maruti suzuki training report

8/11/2019 maruti suzuki training report

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Product Range

Exhaust System Assembly

This consists of exhaust manifold, catalyst, center muffler, rear

muffler and exhaust.


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Automobiles Part Business

Contributing To Both Improved Engine Performance and Lower Noise

1 Role of Product ,Exhaust Pipe

These parts are mounted beneath the floor of the automobile and their role is to

cleanse the exhaust gas coming from the engine, mute its sound, and then

discharge the gas from the rear of the automobile

2 Required Elements of Products

The exhaust system products are required to discharge the exhaust gas from the

engine both smoothly and quietly to satisfy the competing demands for improved

engine performance and quietness. In addition, these products are exposed to

high temperatures and a corrosive external environment, so it is also essential

that they have good heat resistance and corrosion resistance.

3 Unique Strengths of Our Products

We make full use of analysis technologies and carry out optimized design to

reduce the effects of exhaust gas heat and improve the noise reduction.

4 Direction of Product development

These products have a large impact on the amount of CO2emissions from the

automobile and so the performance of these products largely controls the overall

environmental performance of the automobile as a whole.

We are advancing and promoting research and development for the purpose of

reducing CO2emissions even further


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Exhaust Manifold

Inautomotive engineering,an exhaust manifold collects theexhaust gases frommultiplecylinders into one pipe. The wordmanifold comes from the Old English

word manigfeald and refers to the folding together of multiple inputs and

outputs.

In contrast, aninlet manifold is the part of an engine that supplies the air to the

cylinders.

Exhaust manifolds are generally simplecast iron or stainless steel units which

collect engine exhaust from multiple cylinders and deliver it to the exhaust pipe.

For many engines, there are aftermarket tubular exhaust manifolds knownas headers inUS English,asextractor manifolds in British andAustralian

English,and simply as "tubular manifolds" inUK English.These consist of

individual exhaust head pipes for each cylinder, which then usually converge into

one tube called acollector.Headers that do not have collectors are called 'zoomie

headers'.

The most common types of aftermarket headers are made of mild steel or

stainless steel tubing for the primary tubes along with flat flanges and possibly a

larger diameter collector made of a similar material as the primaries. They may be

coated with a ceramic-type finish (sometimes both inside and outside), or painted

with a heat-resistant finish, or bare. Chrome plated headers are available but they

will tend to blue after use. Polished stainless steel will also color (usually a yellow

tint), but less than chrome in most cases.

Another form of modification used is to insulate a standard or aftermarket

manifold. This decreases the amount of heat given off into the engine bay,

therefore reducing the intake manifold temperature. There are a few types of

thermal insulation but three are particularly common:

Ceramic paint is sprayed or brushed onto the manifold and then cured in an

oven. These are usually thin, so have little insulatory properties; however, they

reduce engine bay heating by lessening the heat output via radiation.

