Experimental study on the comprehensive performance of the application of U-shaped corrugated pipes into reactive mufflers

Reactive muffler is widely used to reduce the low-frequency noise generated by internal combustion engines. Though researchers have put forward the methods to optimize the performance of muffler recently, it is often difficult to obtain ideal noise reduction performance in the high-frequency range. This paper presents an experimental study on the comprehensive performance of the application of U-shaped corrugated pipes into a simple expansion chamber muffler, which is aimed to optimize the noise reduction performance over the upper cutoff frequency range for the reactive mufflers. Then, the noise reduction performance and aerodynamic performance are experimentally evaluated. Subsequently, the experimental results of the muffler with corrugated pipes are analyzed and compared to that of the muffler with insertion pipes. Furthermore, improvement coefficient η is proposed to evaluate the comprehensive effect of U-shaped corrugated pipes on the noise attenuation and aerodynamic performance. Results demonstrate that the application of corrugated pipes in reactive muffler significantly improves the noise reduction performance above the upper cutoff frequency range. Besides, the insertion loss of the muffler with corrugated pipes is 4.0-4.3 dB(A) higher than the muffler with insertion pipes. Moreover, the improvement coefficient η reaches 1.12-1.13, indicating the corrugated pipes make more contribution in noise reduction than in pressure loss. Furthermore, the whistling frequency is not observed at different airflow velocities, indicating the corrugated pipes are probably unlikely to generate the whistling noise. What's more, it is observed that the muffler with corrugated pipes have a better ability of lowering the regenerative noise in low frequency than the muffler with insertion pipes. In conclusion, this study verifies that the application of U-shaped corrugated pipes into reactive mufflers is feasible and acceptable, and it provides a novel method in the acoustical design of reactive mufflers.