Abstract
A muffler in the exhaust pipe is used for reducing noise. Due to varying noise frequencies of the exhaust gas flow at different engine speeds, the muffler must be designed to work at best performance in the frequency range of maximum sound level; which is a very difficult task due to the wide range of noise spectrum. Hence, good design of the muffler should give the best noise reduction and offer optimum backpressure for the engine. In this paper, two test rigs are examined to analyze the muffler in terms power spectrum. In the first test rig, the task is to scan the muffler which is acoustically excitedby known frequencies by using signal generator. In the second test rig, measurements of noise power spectrum were carried out using the microphone system for a car engine at different engine speed (1400-3000rpm). A National Instrument DAQ card and LabVIEW software have been utilized for data acquisition, monitoring and analyses. This study makes available very detailed spectra of the muffler, and the method of cross-correlation has also been applied. In the first rig, the results show that there is a great potential for the muffler system to attenuate the noise over a wide range of excited frequencies. Results showed that, the effective reduction of noise was in the wide frequencies range and only a very narrow range was destructive. In the second test rig, the results show that the measured of engine firing rate (EFR) Harmonics are in very agreement with the theoretical analysis and that the pulse repeats at the firing frequency of the engine. Results show that the muffler is very important for a passive control and reduction of noise in internal combustion piston engines applications.