Muffler Design Research Articles

Effect of Variations in Diameter of Extended Inlet on Transmission Loss of Single Expansion Chamber Reactive Muffler with Extended Inlet

Objectives: Muffler with extended inlet has an additional dimension of variable compared to normal mufflers, that is the diameter. Understanding the effect of change in this diameter value affects Transmission Loss. Muffler used for experimentation is a reactive muffler, which cancels the noise waves using reflection phenomenon. Comparison of Computer Aided Engineering (CAE) in experiments to signify the technology advancement. Methods: MATLAB program is created for running the data and analytical solution. Finite element analysis with COMSOL Multiphysics using 3D model of muffler and computer aided engineering is done considering boundary conditions. The real experiment is carried out to evaluate confidence in simulated results where two load method is applied. Findings: Experimental setup results are showing results close to Numerical analysis. Analysis of the study suggest increase in diameter leads to rise in transmission loss. The experimental results of selected dimensions setup also prove same. Various geometric variation in muffler have effect of 10 to 30% on TL, while changing diameter from 10 to 20 mm of extended inlet raise the peak of TL to almost double and increase the average TL by 28%. Novelty: A diameter variation in extended inlet is an empty space in literature till now. This research combines analytical and experimental setups and comparison of results leads to a strong conclusion toward better muffler design. Keywords: Transmission Loss (TL); Single Expansion Chamber reactive muffler; Numerical analysis; Twoload method; Acoustics

Multi-domain acoustic topology optimization based on the BESO approach: applications on the design of multi-phase material mufflers

Multi-domain acoustic topology optimization based on the BESO approach: applications on the design of multi-phase material mufflers

Research on Suppression of Airflow Secondary Noise in a Muffler Based on Large Eddy Simulation

Based on the Large Eddy Simulation (LES), the problem of the performance of a muffler being weakened by the airflow secondary noise in the expansion chamber was analyzed. Based on the different relative positions of the inlet and outlet, a single-chamber muffler is divided into four structures and a numerical simulation model of the flow field is developed. The LES was used to analyze the flow field and secondary noise in the expansion chamber. First, the LES is used to calculate the unsteady flow in the expansion chamber to obtain the turbulent intensity and the pressure pulsation distribution of the flow in the muffler chamber. Subsequently, a simulation model of the acoustic field was built separately to obtain the secondary noise distribution of the flow in the muffler by computing the flow field information. It is shown that the secondary noise properties in the muffler are related to its geometrical configuration. The turbulence intensity of the flow field in the chamber can be reduced by changing the airflow pattern in the chamber, to weaken the intensity of the airflow secondary noise. Finally, a structural modification of the two-chamber muffler was performed based on the findings of the study, and the improved muffler performance was evaluated through numerical simulations and field tests. Experimental results show that the improved muffler has better acoustic properties and increases the noise reduction capacity by about 18 percent. It further confirms that the intensity of secondary noise can be substantially suppressed by changing the internal structure of the muffler, which opens up new ideas for the future design and modification of exhaust mufflers.

Using Response Surface for Searching the Nearly Optimal Parameters Combination of the Foam Concrete Muffler.

A car muffler is a device to improve car noise emission. Some conventional mufflers use layers of glass fiber as a material to absorb noise. However, filling glass fiber is an environmentally unfriendly work, mainly manually filling with chop strand fiber. This research selected a composite material of glass fiber and foam concrete to replace chop strand fiber to avoid this hazard and maintain the muffler's good noise reduction performance. A response surface methodology with a two-way factorial experimental design repeated the center point twice is performed. The density of the foamed concrete and the weight of the glass fiber is being considered in order to determine the nearly optimal combination of the values in two factors. The response variable is the loudness sensation in Sone of the noise generated from the muffler. At present, the lowest loudness sensation from the two-way factorial design is 16.6494 Sones, which occurred for a muffler with a formula combination of a density of 0.2 g/cm3 and 40 g of glass fiber. The significance of this paper is the presentation of a new application of foam concrete to the green muffler design. To the best of our knowledge, this unique area has never been tackled in the material application of concrete. We have discovered that foam concrete indeed does an excellent job in terms of noise reduction as compared with that of a market muffler.

