Hybrid Muffler Research Articles

Investigating the Effect of Acoustic Performance on Vibration Signatures for Optimized Hybrid Muffler

Investigating the Effect of Acoustic Performance on Vibration Signatures for Optimized Hybrid Muffler

Acoustic performance analysis of muffler by varying sound absorption materials

Noise is an unwanted sound which is greatly affecting the human health over the years. The high pressure gases coming out from the exhaust system of automotive vehicle is one such unwanted noise, which is increasing drastically. This lead to increase in health issue and looking into it, various legislative bodies have set limitation on the overall sound level coming from the exhaust system. Muffler is one such device which is used for reducing this exhaust system noise. These mufflers are composed of different acoustic elements such as perforated tube, baffles, sound absorption materials etc. Hybrid muffler is one such muffler which is composed of baffles, uniform tube, and sound absorption materials which dissipates the high pressure gases. In this study, the acoustic performance of hybrid muffler is obtained by implementing different grades of sound absorption materials such as Glasswool, rockwool, melamine etc. Pressure acoustic frequency domain analysis was performed for these mufflers to determine the acoustic performance parameters i.e. transmission loss and sound pressure level using Comsol Multiphysics. The maximum transmission loss value was obtained for the muffler, when Glasswool 701 with flow resistivity of 14000 Pa.s/m2 was used as the sound absorption material. The results obtained through this analysis was validated through experiment performed in impedance tube setup This hybrid muffler helped in reducing maximum exhaust system noise and the overall sound pressure level also decreased at the outlet of the hybrid muffler.

Finite Element Approach for Three-Dimensional Linearized Potential Equation with Application to Muffler Acoustic Attenuation Prediction

In this paper, a three-dimensional finite element method for solving the linearized potential equation (LPE) is implemented to predict the acoustic attenuation performance of mufflers in the presence of nonuniform flow. For accurate physical representations, the porous material is modeled as equivalent fluid with complex speed of sound and density while the background mean flow in fluid domain is captured by solving Reynolds-averaged Navier–Stokes equations. The treatment details for boundary integrals at different boundary conditions and expressions for transmission loss are presented. Good agreements of predicted and measured transmission loss of two reactive and a hybrid mufflers validated the present approach. Finally, the convective effect of nonuniform flow on the acoustic attenuation behavior of the hybrid muffler is examined numerically in detail.

Optimization of Circular Silencers Internally Hybridized with Multiple Reverse Chambers Using the GA Method

A noise abatement method using an eigen function in conjunction with an optimizer (Genetic Algorithm) under a space-constrain situation is proposed in this study concerning a high order wave propagation effect. An eigen function is used to describe an acoustical field and shorten the acoustical model in a four-pole transfer matrix form. The system’s four-pole matrix estimates the Transmission Loss (TL) for the silencers by multiplying individual four-pole matrices. Additionally, a case study of an air compressor’s broadband noise elimination is introduced. Three types of circular reverse silencers (silencers A-C) internally hybridized with multiple straight chambers are adopted to efficiently suppress the noise wave. Considering broadband characteristics and space-constrained situations, an average-deviation-integrating form used as an objective function is presented and linked to an optimizer-GA (Genetic Algorithm). Acoustical models for silencers A to C are checked before the numerical optimization is performed. A pure tone optimization is executed to assure the consistency of the GA scheme. The result shows that the overall noise drop is enhanced and the number of straight expansion chambers installed at the inlet/outlet of the circular reverse silencer increases. Consequently, concerning a space-constrained situation in the real world and the characteristics of the broadband noise spectrum, an efficient method is proposed in this paper for designing an optimally shaped hybrid muffler using the objective function in conjunction with an optimization scheme.

