Muffler Design Research Articles

A hybrid method technique for design and optimization of Formula race car exhaust muffler

AbstractIn this work a multilevel Computational Fluid Dynamics (CFD) analysis has been applied for the design of a Formula race car exhaust muffler with improved characteristics of sound pressure level (SPL) and fluid dynamic response. The approaches developed and applied for the optimization process range from the 1D to fully 3D CFD simulation, exploring hybrid approaches based on the integration of a 1D model with 3D tools. Modern mufflers typically have a complex system of chambers and flow paths. There are a variety of sound damping and absorbing mechanisms working to quiet the sound flowing through a muffler and piping system. Two calculation methods were selected for this study. The muffler has a complex inner structure containing perforated pipe and fiber material. Computer-aided design (CAD) file of the muffler was established for developing Finite Element Analysis (FEA) model in AVL BOOST v2017 and another commercial advanced design software (SolidWorks 2017). FEA model was made to monitor the flow properties, pressure and velocity. After the model was verified, sensitivity studies of design parameters were performed to optimize the SPL of the muffler. The software analysis results are included in the paper. Recommendations are made for obtaining smoother SPL curves for various measurement methods.

System Design and Characteristic Analysis of Intelligent Follow-up Hydraulic Muffler

The pulsating flow output of plunger pump will produce pressure pulsation after flowing through the pipeline. Using hydraulic muffler to attenuate the pressure pulsation of the pipeline is an economical, reliable and easy to implement method. Intelligent follow-up hydraulic muffler, which adapts to pressure pulsation changing at any time by changing its own parameters, has become a research hotspot. Intelligent follow-up hydraulic muffler can accurately and effectively attenuate the pressure pulsation of the system and maximize the attenuation performance of the hydraulic muffler. The structure and performance of the existing intelligent follow-up hydraulic muffler are mainly introduced. The general methods, principles, advantages and disadvantages of intelligent follow-up hydraulic muffler design are summarized. On this basis, the development trend of intelligent hydraulic muffler is predicted and prospected.

Research on Computational Data Simulation of Automobile Engine Exhaust Muffler Performance

In this paper, the transfer matrix method is used to simulate and calculate the insertion loss of muffler. This simulation method can evaluate the acoustic characteristics of the exhaust system. After deriving the transfer matrix of six kinds of silencing units, it is applied to the calculation of insertion loss. In this paper, a mathematical model of noise attenuation is established to analyze the relationship between the characteristics of muffler and acoustic attenuation. We can take the noise reduction as the objective function to optimize the muffler design. The mathematical model of pressure loss can be used to evaluate the aerodynamic performance of muffler.

Design and Analysis of Automotive Mufflers for Noise Attenuation: A Review

Noise pollution is the major drawback of I.C. engines. Automotive engineers and researchers have been working consistently on reducing automotive noise as well as pollution. While designing the mufflers; care has to be taken not only for noise reduction but also for exhaust emission, back pressure, space constraints, cost incurred, etc. Various methods to design and analyze the mufflers have been devised by researchers across the globe. Many guidelines have been provided by the authors in this regard. In the present paper, an attempt is made to present a comprehensive review of literature in context to design and analysis of automotive mufflers.

Calculation of the required noise reduction of a engine exhaust system

The problem of reduction of internal combustion engine (ICE) noise is most urgent at present when the fleet of vehicles has significantly expanded and their power has increased. Reactive mufflers are often used to solve it. The initial stage in the design of mufflers is a theoretical assessment of the frequency spectrum of sound power level (SPL) of an unmuffled ICE noise source, comparing it with the calculated maximum permissible spectrum and determining the required amount of its reduction in standard frequency bands. The paper presents a method for calculating the required noise reduction of a transport engine exhaust using the example of a two-stroke ICE of the class of 125 cm3. Thus, the designer has the opportunity to develop mufflers, the acoustic efficiency of which meets the calculated required noise reduction values, already at an early stage of the vehicle design.

