Browse Topic: Mufflers
Primarily, Acoustic performance of muffler are evaluated by insertion loss (IL) and backpressure/restriction. Where Insertion loss is mainly depends upon proper selection of muffler volume, which is proportional to Engine Swept volume, along with internal design configuration, which drives the acoustic principle. Same time, meeting the vehicle level pass by noise (PBN) value as per regulatory norms and system level backpressure as per engine specification sheet are the key evaluating criteria of any good exhaust system. Here, a new Reactive/Reflective type muffler of tiny size have been designed for heavy commercial vehicle application, which is unique in shape and innovative to meet desire performance. In this design, mainly sudden expansion, sudden contraction, flow through perforation and bell-mouth flow phenomenon are used. The performance of this tiny muffler are optimized using multilevel design of experiments (DoE) by the measurement of pass by noise (PBN) and near exhaust noise (NEN) level and Backpressure of exhaust system along with predictive design calculation. The primary objective of this research is to investigate the effect of four design factors namely perforation percentage, perforation hole diameter, baffle thickness and baffle position on both acoustic performance and backpressure. The other objective is to do the comparative assessment between tiny size reactive muffler and existing 3-chamber hybrid or combination type muffler in holistic approach on typical heavy commercial truck. This comprehensive study reveals the importance of perforation baffle feature (preformation percentage, Perforation-hole diameter, baffle thickness) and baffler positioning in two chamber muffler to tradeoff between Noise (PBN & NEN) and Backpressure. Even though, the new muffler is meeting the regulatory norms but acoustic performance is marginally inferior to available hybrid type muffler. The predictive insertion loss value found matching with 98% accuracy. Further, the new muffler found very much cost effective, lighter weight and ease package-able/manufacture-able than existing one.
The application of turbochargers in fuel vehicles brings high-frequency noise, which seriously affects the vehicle's ride comfort. The hiss noise of a turbocharged car is improved in this paper. Firstly, under different operating conditions and whether the air intake system is wrapped, the noise in the vehicle cabin and the driver's right ear is tested, and the noise sources and noise characteristics are identified. Then, the acoustic calculation model of the muffler is established, and the transmission loss (TL) of the original muffler behind the turbocharger (MBT) is calculated. The TL of the muffler is measured by the double-load impedance tube method. The finite element calculation model is verified by comparing the TL of muffler calculated with tested. Thirdly, the MBT is redesigned. The improved muffler significantly improves the performance of eliminating high-frequency noise, and its TL beyond 20 dB is expanded to the band of 1600 ~ 3500 Hz. The improved muffler is trial-manufactured and installed on the test vehicle, and the vehicle noise is tested again. The test results show that the noise in the frequency band of 1600 ~ 2400 Hz is obviously reduced in the near field of the MBT, and the maximum reduction is 9 dB. The subjective evaluation also shows that the high-frequency hiss noise also improved significantly in the car. This paper proposes a method of designing a muffler and optimizing its structure to reduce hiss noise of turbocharged vehicles. The influence of airflow on engine performance is considered. It can provide a reference for the application of engineering development of turbochargers.
For motorcycles, the exhaust system is one of the major contributors to the overall acoustic performance. Above all, the radiated noise from the muffler surface needs to be considered sufficiently for rider acoustical comfort. In many cases, countermeasure parts need to be applied to reduce the radiated noise, which, consequently, hinders weight and cost reduction. This paper reports our study on reducing the radiated noise from the muffler surface by applying to the muffler shell a laminated panel structure in which two steel sheets contact each other. We identified the major factors affecting noise radiation from the muffler surface and used the dynamic stiffness of the outer body surface as a physical quantity to evaluate the damping effect of the laminated steel plate. Based on the idea that the damping effect of laminated steel plates mainly depends on the friction force generated by fine relative displacement between the layers, the surface dynamic stiffness was evaluated with various thickness combinations of the square plate, and it was found that the surface dynamic stiffness was maximized when the thickness ratio was about 2:1. In light of this finding, we produced two prototypes of laminated shell mufflers with circular and non-circular cross-sections, and evaluated their noise reduction performance on actual motorcycles. The results showed that the radiated noise reduction performance of the new mufflers was equivalent to that of a conventional structure muffler. Using the laminated muffler shell of the proposed thickness ratio, we achieved 13% weight reduction in a newly developed muffler.
