A Study on the Muffling Method Using New Materials

Since the engine noise of a small portable single cylinder 2 or 4 cycle gasoline engine exceeds 100 dB (A), making the reduction of noise levels is very important. Conventional noise reduction measures have been to expend the pulse flow energy of the exhaust gas even at some sacrifice of engine performance, that is, resistance is introduced to lower the flow rate.

Recently, we have developed a carbon fiber felt from coal tar pitch, which shows high resistance to oxidation and physically and chemically stable properties, and used it in the exhaust muffler and in the bottom of the engine crankcase, enabling the reduction of noise emitted from the engine package by approximately 3 dB (A). Compared with rock wool and glass wool, this carbon felt has the superior characteristics of (a) lower mass and (b) larger surface area per unit weight (1)*.