Project On_ Losses in Reactive Muffler Analysis

 SYNOPSIS

Project Name - Analysis Of Transmission Losses In Reactive Muffler by Boundary Element Method, Numerical Method and Experimental Method.

Relevance:

                            Combustion process in the I.C. engines and exhaust process produces gaseous pollutants as well as acoustic pollutants. The pulsating flow from each cylinder's exhaust process of automobile engine sets up pressure waves in the exhaust system having average pressure levels higher than the atmospheric. The pressure waves propagate at speed of the sound relative to the moving exhaust gas, which escapes with a high velocity producing an objectionable exhaust noise. A suitably designed exhaust muffler accomplishes the muffling of this exhaust noise.  

                                There are a number of methods currently used to model and investigate the acoustic performance (TL) of mufflers including analytical methods such as the Transfer Matrix method (TMM), computational methods including the use of BEM and experimental measurement techniques. The use of computational methods (BEM) can aid in the prediction and design. The purpose of this project was to investigate the acoustic performance (TL) of reactive silencer by using boundary element method. A literature review considering sources of exhaust noise, muffler types and components, sound measurement, and prediction techniques was undertaken. Test facilities were constructed that allowed testing of muffler systems with a speaker as the source of excitation. This measurements made with a speaker to be compared to computational method i.e. Boundary Element Method with the help of LMS Virtual Lab. A number of different muffler systems were tested and their acoustic performance predicted using a transfer matrix technique. Comparing measured and predicted results allowed assessment of the accuracy of the predictions, the performance of various muffler components and the reliability of measurements.  

                               The boundary element method can be successfully used for predicting the acoustical
performance of a reactive muffler. Three addition models of Simple Expansion Chamber with central baffle with one, two & three holes by keeping the same volume as that of simple expansion chamber are modeled numerically for evaluation of TL. The experimentation is carried out and all four models are then compared for predicting the best quality of muffler. The numerically evaluated results of models show good agreement with experimental results for a lower frequency range. The simple expansion chamber with central baffle give more TL as well as wider attenuation band than that of the basic model. 

 Objectives of Project:

1)  Calculate the transmission loss of a simple expansion chamber muffler by numerical modeling using boundary element method (BEM), and validate the experimental setup for the known model of Simple Expansion Chamber. 

2) Considering simple expansion chamber as a standard model, modify this model to different configuration by keeping volume same i.e. simple expansion chamber with central baffle with one, two & three holes. Calculate the transmission loss of these models by BEM and compare with experimental results. 

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