When developing a motorcycle exhaust system, it is important to predict the fatigue durability of the exhaust system during the design stage. We have been predicting fatigue durability using our own methods [1]. In recent years, however, in order to meet stricter emission regulations, the installation position of a catalyzer has been changed and the temperature of the exhaust system has been increased. Accordingly, the required fatigue durability of mufflers is at higher temperatures than before. With such a change in situation, a prediction method with higher accuracy for fatigue durability that can handle a higher temperature range, was required. The exhaust system temperature distribution and the physical properties of the material change depending on the temperature. Therefore, in the simulation model developed this time, the temperature distribution of the exhaust system is calculated by a heat conduction analysis method applying FEM. Furthermore, based on the temperature distribution, the values of the material properties are set for each element. In order to verify the effectiveness of the constructed model, measurements were performed on a real motorcycle. In the measurement on an actual vehicle in this study, a glass bonding method was developed and adopted for the purpose of bonding the optical fiber strain gauge. The results yielded by using the fatigue durability prediction method, constructed in this study, were in agreement with the results of the actual vehicular tests, confirming the effectiveness of this analysis method.
Researchers have determined how built-in resonators handle vibrations under a variety of scenarios. Resonators are devices that help manage vibrations — some vehicles have them to limit the sound emitted from a car’s muffler and some bridges and buildings use them to limit noise and movement from those structures. Resonators use spring-like oscillation to control and change vibrations — some absorb and neutralize them while others amplify and direct them to specific places.
The primary function of exhaust muffler is to reduce noise from the internal combustion engine without affecting its performance due to the impact of higher back pressure. The exhaust system back pressure is directly related to the engine fuel efficiency. The consumption of back pressure by the emission control system in BS IV regulation is about 30% from the total permissible engine limit, whereas in BS VI consumption is about 70%. The combination technologies used in BSVI and forthcoming RDE regulations such as TWC, GPF, DOC, DPF and SCR increases significant back pressure in exhaust system, hence the engine performance decreases. This demand robust method to control the exhaust back pressure for better fuel efficiency. Emission, noise and back pressure are the non-complimentary parameters in exhaust system development. The variable valve technology introduction in muffler is one method to optimize the above parameters. In general, mechanical variable valve in muffler containing torsional spring is used to improve the acoustics in lower rpm and to reduce exhaust backpressure in higher rpm. This paper deals with development of variable valve with compression spring as an alternative of torsional spring valve by using GT-POWER 1D tool. The conceptual design and working progress of new valve followed by comparative performance evaluation in acoustics and back pressure are dealt with in detail through simulation and validation. The new valve functioning with compression spring achieved 15% improvement in back pressure at higher rpm and 7% improvement in exhaust order noise at lower rpm.
Short development cycles, less packaging space and stringent noise emission rules have increased the need of CAE usage and first time right design approach. Engine exhaust noise is the main contributor of automotive noise when vehicle speed is low to moderate. Exhaust noise contains tailpipe noise and shell radiation noise. As vehicle speed increases, contribution of flow noise and tire noise is comparatively at higher side. The cold end development engineer is responsible to design a muffler to meet tailpipe and shell radiation noise targets. Muffler shell stiffness is a key characteristic for deciding shell radiation noise. High intensity pulses of exhaust gas passes through the exhaust pipe and hits cold end from inside which causes shell vibration and respectively shell noise. There are several conventional methods available to improve shell stiffness, but all of them are not applicable for ‘double layered critically shaped mufflers’ and all of them are not cost-effective. The purpose of this study is to review all traditional countermeasures, to propose and validate new cost-effective techniques to maximize shell stiffness of critically shaped muffler. The muffler boxes of turbocharged and non-turbocharged engines ranging from 1.4 to 1.6L engine volume were considered for investigation. Several trails have been taken for increasing muffler stiffness and the most effective methods are presented here. The use of impact hammer test is done for measuring muffler shell stiffness. At initial stages muffler shell was having 350 Hz natural frequency; with the use of new techniques, we observed that natural frequency of shell can be improved up to 500 Hz. From several experimental studies it has been found that proposed countermeasures are helpful to increase average natural frequency of muffler by 130 to 170 Hz and reducing shell noise by 4-6 dB (A) across all vehicle operating range. Proposed methods are simple, cost-effective and easy to apply in manufacturing.