The design of noise attenuation for gas turbine GTS 22 engine

Nowadays, awareness of global society to the green concept where life should be in harmony with nature has been increasing. One of the ideas in the green concept is to reduce excessive sound exposures or noise. Within this context, gas turbine GTS 22 engine is one of mechanical system that generates a very high sound pressure level. Hence, it is instructive to develop noise controls for the gas turbine in order to have acceptable sound pressure level. This research is focused on the design of muffler as noise control treatment after carefully analyzing the dominant noise spectrum of the gas turbine. In this paper, numerical approach is employed to design the muffler. The results are then validated by experimental ones. Moreover, noise reduction (NR) is used to assess the muffler performances. The design of muffler in this research contains all of combination treatment: area cross section expansion chamber, perforated system (micro perforated panel), porous material, partition chamber and concentric tube. The chosen final design of muffler is combination treatment design where NR 38.77 dB is present. This NR leads to sound pressure level of 80.82 dB or 68.95 dBA exist after the muffler applied on the exhaust of gas turbine. The deviation of experimental results compared to numerical ones is 7.14% in average. Moreover, the pressure drop (ΔP) of the muffler is only 0.4042% which is acceptable to keep the mechanical performance.

Optimal Design of Mufflers Equipped with Pod and Concentric Acoustical Rings using the SA Method

There has been, of recently, much research on mufflers lined with sound absorbing material. In dealing with high frequency noise emitted from venting systems, a sound absorbing material inside a tube covered with a perforated plate has been used. However, the acoustical performance of mufflers equipped with one-layer of sound absorbing material has still proved to be insufficient. In order to promote acoustic performance, a design and theoretical assessment on pod mufflers hybridized with multi-layer concentric sound- absorbing rings is proposed. By using the acoustical-lumped-method, a four-pole system matrix for evaluating the acoustic performance (STL) will emerge. During the optimization process, the simulated annealing (SA) method, which is a robust scheme utilized to search for the global optimum by imitating a physical annealing process, is used. Before dealing with a broadband noise, the STL’s maximization relative to a one-tone noise (1000Hz) is offered to confirm the SA method’s reliability. To appreciate the influence of acoustical efficiency with respect to the design parameters, an analysis of design parameters (dh: the diameter of a perforated hole; W: the width of an air channel; R: acoustic flow resistivity of the acoustic fiber; σ : the porosity of the perforated plate; Df: the thickness of the acoustic fiber; L1: the horizontal length of the sound absorbing ring) is completed. Subsequently, to bring into focus the acoustical interaction with respect to the number of air-channels (between the sound absorbing rings), three types of mufflers (mufflers A∼C) hybridized with one, two, and three air-channels have been surveyed. Results reveal that for a rectangular muffler internally conjugated with one air-channel, the maximal STL is located at the desired tone, and the acoustical performance of a cone muffler will increase if the number of air-channels internally conjugated within the cone muffler increases. Consequently, the approach used for the optimal design of the STL on pod mufflers internally equipped with multiple air-channels within a space-constrained situation can be easily assessed.

Design and Optimization of an Exhaustive Muffler and Experimentation to reduce Emission using Fly ash

Exhaust gases from the combustion of the air-fuel mixture are reduced to non-harmful gases before releasing them into the atmosphere using a catalytic converter. Exhaust muffler or silencer are used to reduce noise and vibrations level due to the expansion of gases. In this research, a novel muffler is designed for 4-stroke, 125cc single-cylinder petrol engine and structural analysis are carried out for optimization using ANSYS Static Structural solver. The muffler is subjected to various pressure loads, acceleration loads, and load due to self-weight. Fatigue analysis is further carried out using stress-life approach and mean Soderberg theory of failures to determine Life, Damage, Safety factor, Biaxiality Indication, and Alternating equivalent stress under dynamic loading. Experimental analysis is carried out using an optimized muffler with fly ash as a catalyst to determine the reduction in emission. Structural analysis of the initial model was optimized by slight modification in design which reduced total deformation from 0.0379 mm to 0.0374 mm and equivalent stress from 52.878 Mpa to 50.969 Mpa. The safety factor was also increased from 1.6302 to 1.6902. Experimental results using Gas analyzer used for emission readings have shown a reduction in the emission of carbon monoxide and hydrocarbons by 21.06% and 23.07% respectively as compared to a standard muffler.

