Emission control technique report

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INDEX
Sr. No. Content Page no.
Certificate i
Acknowledgement ii
Abstract ii
1 Introduction 4
1.1 Types of emission 4
1.1.1 Hydrocarbons 4
1.1.2 Carbon monoxide 5
1.1.3 Nitrogen oxides 5
1.1.4 Particulate matter 5
1.1.5 Sulfur oxide 5
2 Exhaust gas recirculation 6
2.1 EGR implementation 7
2.2 EGR in spark-ignited engines 7
2.3 Reduced throttling losses 8
2.4 Reduced heat rejection 8
2.5 Reduced chemical dissociation 8
2.6 Reduced specific heat ratio 8
3 Catalytic converter 9
3.1 Types of catalytic converters 10
3.1.1 Two-way catalytic converters 10
3.1.2 Three-way catalytic converters 10
4 Air injection 14
5 Fuel evaporative emission control 16
6 Use of hybrid vehicle 17
6.1 Fuel consumption and emissions reductions 17
6.2 Hybrid vehicle emissions 18
7 Alternate fuels 18

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7.1 Bio-fuel 19
7.2 Biodiesel 20
7.3 Alcohol fuels 20
7.4 Hydrogen 21
7.5 Liquid nitrogen 21
7.6 Compressed air 21
7.7 Natural gas vehicles 21
7.8 Ammonia 21
7.9 Algae based fuels 21
7.10 CNG fuel types 21
8 Conclusion 21
9 References 23

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LIST OF FIGURES
Sr. No. Names of figures Page no.
1 EGR System 6
2 Catalytic converter 11
3 Air injection system 14
4 Hybrid vehicle 17
5 Ecofriendly fuels pump 19
6 Carbon cycle 20

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1. INTRODUCTION
Vehicle emissions control is the study and practice of reducing the emissions
produced by motor vehicles, especially by engines. There is growing concern related
to the health effects of fine particles. Recent studies have demonstrated a consistent
association between the concentrations of fine particulate matter (PM) in the air
adverse effects on human health
The need to control the emissions from automobiles gave rise to the
computerization of the automobile. Hydrocarbons, carbon monoxide and oxides of
nitrogen are created during the combustion process and are emitted into the
atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of
vaporization of gasoline and from the crankcase of the automobile pollutants that
could emit from an automobile.
Like SI engine CI engines are also major source of emission. Several
experiments and technologies are developed and a lot of experiments are going on to
reduce emission from CI engine. The main constituents causing diesel emission are
smoke, soot, oxides of nitrogen, hydrocarbons, carbon monoxides etc. Unlike SI
engine, emission produced by carbon monoxide and hydrocarbon in CI engine is
small. In order to give better engine performance the emission must be reduce to a
great extent. The emission can be reduced by using smoke suppressant additives,
using particulate traps, SCR (Selective Catalytic Reduction) etc.
1.1.TYPES OF EMISSIONS
1.1.1 Hydrocarbons - A class of burned or partially burned fuel, hydrocarbons
are toxins. Hydrocarbons are a major contributor to smog, which can be a
major problem in urban areas. Prolonged exposure to hydrocarbons
contributes to asthma, liver disease, lung disease, and cancer. Regulations
governing hydrocarbons vary according to type of engine and jurisdiction;
in some cases, "non-methane hydrocarbons" are regulated, while in other
cases, "total hydrocarbons" are regulated. Technology for one application
may not be suitable for use in an application that has to meet a total

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hydrocarbon standard. Methane is not directly toxic, but is more difficult
to break down in a catalytic converter, so in effect a "non-methane
hydrocarbon" regulation can be considered easier to meet. Since methane
is a greenhouse gas, interest is rising in how to eliminate emissions of it.
1.1.2 Carbon Monoxide (CO)- A product of incomplete combustion, carbon
monoxide reduces the blood's ability to carry oxygen; overexposure
(carbon monoxide poisoning) may be fatal. Carbon Monoxide poisoning is
a major killer.
1.1.3 Nitrogen Oxides (NOx) - Generated when nitrogen in the air reacts with
oxygen at the high temperature and pressure inside the engine. NOx is a
precursor to smog and acid rain. NOx is a mixture of NO, N2O, and NO2.
NO2 is extremely reactive. It destroys resistance to respiratory infection.
NOx production is increased when an engine runs at its most efficient (i.e.
hottest) part of the cycle.
1.1.4 Particulate Matter– Scooter smoke made up of particles in the
micrometer size range: Particulate matter causes negative health effects,
including but not limited to respiratory disease and cancer.
1.1.5 Sulfur Oxide (SOX)- A general term for oxides of sulfur, which are
emitted from motor vehicles burning fuel containing sulfur. Reducing the
level of fuel sulfur reduces the level of Sulfur oxide emitted from the
tailpipe. Refineries generally fight requirements to do this because of the
increased costs to them, ignoring the increased costs to society as a whole.

