Simulation And Optimization Of Diesel Particulate Filter's Acoustic Characteristics

The demand for diesel particulate filters(DPF) is increasingly strong with the wide application of diesel engines. DPFs can not only reduce the amount of soot from the engine exhaust, but also attenuate noise because of the characteristics of porous materials. At present, attention paid on the study of DPFs' acoustic characteristics is not enough. Therefore, it's very important to find a reliable method for researching the propagation of sound waves in DPFs, simulating and predicting the acoustic characteristics of DPFs.First,The paper gave a brief introduction to the theoretical basis for acoustic calculation and derived the expression of one-dimensional acoustic equation and three-dimensional acoustic equation as well as analyzed three kinds of commonly used methods in the calculation of acoustics. The methods of transfer matrix and electro-acoustic analogy in the application of acoustic calculation were described in detail.Second, the model was built in Virtual Lab software and then the sound pressures, transmission loss and insertion loss were calculated by coupling the 1D transfer matrix method and the 3D acoustic finite element method.Virtual Lab was used to calculate the sound pressures at the inlet and outlet of the simplified DPF model, based on these data, the transfer matrix of the DPF was achieved. The DPF transmission loss was calculated by transmission loss formula and the DPF insertion loss was calculated by the mathematical model of insertion loss.The calculation results show that the transmission loss of DPF has significant peaks and troughs. The transmission loss with the minimum value of-1.8dB at the frequency of 560 Hz indicates that the DPF enhances the noise of exhaust system. When the frequency is 3000 Hz, the maximum transmission loss reaches 18.7dB. With the increase of frequency, the values of peaks and troughs are all gradually increased, indicating that DPF has a better ability of attenuating noise at high frequency. The insertion loss of DPF was distributed between 10 dB and 35 dB, increasing with the increase of frequency. The result of insertion loss also confirmed the result of transmission loss. The reliability of the model was certified by comparing the transmission loss results of the simulation and the experimental results.Finally, the analysis of how the change of structural parameters affecting the acoustic characteristics of DPF and the optimization of DPF were carried out based on the established acoustic model. The main variables include channel shape, porosity, the length of the side of the channel, the thickness of the layer and the aspect ratio. The calculation results show that Octo-square asymmetric and Square-square asymmetric channels, increasing porosity, the thickness of the layer and aspect ratio, decreasing the length of the side of the channel can improve DPF's ability of attenuating noise. In the optimization design, the Square-square asymmetric channels were adopted and the aspect ratio was increased to 1.2. The results show that comparing to the original DPF, the transmission loss of the optimization solution increases by 2dB-3dB, and the insertion loss increases by 6dB-7dB, the maximum value of the insertion loss reaches 39 dB.