The Working of a Muffler

The muffler is a small part in the exhaust system of a vehicle. Mufflers perform a very crucial job – they reduce the noise coming from the combustion engine. One only has to start a car without a muffler to know how important this is. The noise level of the engine is very high and they affect the eardrum.
Sound goes in a wavelike pattern. When the exhaust valve opens intermittently and spews smoke with pressure, the same wave motion is produced within the exhaust pipe producing a lot of sound.

How it works
Sound amplification and reduction
The interference of two sound waves can either amplify them or reduce or nullify them. If two waves combine in phase, it is called a constructive interference. And if they combine out of phase, it is called destructive interference. When two waves that are out of phase hit the ear, nothing will be heard. The muffler uses this technique to reduce sound.

Inside a muffler
The muffler is constructed in a way that it reflects the entering sound waves multiple times so that they interfere with each other.

Inlet
The exhaust gases and sound waves enter the muffler through the inlet.

Resonator chamber
The resonator chamber is where the sound waves cancel themselves out. The waves as they enter, go all the way till the anterior end, strike the surface and return back. When they return back, through a hole, they reach a chamber called the resonator chamber. The resonator chamber has specific measurements and holds a specific volume of air, to produce waves of a particular wavelength to cancel other waves. The length of the resonator is adjusted so that, the higher pressure waves that get reflected off the wall, and meet with the low pressure waves just entering the chamber.

Perforations
There are perforations on the tube that leads from the inlet as well as the tube that carries the exhaust outside the muffler. When the waves enter the first pipe, they are highly pressurized and thus have a high amplitude. The perforations absorb some amount of the shock created by the waves and thus reduce their intensity.

Back-pressure reducing mufflers
When mufflers reduce back-pressure, they also create an impediment in the passage of exhaust gases. This is because the exhaust is routed through a number of turns and reflections by which the wavelength of their sound is reduced. The engine faces a little pressure backwards, and some efficiency is also lost because the exhaust is not evacuated without resistance.

There are mufflers that reduce back pressure. These mufflers are designed in such a way that they do not offer too much resistance. To put this into effect, these mufflers use only the technique of absorption. But, back-pressure reducing mufflers don't reduce noise as effectively as normal mufflers do.

Know How an Automobile Exhaust System Works

The exhaust system is a normally a piping system that is used to evacuate the ignition gases that are produced inside the ignition chamber. These gases are led through a network of pipes to the outside. The components of an exhaust system are:

1) Manifold or header
The manifold is an assembly of pipes that directly collect the ignition gases from the engine's combustion chambers. This is also called a header. The header is designed so each opening mates up with one of the engine's exhaust ports, and they are tightly sealed with the help of flanges which prevent the exhaust gases from escaping. From here, the exhaust gases are routed towards various other pipes and exhaust components.

2) Header-back   
The header-back is the part of the exhaust system that is from the ending of the header to everything till the final outlet. Header-backs are used in exhaust systems which does not come with a turbo charger.

3) Turbo-back
In this case, the system comes with the turbo charger. A turbo-back is an aftermarket performance device that leads from the turbo charger to the outside.

4) Catalytic converters
Catalytic converters reduce the level of toxic waste in the ignition gases. For this, the insides of the catalytic converters are coated with different kinds of metals. Different types of catalytic converters use different combinations of platinum, palladium and rhodium. The gases that pass from the ignition chamber through the header contain super-toxic combination of carbon monoxide, nitrogen oxide and hydrocarbons. These are the chemicals whose presence is tested in an emission test for automobiles. When the metals inside the catalytic converter comes into contact with the gases, chemical reactions happen and hey reduce the toxicity of the gases. As the exhaust passes through the catalytic converter, the toxicity is reduced thereby satisfying environmental health issues.

5) Cat-back
Cat-back (also called as axle back) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This generally compresses of the passage from the catalytic converter to the muffler, from the muffler to the tail pipe and to the outside.

6) Muffler
One only needs to custom-remove the muffler and check what noises an engine produces. The noises that an engine produces along with other components are simply too loud and disallows any comfort for the passengers and the others. Thus, the muffler does a very crucial job. With some very simple but efficient acoustic techniques, it reduces the noises that reach it through the exhaust system to a very high extent.

7) Tail-pipe or exhaust
The tail pipe is the final part of the exhaust system. This is the exit for exhaust gases which pass through an array of pipes, gotten processed and muffled, to the outside. The tail pipe usually points towards the opposite direction to the direction of travel. However, this might differ in some cases as the tail pipe points sideways. The tailpipe is usually the only visible part of the entire exhaust system.

Technical features of Liquid-cooled engines

Liquid-cooled engines are ones using circulation of liquids to cool the engines. A mixture of water and a fluid called the coolant are circulated through pipes into specially built sections of the engine, and then back to the radiator. In radiator, water is cooled and sent back into the engine. Even though it is called 'water cooling', the actual cooling in the radiator happens with the use of air. Liquid-cooling systems cool better because of their heat carrying capacity.

There are two kinds of Liquid cooled-engines:

Thermo-siphon: Thermo-siphon is based on the convective property of liquids. Convection is a property in liquids by which the part of liquid higher in temperature move up against gravity and the amounts that are lower in temperature settle down. This is the property that is used in a thermo- siphon. In the engine, when the coolant comes out of the engine, it is hot. Thus, it automatically flows to the radiator where there is cooler air and simultaneously, cold coolant moves into the engine.

Pump-circulation: However, as a lot of advancements were made in the engine, their efficiencies also increased. Now, it became a requirement that their cooling is faster. So, instead of using a thermo-siphon, the coolant was circulated using the method of pump-circulation, which does it by pressurizing the coolant through to the engine and back to the radiator.

Advantages
Unlike air-cooled systems, the liquid cooled system is generally more effective and faster in cooling. Liquid cooling systems less noisy too. They are also compact and economical to manufacture.

Disadvantages
At low temperatures, the liquid coolant has a tendency to freeze. Another disadvantage is that, the liquid cooling system has pipes fitted to various components. Thus, it naturally becomes necessary that they are fixed properly and there are no leakages. If there are openings in the fittings or if the sealant gives way, leakage happens, and it doesn't just affect the cooling, but also can affect other parts surrounding the cooling. While cleaning the inner parts of car machinery, extra care is needed since water could feel messy with components.

Usage
Very commonly used in maritime vessels, because of the availability of water externally. Other than that, majority of cars today use liquid cooling system. However, Porsche has used it extensively in the 911 series, BMW in its motorcycles. Another notable model to have used this kind of engine is the Volkswagen Beetle.