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2.EXHAUST GAS RECIRCULATION
Fig(1)EGR System
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen
oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel
engines. EGR works by recalculating a portion of an engine's exhaust gas back to
the engine cylinders. In a gasoline engine, this inert exhaust displaces the amount
of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces
some of the excess oxygen in the pre-combustion mixture
.Because NOx forms primarily when a mixture of nitrogen and oxygen is
subjected to high temperature, the lower combustion chamber temperatures caused
by EGR reduces the amount of NOx the combustion generates. Most modern
engines now require exhaust gas recirculation to meet emissions standards.EGR is
typically not employed at high loads because it would reduce peak power output.
This is because it reduces the intake charge density. EGR is also omitted at idle
(low-speed, zero load) because it would cause unstable combustion, resulting in
rough idle. The EGR valve also cools the exhaust valves and makes them last far

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longer (a very important benefit under light cruise conditions. Since the EGR
system recalculates a portion of exhaust gases, over time the valve can become
clogged with carbon deposits that prevent it from operating properly. Clogged
EGR valves can sometimes be cleaned, but replacement is necessary if the valve is
faulty.
2.1 EGR Implementations:-Usually, an engine recalculates exhaust gas by piping it
from the exhaust manifold to the inlet manifold. This design is called external
EGR. A control valve (EGR Valve) within the circuit regulates and times the
gas flow. Some engines incorporate a camshaft with relatively large overlap
during which both the intake valve and the exhaust valve are open, thus
trapping exhaust gas within the cylinder by not fully expelling it during the
exhaust stroke. A form of internal EGR is used in the rotary Atkinson cycle
engine.EGR can also be implemented by using a variable geometry
turbocharger (VGT) which uses variable inlet guide vanes to build sufficient
backpressure in the exhaust manifold. For EGR to flow a pressure difference is
required across the intake and exhaust manifold and this is created by the VGT.
Another method that has been experimented with is using a throttle in a
turbocharged diesel engine to decrease the intake pressure, thereby initiating
EGR flow. Modern systems utilizing electronic engine control computers,
multiple control inputs, and servo-driven EGR valves typically improve
performance/efficiency with no impact on drivability. In most modern engines,
a faulty or disabled EGR system will cause the computer to display a check
engine light and the vehicle to fail an emissions test
2.2 EGR in spark-ignited engines:-The exhaust gas, added to the fuel, oxygen,
and combustion products, increases the specific heat capacity of the cylinder
contents, which lowers the adiabatic flame temperature. In a typical automotive
spark-ignited (SI) engine, 5 to 15 percent of the exhaust gas is routed back to
the intake as EGR. The maximum quantity is limited by the requirement of the
mixture to sustain a applications can cause misfires and partial burns.
Although EGR does measurably slow combustion, this can largely be
compensated for by advancing spark timing. The impact of EGR on engine
efficiency largely depends on the specific engine design, and sometimes leads

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to a compromise between efficiency and NOx emissions. A properly operating
EGR can theoretically increase the efficiency of gasoline engines via several
mechanisms:
2.3 Reduced throttling losses:- The addition of inert exhaust gas into the intake
system means that for a given power output, the throttle plate must be opened
further, resulting in increased inlet manifold pressure and reduced throttling
losses.
2.4 Reduced heat rejection:-A lowered peak combustion temperature not only
reduces NOx .formation, it also reduces the loss of thermal energy to
combustion chamber surfaces, leaving more available for conversion to
mechanical work during the expansion stroke.
2.5 Reduced chemical dissociation:- The lower peak temperatures result in more
of the released energy remaining as sensible energy near TDC, rather than
being bound up (early in the expansion stroke) in the dissociation of
combustion products. This effect is minor compared to the first two. It also
decreases the efficiency of gasoline engines via at least one more mechanism:
2.6 Reduced specific heat ratio:-A lean intake charge has a higher specific heat
ratio than an EGR mixture. A reduction of specific heat ratio reduces the
amount of energy that can be extracted by the piston.