Studying Acoustic Behavior of BFRP Laminated Composite in Dual-Chamber Muffler Application Using Deep Learning Algorithm.

Over the last two decades, several experimental and numerical studies have been performed in order to investigate the acoustic behavior of different muffler materials. However, there is a problem in which it is necessary to perform large, important, time-consuming calculations particularly if the muffler was made from advanced materials such as composite materials. Therefore, this work focused on developing the concept of the indirect dual-chamber muffler made from a basalt fiber reinforced polymer (BFRP) laminated composite, which is a monitoring system that uses a deep learning algorithm to predict the acoustic behavior of the muffler material in order to save effort and time on muffler design optimization. Two types of deep neural networks (DNNs) architectures are developed in Python. The first DNN is called a recurrent neural network with long short-term memory blocks (RNN-LSTM), where the other is called a convolutional neural network (CNN). First, a dual-chamber laminated composite muffler (DCLCM) model is developed in MATLAB to provide the acoustic behavior datasets of mufflers such as acoustic transmission loss (TL) and the power transmission coefficient (PTC). The model training parameters are optimized by using Bayesian genetic algorithms (BGA) optimization. The acoustic results from the proposed method are compared with available experimental results in literature, thus validating the accuracy and reliability of the proposed technique. The results indicate that the present approach is efficient and significantly reduced the time and effort to select the muffler material and optimal design, where both models CNN and RNN-LSTM achieved accuracy above 90% on the test and validation dataset. This work will reinforce the mufflers' industrials, and its design may one day be equipped with deep learning based algorithms.

Auxiliary algorithm to approach a near-global optimum of a multi-objective function in acoustical topology optimization

In this study, an auxiliary algorithm is proposed to avoid local optima in solving an acoustical topology optimization problem by using a gradient-based optimizer. A local optimum convergence issue often occurs in the multi-objective function problem because the sub-objective functions are non-convex in general. In order to overcome this issue and find a near-global optimum, the sign change of sensitivity is heuristically conducted based on the objective function difference at every step of design variable updating. An acoustical topology optimization problem is formulated for improving a noise attenuation performance of a muffler. The heuristic-based auxiliary algorithm is combined with a well-known optimization algorithm to solve the topology optimization problem for a single target frequency as well as a multi-target frequency. Diverse optimal topologies were successfully obtained for various design conditions. Comparison of the optimized solutions by the proposed method and the previous methods strongly supported the validity of the proposed auxiliary algorithm. The application of the proposed method to a suction muffler design problem showed the industrial applicability of the method.

Development of psychoacoustics index for motorcycle exhaust noise by multiple regression method

Exhaust sound is an essential characteristic of a motorcycle when it comes to the interest of young motorcycle riders. It has become such an essential characteristic that riders, after looking into the performance, style, and ergonomics, look into the exhaust sound produced by the muffler. It has thus become critical for motorcycle manufacturers to tune their mufflers in such a way that they are appealing to the customers while adhering to sound emission regulations. As per the current trend of Indian motorcycle rider’s scenario, more attention is given to sound attributes like beat feeling, sportiness, and pleasantness. This research paper aims to develop a psychoacoustic model that can rate the exhaust sound of motorcycles targeting the Indian customer’s preferences and interests with regard to the engine exhaust sound. Presently, a study has been carried out on beat feeling, sportiness, and pleasantness, a perceivable attribute of sound in the family of motorcycles. Motorcycle buyers often perceive the exhaust sound of motorcycles in idling conditions at some distance away from the muffler, which formed the basis while recording exhaust sounds. Initially, exhaust sounds were recorded, which led to the calculation of psychometrics as objective variables. The calculated objective variables were given as input to the multiple regression model. A jury panel consisting of experienced NVH professionals and riders evaluated these sounds on a 7-point evaluation scale. These subjective ratings were given as the target variable to the multiple regression model. The obtained model was later validated with subjective data of motorcycles, including those at the prototype stage. Thus, a model has been established to aid exhaust designers in comparing their motorcycle at different prototype stages with the competitor’s vehicle, allowing them to make an early decision with respect to the muffler design modifications, thereby reducing the time-consuming and expensive jury tests.

