Acoustic Performance Of Muffler Research Articles

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.

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.

Muffler structure improvement based on acoustic finite element analysis

Aiming to obtain the acoustic attenuation performance of exhaust muffler of diesel engine and the influence of main structural parameters on its acoustic attenuation characteristics, the finite element analysis method and acoustic theory were adopted to numerically investigate the acoustic attenuation performance under the boundary condition of acoustic adiabatic propagation and muffler wall. It suggested that the noise cancellation effect of muffler was poor at the middle and low frequency in range of 0–3000 Hz, and the transfer loss of muffler was basically 0 dB pass frequency at 1100 Hz. According to previous single-factor study experience, the structural factors, such as the expansion ratio, insertion length of outlet perforated pipe, the distance between the diaphragm and the front part of muffler, have influences on the acoustic performance of muffler at low frequency. Thus, they were taken as the starting point to study the influence of multiple interaction factors on the muffling performance by using orthogonal design method combined with the finite element analysis method. The influence degree of different structure parameters on the acoustic performance of muffler and the optimized structure parameters were obtained. Through the analysis on the acoustic characteristic of the optimized muffler, it indicated that the transmission loss of the improved muffler had significant increase in other frequency range except the range of 650–800 Hz and 2500–2700 Hz, especially at frequency of 1100 Hz compared with the original muffler. In the range of 0–3000 Hz, the mean of transmission loss of the improved muffler was about 9.8 dB larger than that of original muffler, which indicated that better noise cancellation effect was achieved. The improved muffler also provided a certain reference for the structural improvement of similar muffler.

Shape optimization of reactive mufflers using threshold acceptance and finite element methods

Recently, research on the acoustic performance of reactive mufflers under space constraint becomes important. The attenuation performance of single and double expansion-chambers under space constraint is presented in this paper. A shape optimization analysis is performed using a novel scheme called Threshold Acceptance (TA), the best design obtained by the shape optimization method are analysed by Finite Element Method (FEM). The acoustical ability of the mufflers obtained is than assessed by comparing the FEM solution with the analytical method. Results show that the maximal STL is precisely located at the desired targeted tone. In addition, the acoustical performance of mufflers with double expansion-chamber is found to be superiors to the other one. Consequently, this approach provides a quick and novel scheme for the shape optimization of reactive mufflers.

Simplification of the Delany–Bazley approach for modelling the acoustic properties of a poroelastic foam

The acoustic performance of mufflers is often enhanced by the inclusion of dissipative materials. A simplified implementation of the Delany–Bazley method is presented which facilitates the acoustic characterisation of poroelastic foam in computational models in the absence of material airflow resistivity data. The acoustic characteristics of a polyurethane foam material were experimentally obtained using a two-cavity impedance tube method. A finite element model of an expansion chamber design incorporating foam is presented. Numerical results of the transmission loss for the foam-filled muffler are compared with results obtained experimentally using a two-microphone acoustic pulse method.

Analysis and Improvement on Acoustic Performance of Muffler with the Consideration of Temperature and Flow Velocity

Aiming for the acoustic performance of expanded-muffler, the acoustic fields, flow field, temperature field and flow regenerated noise inside the expanded-muffler were studied. Furthermore, with the consideration of temperature and flow velocity, the influence of temperature and flow velocity on acoustic performance was obtained. Based on the research, the acoustic performance of an exhaust muffler was studied. By adjusting the structural parameters, without affecting the engine output power, the insertion loss of muffler has average increased by 5.1 dB (A).

Prediction of Muffler Transmission Loss and Shell Noise by a Coupled Structure-Acoustic Model

Based on the vibration-acoustic analysis software VA One, a fully coupled structural-acoustic muffler FE model and a muffler cavity FE model are built. Then, a comparison is drawn between transmission loss of the coupled FE model and the cavity FE model, which demonstrates that the structure vibration has a big influence on the prediction of acoustic performance of muffler. Besides, radiated noise by muffler is calculated in this paper, which can provide a reference for the designanalysis and improvement of a muffler.

Shape optimization of reactive mufflers using threshold acceptance and finite element method methods

Recently, research on the acoustic performance of reactive mufflers under space constraint becomes important. In this paper, the attenuation performance of single and double expansion-chambers under space constraint is presented. To assess the reactive mufflers, a shape optimization analysis is performed using a novel scheme called threshold acceptance (TA), the best design obtained by the shape optimization method are analyzed by Finite Element Method (FEM). The numerical assessment is based on the maximization of the sound transmission loss (STL) using the Transfer Matrix Method (TMM), a modeling method based on the plane wave propagation model. The FEM solution used to analyze the STL of the shape optimized mufflers is based on the Acoustic Power method, a standard computational code COMSOL Multiphysics is used to analyse in 3D the sound attenuation of the mufflers by the FE method. The acoustical ability of the mufflers obtained is than assessed by comparing the FEM solution with the analytical method. Results show that the maximal STL is precisely located at the desired targeted tone. In addition, the acoustical performance of mufflers with double expansion-chamber is found to be superiors to the other one. Consequently, this approach provides a quick and novel scheme for the shape optimization of reactive mufflers.