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3 CATALYTIC CONVERTER
A catalytic converter is a vehicle emissions control device which converts toxic
byproducts of combustion in the exhaust of an internal combustion engine to less
toxic substances by way of catalyzed chemical reactions. The specific reactions vary
with the type of catalyst installed. Most present-day vehicles that run on gasoline are
fitted with a "three way" converter, so named because it converts the three main
pollutants in automobile exhaust. The 3 main pollutants are carbon monoxide,
unburned hydrocarbon and oxides of nitrogen. The first 2 are converted to 2 new
molecules. This happens through an oxidizing reaction which converts "carbon
monoxide (CO) and unburned hydrocarbons (HC)" to "CO2 and water vapor". The
last pollutant is converted to 3 new molecules. This happens through a reduction
reaction which converts "oxides of nitrogen (NOx)" to "CO2, nitrogen (N2) and water
(H2O)".
The first widespread introduction of catalytic converters was in the United
States market, where 1975 model year gasoline-powered automobiles were so
equipped to comply with tightening U.S. Environmental Protection Agency
regulations on automobile exhaust emissions. These were "two-way" converters
which combined carbon monoxide (CO) and unburned hydrocarbons (HC) to produce
carbon dioxide (CO2) and water (H2O). Two-way catalytic converters of this type are
now considered obsolete, having been supplanted except on lean burn engines by
"three-way" converters which also reduce oxides of nitrogen (NOx).
Catalytic converters are still most commonly used in exhaust systems in
automobiles, but are also used on generator sets, forklifts, mining equipment, trucks,
buses, locomotives, motorcycles, airplanes and other engine-fitted devices. They are
also used on some wood stoves to control emissions. Catalytic oxidization is also
used, but for the purpose of safe, flameless generation of heat rather than destruction
of pollutants, in catalytic heaters.
2NO => N2 + O2 or 2NO2 => N2 + 2O2
2CO + O2 => 2CO2

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3.1 Types of Catalytic Converters
3.1.1 Two-way Catalytic Converters:-
A two-way catalytic converter has two simultaneous tasks:
1. Oxidation of carbon monoxide to carbon dioxide:
2CO + O2 → 2CO2
2. Oxidation of hydrocarbons (unburnt and partially burnt fuel) to carbon dioxide
and water.
CxH2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)
This type of catalytic converter is widely used on diesel engines to reduce
hydrocarbon and carbon monoxide emissions. They were also used on
gasoline engines in American- and Canadian-market automobiles until 1981.
Because of their inability to control oxides of nitrogen, they were superseded
by three-way converter.
3.1.2 Three-way Catalytic Converters :- Since 1981, "three-way" (oxidation-
reduction) catalytic converters have been used in vehicle emission control
systems in the United States and Canada; many other countries have also
adopted stringent vehicle emission regulations that in effect require three-
way converters on gasoline-powered vehicles. The reduction and oxidation
catalysts are typically contained in a common housing, however in some
instances they may be housed separately. A three-way catalytic converter
has three simultaneous tasks:

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Fig(2) Catalytic converter
1. Reduction of nitrogen oxides to nitrogen and oxygen.
2NOx → xO2 + N2
2. Oxidation of carbon monoxide to carbon dioxide.
2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water:

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CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O.
These three reactions occur most efficiently when the catalytic converter
receives exhaust from an engine running slightly above the stoichiometric point. This
point is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. The
ratio for Auto gas natural gas and ethanol fuels is each slightly different, requiring
modified fuel system settings when using those fuels. In general, engines fitted with
3-way catalytic converters are equipped with a computerized closed-loop feedback
fuel injection system using one or more oxygen sensors, though early in the
deployment of three-way converters, carburetors equipped for feedback mixture
control were used.
Three-way catalysts are effective when the engine is operated within a narrow
band of air-fuel ratios near stoichiometry, such that the exhaust gas oscillates between
rich (excess fuel) and lean (excess oxygen) conditions. However, conversion
efficiency falls very rapidly when the engine is operated outside of that band of air-
fuel ratios. Under lean engine operation, there is excess oxygen and the reduction of
NOx is not favored. Under rich conditions, the excess fuel consumes all of the
available oxygen prior to the catalyst, thus only stored oxygen is available for the
oxidation function. Closed-loop control systems are necessary because of the
conflicting requirements for effective NOx reduction and HC oxidation. The control
system must prevent the NOx reduction catalyst from becoming fully oxidized, yet
replenish the oxygen storage material to maintain its function as an oxidation catalyst.
Three-way catalytic converters can store oxygen from the exhaust gas stream, usually
when the air-fuel ratio goes lean.When insufficient oxygen is available from the
exhaust stream, the stored oxygen is released and consumed. A lack of sufficient
oxygen occurs either when oxygen derived from NOx reduction is unavailable or
when certain maneuvers such as hard acceleration enrich the mixture beyond the
ability of the converter to supply oxygen.
Diesel exhaust contains relatively high levels of particulate matter (soot),
consisting in large part of elemental carbon. Catalytic converters cannot clean up

