Exhaust System Manufacturing
Fig. 1 Shaun Eiler's 442
Shaun Eiler
April 14, 2004
Introduction Exhaust Manifold Manifold Manufacturing
Catalytic Converter Muffler Exhaust Pipe Conclusion
What exactly is an automobile exhaust system? and how are manifolds manufactured? This research document will touch on exhaust systems and the manufacturing of manifolds. "Exhaust systems carry out several functions. These include: 1) Getting hot, noxious exhaust gasses from your engine to a place away from the engine compartment; 2) Significantly attenuating noise output from the engine; and 3) In the case of modern cars, reducing exhaust emissions" (Exhaust Theory, 2000). An internal combustion engine must be allowed to breathe. Gas is ignited and it must have somewhere to go after it has been burned. When this gas is ignited it propels the engine forward.
"After your air/fuel mixture (or nitrous/fuel mixture) burns, there will be some leftovers consisting of a few unburned hydrocarbons (fuel), carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, phosphorous, and the occasional molecule of a heavy metal, such as lead or molybdenum" (Exhaust Theory, 2000). With all of these gaseous forms, there is a lot of pressure that goes with it. The pressure along with the explosions that occur makes the exhaust manifold or header, extremely hot. In the following section, the major components, and their functions, of the exhaust system will be examined. These major components include exhaust manifolds, catalytic converters, mufflers and pipes.
"The exhaust manifold provides an easy, durable way to exhaust (vent) hot gases from the combustion chamber" (Torbjornsen, T, Exhaust Systems do More than Remove Exhaust). Exhaust manifolds are usually manufactured out of iron, due to the extremely hot temperatures that they face on a daily basis. They must be compact in order to fit in the engine space. Exhaust manifolds must be tuned in order to allow the smoothest and free flowing path for the gas to escape. Doing this causes the "venturi" effect to occur. The venturi effect means the speeding up of air flow. When the driver accelerates or decelerates, the engine is allowed to breathe and this makes the engine perform much better.
The problem with exhaust manifolds is that they are very restrictive. They do not allow a very good exhaust flow. A lot of power is lost because the manifolds are spending the majority of the power trying to force the exhaust gas out. Automobile manufacturers use manifolds because they are cheap to produce and very easy to mount on the engine. For more power, it is recommended that headers replace the manifold. Headers allow a very high increase in power, and they come in different power ranges and fuel efficiencies. Certain headers will work better on certain cars.
Manifolds must be produced so they are able to withstand the extreme temperatures that they face on a daily basis. "Ideally, the exhaust manifold should be capable of withstanding continuous gas temperatures as high as 980 degrees Celsius with occasional peaks of 1020 degrees Celsius. Thus austenitic or ferritic heat resistant steels which exhibit excellent heat deformability and oxidation resistance at elevated temperature are being developed and applied." (Casts Steel Exhaust Manifolds, 1999). Today, the most common types of materials that are used in the manufacturing of manifolds are high silicon molybdenum iron and austenitic ductile iron. These materials are able to resist the high temperatures that affect manifolds. These manifolds are manufactured using a casting process. "The casting process provides the best opportunity to produce parts with thin walls and compact geometry in order to maximize space in the engine compartment - a benefit rarely achievable with fabricated parts. Moreover, due to greater design flexibility the cast manifold is more mechanically robust than a fabricated option" (Casts Steel Exhaust Manifolds, 1999). These manifolds are produced using the "push" or "suck" casting methods. These processes can be quite expensive. If it were not for these processes, the cost of purchasing manifolds would be relatively low. As long as engines keep producing the extreme temperatures that they do, there will always be need for the manufacturing of manifolds. Companies are looking to come up with new ways to make the manufacturing process cheaper, so that manifolds can be sold to the public at a lower cost.
The main function of the catalytic converter is to lower exhaust emissions. They produce a catalysis, which is also known as a chemical reaction. "The converter is filled with a chemical agent called a catalyst that heats up to cherry-red when hot exhaust gas flows through the converter" (Torbjornsen, T, Exhaust Systems do More than Remove Exhaust). The catalyst takes place when there are any unburned gases left in the flow of exhaust, the gases are burned out and this cleans out the exhaust emissions. Blockage can sometimes occur in the converter when more unburned gas is being produced, then what is being burned out. The engine's exhaust flow is cut and the car will then lose power. The following is a picture of a catalytic converter.
The sound of exhaust is naturally very loud. With all the cars on the road today, this would cause an unbearable amount of noise. To cure this problem, most cars use mufflers. Mufflers get rid of the noise by three different methods. These methods include absorption, restriction, and reflection. "The absorption method is probably the least effective at quelling engine roar, but the benefit is that "absorbers" are also best at letting exhaust gas through" (Exhaust Theory, 2000). These absorption type mufflers are also the simplest. "All of the above named mufflers utilize a simple construction consisting of a perforated tube that goes through a can filled with a packing material, such as fiberglass or steel wool: this is similar to simply punching holes in your exhaust pipe, then wrapping it up with insulation" (Exhaust Theory, 2000). Another type of absorption muffler, is one the uses a chamber instead of a perforated tube. This chamber is larger then the rest of the exhaust pipe. When exhaust gases enter this chamber, they tend to slow down. This cuts down on sound a lot more. The sound insulators in this section have much more time to absorb the sound that is coming out.
The next type of muffler is the restriction type. This muffler is the cheapest from companies to manufacture. Almost every OEM exhaust system comes with a restrictive muffler. Restrictive mufflers are not very good at all.
The final type of muffler is the reflection. "They often utilize absorption principles in conjunction with reflection to make the ultimate high-performance silencer" (Exhaust Theory, 2000). Reflective mufflers work by having two sound waves collide, this makes each wave disappear, all that is left is a low grade heat spot.
There is another way that reflective mufflers work. "The outer casing is sized just so that high pitched engine noise is reflected back into the core of the muffler, where those sound waves slam into a torrent of more sound waves of like wavelength coming straight from the engine" (Exhaust Theory, 2000). Fiberglass is usually packed in these mufflers to get rid of any excess sound that is left. Mufflers are essential in getting rid of exhaust noise. Some do a better job then others, but they all work to obtain the same goal. Some people believe that having mufflers creates more power in their vehicles. This is not true, the bad thing about mufflers is that they restrict power. If a power increase is desired then the mufflers must be removed from the vehicle.
Most exhaust pipes are produced out of either standard or stainless steel. Exhaust pipe is really a term used to described the different pipes that are used throughout the whole system. The purpose of exhaust pipes is to lead the exhaust gas away from the engine. Exhaust pipes reduce the amount of pollution and sound that are emitted. They also make vehicles safer due to the fact that they lead the harmful exhaust gas away from the vehicle and its passengers.
The manufacturing of exhaust systems is extremely important. With the high reliance that society has on using vehicles, it is important to have something that can reduce the amount of noise and pollution. Each automobile that rolls off of the assembly line is going to be equipped with an exhaust system. Different vehicles demand different types of exhaust systems. Exhaust systems must be manufactured to be able to withstand the extreme temperatures. It is expensive to manufacture exhaust systems, so there they are expensive for consumers to buy. It is important that we continue to search for ways to make better and safer exhaust systems so that we can keep the environment clean.
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