Transmission Loss Of Muffler Research Articles

Analytical, computational, and experimental investigations on the impact of side outlet on the simple expansion chamber with axial outlet

In this study, an investigation on the acoustic performance of a simple expansion chamber muffler with side outlet has been presented. The investigation for the muffler is done in the 10–2400 Hz frequency range. The muffler is analyzed analytically, computationally, and experimentally. The computational and analytical modellings of the muffler have been done by using the finite element and transfer matrix methods, respectively for the determination of transmission loss. As the transfer matrix method is unable to capture the higher order modes above the cut-off frequency of the muffler, the finite element method has been adopted as the computational method. Additionally, the accuracy in the analytical and computational modelling of the muffler is checked with the experimental investigation. The two-load method is used in this study for muffler to determine the transmission loss and band power. The side outlet of the muffler introduces an extra impedance due to the shunt element and hence the effectiveness of the muffler can be improved. This muffler shows an overall improvement of 24.73 dB in the transmission loss when compared with the transmission loss of the simple expansion chamber muffler with an axial outlet in 10–2400 Hz frequency range. Specifically, the simple expansion chamber muffler with side outlet is more effective than the simple expansion chamber muffler with an axial outlet in 350–680 Hz, 1040–1350 Hz, 1570–1590 Hz, and 1850–2400 Hz frequency ranges. The comparison among the different techniques shows a fair agreement in the results. The transmission loss, variation of the band power in the 1/3rd octave band, and sound pressure level contours for the muffler at the selected frequencies have been presented. This study offers an advantage in the design of the automotive mufflers.

Research on the Influence of Characteristics of the Annular Connecting Pipe on the Transmission Loss of the Expanded Exhaust Muffler

In order to broaden the muffler frequency band in the low-frequency range of the exhaust muffler and to achieve the purpose of broadband noise reduction, in this paper, a model of an annular connecting pipe muffler is proposed using the finite element method (FEM) to simulate the nonreflection boundary condition and to solve the transmission loss (TL). In addition, the experimental value is obtained by the spatial five-point measurement method and compared with the simulated value, and the validity and reliability of the solution model are verified. Compared with a simple expansion muffler, the average TL of the annular connecting pipe muffler is increased by 11.86 dB, and the maximum TL is increased by 18.31 dB, effectively widening the muffler frequency area, and the overall performance is effectively improved. Finally, the influence of structural factors is analyzed, including the width (W) of the annular connecting pipe, the length (L) of the annular connecting pipe, and the length ratio (m) of the front and rear chambers on the TL and on the width of the anechoic frequency band. The results reveal that the width and length of the annular connecting pipe and front-to-back cavity length ratio are the most significant factors to influence the TL, muffler frequency band, and elimination or reduction of the passing frequency, respectively.

Acoustic Attenuation Prediction of Perforated Reactive and Dissipative Mufflers With Flow by Using Frequency-Domain Linearized Navier-Stokes Equations

To comprehensively consider the impact of complex airflow on sound propagation, a numerical approach by solving the three-dimensional (3-D) frequency-domain linearized Navier-Stokes equations (LNSEs) is proposed to accurately predict the transmission losses of perforated tube reactive and dissipative mufflers in the presence of complex airflow. The numerical computations are performed in two steps: (1) solve the time averaged flow by steady-state computational fluid dynamics (CFD) simulation and then map the results into acoustic mesh; (2) treat sound-absorbing material as an equivalent fluid and obtain acoustic perturbation variables by solving the frequency-domain LNSEs. The transmission losses of perforated tube reactive and dissipative mufflers are measured in the presence of flow and compared with the numerical predictions. The excellent consistencies between predictions and measurements validate the present approach. The influence of Mach number on acoustic attenuation performance of perforated tube reactive and dissipative mufflers is then investigated. With Mach number increases, the transmission loss of perforated tube reactive muffler increases somewhat, while the transmission loss of dissipative mufflers decreases obviously in the lower frequency range and change is limited at higher frequencies.