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elemental carbon, though they do remove up to 90 percent of the soluble organic
fraction[, so particulates are cleaned up by a soot trap or diesel particulate filter (DPF).
Historically, a DPF consists of a Cordierite or Silicon Carbide substrate with a
geometry that forces the exhaust flow through the substrate walls, leaving behind
trapped soot particles. Contemporary DPFs can be manufactured from a variety of
rare metals that provide superior performance (at a greater expense). As the amount of
soot trapped on the DPF increases, so does the back pressure in the exhaust system.
Periodic regenerations (high temperature excursions) are required to initiate
combustion of the trapped soot and thereby reducing the exhaust back pressure. The
amount of soot loaded on the DPF prior to regeneration may also be limited to prevent
extreme isotherms from damaging the trap during regeneration. In the U.S., all on-
road light, medium and heavy-duty vehicles powered by diesel and built after 1
January 2007, must meet diesel particulate emission limits that means they effectively
have to be equipped with a 2-Way catalytic converter and a diesel particulate filter.
Note that this applies only to the diesel engine used in the vehicle. As long as the
engine was manufactured before 1 January 2007, the vehicle is not required to have
the DPF system. This led to an inventory run-up by engine manufacturers in late 2006
so they could continue selling pre-DPF vehicles well into 2007.

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4 AIR INJECTION
Fig(3) Air injection system
The mechanism by which exhaust emissions are controlled depends on the
method of injection and the point at which air enters the exhaust system, and has
varied during the course of the development of the technology. The first systems
injected air very close to the engine, either in the cylinder head's exhaust ports or in
the exhaust manifold. These systems provided oxygen to oxidize (burn) unburned and
partially burned fuel in the exhaust before its ejection from the tailpipe. There was
significant unburned and partially burned fuel in the exhaust of 1960s and early 1970s
vehicles, and so secondary air injection significantly reduced tailpipe emissions.
However, the extra heat of combustion, particularly with an excessively rich exhaust
caused by misfiring or a adjusted carburetor, tended to damage exhaust valves and
could even be seen to cause the exhaust manifold to incandesce.

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As emission control strategies grew more sophisticated and effective, the
amount of unburned and partially burned fuel in the exhaust stream shrank, and
particularly when the catalytic converter was introduced, the function of secondary air
injection shifted. Rather than being a primary emission control device, the secondary
air injection system was adapted to support the efficient function of the catalytic
converter. The original air injection point became known as the upstream injection
point. When the engine is cold, air injected at this point cleans up the extra-rich
exhaust and raises the temperature of the exhaust so as to bring the catalytic converter
to operating temperature quickly. Once the engine is warm, air is injected to the
downstream location the catalytic converter itself to assist with catalysis of unburned
hydrocarbons and carbon monoxide.
Since no internal combustion engine is 100% efficient, there will always be
some unburned fuel in the exhaust. This increases hydrocarbon emissions. To
eliminate this source of emissions an air injection system was created. Combustion
requires fuel, oxygen and heat. Without any one of the three combustion cannot occur.
Snide the exhaust manifold there insufficient heat to support combustion, if we
introduce some oxygen than any unburned fuel will ignite. This combustion will not
produce any power, but it will reduce excessive hydrocarbon emissions. Unlike in the
combustion chamber, this combustion is uncontrolled, so if the fuel content of the
exhaust is excessive, explosions that sound like popping will occur.