Bir Dizel Jeneratörde Artan Motor Yükünün Egzoz Geri Basıncı Üzerindeki Etkisinin Sayısal ve Deneysel İncelenmesi

In this study, the exhaust back pressure (EBP) behavior resulting from the gradual increase in engine load of the exhaust muffler system used in a diesel engine generator was investigated numerically and experimentally. By examining the compatibility of numerical analysis and experimental test exhaust back pressure results with each other, the possibility of eliminating the need for experimental exhaust back pressure test is examined. Firstly, the exhaust gas temperature and flow rate of the selected diesel engine under five different engine loads were experimentally measured. A reactive muffler with perforated pipe, designed to be integrated into the selected engine, was subjected to computational fluid dynamics (CFD) analyzes using measured exhaust gas temperature and gas flow rate. Numerical EBP values were obtained with these numerical analysis studies, which were carried out using the finite volume method in the ANSYS-Fluent program. Finally, the exhaust silencer system, which was manufactured, was subjected to experimental EBP tests under five different engine loads that were gradually increased. According to the numerical and experimental EBP results obtained, it has been observed that the gradual engine load increase in a diesel generator increases the EBP as parabolic. It was understood that the numerical and experimental results of the EBP for different load conditions became more compatible as the engine load increased, and the numerical analysis error rate was found as 4.06% under the 110% engine load which is the critical load condition. In addition, it was concluded that the need for experimental EBP tests can be eliminated by using only numerical studies in the generator exhaust muffler design.

Barrier-free duct muffler for low-frequency sound absorption

We demonstrate a duct muffler design that operates in the low-frequency range (<2000 Hz). The device contained a pair of coupled annular Helmholtz resonators (HRs) and porous material stuffing. HRs were installed as side branches of a circular tube to avoid affecting the ventilation. Porous materials were employed to form an asymmetric intrinsic loss in the HR pair and enable the device to achieve perfect sound absorption. An analytical model based on the temporal coupled-mode theory was derived, and a numerical simulation technique for structural design was introduced and verified. The experimental study demonstrated the effectiveness of the design methodology and illustrated that the device can achieve near-perfect sound absorption in the desired frequency range. A symmetrical configuration of the HRs also experimentally proved to be able to conduct sound absorption for sound incident from both sides of the duct. This study provides a solid foundation for the application of the designed muffler and an analytical explanation of the corresponding sound absorption mechanisms.

Partition layout inside a muffler integrated with a thermoelectric generator: Multi-physics analysis and optimal design

A multi-physics-analysis-based topology optimization (TO) method is proposed to optimally design the internal partition layout of a muffler integrated with a thermoelectric generator (TEG). The basic equations governing the acoustical behavior, heat transfer, and fluid flow in the muffler are introduced, and their interaction is designated for exact numerical analysis in terms of acoustics, heat transfer, and fluid mechanics. To implement density-based TO, one design variable is assigned to each finite element in the design domain, and interpolation functions suitable for each physics phenomenon are employed. In the TO problem formulation, the sum of the squared acoustic pressures at the outlet of the muffler for multi-target frequencies is selected as an objective function to achieve broadband noise attenuation. The temperature of the TEG and the pressure drop are constrained for high energy recovery efficiency and fluid passage, respectively. The optimization problem formulated for the muffler design is solved for various design conditions. Optimal partition layouts are obtained depending on the location and length of the TEG, the upper limit value of the pressure drop, and the number of target frequencies in the same frequency band. The noise attenuation performances of each partition layout are compared, and their expected recovery energies are calculated. One optimal partition layout is discussed in terms of acoustics, heat transfer, and fluid mechanics. The numerical results strongly support the validity of our proposed method for the optimal design of a muffler integrated with a TEG.