Sensitivity analysis and noise reduction optimization design of the insert-pipe double expansion chamber muffler

The insert-pipe double expansion chamber muffler has less passbands and higher sound attenuation in the plane wave range, which is widely used to reduce noise of industrial equipment. But there are many parameters that affect the transmission loss of the insert-pipe double expansion chamber muffler, and the sensitivity of each factor is not clear. Identifying the most influential factor among numerous parameters is an important challenge. It is necessary to investigate the sensitivity of all parameters and study parameter optimization algorithms. Based on the method of transfer matrix analysis, this paper studies the insert-pipe double expansion chamber muffler and its sound elimination mechanism. The global sensitivity analysis of the transmission loss of insert-pipe double expansion chamber muffler was conducted using Sobol's method, and the influence of each parameter sensitivity was examined. According to the noise characteristics of an air conditioner compressor, the external penalty function method (EPFM) algorithm is used to optimize the insert-pipe double expansion chamber muffler, and the maximum transmission loss is obtained in a specific frequency band. According to the optimized parameters, the muffler is designed, manufactured, and installed in a pipeline system to carry out a noise experiment to verify the effectiveness of the optimization scheme.

Acoustic impedance extraction method and acoustic characteristics analysis of perforated plates under grazing flow

As an important component of inlet and exhaust mufflers, the acoustic characteristics of perforated components are inevitably affected by the flow of air. Therefore, obtaining the acoustic impedance of the perforated element under airflow conditions is a prerequisite for accurate calculation of the muffler’s muffling performance. In this work, the frequency domain linear Navier–Stokes (L-NS) method is used to extract the acoustic impedance of perforated plates under grazing flow. The predicted perforated acoustic impedance is consistent with the calculation results of published acoustic impedance expression, and the impedance boundary condition is defined to calculate the transmission loss (TL) of the perforated muffler, which agrees well with the experimental results and verifies the accuracy of the method. The effect of perforation angles on the transmission loss of mufflers in different Mach numbers ( Ma) and aperture plate thickness ratio ( dh/ tp) is analyzed by the frequency domain L-NS method. The results show that when 1≤ dh/ tp<2 and Ma≤2, the effect of perforation angles on the muffler performance is obvious, and the angle tilted upstream shifts the resonant frequency to a lower frequency while its corresponding peak value is also increased. As an engineering application, it has certain significance for the prediction of muffler muffling performance and the regulation of the muffling frequency band.

Case study: Noise attenuating performance of perforated corrugated lined straight-through perforated pipe-resistant muffler

Noise of internal combustion engine is the main source of noise pollution, and mufflers are the main means to reduce exhaust noise of internal combustion engine. In the process of improving the acoustic performance of the exhaust muffler based on the three-dimensional numerical method, the influence of the high speed and high temperature airflow discharged by the engine in the actual working process on the acoustic performance of the exhaust muffler is often ignored, which leads to the obvious deviation between the predicted results and the actual situation. In this paper, based on the structural optimization design of the straight-through perforated pipe resistance muffler, the noise characteristics of the straight-through perforated pipe resistance muffler with perforated corrugated lining was analyzed considering the airflow velocity and temperature inside the muffler. The influence of temperature and velocity fields on the acoustic performance of muffler was studied by using numerical simulation method, which takes the solution results inside muffler as boundary conditions of sound field analysis. The influence of changing the internal structure of muffler on the aerodynamic performance of muffler was discussed, and the pressure loss is analyzed. The research has shown that adding perforated corrugated lining inside muffler could effectively improve the transmission loss of muffler and the noise reduction performance of prototype straight-through perforated pipe-resistant muffler.