A ceramic mixture is bonded to the manifold viathermal spraying to give a

tough ceramic coating with very good thermal insulation. This is often used on

performance production cars and track-only racers.
http://en.wikipedia.org/wiki/Automotive_engineeringhttp://en.wikipedia.org/wiki/Exhaust_gashttp://en.wikipedia.org/wiki/Cylinder_(engine)http://en.wikipedia.org/wiki/Manifold_(engineering)http://en.wikipedia.org/wiki/Inlet_manifoldhttp://en.wikipedia.org/wiki/Cast_ironhttp://en.wikipedia.org/wiki/US_Englishhttp://en.wikipedia.org/wiki/Extractor_manifoldhttp://en.wikipedia.org/wiki/Australian_Englishhttp://en.wikipedia.org/wiki/Australian_Englishhttp://en.wikipedia.org/wiki/UK_Englishhttp://en.wikipedia.org/w/index.php?title=Collector_(automotive)&action=edit&redlink=1http://en.wikipedia.org/wiki/Zoomie_headerhttp://en.wikipedia.org/wiki/Zoomie_headerhttp://en.wikipedia.org/wiki/Thermal_sprayinghttp://en.wikipedia.org/wiki/Thermal_sprayinghttp://en.wikipedia.org/wiki/Zoomie_headerhttp://en.wikipedia.org/wiki/Zoomie_headerhttp://en.wikipedia.org/w/index.php?title=Collector_(automotive)&action=edit&redlink=1http://en.wikipedia.org/wiki/UK_Englishhttp://en.wikipedia.org/wiki/Australian_Englishhttp://en.wikipedia.org/wiki/Australian_Englishhttp://en.wikipedia.org/wiki/Extractor_manifoldhttp://en.wikipedia.org/wiki/US_Englishhttp://en.wikipedia.org/wiki/Cast_ironhttp://en.wikipedia.org/wiki/Inlet_manifoldhttp://en.wikipedia.org/wiki/Manifold_(engineering)http://en.wikipedia.org/wiki/Cylinder_(engine)http://en.wikipedia.org/wiki/Exhaust_gashttp://en.wikipedia.org/wiki/Automotive_engineering


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Exhaust wrap is wrapped completely around the manifold. Although this is

cheap and fairly simple, it can lead to premature degradation of the manifold.

The goal of performance exhaust headers is mainly to decrease flow resistance

(back pressure), and to increase the volumetric efficiency of an engine, resulting

in a gain in power output. The processes occurring can be explained by thegaslaws,specifically theideal gas law and thecombined gas law.

The role of the exhaust manifold is to send the high-temperature exhaust gas

from the engine onto the exhaust system (catalyst). In the past this part was

made from cast iron, but here at Futaba we began producing exhaust

manifolds made from stainless steel pipe and sheet metal in the spring of 1989,

long before any of our competitors, and now it has become the mainstream

material for this product.
http://en.wikipedia.org/wiki/Back_pressurehttp://en.wikipedia.org/wiki/Gas_lawhttp://en.wikipedia.org/wiki/Gas_lawhttp://en.wikipedia.org/wiki/Ideal_gas_lawhttp://en.wikipedia.org/wiki/Combined_gas_lawhttp://en.wikipedia.org/wiki/Combined_gas_lawhttp://en.wikipedia.org/wiki/Ideal_gas_lawhttp://en.wikipedia.org/wiki/Gas_lawhttp://en.wikipedia.org/wiki/Gas_lawhttp://en.wikipedia.org/wiki/Back_pressure


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Exhaust System

An exhaust system is usuallypiping used to guide reactionexhaust gases away

from a controlledcombustion inside anengine orstove.The entire systemconveys burnt gases from the engine and includes one or more exhaust pipes.

Depending on the overall system design, the exhaust gas may flow through one or

more of:

Cylinder head andexhaust manifold

Aturbocharger to increase engine power.

Acatalytic converter to reduceair pollution.

Amuffler (North America) /silencer (Europe), to reducenoise.

This system is composed of parts such as the exhaust manifold, catalyst, center

muffler, rear muffler, and the exhaust pipes that connect these parts together.

The role of the exhaust system is to reduce both the temperature and the noise

of the exhaust gas, as well as to remove any harmful components of the gas.

