Muffler in Cars
The muffler is an important structural element of the exhaust system, without which the operation of a modern car is simply impossible. The car muffler performs the following main functions:
- exhaust gas noise reduction;
- energy conversion of exhaust gases, reduction of their speed, temperature, pulsation.
The exhaust gases leaving the engine cylinders have high pressure. When exhaust gases travel through the exhaust system, sound waves are generated that propagate faster than the gases. The muffler converts the energy of sound vibrations into thermal energy, thereby reducing the noise level to a certain (predetermined) value. However, with the use of a silencer, backpressure is created in the exhaust system, which leads to a slight decrease in engine power.
The muffler uses several noise reduction technologies:
- expansion (narrowing) of the flow;
- change in flow direction;
- interference of sound waves;
- absorption of sound waves.
The expansion of the flow is realized through several chambers of different volumes, separated by partitions. Allows you to effectively absorb low-frequency sound vibrations. Along with the expansion in the silencer, the flow is narrowed by means of a diaphragm opening (throttle). Used to suppress high-frequency noise.
In the silencer, with the exception of exhaust silencers, a change in the direction of flow of the exhaust gas is provided. The angle of rotation of the stream is in the range of 90-360 °, which is achieved by damping the medium and high-frequency sound vibrations.
The interference of sound waves, depending on the nature of their superposition, leads to an increase (constructive interference) or a decrease (destructive interference) in the amplitude of the oscillations. Both types of interference are used in the silencer. The technology is implemented using perforations in the silencer pipes. By changing the size of the holes and the volume of the chamber surrounding the pipe, it is possible to damp sound vibrations in a wide frequency range.
When sound waves pass through a special sound-absorbing material, they are absorbed. This method is effective in damping high-frequency sound vibrations.
To achieve the greatest effect, these technologies in silencers are used, as a rule, in combination.
In modern cars, one to five silencers are installed, mostly two. The muffler closest to the engine is called the front (front) muffler or resonator. It is followed by the main (rear) muffler. For each specific car model and engine brand, its own set of silencers is used.
The resonator serves to preliminary reduce the noise level and balance the pulsations of the exhaust gas flow. Structurally, the resonator is a perforated tube placed in a metal casing. To increase the efficiency of vibration damping in the pipe, a throttle hole is made.
The main silencer provides ultimate noise reduction. It has a more complex design. The metal casing accommodates several perforated tubes. The case is divided by partitions into 2-4 cameras. Some cameras may be filled with sound-absorbing material. In the main silencer, the exhaust gas stream repeatedly changes its direction – the labyrinth silencer.
Of all the structural elements of the exhaust system, the muffler is the most modernized (tuned). When tuning the exhaust system, the so-called exhaust pipe silencer (one exhaust pipe to all chambers without changing the direction of flow). Such a silencer has less back pressure, but it does not give a significant increase in engine power. The main advantage of the once-through muffler is the “noble” or “sporty” sound of the car (who likes it more).
The in-line silencer design combines a stainless steel housing in which a perforated pipe is wrapped in a steel mesh and sound-absorbing material. Steel mesh provides mainly the protection of sound-absorbing material from blowing. Fibreglass is used as a sound-absorbing material. In a direct-flow muffler, sound waves freely pass through the holes of a pipe, a metal grid and are absorbed by fibreglass ( converted into thermal energy ).
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