Optimization of absorption material layer thickness in different chambers of hybrid muffler using Taguchi approach

Optimization of absorption material layer thickness in different chambers of hybrid muffler using Taguchi approach

Acoustic attenuation characteristics of the muffler phononic crystal with hybrid resonators

Aiming at achieving broadband and strong sound attenuation in the duct, this study proposes one compact and hybrid muffler phononic crystal. The two-dimensional (2D) transfer matrix method is applied to calculate the transmission loss (TL) of one unit cell validated by the numerical simulation and experiment. On this basis, the unit cell dispersion theory is employed to predict the bandgap properties of the infinite periodic mufflers. The sound reduction mechanism in the hybrid muffler is disclosed, while the effect of the period number on the acoustic performance is examined. It demonstrated that the acoustic resonant behaviors of the short-length mufflers are conducive to the continuous and superior attenuation band through the compact structure. The number of the TL domes and the boundary length of the short chamber could be evaluated by the cut-off frequency at the (0,1) radial mode and the first passing frequency for the muffler. Although each resonant-type component of the hybrid muffler is responsible for the TL peaks at different frequency ranges, via the coupling effect, they provide remarkably improved performance over a wide frequency range. The unit cell periodicity brings two types of bandgap, the locally resonant bandgap (LRG) and Bragg bandgap (BG), further enhancing the attenuation amplitude. Utilizing the different resonance mechanisms as well as the merging of the LRG and BG, the hybrid muffler phononic crystal is improved, which possesses a wide attenuation range with a tinier structure. The results develop new approaches for broadband and strong sound attenuation using the concept of the phononic crystal and offer a promising application in duct noise control.

Optimization of a reactive muffler used in four-cylinder petrol engine into hybrid muffler by using CFD analysis

Four-wheeler automotive vehicle is the basic need of people in today’s life all over the world. But the noise coming from the exhaust system is highly affecting the human health. Among all the noise produce in vehicle, exhaust system noise is maximum. Muffler is one such acoustic filter used for reducing this exhaust noise. Hybrid muffler is one type of muffler which combines the properties of both reactive muffler and dissipative muffler and it operates at wide frequency range. In this study an already existing muffler (Reactive type muffler) used in 91bhp, 6000 RPM four-cylinder petrol engine was optimized to hybrid muffler. Aerodynamic and acoustic performance parameters were the main performance parameter and were determined by CFD analysis and acoustic analysis. The existing reactive muffler of the four-cylinder petrol engine could be replaced by the hybrid muffler. Here the mufflers were designed in ANSYS design modular and analyses were performed in ANSYS Fluent and COMSOL software. CFD analysis was performed for the existing muffler and three other newly designed muffler by considering inlet velocity boundary condition at inlet velocity 40 m/s and 80 m/s. It was observed that increase in pressure drop (aerodynamic performance) in model 4, model 3 and model 2 is around 38%, 33.2% and 29% respectively. Again, from acoustic analysis the transmission loss (TL) in model 4 was observed to be 47 dB whereas in other models it was around 20 dB. Further it was observed that the sound pressure level from model 1 at the exit is around 75–78 dB whereas in model 4 it was observed to be around 45–50 dB at the exit. Hence from both the analysis it is concluded that model 4 which is hybrid type muffler is the most optimized muffler.

Upoređivanje tehnike hibridne metode i metode transfer matrice kod optimizacije dizajna prigušnika motornog vozila

Hybrid mufflers are now commonly equipped to decrease vehicle noise and are a crucial tool for regulation of the acoustic system. In order to ensure optimum engine efficiency, the system is intended to dump the strength of the acoustic pulses generated from the engine, and the back pressure created by these systems must be held to a minimum. Typically, modern mufflers have a complex structure of chambers and flow paths. There are a number of mechanisms for sound dampening that operate to silence the sound flowing through a muffler and piping device. This research introduces an important approach to optimize the transmission loss of hybrid muffler Formula student race car (FS) by using both experimental and analytical methods. For this analysis, two methods of calculation were chosen. The muffler has a complex partition located within the muffler chamber, which is a perforated pipe. For the creation of the Finite Element Analysis (FEA) model in AVL BOOST solver and another commercial advanced design software, the muffler CAD file was developed. Experimental measurements using a two-load method validated the FEA model. Reliable tests were conducted to verify the design parameters and optimize the muffler's transmission loss (TL) after the model was checked. The findings of experimental and machine analysis are included in the paper. For different measurement methods, recommendations are made for achieving optimum transmission loss curves.