Case study: Analysis of acoustic-structure coupling noise characteristics of the exhaust muffler of an internal combustion engine

Exhaust noise produced by internal combustion engines is one of the main problems of vehicle noise, and exhaust mufflers can significantly improve this problem. In fact, the sound waves inside the exhaust muffler will cause the muffler shell to vibrate, causing the muffler to produce shell radiation noise. Therefore, it is necessary to carry out the acoustic-structure coupling analysis of the muffler. This paper improved the design of a prototype straight-through perforated pipe-resistant muffler (design A) and designed a straight-through perforated pipe-resistant muffler with a corrugated lining (design B). Structural modal analysis, acoustic modal analysis, and transmission loss analysis of the two mufflers were carried out. The coupling of the acoustic cavity and structure was considered, and the radiation noise of two kinds of resistant mufflers was comparatively analyzed by the direct-boundary-element method. The acoustic radiation of two kinds of resistant mufflers was studied. The pressure loss of the two kinds of mufflers was studied by aerodynamic analysis. The results suggested that the design B muffler effectively improved the noise reduction performance of the prototype muffler, reduced the vibration displacement amplitude of the shell, and reduced the sound power level of the design A muffler.

A broadband low-frequency muffler based on neural network method and Helmholtz resonator with helical neck

In this study, a design method of broadband low-frequency muffler based on NN method and Helmholtz resonators with helical necks is proposed, which ensures almost perfect ventilation and broadband sound insulation in the low- and medium-frequency range. First, the sound insulation performance of the muffler is improved by adding a helical structure at the port. The slit Helmholtz resonator with a helical structure is able to reduce the cross-sectional area of the resonator port and increase the contact area of thermal viscosity loss, thus reducing the peak frequency of sound insulation and increasing the sound energy loss. Using finite element analysis software, the structural transmission loss is simulated. At the same time, the neural network method is used to predict the combined structure, then, the combined structure can be designed quickly and reasonably to achieve the sound insulation of medium- and low-frequency broadband. Experimental and simulation results show that in the target range of 430 Hz–2220 Hz, the overall TL exceeds 30 dB and the maximum exceeds 60 dB. In addition, when a helical structure is added, the overall pipeline remains unchanged; and when a muffler is added on the basis, the perfect ventilation effect can be achieved. The proposed structural model and the idea of rapid design lay a great foundation for the design and optimization of broadband muffler.

Applying the phononic crystal concept to the intake muffler of a refrigeration compressor

Many previous works explore the creation of wave stop bands (bandgaps) using periodic structures. Aiming at improving the transmission loss of a muffler used in a refrigerant compressor, this work proposes the redesign of an existing intake muffler using the concept of wave attenuation bands caused by Bragg scattering. The challenge consists in designing a phononic crystal (PnC) with bandgaps in the audio frequency range with the size constraints of a practical muffler application. The first part of the research focuses on the development and validation of numerical and experimental techniques to provide guidelines for periodic muffler design. The second part consists in applying the developed concepts and tools to a real compressor muffler following the constraints of the product specifications. A shape optimization technique is used to enlarge the bandgap while keeping the unit cell length in the order of tens of millimeters. Two designs were 3D-printed and tested on the real compressor, reaching 7 dB reduction on the sound power level (SPL) in the aimed frequency band and 4 dB reduction on the overall compressor noise level.

