust system temperatures, and much of this data is confounded by thermocouple attachment techniques and undocumented variations in driving conditions. In the present study, engine exhaust system temperature measurements were conducted using six test vehicles on a level, 2-mile oval test track at constant vehicle speeds ranging from 0 (idle) to 70 mph. By normalizing transient temperature curves with these steady-state temperatures along with ambient temperature, the rates at which the exhaust system components warm up and cool down are also compared. The effect of thermocouple mounting technique was evaluated by conducting identical testing with the thermocouples located at identical locations on the exhaust system but with two different mounting techniques, namely hose clamps and welding.
Colwell, Jeff D., Biswas, Kaushik
Accurate Measurement of Small Absorption Coefficients2007-01-22245/15/2007
In this paper procedures for estimating the sound absorption coefficient when the specimen has inherently low absorption are discussed. Examples of this include the measurement of the absorption coefficient of pavements, closed cell foams and other barrier materials whose absorption coefficient is nevertheless required, and the measurement of sound absorption of muffler components such as perforates. The focus of the paper is on (1) obtaining an accurate phase correction and (2) proper correction for tube attenuation when using impedance tube methods. For the latter it is shown that the equations for tube attenuation correction in the standards underestimate the actual tube attenuation, leading to an overestimate of the measured absorption coefficient. This error could be critical, for example, when one is attempting to qualify a facility for the measurement of pass-by noise. In this paper we propose a remedy - to measure the actual tube attenuation and to use this value, as opposed to the value recommended by the standards, to correct the measured sound absorption. We also recommend an alternative way to determine the microphone phase error.
Han, J., Herrin, D. W., Seybert, A. F.
Investigations on Whistle Noise in Automotive Exhaust System Mufflers2005-01-23615/16/2005
Automotive exhaust mufflers are not only attenuating noise, but can, in fact, along with other exhaust components, generate noise within the exhaust system. This type of noise is commonly called “flow generated noise” to distinguish it from the “pulsation noise” excited by the combustion engine. Flow generated noise is normally very broad band but it can also have tonal regions. This tonal flow noise can sound like a whistle. In this contribution an experimental study of the generation and prevention of such whistle tones will be presented. The study was focused on perforated pipes in mufflers with different perforation patterns, hole sizes and hole shapes. The noise spectra have been measured on a flow bench at room temperature as well as under real (hot) conditions on a vehicle. The results will be correlated in terms of frequency and Strouhal number. Concepts to avoid or suppress these tones will also be discussed.
Jebasinski, Rolf, Leng, Sascha, Jess, Marco, Rose, Thomas
An Optimization Tool for Exhaust System Design With Respect to Tail Pipe Noise Reduction2003-01-16465/5/2003
Faurecia has developed a numerical tool which allows an automatic optimization of an exhaust line with respect to tailpipe harmonic noise. An optimizer pilots an in-house acoustic software in order to find the exhaust line configuration which fulfills the targets on the two first harmonics. The optimization method as well as the acoustic prediction tool are presented in this paper. Then, two examples of application of the methodology are detailed.
Boudoy, Marianne, Jaskulski, Jean-Yves
Medium- and Heavy-Duty Truck Converter/Muffler ConfigurationJ1642_200111 (Current)11/15/2001
This SAE Draft Technical Report is intended to document the technical consensus of the current design state of converter/mufflers for heavy-duty emission classification diesel vehicle applications. This will maximize standardization and promote interchangeability of parts from different manufacturers. The purpose of this SAE Draft Technical Report is to give the technical community the opportunity to review, comment on, and use the Draft Technical Report prior to its final approval by SAE.