This system is one of the most critical parts of the automobile because it has a

large effect on the tone of the exhaust noise and the power performance
http://en.wikipedia.org/wiki/Pipe_(fluid_conveyance)http://en.wikipedia.org/wiki/Exhaust_gashttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Stovehttp://en.wikipedia.org/wiki/Cylinder_headhttp://en.wikipedia.org/wiki/Exhaust_manifoldhttp://en.wikipedia.org/wiki/Turbochargerhttp://en.wikipedia.org/wiki/Catalytic_converterhttp://en.wikipedia.org/wiki/Air_pollutionhttp://en.wikipedia.org/wiki/Mufflerhttp://en.wikipedia.org/wiki/Mufflerhttp://en.wikipedia.org/wiki/Noise_(environmental)http://en.wikipedia.org/wiki/Noise_(environmental)http://en.wikipedia.org/wiki/Mufflerhttp://en.wikipedia.org/wiki/Mufflerhttp://en.wikipedia.org/wiki/Air_pollutionhttp://en.wikipedia.org/wiki/Catalytic_converterhttp://en.wikipedia.org/wiki/Turbochargerhttp://en.wikipedia.org/wiki/Exhaust_manifoldhttp://en.wikipedia.org/wiki/Cylinder_headhttp://en.wikipedia.org/wiki/Stovehttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Exhaust_gashttp://en.wikipedia.org/wiki/Pipe_(fluid_conveyance)


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Truthfully, an individual car's emissions are relatively low, compared to other

sources of pollution. But when hundreds of thousands of people are each sitting

in a car, packing a highway to capacity, the cumulative effects are enormous. As

you're sitting in a traffic jam, gazing at the smoke coming out of the tailpipe in

front of you and rising to join the smog in the sky, think for a moment about what

that smoke is. It might not look like much, but that smoke has come a long way

since it was pushed through the car's engine just moments before.

Concern about our automobiles' effect on the environment is nothing new. The

1970 version of the Clean Air Act gave the EPA its sweeping authority to regulate

automotive emissions. As technology advanced, the EPA pushed for more strict

standards. And while new cars are much cleaner than those of 40 years ago,

people tend to drive greater distances and a lot more often today, contributing toa lot more pollution. The Clean Air Act was revamped and increased in scope in

1977, and then again in 1990.

Automotive manufacturers and parts suppliers have had to keep pace with these

changes, and as you can imagine, a car's exhaust system has had to evolve

considerably, too.

Components of an Exhaust -- Smokin' Pipes

The exhaust system is comprised mainly of pipes in several different shapes, each

designed to connect to one another, and each shaped to conform to a specificpart of the underside of the car. (The pipes are often bent to wrap around or

otherwise accommodate other nearby components of the car, such as the axles.)

Each pipe is responsible for moving the exhaust gases toward the back, but many

of the segments are specialized. In other words, from the exterior, the system

simply looks like a bunch of connected pipe segments that run from the engine


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bay to the back bumper, though some serve an additional purpose as the exhaust

flows through that particular pipe.

For example, the Y pipe (which is simply, well, a Y-shaped pipe) might be installed

so the end with two openings bolts up to two corresponding openings in theexhaust manifold, combining the engine's waste to progress through the system.

Or, when installed at the back end of the car, a Y pipe can help create a dual

exhaust system with a tailpipe on each side of the car (for an often sought-after

sporty look). Intermediate pipes might be attached to the muffler or resonator,

which are other important system components (we'll get to these on the next

page). Balance pipes, found in dual exhaust systems, help equalize the exhaust

pulses traveling under the driver and passenger sides of the car. Air gap pipes are

specialized nested pipes that act as a heat shield and insulator by providing anextra layer for airflow. And the tail pipe, which is typically peeking out from

underneath the rear bumper, usually has a larger opening and might be made of

more substantial-looking metal, to give the appearance of a performance exhaust

that's a common feature of high-end cars.

Though it might seem inefficient to have a ton of pipes instead of just one, really,

all those segments serve a purpose. For one, bending pipes is hard work, and it's

easier to connect small angled segments to straight pipes than it is to shape onelong, expensive, heavy pipe to fit every contour of a car. Also, exhaust system

components wear out at regular intervals (depending, of course, on the

manufacturer, its materials, driving conditions and environmental factors). It's

easier and less expensive to replace one rusted-out segment of pipe, banged-up

muffler, or worn-out catalytic converter than it would be to install a whole new

system.

You might wonder how all those pipes fit together. Well, some ends overlap,

while others are mated end-to-end; but not without a little bit of assistance.