Acoustical Performance of a Double-Expansion Chamber Muffler: Design and Evaluation

Background: Exhaust noise is known to be a major pollutant in the environment and workplaces due to the development of industry and transportation. Exhaust noise can be reduced to normal levels by mufflers or silencers. A reactive muffler efficiently dampens noise at low frequencies by reflecting sound waves. Therefore, muffler design is of great importance in exhaust noise reduction. Transmission loss (TL) is an essential characteristic of mufflers, demonstrating their acoustical properties. Any acoustical appliance is selected based on its damping performance and reliability. Predicting TL through experimentation is different from theoretical calculations. Methods: In the present study, a double-expansion chamber muffler was designed as a reflective muffler on a laboratory scale by equations. Next, TL was evaluated by an impedance tube applying a 4-microphone technique to determine the acoustical performance of the designed muffler. Results: Findings revealed that the TL of the muffler at 312 Hz frequency obtained 27.5 dB agreement with the required TL of the muffler of 25 dB. In addition, the TL of the muffler against frequency attenuates noise in broadband frequencies. Conclusions: These results indicated that the built muffler provides desired TL for exhaust chambers. Therefore, equations can be used as a precise method for muffler design. Furthermore, multi-expansion chamber mufflers are useful for reducing noise at a wide range of frequencies.

Analysis of coupling effect between chambers of reactive muffler

The efficient optimisation of the sound reduction performance of multi-chamber reactive mufflers has always been a challenging problem, not only because of the presence of multiple muffler units but also because of the complicated interactions between the chambers. Previous studies have shown that the interactions between chambers can significantly affect the performance of mufflers. To better understand the coupling mechanism between the chambers and thus provide guidance for the optimisation design of reactive mufflers, first, the sound propagation characteristics in (1) a muffler with two expansion chambers and (2) a muffler with a resonant chamber and an expansion chamber were solved using a two-dimensional (2D) axisymmetric analytical method, combined with a new analytical model of transmission loss (TL), by considering multiple acoustic modes in the mufflers. The influences of key structural parameters on the chamber-coupling effect of the mufflers were investigated. The results reveal that the noise reduction performance of the first chamber deteriorated while that of the second chamber was improved by the coupling effect. To further understand the coupling effect, the coupling mechanism was analysed using acoustic impedance transfer theory. Impedance-tube measurements were carried out to validate the proposed analytical model and inter-chamber coupling effect. Based on the results, the optimisation of a reactive muffler for a bulldozer was carried out. The results obtained by numerical analyses and experiment reveal that the noise attenuation characteristics of the optimised muffler are obviously better than those of the original muffler, and the average insertion loss (IL) increased by 8 dB.

Case study: Numerical study of the noise reduction characteristics of corrugated perforated pipe mufflers

Resistant mufflers are commonly used in the wide band noise control of the exhaust of tractor internal combustion engines due to their simple structure, broadband frequency performance and long service life. In this paper, a corrugated perforated pipe muffler was proposed based on an improved design of a straight-through perforated pipe muffler to reduce the exhaust noise of internal combustion engines. The acoustic attenuation performance of the corrugated perforated tube muffler under the action of nonuniform flow and a temperature gradient was predicted by using the one-way flow-acoustic coupling method, which combines computational fluid dynamics and the acoustic finite element method. The pressure loss and self-noise of the corrugated perforated tube muffler were compared with those of the straight-through perforated tube muffler. The influence of the structural parameters of the corrugated perforated tube mufflers on the transmission loss was analyzed. The significance level of the perforation diameter, peak height, distance between adjacent peaks, and peak width on the transmission loss of the corrugated perforated tube muffler was studied by multiple linear regression analysis.