Methods for evaluating in-duct noise attenuation performance in a muffler design problem

In this study, methods for evaluating the noise attenuation performance of a muffler in a muffler design problem are investigated, and a proper evaluation method is suggested for actual noise reduction in a duct when an optimally designed muffler is mounted on a duct. Mathematical expressions of the transmission loss, insertion loss, and level difference for a simple expansion chamber muffler are developed from basic acoustic equations. The effects of the locations of the measurement points, tailpipe length, and impedance at the end of the duct on the noise attenuation performance calculated using the three evaluation methods are discussed. The TL and IL maximization problems formulated using topology optimization are solved for a muffler unit, and the noise attenuation performances of the optimally designed mufflers are compared when mounted on a duct. Another acoustical topology optimization problem, a partition volume minimization problem for a muffler design, is formulated to reduce the in-duct broadband noise, and the noise attenuation performance of the optimal muffler obtained using this formulation is experimentally validated. These research results will contribute to the development of a muffler design method with high accuracy by reducing the discrepancy between the noise attenuation performances of a muffler unit and a muffler mounted on a duct.

A tunable metamaterial muffler with a membrane structure based on Helmholtz cavities

With the recent advances in acoustic metamaterial science, the possibility of sound attenuation using Helmholtz cavity structures while reducing low-frequency noise has been demonstrated. However, the ongoing challenge addressed herein is the fact that among Helmholtz cavity structures to date, the silencing frequency is fixed in the traditional muffler. It is very inflexible in practical applications. To address this challenge, we first proposed a muffler with a membrane structure and multi-Helmholtz cavities. By simplifying the structure into a mass-spring model, we derived the negative mass density of a varying number of membranes. Next, we calculated the transmission loss (TL) through simulation using COMSOL software. The results of our analysis confirmed that the muffler can reduce noise when the mass density is negative, and the silencing frequency can be tuned by changing the number of membranes. The proposed adjustable muffler was validated experimentally, demonstrating a reduction in the transmission loss over 20 dB. This multi-cavity and multi-membrane metamaterial design enables the silencing frequency to be controlled based on the number of membranes, which may be used in applications in which the silencing frequency needs to be adjusted based on different environments. Our findings can be widely applied to guide the design and optimisation of metamaterial mufflers.

Measurement of fluctuation at the discharge of positive displacement compressors

All positive displacement compressors (PDC’s) experience pressure fluctuation at the discharge ports of the compression mechanism, and these fluctuations can adversely affect compressor performance. These pressure fluctuations are caused by the nature of PDC’s; when a pocket of working fluid is exposed to system piping at differing pressure levels, a wave of pressure equalization flows through the line, potentially causing the compressor and piping to vibrate and generate noise (Soedel 2007). Compressor manufacturers currently use serial muffler designs, discharge plenums, and valves to minimize this fluctuation, but pressure fluctuation may persist at the outlet of serial muffling methods. A parallel muffling design has been developed for use in Roots blowers, having significantly reduced noise and pressure fluctuation seen in these machines (Huang et al. 2014). To identify the potential for use of this parallel muffling design in refrigeration systems and PDC’s, the magnitude of fluctuation at the discharge of a scroll compressor and a dual rotary compressor have been measured at various operating conditions. The compressors were left unmodified, with any current internal muffling methods in place. The measurement of these unmodified compressors determined the effectiveness of current muffling methods, with the intent to determine if using a parallel muffling technique is warranted. Pressure measurements were taken at 1000 Hz, and Fast Fourier Transform implemented to isolate pressure fluctuation based on frequency. Measurements lead to magnitudes of up to 16 kPa in pressure fluctuation with current muffling methods, indicating that further fluctuation reduction is possible.

Numerical analysis of circular straight mufflers equipped with three chambers at high-order-modes