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5 FUELEVAPORATIVE EMISSIONS CONTROL:-
Evaporative (EVAP) emissions control systems are designed to prevent the release of
hydrocarbons into the atmosphere. Evaporative emissions are the result of gasoline
vapors escaping from the vehicle’s fuel system. Since 1971, all U.S. vehicles have
had fully sealed fuel systems that do not vent directly to the atmosphere; mandates for
systems of this type appeared contemporaneously in other jurisdictions. In a typical
system, vapors from the fuel tank and carburetor bowl vent (on carbureted vehicles)
are ducted to canisters containing activated carbon. The vapors are absorbed within
the canister, and during certain engine operational modes fresh air is drawn through
the canister, pulling the vapor into the engine, where it burns. The early version of the
EVAP system was the Positive Crankcase Ventilation (PCV) valve. This valve
measured the pressure in the crankcase and released the vapors into the combustion
chamber for re-ignition. Gradually, automotive manufacturers added more items, such
as ODB-II computers, purge valves, charcoal canisters and liquid/vapor separators, as
emission regulations became stricter.
The EVAP (Evaporative Emissions) System allows fuel tank vapors to be purged into
the engine and burnt rather than expelled into the atmosphere as harmful emissions.
The EVAP system contains a pressure sensor to check the integrity of the system.
Periodically, the EVAP system performs a pressure test to check that there are no
leaks in the system. It uses this sensor, also known as a fuel tank pressure (FTP)
sensor to check for leaks.

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6.USEOF HYBRIDVEHICLES
Fig (4) Hybrid vehicle
6.1 FUEL CONSUMPTION AND EMISSIONS REDUCTIONS:-
The hybrid vehicle typically achieves greater fuel economy and lower
emissions than conventional internal combustion engine vehicles
(ICEVs), resulting in fewer emissions being generated. These savings
are primarily achieved by three elements of a typical hybrid design.
Relying on both the engine and the electric motors for peak power
needs, resulting in a smaller engine sized more for average usage rather
than peak power usage. A smaller engine can have less internal losses
and lower weight. Having significant battery storage capacity to store
and reuse recaptured energy, especially in stop-and-go traffic typical of
the city cycle. Recapturing significant amounts of energy during
breaking that are normally wasted as heat. This regenerative braking

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reduces vehicle speed by converting some of its kinetic energy into
electricity, depending upon the power rating of the motor/generator.
Other techniques that are not necessarily 'hybrid' features, but that are
frequently found on hybrid vehicles include. Shutting down the engine
during traffic stops or while coasting or during other idle periods.
Improving the shape and aerodynamics of a car is a good way to help
better the fuel economy and also improve handling at the same time.
Using low rolling resistance tires (tires were often made to give a quiet,
smooth ride, high grip, etc., but efficiency was a lower priority). Tires
cause mechanical drag, once again making the engine work harder,
consuming more fuel. Hybrid cars may use special tires that are more
inflated than regular tires and stiffer or by choice of carcass structure
and rubber compound have lower rolling resistance while retaining
acceptable grip, and so improving fuel economy whatever the power
source. Powering the a/c, power steering, and other auxiliary pumps
electrically as and when needed; this reduces mechanical losses when
compared with driving them continuously with traditional engine belts.
These features make a hybrid vehicle particularly efficient for city traffic
where there are frequent stops, coasting and idling periods. In addition
noise emissions are reduced, particularly at idling and low operating
speeds, in comparison to conventional engine vehicles. For continuous
high speed highway use these features are much less useful in reducing
emissions.
6.2 Hybrid vehicle emissions:-Hybrid vehicle emissions today are getting
close to or even lower than the recommended level set by the EPA
(Environmental Protection Agency). The recommended levels they
suggest for a typical passenger vehicle should be equated to 5.5 metric
tons of carbon dioxide. The three most popular hybrid vehicles, Honda
Civic, Honda Insight and Toyota Priors, set the standards even higher by
producing 4.1, 3.5, and 3.5 tons showing a major improvement in carbon
dioxide emissions. Hybrid vehicles can reduce air emissions of smog-

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forming pollutants by up to 90% and cut carbon dioxide emissions in
half.
7 ALTERNATE FUELS
Fig (5) Ecofriendly fuels pump
Alternative fuels, known as non-conventional or advanced fuels, are any
materials or substances that can be used as fuels, other than conventional fuels.
Conventional fuels include: fossil fuels (petroleum (oil), coal, propane, and
natural gas), as well as nuclear materials such as uranium and thorium, as well
as artificial radioisotope fuels that are made in nuclear reactors. Some well-
known alternative fuels include biodiesel, bio alcohol (methanol, ethanol,
butane), chemically stored electricity (batteries and fuel cells), hydrogen, non-
fossil methane, non-fossil natural gas, vegetable oil, and other biomass
sources.
7.1 Biofuel:-Alternative fuel dispensers at a regular gasoline station in
Arlington, Virginia. B20 (biodiesel ) the left and E85 ethanol at the
right.Biofuels are also considered a renewable source. Although
renewable energy is used mostly to generate electricity, it is often
assumed that some form of renewable energy or a percentage is used to
create alternative fuels.