Topology and shape optimization of dissipative and hybrid mufflers

This article presents a topology optimization (TO) method developed for maximizing the acoustic attenuation of a perforated dissipative muffler in the targeted frequency range by optimally distributing the absorbent material within the chamber. The finite element method (FEM) is applied to the wave equation formulated in terms of acoustic pressure (chamber) and velocity potential (central duct, due to the existence of thermal gradients and mean flow) in order to evaluate the acoustic performance of the noise control device in terms of transmission loss (TL). Sound propagation through the chamber fibrous material is modeled considering complex equivalent acoustic properties, which vary spatially not only as a function of temperature but also as a function of the filling density, since non-homogeneous density distributions are considered. The acoustic coupling at the perforated duct is performed by introducing a coordinate-dependent equivalent impedance. The objective function to maximize is expressed as the mean TL in the targeted frequency range. The sensitivities of this function with respect to the filling density of each element in the chamber are evaluated following the standard adjoint method. The method of moving asymptotes (MMA) is used to update the design variables at each iteration of the TO process, keeping the weight of absorbent material equal or lower than a given value, while maximizing attenuation. Additionally, several particular designs inferred from the topology optimization results are analyzed. For example, the sizing optimization of a number of rings is carried out simultaneously with the aforementioned TO process (density layout). A reactive chamber is added in order to evaluate the TL of a hybrid muffler and its shape optimization is also carried out simultaneously with the aforementioned TO. Results show an increase in the muffler’s mean TL at target frequencies, for all cases under study, while the amount of absorbent material used is maintained or even reduced.

Effects of Parameters of Helmholtz Resonator on Transmission Loss of Hybrid Muffler

Expansion chamber and Helmholtz resonators are widely used in noise control. In this paper, they are combined to use as a hybrid muffler. The analysis is done to investigate the influence of the parameters of Helmholtz resonator on transmission loss. The transfer matrix method is used in the analysis. The result of transmission loss from the transfer matrix method is validated with the result from experimental two-load method using four microphones impedance tube. After had the transmission loss of the hybrid muffler been validated, the study was proceeded to investigate the effects of parameters of Helmholtz resonator on the transmission loss. The root mean square value of transmission loss were also calculated to compare the transmission losses clearly. In this paper, we investigated the effect of length of the neck of Helmholtz resonator, the effect of diameter of the neck of Helmholtz resonator, the effect of the length of the Helmholtz resonator cavity and the effect of the diameter of the Helmholtz resonator cavity for stationary medium. It is found that the transmission loss is increased when the diameter of the neck of Helmholtz resonator is increased. When the length of the neck is reduced, the transmission loss is increased. The transmission loss can also be increased by reducing the diameter of resonator cavity. It is better to increase the transmission loss at low frequencies by increasing the length of the resonator cavity.

The effect of using passive hybrid muffler on a small generator set noise fuelled by natural gas

A detailed experimental study has been conducted to evaluate the effect of a hybrid muffler (HM) installation on sound emission of a small generator set fuelled by natural gas, which was covered by an acoustic enclosure. Specifications of a reactive muffler were calculated according to recommendation of ASHRAE 2.6 technical committee and based on an appropriate muffler was selected. The selected muffler was added to the muffler installed by manufacturer on generator (GM) and formed hybrid muffler (HM). The sound of generator set was measured for GM and HM setups on four sides of the generator at five different loading conditions (0, 25, 50, 75 and 100% load) using a sound level meter. The results showed that application of HM could reduce the sound of generator at firing frequency (31.5 Hz) and frequencies greater than 1000 Hz, with the maximum values of 11.7 and 26 dB, respectively. The overall A-weighted generator sound was in the range of 73.2–85.8 dB (A) at all the loading conditions and sides by using HM. The acoustical performance of HM on the side with the maximum generator sound (side 1) increased from 5.1 dB (A) at no load to 10.61 dB (A) at full load conditions. Therefore, the HM usage could be recommended as a useful approach to attenuate the generator sound.

