Design and test research on semi-active muffler system based on the H-Q tube

In this paper, one type of semi-active muffler system is designed to reduce diesel engine exhaust noise, especially the low frequency noise. The muffler is based on the principle of Herschel-Quincke tube. Different from other mufflers, this one can change the control fundamental frequency with valves. In the certain control frequency interval between two adjacent fundamental frequencies, it can meet the resonance condition by the stepper motor automatically. Both the valves and the stepper motor are under command of the designed controller. Transmission loss and insertion loss experiments of the muffler have been conducted. Experimental results show that the semi-active muffler has a substantial noise reduction: from 35 to 100 Hz. The maximum TL of the muffler is approaching 35 dB. The IL has an average of 11 dB attenuation in the entire range of 35 to 100 Hz.