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Other Exhaust Components -- Headers,

Hangers and More

We discussed the various pipes first, because they're the most visible and

prevalent components of the exhaust system, and because they're all over the

place. But the exhaust system really starts at the exhaust header (also known as

the exhaust manifold). The header looks like a series of adjacent tubes stuck

together (though it's often made of heavy-duty cast metal). It collects the exhaust

directly from the engine, so it's designed so each opening mates up with one of

the engine's exhaust ports, with flanges that form a tight seal to prevent exhaust

from escaping. From here, the exhaust begins its flow through the various pipesand other components.

The gaskets that are fitted between each pipe play a very important role. It's

difficult, if not impossible, to form a flawless metal-to-metal seal, so gaskets are

sandwiched between each connection to prevent the poisonous gases from

escaping prematurely. They're made of fiberAd by save net or other heavy-duty,

heat resistant materials, which have just enough flexibility to compress slightly

when the pipes are clamped tightly together. This helps form a tight seal.

The muffler is another key part of the exhaust system. It looks like a large round

or oval chamber (usually, but not always, found near the back of the car). That

chamber has a very complex design, though -- it's responsible for silencing most

of the engine's noise, even though it has to allow the exhaust to continue flowing

smoothly. A series of chambers and tubes, filled with rock, wool, or synthetic

fibers, absorbs and controls the noise. And that's not all -- the muffler must be

reasonably resistant to damage, corrosion and heat retention. The resonator is a

secondary or substitute sound elimination component, used to augment the

muffler, or in cases where space is at a premium it might even be used instead of

a muffler.

Catalytic converters, which became commonplace in the 1970s, are the primary

and most efficient means of reducing the level of toxins in a car's exhaust. The


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innards of a catalytic converter (or "cat") are coated with metals. Different types

of catalytic converters use different combinations of platinum, palladium and

rhodium. Before the exhaust reaches the cat, it contains a potent, super-toxic

combination of carbon monoxide, nitrogen oxide and hydrocarbons. (When you

take your car for its emissions test, these are the chemical levels that are being

tested.) When these poisons come into contact with the metals coating the inside

of the cat, a chemical reaction takes place that makes the exhaust gases less

harmful. As the exhaust passes through the cat, the level of chemicals should be

reduced enough to comply with government regulations.

We already talked about gaskets, but the exhaust system requires other basic

pieces of hardware. Flanges generally serve the same purpose as gaskets, but

these are made of metal (and are sometimes formed right onto the end of apipe). Assorted clamps and brackets mount the exhaust pieces together and hold

them to the vehicle, and exhaust hangers literally hang the pipes from the

underbody of the car, with enough strength to keep them in place but also

enough flexibility to withstand movement caused by driving. And last, but not

least are the heat shields: Metal (sometimes insulated) plates that are used as an

extra barrier whenever hot exhaust parts are particularly close to another part of

the car or directly below the passenger compartment.

The Exit Route

If an engine ran perfectly, it would combust all its available fuel as it ran through

its cycles, converting all the dirty bits to a source of power. However, leftovers

exist as pollutants because an engine simply cannot be engineered to run

perfectly -- there are far too many variables. Some amount of fuel will always

remain unburned or partially burned, and these remnants must be quickly


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processed out of the vehicle, in the form of exhaust, to make room for the next

cycle of engine combustion.

As we mentioned earlier, the exhaust first exits the engine and enters the system

through the exhaust manifold. From there, it travels down the system throughinterconnected pipes until it exits through the tailpipe, near the back bumper. The

pipes themselves actually help cool the exhaust, but they're mostly a way for the

exhaust to travel to (and through) the catalytic converter and muffler.

The cat has to be as close to the engine as possible, because it isn't fully

functional until it rises to operating temperature. In many cases, the

manufacturer places the cat shortly after the manifold, so heat from the engine

helps warm the cat and quickly bring it up to temp.

