The normal operation of an engine generates fumes that are thrown out of the vehicle's exhaust system. A gaseous medium through which the sound waves of the internal combustion engine propagate. if not for him exhaust pipe muffler, this noise could become deafening.
This element is essential to comply with the necessary regulations so that a vehicle can circulate on the street (such as UNE EN ISO 14163). They resort to several techniques that muffle the sound, without interfering with the power of the engine or, at least, interfering as little as possible.
What is exhaust pipe muffler
As indicated by the Spanish standard UNE EN ISO 14163, a silencer is the applicable element for «attenuate noise generated at the inlet or outlet of internal combustion engines«. That is, in cars, motorcycles, trucks or any vehicle with this type of engine, and also in other types of machinery. A task that has been perfected over many years of development and that today is achieved thanks to several methods combined in the same silencer.
Focusing on the vehicles, the silencers are always on the way out or escape And they don't just reduce sound. In many cases They are also responsible for modifying it. to make it more attractive. For example, in many motorcycles or cars they are designed so that the noise that comes out of them is more serious and they help the exhaust pipes to achieve that effect.
They usually have rectangular, cylindrical or a mixture of the two, because they are part of the vehicle's exhaust system. So they are inserted in one of the pipes that make it up.
What does a muffler look like inside?
It all depends on the needs of the vehicle in question. The simplest are limited to having a fiberglass wrapped perforated inner tube and all this covered by another smooth tube of greater diameter. A typical system on motorcycles and some cars.
On the other hand, if we go to those that are used more frequently in cars, the interior can be somewhat more complex. They are made up of several chambers responsible for damping different sound frequencies. Each car will have a different distribution, but in many cases it is about making the sound travel as far as possible.
To get this it's not about creating tremendously long conduits, but to force the sound to bounce as much as possible within the different chambers. The compartment in question may be only a few centimeters wide, but if the sound bounces thousands of times inside an interior, it will be like having traveled much further than it seemed at first. Next we are going to detail how this type of exhaust pipe muffler works.
How does the exhaust muffler work?
Let's start with the path that the noise travels from the engine until it reaches the muffler: when the Exhaust valves of the combustion chambers open, the smoke is pushed out at high speed. In other words, it discharge the burnt gases at high pressure towards the manifold. From there they pass to an intermediate pipe, where they expand and progressively lose their pressure and speed.
This increase in volume will generate sound waves with a shorter retention time than the exhaust gases, which interact directly with the muffler, where they are minimizes and modifies noise that produce.
The muffler then converts this energy of sound waves into heatthrough vibrations and friction. He makes them go through various chambers and tubes with different absorption systems. Each manufacturer decides the best combination of methods to reduce the noise of their engine, depending on their needs, space and budget. Below we describe the most common methods. Although it is very common to find combinations of all of them.
Side resonator plus absorption silencer
Sound enters the muffler through a main pipe that is perforated and surrounded by a larger tube. Is named side resonator and is effective with certain sound frequencies.
Works thanks to which part of the sound waves are forced to pass through some small holes and to bounce inside the large pipe that surrounds it. On each bounce, some comes out of the holes, some bounces back, and so on. That way, every time it goes through the holes again, it does so having lost some of its energy.
To improve your effectiveness are combined with absorption silencers, which is simply a very porous material that reduces noise. It is usually glass wool and is placed wrapping the perforated cylinder separating it from the outer cylinder.
Expansion chamber plus interference silencer
In these silencers the first noise reduction system is the expansion chambers. These are larger chambers than the main pipe, through which part of the gases will pass. They will then have to re-enter a pipe the same size as before.
Thanks to this and its geometry, sound frequencies diversify and some return where they came from. Others simply lose energy inside the chamber bouncing off its walls. Your design is focused on reducing the volume of higher frequencies of the engine in question.
Since it is actually a container, it is not usually used on its own. Other noise reduction systems fit inside. In their case they usually put perforated plates placed in parallel to generate echoes (interference silencer). They work in a similar way to sidewall resonators, but instead of being a perforated cylinder inside another tube, they are perforated plates that divide the expansion chamber muffler into multiple rooms. Thanks to them, interferences are created in the sound waves and they are bounced multiple times. They also usually carry noise absorbing materials like the aforementioned lateral resonators.
Notice that side resonators also create an expansion chamber effect, although usually less.
Helmholtz resonator
They also often resort to Helmholtz resonator. A chamber where the most powerful frequencies generated by the motor will also be eliminated. Actually, it is a resonance silencer with a very curious operation.
Depending on its size and thickness and the material it is made of, it will return a specific sound frequency. So it's designed to return the same frequency of sound that enters it, but in the opposite direction. This cancels the sound waves with equivalent but opposite ones.
To understand in more detail the operation of each noise reduction system We recommend the following article:
Do muffled engines lose power?
Even though the exhaust pipe muffler succeeds in reducing noise dissipating its energy, it also causes exhaust gases take longer to come out. An effect that is not only due to having to go through more ducts, but also due to the back pressure that is generated in each of the compartments.
The result is that the engine cannot exceed certain power levels without overloading the exhaust system. A circumstance that should not imply that the engine will have more power if the muffler is removed. Even if this component is removed, a car will not perform any better because it is programmed to perform at a certain level. So you will only get to make more noise and receive the occasional fine.
Another thing is that the engine is modified to perform above the levels set by the manufacturer. When its potency is greatly increased, the exhaust ducts have to be at the height of the greatest flow, which can be achieved by removing parts such as the silencer. In other words, a transformation that would violate several laws in Spain and many other countries if it is not a racing car. If it is a street-legal car, you would have to be replaced by one that does not limit smoke output as much, but that continues to dampen the noise within legal limits. A change made by many trainers like Brabus or ABT.
Pictures – Bike “Club4AG” Miwa, Robert Couse-Baker, Mike, 70_musclecar_RT+6, Dennis Elzinga, Txemari (Argazki), Kevin Fanciulli
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It depends on the car, if it's small, you can't because it would damage the engine, if it's big, nothing would happen to the car.