Search

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. [ABSTRACT FROM AUTHOR]

• The transmission loss variation law of exhaust muffler of agricultural single cylinder diesel engine. • Research and analysis on the prominent parameters of muffler transmission loss in its structural design. • Comparative analysis of the influence degree of various structural parameters of muffler on acoustic performance. The TL (transmission loss) is an important index to evaluate muffler performance. The design of muffler should not only consider acoustic performance, but also its volume, manufacturing cost and its influence on comprehensive performance of diesel engine. If the prominent structural parameters of muffler can be found, the TL can be maximized without sacrificing the overall performance of diesel engine and the exhaust noise can be reduced. In this paper, the sound pressure nephogram of muffler at different frequencies is analyzed in depth, and the TL diagram of muffler under various design parameters is calculated by using the AML (Automatic Matched Layer) technique. According to previous studies, the influence laws of several main parameters of muffler, such as F (length to diameter ratio), N (long and short axis ratio) and T (sieve separator perforation rate), on TL are compared and analyzed. The results show that in low-frequency range, the change of each structural parameters of muffler has little effect on TL, while in high-frequency range, the TL changes are obvious. The study found the TL of muffler is most obviously affected by the change of its F, followed by N and T. It provides a theoretical basis for the design of muffler parameters. [ABSTRACT FROM AUTHOR]

• Proposed the model of exhaust purification muffler. • The transmission loss is much improved in the key improvement frequency band. • The influence of structure factors on transmission loss in different frequency bands. The main purpose of exhaust mufflers design is to improve the TL (transmission loss) of the target frequency band. Therefore, this paper first proposed an exhaust muffler model with foam ceramics as sound-absorbing material for a diesel engine. The finite element AML (Automatic Matched Layer) method is used to simulate the non-reflective boundary conditions and calculate the TL. In addition, the validity and reliability of the solution model are verified by comparing the experimental value and simulation value of the TL. Compared with the prototype muffler, the TL of the exhaust purification muffler has increased by an average of 6.96 dB in the frequency range of 20–4500 Hz. Finally, the influence law of structure factors m (expansion ratio), n (cavity-length ratio) and p (length-diameter ratio) on TL in different frequency bands shows that: when changing the structure factors to increase the TL value of the exhaust purification muffler, the expansion ratio should be prioritized in the low-medium frequency bands, the cavity-length ratio should be prioritized in the medium–high frequency bands, the length-diameter ratio should be prioritized in the high frequency bands. [ABSTRACT FROM AUTHOR]