Digital design and experimental testing of a compressor's suction muffler transmission loss

Abstract The purpose of this paper is to provide a fast, efficient, and low-cost digital design method for the design of suction mufflers in refrigerator compressor plants. The main content of this paper is to establish a three-dimensional acoustic model of the compressor suction muffler by using Solidedge software, combine the upper suction port of the muffler with the valve group, then use Hypermesh to mesh the acoustic model and carry out the theoretical calculation, transform the control differential equation in the solution domain into the integral equation on the boundary by Green's function, discretize the boundary and carry out the numerical solution. The boundary is discretized and solved numerically. The transfer matrix quadrupole parameters are used to describe the acoustic components, and the transfer matrix of the discontinuous cross section is obtained to transform the complex system into a chain superposition of simple systems. The dependent variable in the partial differential equation to be solved is changed to a linear system of equations, and the transmission loss is calculated from the incident and transmitted sound pressure. The theoretical calculation of the transmission loss of the muffler is performed using LMS. Virtual. Lab software and the design solution is continuously optimized using this software. The experimental analysis shows that the designed muffler is printed and trimmed by 3D printing equipment and loaded onto the transmission loss test bench for experimental testing, and the highest theoretical value differs from the test result by 10dB.

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

A single-step measurement method for transmission loss of the muffler based on improved transfer matrix

Transmission loss is a very important acoustic characteristic of the muffler. In order to improve the efficiency of the double-load method for measuring the transmission loss of the muffler, this paper proposes a single-step measurement method for transmission loss of muffler. In addition, the simulation model of the single-step measurement method is established based on the finite element acoustic analysis. For the model, the calculation method of the transmission loss of the muffler is deduced from the theoretical knowledge of the transfer matrix. In the simulation, the sound pressure data of six positions in the model are obtained, and the transfer matrix is used to calculate the transmission loss of the muffler. Then, two simulation comparison experiments were done. In order to verify the validity of the single-step measurement method, the first comparison experiment was to compare the transmission loss of the muffler simulated by the single-step measurement method with their theoretical transmission loss in the finite element acoustic analysis. The results of the simulation validation test cases showed that the transmission loss of the muffler obtained by the single-step measurement method was consistent with the theoretical value. The second comparison experiment was to compare the transmission loss obtained by the single-step measurement method with the transmission loss obtained by the double-load method. The results of the simulation validation test cases showed that at certain frequencies, the transmission loss obtained by the single-step measurement method was more accurate than the transmission loss obtained by the double-load method. In conclusion, the single-step measurement method proposed in this paper can accurately obtain the transmission loss of the muffler with only one measurement, which improves the measurement efficiency.

Effect of Extended Inlet and Outlet Lengths on Transmission Loss of Double Expansion Chamber Reactive Muffler

Internal combustion engines are one of the major causes of noise emissions. As in different industrial equipment, locomotives, and vehicles, the engines have a wide application base. Exhaust noise and noise that is created due to friction of different parts share the extreme input to noise pollution. A muffler is a means used by the exhaust system to reduce noise. For the reduction of noise, it is placed alongside the exhaust pipe. The decrease in the exhaust noise level is controlled by muffler construction and operating techniques. Therefore, the muffler configuration plays an important role. In this research work, an effort has been made to study the effect of parameters like different lengths of Extended Outlet (EO) for constant lengths of Extended Inlet (EI) elements in both chambers of Double Expansion Chamber (DEC) reactive muffler with an external connecting tube on transmission loss. It is observed that, as the length of EO is increased from L/5 to L/3 keeping EI constant, the average transmission Loss for the models decreases. The acoustic performance of the muffler is assessed by using COMSOL Multi-Physics and experimental validation.

Muffler Transmission Loss optimization for a Vehicle using Genetic Algorithm

Automotive reactive muffler attenuate sound using interference which is produced by engine exhaust sound waves are partially or fully cancelled. to reduce the complexity of design this process is carried, which involves CAE modelling and analysis followed by optimization technique for maximization TL.TL constitutes a spectrum it has a function of frequency, to obtained single global measure RMS is calculated known as RMSTL. For optimization Genetic algorithm provide variation. for experimental validation of data, the Experimental is carried on Impedance tube, Conical adapters are designed to accommodate different diameter openings of Impedance tube and muffler. optimization done, by taking design variable as length and diameter of inlet outlet and muffler chamber varied in range of -15% - +15% of original dimensions. Later simulation results of this variable muffler are compared with base muffler results. In the optimized solution we obtain 10.24% maximization in TL suggested by this optimized solution.