CFD analysis of a transfer matrix of exhaust muffler with mean flow and prediction of exhaust noise

A multi-dimensional computational fluid dynamics (CFD) approach was proposed in this study aiming to calculate the transfer matrix of an engine exhaust muffler in the conditions with and without mean flow. The CFD model of the muffler with absorptive material defined as porous zone was calibrated with the measured noise reduction without mean flow, and was further employed to study the effect of the mean flow on the acoustic performance of the muffler. Furthermore, the exhaust acoustical source was derived from the calculated transfer matrices of six different additional acoustic loads obtained by the proposed CFD approach as well as the measured tail noise based on a multiload least squares method. Finally, the exhaust noise was predicted based on Thevenin’s theorem. The proposed CFD approach was suggested to be able to predict the acoustic performance of a complex muffler considering mean flow (without and with mean flow) and heat transfer, and provide reasonable results of the exhaust noise.

Optimal Design of Side-Inlet/Side-Outlet Expansion Mufflers with Open-Ended Perforated Tubes Using Simulated Annealing

ABSTRACTResearch on new techniques of multi-chamber mufflers equipped with a side inlet and internal nonperforated intruding tubes has been discussed in recent literature; however, the research work of multichamber mufflers in conjunction with side inlet and open-ended perforated intruding tubes which may efficiently increase the acoustical performance has been neglected. Therefore, the main purpose of this paper is to optimize the best design shape of multi-chamber side mufflers with open-ended perforated intruding tubes within a limited space.In this paper, the four-pole system matrix in evaluating the acoustic performance is also deduced in conjunction with a simulated algorithm (SA). Results reveal that the maximum sound transmission loss (STL) is precisely located at the desired target tone. In addition, the acoustical performance of mufflers conjugated with perforated intruding tubes is superior to those equipped with non-perforated tubes. Additionally, the noise reduction ability for a three-chamber side muffler with a non-perforated intruding tube and a two-chamber side muffler with perforated intruding tubes are equivalent. Moreover, mufflers with more chambers will increase the acoustic performance for both pure tone and broadband noise.

The Optimal Design of Multi-Chamber Side Mufflers Equipped with Perforated Cross-Flow Tubes and Intruding Tubes using Simulated Annealing

ABSTRACTResearch on new techniques of side-inlet/outlet mufflers equipped with internal non-perforated intruding tubes has been discussed in recent literature; however, the research work of multi-chamber sideinlet/outlet mufflers in conjunction with cross-flow tubes and open-ended perforated intruding tubes which may efficiently increase the acoustical performance is rare. Therefore, the main purpose of this paper is not only to analyze the sound transmission loss (STL) of three kinds of side-inlet/outlet mufflers (a three-chamber muffler with cross-flow tubes, a five-chamber muffler with cross-flow tubes and a nonperforated tube, and a five-chamber muffler with cross-flow tubes and a perforated tube) but also to optimize their best design shape within a limited space.In this paper, both the generalized decoupling technique and plane wave theory in solving the coupled acoustical problem are used. A four-pole system matrix in evaluating the acoustic performance is also deduced in conjunction with a simulated algorithm (SA). A numerical case in finding the optimalSTLof mufflers, which is constrained within a basement with a side-inlet/outlet, at targeted tones has been introduced. Before the optimization is carried out, an accuracy check of the mathematical model is performed. Results reveal that the maximalSTLis precisely located at the desired target tone. Moreover, it has been seen that mufflers with more chambers will increase the acoustic performance for both pure tone and broadband noise. Additionally, the acoustical performance of mufflers conjugated with perforated intruding tubes is superior to those equipped with non-perforated tubes.Consequently, the approach used for seeking the optimal design of theSTLproposed in this study is indeed easy and quite effective.

The Testing and Improving of Acoustic Performance on Muffler

The main sound source of motorcycle noise is engine exhaust noise in the paper. Installing muffler can effectively reduce the exhaust noise, in the other word, if the acoustic performance of muffler can be improved, exhaust noise of engine will effectively be suppressed. Based on the FEM, establishing the acoustic simulation model, the performance of muffler relates to acoustic is studied. Based on muffling theory, the optimal projects of the interior structure for muffler are proposed. Through doing experiments of insertion loss for muffler and the pass-by noise for motorcycle, these confirmed that the improved muffler can reduce the motorcycle’s noise.

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.