The primary task of the exhaust system is conducting the combustion gases of the engine past the driver's cab into the open air. Noise caused by combustion is reduced to the permissible volume by integrated mufflers. For exhaust gas purification, catalytic converters or particulate filters are also installed in modern motor vehicles with internal combustion engines.
The actual exhaust noise is produced by the pulsating exhaust gas flow from the individual cylinders. Reflection and absorption can be used to dampen the sound energy in the exhaust system. The mufflers take over this task and reduce the noise generated by the combustion engine while regulating the exhaust gas back pressure to optimise engine performance.
In the muffler, obstacles are deliberately placed in the way of the exhaust gas flow to reflect the sound waves and prevent further proliferation. These can be implemented using cross-section changes, pipe deflections or chambers. As a result, the sound waves are deflected and are partially cancelled by superposition.
With absorption, the exhaust gas flow passes unhindered through one or more chambers in the muffler. The chambers contain a perforated pipe and porous material such as stone wool or glass fibre. The sound waves pass through the holes into the filling material, which absorbs the higher frequencies.
Since both types of sound damping are suitable for different frequencies, they can also be combined in one muffler.
In addition to combustion noise, the exhaust system also generates noise due to vibrations and natural frequencies that are transmitted to the vehicle body via the fastening elements. These can be specifically reduced through the positioning and design of the components or by using elastic suspensions or additional vibration dampers.
