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How does Muffler works?

By:prayag nao

Why muffler is used in vehicals ?

Sound is a pressure wave formed from pulses of alternating high and low air pressure. These pulses makes their way through the air at -- you guessed it -- the speed of sound.
In an engine, pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other.They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do.When these pressure pulses reach your ear, the eardrum vibrates back and forth. Your brain interprets this motion as sound.

This sound pollute the enviorment that's why muffler is used.

Inside a Muffler

Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. Take a look at the inside of this muffler:
The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler.
A chamber called a resonator is connected to the first chamber by a hole. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound.

The Resonator

When a wave hits the hole, part of it continues into the chamber and part of it is reflected. The wave travels through the chamber, hits the back wall of the muffler and bounces back out of the hole. The length of this chamber is calculated so that this wave leaves the resonator chamber just after the next wave reflects off the outside of the chamber. Ideally, the high-pressure part of the wave that came from the chamber will line up with the low-pressure part of the wave that was reflected off the outside of the chamber wall, and the two waves will cancel each other out.
The animation below shows how the resonator works in a simplified muffler.


 

In reality, the sound coming from the engine is a mixture of many different frequencies of sound, and since many of those frequencies depend on the engine speed, the sound is almost never at exactly the right frequency for this to happen. The resonator is designed to work best in the frequency range where the engine makes the most noise; but even if the frequency is not exactly what the resonator was tuned for, it will still produce some destructive interference.
Some cars, especially luxury cars where quiet operation is a key feature, have another component in the exhaust that looks like a muffler, but is called a resonator. This device works just like the resonator chamber in the muffler -- the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.



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