After the gases pass through the cat, which will burn off and remove up to 90

percent of the exhaust's toxins, the next priority is to filter the engine sound

[source: Allen]. The muffler and resonator are usually situated right beyond the

cat. There are many variations on this combination -- some will soothe the

exhaust as much as possible, while others are specifically tuned for aggressive

tones. From there, the exhaust moves through the remainder of the pipes until it

exits the car.

With all those chemicals swirling around, it's quite a feat that the exhaust system

actually works as well as it does. A well-maintained exhaust system should last

two to three years, but the pipes incur damage both inside and out. On the

outside, they're susceptible to road conditions, such as impact from debris and

environmental factors, such as snow, ice and road salt.

However, a more substantial cause of exhaust system degradation is internal, and

it can't be seen until the pipes have corroded through with rust. We know that as

the engine combusts fuel to make power, byproducts of this process are left over

-- that's why the exhaust system is needed. One of these byproducts is acidic

moisture, and it's really damaging to metal. Unfortunately, there's really no way

to keep the insides of the pipes clean.


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When an exhaust pipe rots through or a connection comes loose, an exhaust leak

occurs. A leak is almost always immediately apparent with a loud, obnoxious

sound and, possibly, drivability issues like an intermittent fluctuation in power.

But, believe it or not, these aren't the real problems. It gets a little more serious if

the leak occurs before the catalytic converter, which means the exhaust isn't

being properly processed and all those hot chemicals are spilling everywhere into

the atmosphere. It's always a good idea to get leaks fixed as soon as possible to

avoid subjecting yourself, your passengers and your surroundings to unfiltered

exhaust fumes.


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Muffler

If you've ever heard a car engine running without a muffler, you know what a

huge difference a muffler can make to the noise level. Inside a muffler, you'll find

a deceptively simple set of tubes with some holes in them. These tubes and

chambers are actually as finely tuned as a musical instrument. They are designed

to reflect the sound waves produced by the engine in such a way that they

partially cancel themselves out.

Mufflers use some pretty neat technology to cancel out the noise. In this article,

we'll take a look inside a real car muffler and learn about the principles that makeit work.

But first, we need to know a little about sound.


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Where Does the Sound Come From?

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 -- thespeed 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. Two main characteristics of the wave

determine how we perceive the sound:

Sound wave frequency - A higher wave frequency simply means that the air

pressure fluctuates faster. The faster an engine runs, the higher the pitch we

hear. Slower fluctuations sound like a lower pitch.

Air pressure level - The wave's amplitude determines how loud the sound is.

Sound waves with greater amplitudes move our eardrums more, and we register

this sensation as a higher volume.

It turns out that it is possible to add two or more sound waves together and get

less sound. Let's see how.


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How Can You Cancel Out Sound?

The key thing about sound waves is that the result at your ear is the sum of all the

sound waves hitting your ear at that time. If you are listening to a band, eventhough you may hear several distinct sources of sound, the pressure waves hitting

your ear drum all add together, so your ear drum only feels one pressure at any

given moment.

Now comes the cool part: It is possible to produce a sound wave that is exactly

the opposite of another wave. This is the basis for those noise-canceling

headphones you may have seen. Take a look at the figure below. The wave on top

and the second wave are both pure tones. If the two waves are in phase, they add

up to a wave with the same frequency but twice the amplitude. This is called

constructive interference. But, if they are exactly out of phase, they add up to

zero. This is called destructive interference. At the time when the first wave is at

its maximum pressure, the second wave is at its minimum. If both of these waves

hit your ear drum at the same time, you would not hear anything because the two

waves always add up to zero.


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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. Howdoes this happen? Let's take a closer look ...


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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 mufflerand 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.

Waves canceling inside 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 helpcancel out certain frequencies of sound in the exhaust.

