Types, composition, and processes in car mufflers.
22.08.2019 | 1784
The car muffler is intended to reduce exhaust noise in the exhaust system to meet general standards. It is a metal body with barriers and chambers inside, forming channels with difficult paths. Following these paths, exhaust gases pass through, and the sound vibrations of various frequencies are absorbed and converted into thermal energy.
The functions of a muffler in the exhaust system.
In the exhaust system of the engine, the silencer is installed after the catalyst (for a car running on gasoline) or the particulate filter (for diesel engines). And, in most cases, it's 2 mufflers installed:
1.Preliminary (silencer resonator) — designed for harsh noise suppression and stabilization of fluctuations in the flow of exhaust gases coming out of the engine. It is installed first and often called "front". One of its main functions is the distribution of exhaust gases in the system.
2. The main silencer is designed for final noise suppression.
Technically, the muffler device provides the following noise-reducing conversion operations:
-Changing the cross section of the exhaust flow. It is achieved by the special construction - cameras with various cross-sections, allowing to absorb high-frequency noises. The principle of this technology is simple: firstly, the exhaust gases flow is narrowed, creating some acoustic resistance, and then rapidly expands, resulting in sound waves distribution.
-Redirection of exhaust gases. It is carried out by barriers and repositioning of the tube poles. When the exhaust flow is rotated by an angle of 90 degrees, high-frequency noise cancellation is achieved.
-Change of gas vibrations (interference of sound waves). It is achieved due to exhaust gases pass through the perforated tubes. This technology enables to smother the noise of different frequencies.
-Sound waves "self-absorption" in the Helmholtz resonator.
-Absorption of sound waves. In addition to the cameras and perforation, there is a sound-absorbing material in the muffler that isolates the noise.
Features and types of silencers
Two types of mufflers are used in modern cars. They are resonant and direct-flow mufflers. Both can be installed alongside with the resonator (pre-silencer). In some cases, the direct flow design can replace the front muffler.
Muffler resonator is also known as a flame arrester, structurally is a perforated pipe located in a sealed shelter divided into several chambers. It consists of the following elements:
body (cylindrical in shape);
thermal insulation layer (exhaust gases have a very high temperature);
a blank screen (to turn the gas flow);
throttle (enables to change the cross-section of the exhaust gas flow).
Resonant silencer design
The main resonant silencer is more complex in contrast to prior. It consists of several perforated pipes installed in a shared body, separated by walls and located on different axes.
this structure includes:
front pipe with perforation;
rear pipe with perforation;
Thus, the resonant muffler uses all kinds of conversion of sound waves of different frequencies.
Features straight-through muffler
The resonant muffler disadvantage is the effect of back pressure, occurring as a result of the redirected flow of exhaust gases (when it collides with the barriers). Many motorists, therefore, perform tuning of the exhaust system by installing a direct current muffler.
Structurally, straight through muffler consists of the following elements:
exhaust and inlet pipe;
noise insulation material — most often used fiberglass, which is resistant to high temperatures and good sound-absorbing properties.
Straight-through muffler practically operates within the principle of - one perforated pipe passes through all the chambers. Therefore, the noise isn't eliminated by changing the direction and cross-section of the gas flow but obtained exclusively due to interference and absorption.
Due to the smooth passage of the exhaust gases within the straight-through muffler system, the back pressure is very small. However, in practice, it does not provide a large increase in power (only from 3% to 7%). On the other hand, the car has a specific sound for sports cars, because the noise-absorbing technologies eliminate only high-frequency noises.
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