SAE IC Powertrain Steering Committee
The numerical analysis and technique development on light truck muffler bracket forming2000-05-02196/12/2000
The light truck muffler bracket is a kind of deep and complicated stamping part which has curve flange. It is formed by once drawing with 3 mm thick 08TIL sheet. Since it is difficult to design good technique for the workpiece, after the muffler bracket was put into production, problems such as cracks at the bottom projecting corner and wrinkles at the curved flange corner often occurred. This led to high waste product ratio of 15 (and high substandard product ratio of 30). Therefore the part quality was heavily influenced, the production cost kept at high state for long term. In this paper, the geometry model of forming process part is built with the software Euclid3, the forming process of muffler bracket is numerically analyzed with the software LS-DYNA3D. The metal flow law and deformation character under the curve blankholding surface is revealed, in the meantime, the main reason of cracks and wrinkles appearing in the part during the forming process is studied, the direct reason of cracks at the projecting corner of muffler bracket bottom is verified as the metal flow resistance is too large at the preformed flange corner. The new technique that the preformation is finished by punch and die, the formation is finished by punch, die and binder have been developed. The waste product ratio and substandard product ratio have been descended below 0.05. Thus the quality problem which has puzzled production for a long time is successfully solved by using numerical simulation technology, theory bases are offered for the designing of stamping and die of similar workpieces.
Xu, Cheng Lin, Zhu, Wei Cheng
Acoustic Three Dimensional Finite Element Analysis of a Muffler9601892/1/1996
Three dimensional finite element analysis of mufflers has been carried out using ANSYS general purpose program. Analysis of simple expansion chamber muffler, extended tube muffler, tapered chamber muffler, offset chamber muffler and flow reversing chamber muffler has been carried out to predict the transmission loss. This three dimensional FEA technique has proved to be successful for the analysis of geometrically complicated mufflers where one dimensional theories can not be used. Parametric analysis of a simple expansion chamber muffler has been carried out to study the effect of expansion ratio, expansion chamber length, number of partitions within a chamber and unequal partitions. Analysis of acoustic cavity of a simple expansion chamber muffler has also been carried out to predict the natural frequencies and acoustic mode shapes.
Patil, Avinash R., Sajanpawar, P. R.
Collector/Catalyst/Muffler Package: Racing Car Exhaust Noise Reduction9510602/1/1995
Significant reduction in the exhaust noise levels of racing cars has been achieved through the use of a special header-collector design. This design combines the primary header tubes, the collector, and the muffler into a compact package. The accommodation of exhaust systems on race cars -- especially those with mid or rear engine designs -- upsets the weight bias of the vehicle by moving the mass of the exhaust behind the rear axle, thus increasing the polar moment. The ducting of the exhaust to the rear also exposes vital components to extreme heat generated by the exhaust system. The CCM occupies fractionally more space than the header alone, allowing great flexibility in the design of the rest of the exhaust system. Testing has demonstrated that this design not only attenuates noise, but it provides increased horsepower and torque as well.
Borla, Alexander, Guzek, Joseph
Medium- and Heavy-Duty Truck Converter/Muffler ConfigurationJ1642_199302 (Historical)2/19/1993
This SAE Draft Technical Report is intended to document the technical consensus of the current design state of converter/mufflers for heavy-duty emission classification diesel vehicle applications. This will maximize standardization and promote interchangeability of parts from different manufacturers. The purpose of this SAE Draft Technical Report is to give the technical community the opportunity to review, comment on, and use the Draft Technical Report prior to its final approval by SAE.
SAE IC Powertrain Steering Committee
Rev-74-The University of Cincinnati ATV with Independent Suspension7501432/1/1975
The history and structure of the Recreational Ecological Vehicle Design Competition, REV-74, is discussed. In this competition, held at Houghton, Mich., several universities designed and constructed all-terrain vehicles which were evaluated in a series of test events. The University of Cincinnati's six-wheeled all-terrain vehicle is described in detail. Features included in the discussion are the vehicle's twin hydrostatic drive transmission, independent suspension, high-frequency muffler, and jet pump drive for water propulsion.
Morse, Ivan E., Shapton, William R.
Control of Diesel Engine Exhaust Noise7007012/1/1970
The contribution of exhaust noise to total vehicle noise is identified by isolation and near field techniques. Control of exhaust noise by using the principles of absorptive, reactive, and dispersive mufflers and their combinations is examined. Guidelines are presented to help the engine designer in the selection of mufflers within the design limitations of size, weight, and engine performance loss.
Wu, Tang
MUFFLER LOCATION IS IMPORTANT5900941/1/1959
DANNER, T. A.
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