In recent times there has been rising demand for noise level reduction in commercial vehicles. Vehicle engine exhaust system is one of the key sources of noise at driver ear, especially in smaller wheel base vehicles, as well as critical for meeting pass by noise regulations. Several techniques are used to reduce the noise level of an exhaust system such as resonators, dissipative mufflers for low & high frequencies respectively. In this paper sound transmission loss (STL) measurement for a LMD bus exhaust system was carried out at rig level. It has been found from the measured data that noise attenuation of current exhaust system is poor in low frequency zone & therefore lower STL frequencies were identified. To attenuate the noises at identified frequencies Helmholtz resonator was introduced, which is particularly effective for low frequency noise attenuation. A design is conceptualized and developed based on Helmholtz resonator calculation for target frequencies and duty cycle gas temperatures. Further, effect of designed resonators on exhaust back pressure in CFD was analyzed. Prototypes were developed & NVH performance trials were carried out at vehicle level. It has been observed from the results that noise reduction can be achieved at passenger ear level (PEL) & in pass by noise (PBN) test. This paper covers complete NVH development cycle for a real-time noise scenario i.e. measurements & analysis, design, development & final verification on vehicle level. It explains possible measures for decreasing exhaust noise and can be used as guideline for related applications.
Engine exhaust noise and heat are significant sources of emissions in the environment. Engine exhaust systems are designed to minimize noise and heat while maintaining the necessary db levels and sound quality, as well as emissions in accordance with environmental regulations. Mufflers remain an integral portion of the IC engine arrangement are widely used in IC engine exhaust arrangements to reduce sound generated by engine exhaust gases as well as to reduce heat. The most efficient way to reduce noise and heat is to install a exhaust muffler in the engine tail pipe. The aim of our project is to design and analysis an engine exhaust muffler for reducing exhaust noise and heat. Appropriate design and analysis would aid in the reduction of noise and heat, while at the same time, the backpressure generated by the muffler should not affect the engine's efficiency. 3D models are developed in Solid Works software before being exported to ANSYS FLUENT CFD software for review in this report. Pressure conditions will be defined as the inlet and outlet boundary conditions in ANSYS/FLUENT, respectively. Then, in the proposed model, the problem is solved to simulate internal fluid flow (exhaust gas). The simulation result and experimental results are compared.
Exhaust Noise attenuation is one of the important functions of exhaust muffler. Transmission Loss (TL) is a measure of noise attenuation used in designing exhaust mufflers for NVH. TL is a logarithmic difference between inlet and outlet pressures for unit velocity input at inlet of the muffler and anechoic termination at outlet of the muffler as boundary conditions. TL amplitude and its frequency tuning depends on a combination of various muffler design parameters like volume, length, muffler cross section, pipe cross sections, pipe perforations, number of chambers, baffle perforations, etc. Achieving the desired TL performance with no valleys over a wide frequency range is very challenging. Manual design iterations with large numbers of permutations and combinations of design variables are difficult and time-consuming. It also needs a highly experienced professional to balance TL performance, design variables and design constraints. The current paper discusses an exhaust muffler TL optimization simulation process that couples modeFRONTIER for DOEs, & GT-POWER, for acoustic simulation. All identified design variables are iterated in batch mode within specified design limits. DOEs are set up using Non-dominated Sorting Genetic Algorithm (NSGA) or Multi Objective Genetic Algorithm (MOGA) in modeFRONTIER. Based upon pre-defined iterative simulation cycles, muffler design is optimized to meet design constraints and TL performance. This optimization helps to reduce manual efforts in building simulation models, to carry out more iterations, to reduce solver time, to reduce manual intervention for post processing, and to give optimized TL performance.