Plane wave theory has been used in predicting the acoustical performance of one-chamber straight mufflers. But, the acoustical effect of the mufflers at higher frequencies that are beyond the threshold of the cut-off frequency has been neglected. In addition, there is a need for a more compact muffler design for use inside a space-constrained working area. In order to improve the acoustical performance of straight mufflers, a space-constrained multi-chamber muffler using a more accurate predicting model in conjunction with an optimizer is proposed.In this paper, an eigen function that uses a three dimensional wave propagation to deduce the acoustical field as a four-pole matrix form is applied. An overall four-pole system matrix that multiplies individual matrices is adopted in evaluating the Transmission Loss (TL) for the hybrid mufflers. A circular and three-chamber straight muffler is introduced and optimized for various targeted tones using both Genetic Algorithm (GA) and Simulated Annealing (SA) Methods in conjunction with five objective functions (case A–case E). Before the optimization process is carried out, an accuracy check of the mathematical models for the circular one-chamber muffler is carried out. In order to verify the reliability of the GA and SA methods, a single-objective optimization of the three-chamber straight muffler at a targeted tone of 2000 Hz using GA method and SA method has been executed. Results reveal that the TL can be maximized at the targeted frequency when using either the GA method or the SA method. In addition, the noise reduction will increase if the number of chambers increases. Moreover, the acoustical performance of the mufflers will be reversely proportional to the diameter of the inlet/outlet tubes. Consequently, results reveal that the TL of the circular hybrid mufflers at targeted frequencies can be simultaneously improved by using the fourth and fifth strategies of objective functions in which the inverse of the summation summing up the individual target frequency’s deviation square between the targeted transmission loss and the predicted transmission loss has been built.

Exhaust System Muffler Volume Optimization of Light Commercial passenger Car Using Transfer Matrix Method

Nowadays, the automotive industry is focused on weight and size reduction. Main advantage of this weight and size reduction are improving the fuel economy. The specific fuel consumption of a vehicle can be improved through e.g. downsizing area of heat loss, if we focus on vehicle with weight reduction. Weight reduction can be done by replacing material or by changing the size (dimensions) of components. In the present work we have focused on Audi A6 muffler, troubleshooting and optimizing the muffler by changing pipe length of inlet and outlet, also by replacing the original mesh plate to porous pipe. Based on optimization, prototype has been built with the help of 3D design tool CATIA V5 and the calculations of transmission loss (TL) have been performed by MATLAB. Plane wave-based models such as the transfer matrix method (TMM) can offer fast initial prototype solutions for muffler designers. The principles of TMM for predicting the transmission loss of a muffler was used. Result of this present study of an existing muffler has been analysed and then compared with vehicle level test observation data. Noise level have been optimized for new muffler design. Other literatures were played significant rule for validate our results.

Design of muffled singing masks

Nowadays, we are not allowed to speak loudly and sing loudly in outdoor environment and our environment. Based on this, the design of muffler masks is proposed. This design adds a circuit which transmits the electric signals generated by microphones to the earphone on the normal headphones to realize the ear return function. After that, different materials are studied through experiments. The change of penetration rate and respiratory resistance of masks with different structures and layers under different flow rates; and the change of singing voice under different layers was detected by noise analyzer, and the optimum layers of sound-proof cotton were finally determined, so as to achieve the effect of silencing.

Simulation-based structural design of diesel generator mufflers and their performance analysis

Aiming at the frequency spectrum characteristics of diesel generator noise, simulation study and physical experiment are made, in this paper, for the structure design of diesel generator mufflers by means of theoretical analysis and GT-POWER simulation, and the noise reduction performance of the designed diesel generator mufflers is theoretically analysed. The results show that elliptical cross-section mufflers show almost the same muffling effect as square cross-section mufflers, while square cross-section mufflers are more suitable for mass production; the length of the first cavity and the overlapped section of the insertion pipe present a remarkable noise reduction on low- and mid-range frequency; shortening the distance between the 1/4 wavelength pipe and the main pipe's confluence is more conducive to noise reduction; the addition of dissipative materials improves the muffling performance. Based on the above structure, a simulation model of impedance composite muffler was designed, with its A-weighting noise level dropped from the original 92.2 dB to 59.7 dB, thus achieving a good noise reduction effect.

Simulation-based structural design of diesel generator mufflers and their performance analysis

Aiming at the frequency spectrum characteristics of diesel generator noise, simulation study and physical experiment are made, in this paper, for the structure design of diesel generator mufflers by means of theoretical analysis and GT-POWER simulation, and the noise reduction performance of the designed diesel generator mufflers is theoretically analysed. The results show that elliptical cross-section mufflers show almost the same muffling effect as square cross-section mufflers, while square cross-section mufflers are more suitable for mass production; the length of the first cavity and the overlapped section of the insertion pipe present a remarkable noise reduction on low- and mid-range frequency; shortening the distance between the 1/4 wavelength pipe and the main pipe's confluence is more conducive to noise reduction; the addition of dissipative materials improves the muffling performance. Based on the above structure, a simulation model of impedance composite muffler was designed, with its A-weighting noise level dropped from the original 92.2 dB to 59.7 dB, thus achieving a good noise reduction effect.