There are other features inside this muffler that help it reduce the sound level in

different ways. The body of the muffler is constructed in three layers: Two thin

layers of metal with a thicker, slightly insulated layer between them. This allows


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the body of the muffler to absorb some of the pressure pulses. Also, the inlet and

outlet pipes going into the main chamber are perforated with holes. This allows

thousands of tiny pressure pulses to bounce around in the main chamber,

canceling each other out to some extent in addition to being absorbed by the

muffler's housing.

Backpressure and Other Types of Mufflers

One important characteristic of mufflers is how much backpressure they produce.

Because of all of the turns and holes the exhaust has to go through, mufflers like

those in the previous section produce a fairly high backpressure. This subtracts a

little from the power of the engine.


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There are other types of mufflers that can reduce backpressure. One type,

sometimes called a glass pack or a cherry bomb, uses only absorption to reduce

the sound. On a muffler like this, the exhaust goes straight through a pipe that is

perforated with holes. Surrounding this pipe is a layer of glass insulation that

absorbs some of the pressure pulses. A steel housing surrounds the insulation.

Diagram of glass pack muffler

These mufflers produce much less restriction, but don't reduce the sound level asmuch as conventional mufflers.

Active Noise-Canceling Mufflers

There have been a few experiments with active noise-canceling mufflers,

especially on industrial generators. These systems incorporate a set of

microphones and a speaker.


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The speaker is positioned in a pipe, which wraps around the exhaust pipe so that

the sound from the exhaust comes out in the same direction as the sound from

the speaker. A computer monitors a microphone positioned before the speaker

and one positioned after the speaker. By knowing some things about the length

and shape of the pipes, the computer can generate a signal to drive the speaker.

This can cancel out much of the sound coming from the generator. The

downstream microphone lets the computer know how well it is doing so it can

make adjustments if needed.


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How Catalytic Converters Work

There are millions of cars on the road in the United States, and each one is a

source of air pollution. Especially in large cities, the amount of pollution that all

the cars produce together can create big problems.

To solve those problems, cities, states and the federal government create clean-

air laws that restrict the amount of pollution that cars can produce. Over the

years, automakers have made many refinements to car engines and fuel systems

to keep up with these laws. One of these changes came about in 1975 with an

interesting device called a catalytic converter. The job of the catalytic converter is

to convert harmful pollutants into less harmful emissions before they ever leave

the car's exhaust system.

Catalytic converters are amazingly simple devices, so it is incredible to see howbig an impact they have. In this article, you will learn which pollutants are

produced by an engine and how a catalytic converter deals with each of these

pollutants to help reduce vehicle emissions.


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Pollutants Produced by a Car Engine

In order to reduce emissions, modern car engines carefully control the amount of

fuel they burn. They try to keep the air-to-fuel ratio very close to thestoichiometric point, which is the ideal ratio of air to fuel. Theoretically, at this

ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline,

the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline,

14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal

ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel

ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel

ratio lower than 14.7).

The main emissions of a car engine are:

Nitrogen gas (N2) - Air is 78-percent nitrogen gas, and most of this passes right

through the car engine.

Carbon dioxide (CO2) - This is one product of combustion. The carbon in the fuel

bonds with the oxygen in the air.

Water vapor (H2O) - This is another product of combustion. The hydrogen in the

fuel bonds with the oxygen in the air.

These emissions are mostly benign, although carbon dioxide emissions are

believed to contribute to global warming. Because the combustion process is

never perfect, some smaller amounts of more harmful emissions are also

produced in car engines. Catalytic converters are designed to reduce all three:

Carbon monoxide (CO) is a poisonous gas that is colorless and odorless.

Hydrocarbons or volatile organic compounds (VOCs) are a major component of

smog produced mostly from evaporated, unburned .fuel.

Nitrogen oxides (NO and NO2, together called NOx) are a contributor to smog and

acid rain, which also causes irritation to human mucus membranes.


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How Catalytic Converters Reduce PollutionIn chemistry, a catalyst is a substance that causes or accelerates a chemical

reaction without itself being affected. Catalysts participate in the reactions, but

are neither reactants nor products of the reaction they catalyze. In the human

body, enzymes are naturally occurring catalysts responsible for many essential

biochemical reactions.