Acoustic Attenuation Performance of Two-Pass Perforated Hybrid Mufflers with Mean Flow

The one-dimensional (1-D) analytical approach is developed to predict and analyze the acoustic attenuation performance of two-pass perforated hybrid mufflers in the presence of mean flow. The expressions of complex acoustic wavenumber and impedance of long fiber glass wool are presented by using the impedance tube measurement and curve fitting. The 1-D approaches as well as the fitting expressions are validated by comparing the predicted and measured transmission loss of two-pass perforated hybrid mufflers with a different Mach number. Results illustrate that the 1-D predictions agree well with measurements below the plane wave cut-off frequency and deviate in higher frequency range. The influences of geometric parameters including the lengths of extended tubes, perforations on the right bulkhead and the outlet tube, and mean flow on the acoustic attenuation behavior of the hybrid mufflers are examined.

Research on characteristics of thermoelectric generator with integrated muffler and catalytic converter

Automobile exhaust contains a large amount of heat loss, which has a high potential for energy saving. In order to recover the heat in the exhaust gas and improve the compatibility of thermoelectric generator (TEG), muffler and catalytic converter, an integrated automobile exhaust thermoelectric generator (IATEG) integrating muffler, and catalytic converter is proposed. Research on its performance by establishing a three-dimensional model, On the basis of finite element simulation, the model’s surface temperature field, muffler transmission loss, exhaust back pressure and conversion efficiency are compared and studied when the catalytic converter is placed in the front part (A), middle part (B) and rear part (C) of the model. The results show that when the exhaust temperature is 350 °C and the inlet velocity is 30 m/s, the average surface temperature of model B is the highest, which is 291.95 °C. The exhaust back pressure of the three models is almost the same and meets the requirements of QC/T 631-2009 (15 kPa). Compared with the original muffler of the automobile, the transmission loss of the three models is greater than that of the original muffler. From the perspective of improving the conversion efficiency of NOx, the exhaust flow field distribution of the catalytic converter of Model B is more uniform and has a smaller impact on the conversion efficiency of NOx. Therefore, it is recommended that IATEG choose the structure of Model B. This article demonstrates the possibility of IATEG integrating muffler and catalytic converter in terms of performance.

Improving the performance of double-expansion chamber muffler using dielectric beads; optimization using factorial design.

Noise pollution is a common health hazard worldwide which is emitted along with chemical air pollutants, simultaneously from many sources. Some studies have been conducted to control these pollutants, simultaneously with promising results being achieved. Dielectric beads have been used in air pollution control technologies, successfully and probable effectiveness of them in noise reduction can be promising in dual use of them in the exhausts emitting noise and air pollution, simultaneously. In order to investigate the effectiveness of dielectric beads in noise reduction, two types of them; namely glass and ceramic beads, were placed separately inside the connecting tube of a double-expansion chamber muffler. Then the transmission loss (TL) of muffler was examined using impedance tube. A factorial design was used to evaluate and optimize the effect of noise related parameters on TL of such a system. Results show that the presence of dielectric beads has significant effect on TL of muffler. The maximum TL was obtained as 74.76dB for muffler with ceramic beads, under the optimal condition of 5250Hz and 120dB. Measurement of TL and sound absorption coefficient (SAC) of glass and ceramic beads showed that the noise reduction in muffler with ceramic and glass beads is probably due to SAC in ceramic beads and noise reflections in glass beads, respectively. These results promise the dual use of dielectric beads in the exhausts emitting noise and air pollution simultaneously.

