Car muffler, several devices for noise reduction

The muffler is an important structural element of the exhaust system, without which the operation of a modern car is simply impossible. A car muffler has the following main functions:

• reduction of the noise level of the exhaust gases;

• energy conversion of exhaust gases, reduction of their speed, temperature, pulsation.

The exhaust gases leaving the engine cylinders are at high pressure. When exhaust gases move through the exhaust system, sound waves are generated that propagate faster than gases. The muffler converts the energy of sound vibrations into thermal energy, thereby reducing the noise level to a certain (preset) value. At the same time, with the use of a muffler, back pressure is created in the exhaust system, which leads to a slight decrease in engine power.

The muffler uses several noise reduction technologies:

1、Muffler device:

• expansion (narrowing) of the flow;

• change of direction of flow;

• interference hardening of sound waves;

• absorption of sound waves.

• Expansion of the flow is realized by means of several chambers of different volumes, separated by partitions.

• Allows you to effectively damp low-frequency sound vibrations.

• Along with expansion, the flow is reduced in the muffler by means of a diaphragm hole (throttle). Used to suppress high frequency noise.

2、

In the muffler, with the exception of straight-through mufflers, a change in the direction of movement of the exhaust gas flow is provided. The angle of flow rotation is in the range of 90-360 °, thereby damping 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) of the amplitude of oscillations. The muffler uses both types of interference. The technology is implemented using perforations in the pipes of the muffler. By varying 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.

3、

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 are used in mufflers, as a rule, in a complex.

In modern cars, from one to five mufflers are installed, mostly two. The muffler closest to the engine is called the front muffler or resonator. This is followed by the main (rear) muffler. For each specific car model and engine brand, a different set of mufflers is used.

Resonator device

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 case. To increase the efficiency of damping vibrations, a throttle hole is made in the pipe.

Main muffler

The main muffler provides the ultimate in noise cancellation. It has a more complex design. The metal case houses several perforated tubes. The body is divided by partitions into 2-4 chambers. Some chambers may be filled with sound absorbing material. In the main muffler, the flow of exhaust gases changes its direction many times - a labyrinth muffler.

Of all the structural elements of the exhaust system, the muffler is the most subject to modernization (tuning). When tuning the exhaust system, the so-called. straight-through muffler (one straight-through pipe for all chambers without changing the direction of flow). Such a muffler has less back pressure, but it does not give a significant increase in engine power. The main advantage of a straight-through muffler is the "noble" or "sporty" sound of the car (who likes what more).

Direct-flow muffler device

The design of the straight-through muffler combines a stainless steel body, which houses a perforated pipe wrapped in steel mesh and sound-absorbing material. The steel mesh mainly protects the sound-absorbing material from blowing out. Fiberglass is used as a sound absorbing material. In a straight-through muffler, sound waves freely pass through the pipe openings, metal mesh and are absorbed by the glass fiber (converted into heat energy).

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