Measuring and Characterizing the Noise Emission of a Small Combustion Engine after Acoustical Topology Optimization of the Muffler

In portable grass trimmer, most often the engine is placed close to the operator’s head, making a great deal of noise. Therefore, utilization of any type of uncomplicated and inexpensive method to curtail noise level in such devices is of great significance. Hence, in this study, the default muffler was used as a control treatment and two modified mufflers and one redesigned muffler have been examined to investigate. According to the obtained results, the sound pressure level of the redesigned and the modified mufflers decreased by 6.86 and 5.31 percent in compare to the default muffler, respectively. Installing the redesigned muffler increased the transmission loss equal to 7.6 dB in compare to the default muffler. As a general conclusion of this study, by installing the redesigned muffler, the maximum working times of the operator increased by 12.1 hours at 5000 rpm.