EXHAUST SYSTEM
The main function of automobile exhaust system is to discharge automobile exhaust gas. It include the tailpipe, the muffler, the exhaust manifold and header,exhaust pipe gaskets and the exhaust pipe hangers.
1.The Tailpipe
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The tailpipe is a long metal tube attached to the muffler. It sticks out from under the body of a car, at the rear, in order to discharge the exhaust gases from the muffler of the engine into the air outside the car.
2.The Muffler
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Exhaust gases leave the engine under extremely high pressure. If these gases escaped directly from the engine, the noise would be tremendous. For this reason, the exhaust manifold sends the gases to a muffler where they go through metal plates, or tubes, with a series of holes. The pressure of the gases is reduced when they pass through the muffler, so they go out of the tailpipe quietly.
The muffler is made of metal and is located underneath the body of a car. It’s connected between the tailpipe and the catalytic converter.
There are two types of muffler design. One type uses several baffled chambers to reduce noise. The other type sends the gases straight through perforated pipe wrapped in metal or fiberglass. This type of muffler is designed for the purpose of reducing backpressure and, consequently, makes slightly more noise.
The muffler quiets the noise of the exhaust by muffling the sound waves created by the opening and closing of the exhaust valve. When an exhaust valve opens, it discharges the burned gases at high pressures into the exhaust pipe, which is at low pressure. This type of action creates sound waves that travel through the flowing gas, moving much faster than the gas itself (up to 1400 mph) that the muffler must silence.
It generally does this by converting the sound wave energy into heat by passing the exhaust gas and through perforated chambers of varied size. Passing into the perforations and reflectors within the chamber forces the sound waves to dissipate their energy.
Car manufacturers are experimenting with an electronic muffler, which uses sensors to monitor the sound waves of the exhaust noise. The sound wave data are sent to a computer that controls speaker near the tailpipe. The system generates sound wave 180 degrees out of phase with the engine noise.
The sound waves from the electronic muffler collide with the exhaust sound waves and they cancel each other out, leaving only low-level heat to emerge form the tailpipe.
3.The Exhaust Manifold and Header
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The exhaust manifold, usually constructed of cast iron, is a pipe that conducts the exhaust gases from the combustion chambers to the exhaust pipe. It has smooth curves in it for improving the flow of exhaust.
The exhaust manifold is bolted to the cylinder head, and has entrances for the air that is injected into it. It is usually located under the intake manifold. A header is a different type of manifold, it is made of separate equal-length tubes.
For aftermarket, the maker made the exhaust manifold and header by material of stainless steel,which made the gas more fluid and power improved a lot.
4.Manifold to Exhaust Pipe Gaskets
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There are several types of gaskets that connects the exhaust pipe to the manifold. One is a flat surface gasket. Another type uses a ball and socket with springs to maintain pressure. This type allows some flexibility without breakage of the seal or the manifold. A third type is the full ball connector type, which also allows a little flexibility.
5.Exhaust Pipe Hangers
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Hangers hold the exhaust system in place. They give the system flexibility and reduce the noise level. The hanger system consists of rubber rings, tubes and clamps.
6.Exhaust Pipe(cat-back system)
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The exhaust pipe is the bent-up or convoluted pipes underneath a car. Some are shaped to go over the rear axle, allowing the rear axle to move up and down without bumping into the exhaust pipe, some are shaped to bend around under the floor of the car, connecting the catalytic converter with the muffler.
7.Dual Exhaust System
The advantage of a dual exhaust system is that the engine exhausts more freely, thereby lowering the backpressure, which is inherent in an exhaust system. With a dual system, a sizable increase in engine horsepower can be obtained because the breathing capacity of the engine is improved, leaving less exhaust gases in the engines at the end of each exhaust stroke. This, in turn, leaves more room for an extra intake of the air-fuel mixture.
Exercise
1 Carbon monoxide (CO) also increases the rate at which the photochemical smog is formed by speeding up the conversion of nitric oxide (NO) to nitrogen dioxide.
2 Oxide of sulfur were initially ignored in the exhaust system, since the sulfur content of gasoline as a fuel is less than 1/10 of 1 percent. Because of this small amount, it was felt that it contributed very little to the overall pollution problem. However, the automobile exhaust system, when equipped with a catalytic converter, changes the sulfur dioxide into sulfur trioxide. When this combines with water vapors, a sulfuric acid mist is formed and is a very difficult pollutant to handle since it is extremely corrosive.
3 By visually inspecting the tailpipe emission, a determination can be make as to where an engine to defect may exist. An engine with light gray or blue smoke emitting from the tailpipe normally indicates an increase in the oil consumption through burning due to internal engine wear. Black smoke would indicate a defective fuel delivery system, causing the engine to operate in a rich mode.