A Study On Multi-field Analysis And Performance Improvement Of An Exhaust Muffler

Exhaust noise as the main noise source, affects vehicle pass-by noise. Although the new researchmethod to control exhaust noise is put forward, but the exhaust muffler installed as a traditionalmethod of controlling exhaust noise has been the focus of the NVH engineers. Because the research ofthe exhaust muffler involves the acoustics, CFD, aerodynamic etc, so how comprehensively toconsiderate of various factors to evaluate the performance of the muffler is worthy for researchers toexplore and in-depth study.For a type of diesel engine exhaust muffler, from the composite effect of sound field, the flowfield and structure, the multi-field performance of exhaust muffler was studied. On this basis theimproved and design solutions were put forward and the efficiency of the solutions was verified. Thisresearch content is as follow:(1) Based on the CFD theory and pipeline acoustics theory, for several simple muffler units, onthe basis of the analysis of CFD, the acoustic performance of simple muffler units, with theconsideration of temperature and the flow velocity, was discussed by the multi-field analysis method.(2) The resonance frequency of resonant muffler with different characteristic structureparameters was studied. Aiming for the lumped-parameter calculation formula of the resonancefrequency, a new connection tube length correction formula was put forward; the resonance frequencyof the prediction error is reduced to less than4%. By the new formula, the classical lumped parameterfrequency calculation formula estimating low precision problem is solved.(3) For a type of diesel engine exhaust muffler, on engine testing bed, the insertion loss ofexhaust muffler and the spectrum characteristics of exhaust noise were obtained. Combining the fluidFEM model with the boundary conditions, the fluid performance of exhaust muffler was studied, thenthe distribution of temperature, flow velocity, total pressure and fluid regenerated noise were obtained;Based on the fluid simulation analysis results, considering the temperature gradient and the flowvelocity, the muffler acoustic performance in different boundary conditions were analyzed and theacoustic transmission loss curves were compared; Compared transmission loss curve with mufflerexhaust noise spectrum, the frequency band on which the acoustics performance was needed to beimproved was determine; with the analysis of each chamber transmission loss curve and the muffleracoustics modal, the cause of the discrepancy of acoustics performance in different frequency bandwas found; at last, the improvements program of muffler is determined. (4) Based on modal analysis theory, experimental modal testing of the exhaust muffler wascarried, finite element structural model was validated; by using the finite element analysis method, theexhaust muffler suspension point was set up, as a way to improve structural behaviors.(5) By acoustics, fluid simulation method, the acoustics and fluid performance of improved anddesigned muffler were analyzed. The result shows that: without affecting the aerodynamicperformance, the acoustic performance has been greatly improved.In summary, combining with acoustics, fluid and structure, by using multi-field analysis methodthe exhaust muffler performance was studied; the result provides some reference to the improve anddesign of muffler. Above all, the results of this research can be used as the theoretical reference andpractical engineering applications of muffler multi-field analysis.