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Measurement and Calculations of Noise Radiation of the Exhaust Pipe of a Single Cylinder Two Strke Engine
The noise of motorcycles has two main sources; one is the engine; the other is the frame of the motorcycle. The noise radiation from the exhaust pipe of a single cylinder two stroke engine motorcycle is studied in this paper. There were some investigations on the engine noise; however, they usually put emphasizes on the muffler design and the transmission loss. As for the investigation on the exhaust system of two stroke engine, they usually emphasized on how it influences the engine performance. In this paper, we try to combine the two parts of noise radiation and the whole engine cycle operation to study the mechanism of noise radiation and the process which the noise decays in a muffler through the structure of exhaust pipe and the dynamic characteristics of the gas in the exhaust pipe so that we can establish the theoretic basis of noise control.
There are two methods to study the noise of engine exhaust are as follow: one is to use traditional linear acoustic theory to analyze the acoustic characteristics of the muffler, and the other is to use one dimensional unsteady gas dynamic theory. In this paper, the second method is used to calculate pressure variations in the exhaust pipe and the mass efflux at the end of the exhaust pipe thus obtained is then used to calculate the spectrum distribution of sound pressure and the noise level.
Six different configurations of exhaust pipe were studied in this paper: three straight pipes with same diameter and different length, two diverging-converging pipes with different diameter and length,a nd one pipe with an expansion chamber. The engine was driven by a motor at three different speeds. Pressure variations in the exhaust pipes and outside the exhaust pipe noise level were recorded. And the measured data were compared with the calculated result. Results of calculations show the pressure calculated and measured in the six exhaust pipes are fairly close, and the noise spectrum distribution can be predicted approximately. However, because of the restriction on the theory; the noise spectrum of calculation and measurement are some difference under the some frequency.
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