Dual-target-frequency-range stop-band acoustic metamaterial muffler: acoustic and CFD approach

Acoustic metamaterials can control, direct, and manipulate sound waves, hence, they attract more researchers’ attention in the field of automotive, aerospace, and architecture to reduce noise levels. Here, vehicle exhaust noise is investigated through finite element simulation. In this study, an improved muffler is proposed to affect the transmission loss. In the case of acoustic performance, we first designed the acoustic metamaterial baffles (AMBs) with locally resonant structures in order to reduce the noise level in the desired frequency range; a desired frequency range was targeted to be affected by tuned resonators. For describing AMBs, four models were designed to obtain transmission loss peaks and stop-band behavior at the dual-target-frequency range. Hence, in order to prove the effectiveness of the proposed muffler, they were compared with conventional mufflers. Results indicated that AMBs improve the muffler transmission loss by up to 89 dB. The combination of resonators and their configurations, as well as spacing of the AMBs, play a significant role in affecting the transmission loss peak. At the end, to observe and show the actual performance of the proposed acoustic metamaterial muffler, essential aspects like pressure drop and flow are obtained using computational fluid dynamics (CFD) software, and highly reasonable and realistic results are achieved.

Numerical analysis of the transmission loss of dissipative mufflers with polygonal cross-section

Dissipative mufflers are often used for the reduction of broadband noise transmitted in ducts. Many common calculation procedures for the transmission loss of such mufflers require conventional shapes like rectangular or circular cross-sectional areas. In an effort to analyze the effect of the cross-sectional area of dissipative mufflers on the resulting noise reduction, the transmission loss of axially uniform mufflers with polygonal cross-sectional areas was investigated using the finite element method. The mufflers are designed to have the same open area, and hence in a practical application would lead to a similar pressure drop. The results were compared to those obtained with the well known approximative method of Piening. Good agreement between simulation and estimation was found regarding basic trends at low frequencies, while notable differences were revealed regarding the maximum transmission loss.

Analysis for effect of pores on acoustic performance of reactive muffler

The major source of noise pollution was an internal combustion engine. Henceforth, the design of the engine exhaust system was a tough challenge for automotive industries. The mufflers have been used to moderate the exhaust noise from the engine to the neighboring atmosphere. So in domestic as well as the industrial application, it is required to reduce noise levels to prevent human hazards. The performance of muffler is measured in terms of transmission loss. The transmission loss of reactive muffler is depending on its geometry. This article describes the effects of pores at the inlet pipe and outlet pipe of the reactive muffler on its performance capacity at a target frequency. It is found that the muffler performance is dependent on the number and position of pores. The single chamber and double chamber reactive mufflers are used for the study. The numerical analysis is performed by COMSOL Multiphysics software. The numerical analysis result of the different models of the muffler is compared with experimental analysis. The purpose of the study is to investigate the effect of pores in inlet and outlet pipe to maximize the TL at the target frequency of reactive muffler.

Усовершенствованный резонатор Гельмгольца

The three-dimensional acoustic finite element method is used to predict the transmission loss of the Helmholtz resonance muffler. The results are in good agreement with the experimental results, indicating the applicability and accuracy of the numerical method used in this paper. On the one hand, in order to reduce the resonance frequency without changing the shape of the resonator, the connecting tube is extended to the inside of the resonator, and the influence of the extension length and the cross section shape of the extension tube on the acoustic characteristics of the resonator is discussed in detail. On the other hand, in order to broaden the muffled frequency band of the traditional Helmholtz resonators, the resonators are combined in series and parallel, and the influence of the combined structure on the acoustic characteristics is discussed in detail.

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.

Numerical Analysis on Improving Transmission Loss of Reactive Muffler using Various Sound Absorptive Materials

Finite element analysis approach is used to determine the transmission loss for an optimized geometry of reactive multi-chamber muffler. The pressure acoustics theory is involved in the present problem and it examines the wave nature of sound and also the intensity with which it propagates. COMSOL Multiphysics software was used for modelling and analysis. The acoustics module with parallel study in frequency domain was utilized to study the flow and acoustic behaviour of the reactive muffler. Various absorptive liner materials were considered for the muffler and the transmission losses were compared. In addition to the above, the thickness of liner and inlet pressure were varied in order to have profound work for discussion. The validation of predicted transmission loss is in good agreement with the referred experimental data. The result for different types of absorptive liner materials was tracked in comparison with the muffler without liner. The average transmission loss was found to be increased by 8% with the introduction of absorptive liner with 10mm thickness. Finally, the calculated sound pressure level with total acoustic pressure field and streamlines intensity provide insight of the physics involved.