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7.2 Biodiesel:- Biodiesel is made from animal fats or vegetable oils,
renewable resources that come from plants such as, soybean, sunflowers,
corn, olive, peanut, palm, coconut, safflower, canola, sesame,
cottonseed, etc. Once these fats or oils are filtered from their
hydrocarbons and then combined with alcohol like methanol, biodiesel
is brought to life from this chemical reaction. These raw materials can
either be mixed with pure diesel to make various proportions, or used
alone. Despite one’s mixture preference, biodiesel will release a smaller
number of its pollutants (carbon monoxide particulates and
hydrocarbons) than conventional diesel, because biodiesel burns both
cleaner and more efficiently. Even with regular diesel’s reduced quantity
of sulfur from the ULSD (ultra-low sulfur diesel) invention, biodiesel
exceeds those levels because it is sulfur-free.
7.3 Alcohol fuels:-
Fig (6) Carbon cycle
Methanol and Ethanol fuel are primary sources of energy; they are convenient
fuels for storing and transporting energy. These alcohols can be used in
internal combustion engines as alternative fuels. Butane has another

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advantage: it is the only alcohol-based motor fuel that can be transported
readily by existing petroleum-product pipeline networks, instead of only by
tanker trucks and railroad cars.
7.4 Hydrogen:-Hydrogen is an emission less fuel. The byproduct of
hydrogen burning is water, although some mono-nitrogen oxides NOx
are produced when hydrogen is burned with air.
7.5 Liquid nitrogen:-Liquid nitrogen is another type of emission less fuel.
7.6 Compressed air:-The air engine is an emission-free piston engine
using compressed air as fuel. Unlike hydrogen, compressed air is about
one-tenth as expensive as fossil oil, making it an economically attractive
alternative fuel.
7.7 Natural Gas Vehicles:-Compressed natural gas (CNG) and Liquefied
Natural Gas (LNG) are two a cleaner combusting alternatives to
conventional liquid automobile fuels.
7.8 Ammonia:-Ammonia can be used as fuel. A small machine can be set
up to create the fuel and it is used where it is made. Benefits of ammonia
include, no need for oil, zero emissions, low cost,[5] and distributed
production reducing transport and related pollution.
7.9 Algae based fuels:-Algae based biofuels have been hyped in the media
as a potential panacea to our Crude Oil based Transportation problems.
Algae could yield more than 2000 gallons of fuel per acre per year of
production.
7.10 CNG Fuel Types:-CNG vehicles can use both renewable CNG and
non-renewable CNG.Conventional CNG is produced from the many
underground natural gas reserves are in widespread production
worldwide today. New technologies such as horizontal drilling and
hydraulic fracturing to economically access unconventional gas
resources appear to have increased the supply of natural gas in a
fundamental way. Renewable natural gas or biogas is a methane‐based
gas with similar properties to natural gas that can be used as
transportation fuel.

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8 CONCLUSION
In this paper, a review of various types of emission control techniques as been
given. With the increasing threats of global warming and vehicular pollution the
role of emission control becomes mandatory. In maintaining the ecological
balance. Although the technologies like air injection and three way catalysts are
still limited to the financially sound European domains, economically affordable
devices like catalytic converters.

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9 REFERENCES:-
1. International Journal of Automotive Technology, Vol. 14, No. 2, pp. 195−206
(2013)
2. Combustion and Emission of Combustion Engine. Jiang Deming. Xian, Xian
Jiao tong University Press, 2001.
3. '"Case less monolithic catalytic converter". Charles H. Bailey. U.S. Patent
4,250,146: 10 February 1981
4. "General Motors believes it has an Answer to the Automotive Air Pollution
Problem". The Blade: Toledo, Ohio. 1974-09-12. Retrieved 2011-12-14.
5. "Exhaust Gas Made Safe." Popular Mechanics, September 1951, p. 134,
bottom of page.
6. Automotive catalytic converters: current status and some perspectives, Jan
Kašpar, Neal Hickey dipartimento di scienze chimiche, university of trieste,
via l.