The Design of Follow-up Hydraulic Muffler Based on Spring-Damp Regulating Device

The follow-up hydraulic muffler can make the natural frequency of the muffler equal to systematic pulsation frequency in time by changing the section area of the quality chamber so as to achieve the best attenuation effect. In this paper, a spring-damp regulator is installed on the basis of the hydraulic muffler, and the static and dynamic characteristics of the follow-up hydraulic muffler are analyzed by measuring the rotational speed of the pump with the sensor. The results show that the hydraulic muffler based on the spring-damp regulator can effectively attenuate the pulsation.

Effects of Central Tube on Shape of Modal Duct of a Helicoid in a Simple Expansion Chamber

The shape of the modal duct of an acoustic wave propagating in a muffling system varies with the internal geometry. This shape can be either as a result of plane wave propagation or three-dimensional wave propagation. These shapes depict the distribution of acoustic pressure that may be used in the design or modification of mufflers to create resonance at cut-off frequencies and hence achieve noise attenuation or special effects on the output of the noise. This research compares the shapes of acoustic duct modes of two sets of four pitch configurations of a helicoid in a simple expansion chamber with and without a central tube. Models are generated using Autodesk Inventor modeling software and imported into ANSYS 18.2, where a fluid volume from the complex computer-aided-design (CAD) geometry is extracted for three-dimensional (3D) analysis. Mesh is generated to capture the details of the fluid cavity for frequency range between 0 and 2000Hz. After defining acoustic properties, acoustic boundary conditions and loads were defined at inlet and outlet ports before computation. Postprocessed acoustic results of the modal shapes and transmission loss (TL) characteristics of the two configurations were obtained and compared for geometries of the same helical pitch. It was established that whereas plane wave propagation in a simple expansion chamber (SEC) resulted in a clearly defined acoustic pressure pattern across the propagation path, the distribution in the configurations with and without the central tube depicted three-dimensional acoustic wave propagation characteristics, with patterns scattering or consolidating to regions of either very low or very high acoustic pressure differentials. A difference of about 80 decibels between the highest and lowest acoustic pressure levels was observed for the modal duct of the geometry with four turns and with a central tube. On the other hand, the shape of the TL curve shifts from a sinusoidal-shaped profile with well-defined peaks and valleys in definite multiples of π for the simple expansion chamber, while that of the other two configurations depended on the variation in wavelength that affects the location of occurrence of cut-on or cut-off frequency. The geometry with four turns and a central tube had a maximum value of TL of about 90 decibels at approximately 1900Hz.

Muffler Design with Baffle Effect and Performations on Transmission Loss

Abstract A typical sound generated by vibrational waves is usually based on the experience and design experience, which can be enhanced by optimizing the internal structure of the exhaust system. The use of baffles and perforations has a significant effect on reducing the transmission loss in a silencer exhaust system. In order to evaluate the response effect of a silencer, the effect of baffle and perforations, without baffles and perforations, was evaluated in COMSOL5.2 software. Which results in numerical results with close experimental results and the effect of buffaloes and perforations, have shown a good reduction in transmissibility, and their partial differences are due to the features of geometry design.

Modification of Muffler design to increase exit velocity

The Muffler is the most predominant part of an automobile exhaust system. The function of the Muffler is to evacuate the exhaust gases from the combustion chamber, attenuating the sound created by the engine. Any minute change in the Muffler can alter the performance of the engine. The main objective of this work is to increase the exit velocity of the Muffler. A Maruti alto 800cc muffler was taken, examined and a 3d model was created. This model was analyzed for velocity at the outlet of the muffler using CFD. Alternate designs had been developed and were analyzed. Results were compared to obtain an optimized model. Modeling was done in UG NX 11.0, the analysis was carried out in CFX (fluent) Workbench 18.0.