Research and design of broadband muffler based on second-order Helmholtz resonators

Noise is always a serious factor affecting people's quality of life. The most common sound-absorbing materials are porous materials, which work based on the principle that sound waves entering into the pores inside the material are subjected to air friction and viscous resistance, thus converting sound energy into heat. Porous materials have excellent performance of absorbing medium-frequency and high-frequency sound , but they are required to be thick enough to control the low-frequency sound waves with large wavelengths, which limits the application of porous materials in low-frequency noise control. In recent years, acoustic artificial structures have become a research hotspot, which can realize exotic effective acoustic parameters based on periodical structure or local resonance. Acoustic artificial structure provides a new material basis for noise control, in which Helmholtz resonator plays an important role because of its simple geometry. In this study, a broadband muffler is designed based on the second-order neck embedded Helmholtz resonator. In order to achieve low-frequency and broadband sound insulation with a limited number of units and structure length, the second-order resonator is chosen as a basic structure unit, which has a stronger low-frequency noise reduction capability and has one high-frequency transmission loss peak more than a conventional Helmholtz resonator. The acoustic characteristics and insulation performance of second-order resonators are analyzed through theoretical calculation, simulation calculation and experimental test. Then, based on the theoretical model and empirical rules, a broadband muffler composed of nine second-order resonators is designed by carefully adjusting the geometry parameters of each resonator. The three-dimensional printed resonators are installed on the side wall of a square standing wave tube for experimental measurement. In the experiment, the transmission loss curve of the muffler is measured by the two-load method. The result shows that the designed muffler has good sound insulation performances in a frequency range of 267–927 Hz, with the whole transmission loss above 20 dB and the maximum sound insulation up to 60 dB. The experimental result is consistent with the calculation result and simulation result. The muffler has simple structure and high practicability, which will have a wide application prospect in noise control engineering.

Scientific and Practical Approaches to Improving Noise Muffler Designs of Piston Internal Combustion Engines Based on Theory of Numbers

A methodological method based on the use of the theory of preferred numbers has been proposed in order to improve the most important parameters of the working bodies of noise mufflers. As a result of many years of scientific research, the authors have established a previously unknown theoretical relationship between the main series of preferred numbers, golden ratio and Fibonacci series numbers. A new direction in the development of number theory has been considered in the paper, its classification has been compiled, including the geometric theory of numbers, preferred numbers, containing a new basic series of preferred numbers using the Fibonacci sequence. New formulas have been obtained to determine the denominators of geometric progressions for the series of preferred numbers and the area of a circle. Determining the area of a circle using the new formula allows to get more accurate values. A new formula for determining the circumference of a circle has also been derived. The designs of perforated partitions have been developed, in which the laws of the new basic series of preferred numbers are used. Determining the area of a circle using the new formula allows you to get more accurate values. A new formula for determining the circumference of a circle is also obtained. The designs of perforated partitions have been developed, in which the regularities of the new basic series of preferred numbers have been used. A calculated substantiation of the main geometric and structural dimensions of noise mufflers is given using a mathematical model of a perforated golden partition and new basic series of preferred numbers, which allow to obtain a noise muffler design that has the lowest possible aerodynamic resistance with the maximum possible reduction in the noise level of exhaust gases from internal combustion engines. An innovative model of a noise muffler for reciprocating internal combustion engines with improved hydraulic and acoustic characteristics based on the theory of numbers is proposed in the paper. The theory of preferred numbers applies to any technical device.

Optimization of Exhaust Muffler Design Variables for Transmission Loss Using Coupling of modeFRONTIER and GT-POWER

<div class="section abstract"><div class="htmlview paragraph">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.</div></div>

Design of a metamaterial-based muffler for a target frequency range

This work proposes an acoustic metamaterial-based muffler that effectively blocks a transmission noise for a target frequency range. Since the acoustic metamaterial-based muffler consists of arrayed unit cells, its noise attenuation performance is strongly affected by the internal layout of the unit cell. The wave transmission characteristics of an acoustic metamaterial is explained by the effective bulk modulus and dispersion curve of an unit cell. Therefore, the internal layout of the unit cell should be optimally designed so that its band gap should include the target frequency range of a muffler. To the end, an acoustical size optimization problem is formulated to design a unit cell of the muffler and is solved for a given design requirement. The noise blocking frequency range of the unit cell is characterized by the bandgap in its dispersion curve during the optimization process. The wave transmission characteristics of the metamaterial muffler is validated experimentally.