Search Results

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)*.

Evidence has been obtained in this study to indicate that the hybrid muffler made up of heat-resistant thermosetting resin, ceramic paper, and carbon fiber felt used as a noise absorbing material, can reduce the noise without any compromise in engine performance. Further, it has been confirmed that a highly reliable muffler may be designed using this approach.

Automobile and motorcycle mufflers, installed in a restricted space, must effect noise reduction without interfering with engine efficiency. Experiments were performed in this study, using heat-resistant epoxide resin in place of expandable steel as the material for the muffler of a gasoline engine exhaust system. The findings show that use of heat-resistant epoxide resin as the material for a portion of a gasoline engine exhaust system i.e., : the muffler, results in noise reduction, even in a restricted space. This resin is also effective in bringing about weight reduction, vibration reduction and rust-proofing, and is expected to contribute to reduction of back pressure in exhaust piping systems.