Helmholtz resonators are often used in the design of vehicle mufflers to target tonal noise at a few specific low frequencies generated by the engine. Due to the uncertainty of temperature variations and different engine speeds, multiple resonators may have to be built in series to cover a narrow band of frequencies. Double-tuned Helmholtz resonators (DTHR) normally consist of two chambers connected in series. Openings or necks are created by punching small slots into a thin-walled tube which provide a natural neck passage to the enclosing volume of the Helmholtz resonator. In this paper, numerical analyses using both the boundary element (BEM) and the finite element (FEM) methods are performed and simulation results are compared against one another. A typical real-world muffler configuration commonly used in passenger vehicles is used in a case study. It is shown that the proposed slot design concept can improve the low-frequency performance while maintaining similar performance at high frequencies.
This paper presents experimental investigations of determining and analyzing low-frequency, low-SNR (Signal to Noise Ratio) noise sources of an automobile by using a new technology known as Sound Viewer. Such a task is typically very difficult to do especially at low or even negative SNR. The underlying principles behind the Sound Viewer technology consists of a passive SODAR (Sonic Detection And Ranging) and HELS (Helmholtz Equation Least Squares) method. The former enables one to determine the precise locations of multiple sound sources in 3D space simultaneously over the entire frequency range consistent with a measurement microphone in non-ideal environment, where there are random background noise and unknown interfering signals. The latter enables one to reconstruct all acoustic quantities such as the acoustic pressure, acoustic intensity, time-averaged acoustic power, radiation patterns, etc. By combining a passive SODAR and modified HELS methods, engineers will be able to visualize all acoustic quantities. In particular, Sound Viewer enables engineers to extract target information with a negative SNR, for example, SNR < - 30 dB, and identify the precise locations of very low frequency (< 200 Hz) airborne and structure-borne sound sources with very high spatial resolution. Test results of Sound Viewer to analyze the engine sparkplug and muffler noise of an automobile sedan are presented.
This research paper is dealing with development of a Hybrid Exhaust muffler with four different shell configurations (Internal design unaltered) and investigated the impact on noise performance and quality (perceived). Noise performance has been evaluated by measurement of Pass by Noise and near exhaust noise Level on a typical 16T -6-speeds transmission Truck. The experimental activity conducted based on DOE approach. From this study, it observed single shell with lower thickness have the poor NVH performance and perceived quality as well. Shell or booming noise is also observed with this configuration. Double shell with Ceramic blanket (throughout the length) sandwich configuration exhibited the best performance though this design is most expensive among the four mufflers. Remaining two Configurations (i.e. - Single shell of higher thickness and Double shell with Ceramic blanket only around reactive chamber) displayed at per results in both perceived noise quality and Noise performance. There are difference around 0.6 dBA noise at 3rd and 4th Gear Pass by Noise (PBN) level among best and poor performing Shell configuration muffler. The experimental research has revealed the importance of Shell Configuration/Design on acoustic/NVH performance and Noise (perceived) Quality of muffler as well at Vehicle Level.
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 noise in the pipe by ordinary sensor. The correction formula can effectively eliminate the influence of the reflected wave caused by the end load on the calculation of the transmission loss, reduce the performance requirements of the end sound absorbing material, and ensure the accuracy of the aerodynamic noise measurement.
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.
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.