In the catalytic converter, there are two different types of catalyst at work, a

reduction catalyst and an oxidation catalyst. Both types consist of a ceramic

structure coated with a metal catalyst, usually platinum, rhodium and/or

palladium. The idea is to create a structure that exposes the maximum surface

area of catalyst to the exhaust stream, while also minimizing the amount of


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catalyst required, as the materials are extremely expensive. Some of the newest

converters have even started to use gold mixed with the more traditional

catalysts. Gold is cheaper than the other materials and could increase oxidation,

the chemical reaction that reduces pollutants, by up to 40 percent.

Most modern cars are equipped with three-way catalytic converters. This refers

to the three regulated emissions it helps to reduce.

The reduction catalyst is the first stage of the catalytic converter. It uses platinum

and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule

contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and

holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond

with other nitrogen atoms that are also stuck to the catalyst, forming N2. For

example:

2NO => N2 + O2 or 2NO2 => N2 + 2O2

2NO => N2 + O2 or 2NO2 => N2 + 2O2

Ceramic honeycomb catalyst structure.

The oxidation catalyst is the second stage of the catalytic converter. It reduces the

unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a

platinum and palladium catalyst. This catalyst aids the reaction of the CO and

hydrocarbons with the remaining oxygen in the exhaust gas. For example:

2CO + O2 => 2CO2


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There are two main types of structures used in catalytic converters -- honeycomb

and ceramic beads. Most cars today use a honeycomb structure.

In the next section, we'll look at the third stage of the conversion process and

how you can get the most from your catalytic converter.


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Controlling Pollution and Improving

Performance

The third stage of conversion is a control system that monitors the exhaust

stream, and uses this information to control the fuel injection system. There is an

oxygen sensor mounted upstream of the catalytic converter, meaning it is closer

to the engine than the converter. This sensor tells the engine computer how

much oxygen is in the exhaust. The engine computer can increase or decrease the

amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control

scheme allows the engine computer to make sure that the engine is running at

close to the stoichiometric point, and also to make sure that there is enoughoxygen in the exhaust to allow the oxidization catalyst to burn the unburned

hydrocarbons and CO.

The catalytic converter does a great job at reducing the pollution, but it can still

be improved substantially. One of its biggest shortcomings is that it only works at

a fairly high temperature. When you start your car cold, the catalytic converter

does almost nothing to reduce the pollution in your exhaust.

One simple solution to this problem is to move the catalytic converter closer tothe engine. This means that hotter exhaust gases reach the converter and it heats

up faster, but this may also reduce the life of the converter by exposing it to

extremely high temperatures. Most carmakers position the converter under the

front passenger seat, far enough from the engine to keep the temperature down

to levels that will not harm it.

Preheating the catalytic converter is a good way to reduce emissions. The easiest

way to preheat the converter is to use electric resistance heaters. Unfortunately,the 12-volt electrical systems on most cars don't provide enough energy or power

to heat the catalytic converter fast enough. Most people would not wait several

minutes for the catalytic converter to heat up before starting their car. Hybrid

cars that have big, high-voltage battery packs can provide enough power to heat

up the catalytic converter very quickly.


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Catalytic converters in diesel engines do not work as well in reducing NOx. One

reason is that diesel engines run cooler than standard engines, and the converters

work better as they heat up. Some of the leading environmental auto experts

have come up with a new system that helps to combat this. They inject a urea

solution in the exhaust pipe, before it gets to the converter, to evaporate and mix

with the exhaust and create a chemical reaction that will reduce NOx. Urea, also

known as carbamide, is an organic compound made of carbon, nitrogen, oxygen

and hydrogen. It's found in the urine of mammals and amphibians. Urea reacts

with NOx to produce nitrogen and water vapor, disposing more than 90 percent

of the nitrogen oxides in exhaust gases.

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