Three-pass perforated tube muffler with perforated bulkheads

The one-dimensional analytical approach is developed to predict and analyze the acoustic attenuation performance of three-pass perforated tube muffler with perforated bulkhead(s) and validated by comparing the transmission loss results from one-dimensional analytical approach and finite element method. The one-dimensional analytical approach is then used to investigate the effect of perforated bulkhead(s) on the acoustic attenuation performance of three-pass perforated tube reactive and hybrid mufflers. The results indicated that perforates on the bulkhead may change the resonant frequency of the three-pass perforated tube reactive muffler, and the resonance frequency is shifted to higher frequency with the increase in the porosity of perforation. The sound-absorbing material filling in the middle chamber may improve the acoustic attenuation performance of the mufflers from middle to high frequencies, while the acoustic attenuation performance around the resonance frequencies is lowered somewhat; therefore, a flatter acoustic response may be formed for the hybrid muffler than the reactive muffler.

Performance of Transmission Loss on Hybrid Muffler by Using Rock Wool and Glass Fiber as a Absorbing Materials

Performance of Transmission Loss on Hybrid Muffler by Using Rock Wool and Glass Fiber as a Absorbing Materials

Performance of Transmission Loss on Hybrid Muffler by Using Rock Wool and Glass Fiber as a Absorbing Materials

Performance of Transmission Loss on Hybrid Muffler by Using Rock Wool and Glass Fiber as a Absorbing Materials

Genetic Algorithm Optimization on a Venting System With Three-Chamber Hybrid Mufflers Within a Constrained Back Pressure and Space

Recently, research on new techniques for dissipative mufflers in dealing with the higher frequencies has been addressed. However, the shape optimization of hybrid mufflers in reducing broadband noise within a constrained space as well as a pressure-drop limit which are both concerned with the necessity of operation and system venting in practical engineering work was rarely tackled. Therefore, this study will not only analyze the sound transmission loss (STL) of a space-constrained multichamber hybrid muffler but also optimize the best design shape under a specified pressure drop. In this paper, the generalized decoupling technique and plane wave theory used to solve the coupled acoustical problem of perforated mufflers with/without sound absorbing material are presented. The four-pole system matrix used to evaluate acoustic performance is also introduced in conjunction with a genetic algorithm (GA). A numerical case for eliminating a broadband venting noise emitted from a pressure relief valve using four kinds of hybrid mufflers is also introduced. To verify the reliability of the GA optimization, optimal noise abatement for a pure tone (1000 Hz) is exemplified. Before the GA operation can be carried out, the accuracy of the mathematical models need to be checked using the experimental data. The optimal result in eliminating broadband noise reveals that the overall noise reductions with respect to various mufflers under a maximal allowable pressure drop of 100 Pa can achieve 62.6, 54.8, 32.3 and 87.8 dB. Consequently, the approach used for the optimal design of the multichamber hybrid mufflers under space and back pressure constrained conditions is indeed easy and quite effective.

Numerical Assessment of Hybrid Mufflers on a Venting System within a Limited Back Pressure and Space Using Simulated Annealing

Although research in finding optimal muffler shapes for low-frequencies noise using reactive mufflers has already been addressed, research into shape optimization of hybrid mufflers that reduce broadband noise within a constrained pressure-drop backpressure is lacking. Therefore, the shape optimization of four kinds of hybrid mufflers using simulated annealing ( SA) in conjunction with the generalized decoupling technique and plane wave theory are presented. Here, a numerical case in eliminating nitrogen venting noise is introduced. The reliability of the SA optimization is also verified using the optimization of muffler A for a pure tone. Moreover, the accuracy of the mathematical models is acceptable with minor deviations between the theoretical and experimental data. Results reveal that the higher backpressure limit will result in a higher acoustical performance. Consequently, the acoustical performance for a hybrid muffler equipped with multiple reactive chambers and one dissipative chamber is superior to that of reactive mufflers.

On the acoustic performance of hybrid mufflers.