Regulations on noise and gas emissions become more and more stringent resulting in noise abatement devices needing further engineering and optimization. Mufflers are installed at the end of powertrains to reduce the acoustic impact of the sound pressure from the engine. Such acoustic reduction is achieved through internal structures that promote destructive interference within the muffler. However, the muffler increases the backpressure downstream of the aftertreatment line, thus decreasing the engine efficiency. In the following work, an optimization workflow is presented to find the best design for a muffler geometry. The optimization is performed with the Sherpa algorithm that uses several optimization algorithms simultaneously to increase robustness and efficiency. Sherpa is implemented in an optimization tool that manages the workflow of two other software tools. The acoustic transmission loss of the muffler is calculated as a function of the geometrical characteristics of the muffler design. The parametrized muffler CAD is changed at each optimization iteration. For each CAD variation, the transmission loss and the backpressure are calculated. A Pareto front is generated and used to analyze the relation between the backpressure and the transmission loss. A first optimization cycle highlights three distinct regions of the Pareto front. From this first general analysis, a more detailed study is performed on a constrained portion of the Pareto front in order to find the best designs. The methodology allowed for an improvement of the backpressure of 4.3% from the baseline design and an increased transmission loss above all at the higher frequencies.
Dynamic stresses exist in parts of a catalyst muffler caused by the vibration of a moving vehicle, and it is important to clarify and predict the vibration response properties for preventing fatigue failures. Assuming a vibration isolating installation in the vehicle frame, the vibration transmissibility and local dynamic stress of the catalyst muffler were examined through a vibration machine. Based on the measured data and by systematically taking vibration theories into consideration, a new prediction method of the vibration modes and parameters was proposed that takes account of vibration isolating and damping. A lumped vibration model with the six-element and one mass point was set up, and the vibration response parameters were analyzed accurately from equations of motion. In the vibration test, resonance peaks from the hanging bracket, rubber bush, and muffler parts were confirmed in three excitation drives, and local stress peaks were coordinate with them as well. The first resonance peak caused by the rubber bush had relatively low frequency, but the transmissibility was low by damping. The vibration magnitude from other parts was damped several times more by the rubber bush. The dynamic stress amplitudes from the vibration corresponded to the resonance of the catalyst muffler, and were proportional to the vibration accelerations. With an example where the spring coefficient and damping coefficient of a component in the sample were changed, the resonance frequency and transmissibility were obtained by calculation using the model while the dynamic stress was calculated using the stress scale factor, demonstrating the model’s general versatility and making it possible to predict the fatigue durability.
Exhaust systems are a necessary solution to reduce combustion engine noise originating from flow fluctuations released at each firing cycle. However, exhaust systems also generate a back pressure detrimental for the engine efficiency. This back pressure must be controlled to guarantee optimal operating conditions for the engine. To satisfy both optimal operating conditions and optimal noise levels, the internal design of exhaust systems has become complex, often leading to the emergence of undesired noise generated by turbulent flow circulating inside a muffler. Associated details needed for the manufacturing process, such as brackets for the connection between parts, can interact with the flow, generating additional flow noise or whistles. To minimize the risks of undesirable noise, multiple exhaust designs must be assessed early to prevent the late detection of issues, when design and manufacturing process are frozen. However, designing via an experimental approach is challenging. Since the construction process does not exist yet, physical prototypes lack the details associated to manufacturing. In addition, experimental optimization is time-consuming, as each design iteration will require a new physical prototype, thus increasing costs and development times, or limiting the explored design space. Alternatively, larger design spaces may be explored using virtual optimization, while removing the limitations of physical testing. Exhaust flow and acoustic simulations with the Lattice-Boltzmann Method (LBM) have been shown accurate as well as feasible within the product design cycle timing. Using noise sources detection techniques, such as Flow-Induced Noise Detection (FIND), understanding the noise generation mechanism associated to the optimal designs is also possible to orient future design decisions. In this study, after validating the ability of the approach at capturing flow noise and whistles, a characterization of the bracket design connecting tailpipe and muffler is performed to minimize the risk of whistle in the final product.
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.
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.
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