Semi Active Muffler

Abstract

An inherent drawback of IC engines is that it is a major source of noise pollution. That is why the reduction of exhaust noise from engines is, now days, an important issue. Attaching a muffler in the exhaust pipe is the most effective means of reducing noise. But muffler requires specific design and construction considering various noise parameters produced by the engine. Since early development of mufflers, the main objective of design was attenuation of sound in regular mufflers. Which causes a great amount of back pressure at the exhaust port thus losing power, increasing fuel consumption and piston effort to exhale the gases out. For high performance engines, the free flow exhaust is made in which the sound level is not important but zero or less back pressure is. There is no intermediate muffler type in between both these, so semi active muffler is an step between these two, in which it attenuates sound when engine is running at low RPMs , and converts in free flow when engine at higher revs.A semi active muffler basically operates in two operating conditions:1) Normal mode (High noise attenuation) and 2) Free Flow Mode (minimum back pressure). In normal operating the major objective is to attenuation of sound well below legal limits of sound pressure level. This muffler acts as a normal muffler giving typical performance of stock muffler made by vehicle manufacturers. The exhaust gases are forced to pass through various restrictions, baffles and sudden change in directions as a factory muffler is. In the free flow mode, the exhaust gases in the muffler are almost bypassed but not totally, by using only one expansion chamber for sound reduction instead of all three chambers. In this mode the exhaust gases enters the first chamber and then are exhausted to the atmosphere.