The acoustic attenuation of hybrid mufflers including perforated screens and sound‐absorbent materials is investigated in the current study. An analytical method based on a 2‐D mode matching technique is used to model an axisymmetrical hybrid muffler. In the theoretical analysis, the hybrid muffler is divided into a number of sections in different homogeneous media with different acoustical characteristics. The acoustic properties of sound absorbent materials and perforated screens are taken into account to obtain eigenfunctions for wave propagation through the air and sound absorbent materials. A system of equations can be solved by matching the acoustic pressure and axial velocity across different sections, which leads to the solution for the determination of the muffler’s transmission loss (TL). The numerical predictions of TL show good agreements with published experimental data. The developed analytical approach is then used to examine the effect of the inner structure of the hybrid mufflers on their...

Optimization Design of Hybrid Mufflers on Broadband Frequencies Using the Genetic Algorithm

Recently, there has been research on high frequency dissipative mufflers. How- ever, research on shape optimization of hybrid mufflers that reduce broadband noise within a constrained space is sparse. In this paper, a hybrid muffler composed of a dissipative muffler and a reactive muffler within a constrained space is assessed. Using the eigenvalues and eigenfunctions, a coupling wave equation for the perfo- rated dissipative chamber is simplified into a four-pole matrix form. To efficiently find the optimal shape within a constrained space, a four-pole matrix system used to evaluate the acoustical performance of the sound transmission loss (STL) is eval- uated using a genetic algorithm (GA). A numerical case for eliminating a broadband venting noise is also introduced. To verify the reliability of a GA optimization, optimal noise abatements for two pure tones (500 Hz and 800 Hz) are exemplified. Before the GA operation can be carried out, the accuracy of the mathematical models has been checked using experimental data. Results indicate that the maximal STL is precisely located at the desired target tone. The optimal result of case studies for eliminating broadband noise also reveals that the overall sound power level (SWL) of the hybrid muffler can be reduced from 138.9 dB(A) to 84.5 dB(A), which is superior to other mufflers (a one-chamber dissipative and a one-chamber reactive muffler). Consequently, a successful approach used for the optimal design of the hybrid mufflers within a constrained space has been demonstrated.

Optimal Design of Multichamber Mufflers Hybridized With Perforated Intruding Inlets and Resonating Tubes Using Simulated Annealing

Abstract Recently, research on new techniques for single-chamber mufflers equipped with perforated resonating tubes has been addressed. However, the acoustical performance of mufflers having a narrow-band sound transmission loss (STL) is insufficient in reducing a broadband venting noise. To improve the acoustical efficiency, a hybrid muffler with chambers composed of perforated intruding inlets is presented. Here, we will not only analyze the STL of three kinds of mufflers (A: a one-chamber muffler hybridized with a perforated resonating tube; B: a two-chamber muffler hybridized with a perforated intruding tube and a resonating tube; and C: a three-chamber muffler hybridized with two perforated intruding tubes and a resonating tube), but also optimize the best design shape within a space-constrained situation. In this paper, both the numerical decoupling technique and simulated annealing (SA) for solving the coupled acoustical problem of perforated tubes are used. A numerical case for eliminating a broadband air compressor noise is also introduced. To verify the reliability of SA optimization, optimal noise abatements for the pure tones (400 Hz and 800 Hz) are exemplified. Before the SA operation can be carried out, the accuracy of the mathematical model is checked using the experimental data. Results indicate that the maximal STL is precisely located at the desired target tones. The optimal result of case studies for eliminating broadband noise also reveals that the overall noise reduction with respect to the mufflers can be reduced from 131.6 dB(A) to 102.1 dB(A), 89.5 dB(A), and 82.1 dB(A). As can be seen, the acoustical performance will increase when the diameters (at the inlet tubes as well as perforated holes) decrease. Moreover, it is obvious that the acoustical performance will be improved when the chambers equipped with perforated intruding inlets are increased. Consequently, a successful approach used for the optimal design of the multichamber mufflers equipped with perforated intruding tubes and a resonating tube within a space-constrained condition has been demonstrated.