Emission control karim soliman 2

NAME KAREEM AYMAN ABDEL HAMID MOHAMED

SECTION 3

STUDENT ID 0034073

DEPARTMENT AUTOMOTIVE ENGINEERING DEP. 3RD SQUAD

UNIVERISITY HELWAN UNIV. MATARIIA FACULTY OF ENGINEERING

REPORT ON EMISSION CONTROL

COURSE ENGINEERING FUEL SYSTEM

Lecturer Professor / EID SABER

YEAR 2016-2017

E CMISSION ONTROL

(Emission systems , Standards and Filtering control)

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Table of Contents

Abstract: .......................................................................................................................................... 2
Introduction:.................................................................................................................................... 3
Types of emissions | Pollutants of vehicle emissions: .................................................................... 4
History of emissions: ....................................................................................................................... 4
Emissions Diagram: ......................................................................................................................... 5
Cause of emission Studying:............................................................................................................ 5
The ingredients of air pollution ....................................................................................................... 6
Emission Control Types: .................................................................................................................. 7

Air injection | Secondary Air Injection (SAI):............................................................................... 7
History ..................................................................................................................................... 8
Parts and Operation ................................................................................................................ 8

Catalytic converter ........................................................................................................................ 10
History ................................................................................................................................... 11
Parts and Operation .............................................................................................................. 11
CATALYTIC CONVERTER PERFORMANCE............................................................................... 13
CATALYTIC CONVERTER EFFICIENCY CHART.......................................................................... 14
CATALYTIC CONVERTER TYPES .............................................................................................. 14
Acceptable exhaust emissions include the following:........................................................... 18
Advantages and Disadvantages of Catalytic converter ......................................................... 18

Test by Back Pressure on Catalytic converter ........................................................................... 18
EXHAUST GAS RETURN (EGR) ........................................................................................................ 19
EXHAUST GAS RETURN CROSS SECTION........................................................................................ 19

EGR SYSTEM OPERATION .......................................................................................................... 20
POSITIVE AND NEGATIVE BACK PRESSURE EGR VALVES ........................................................... 20
Positive back pressure EGR valves............................................................................................. 20
Negative back pressure EGR valves........................................................................................... 20
Evaporative emission control (EVAP) ............................................................................................ 21
PURPOSE AND FUNCTION ......................................................................................................... 21
EVAP SYSTEM COMPONENTS:................................................................................................... 21
Positive Crank Ventilation (PCV) ................................................................................................... 22
PCV CHECK VALVE OPERATION ................................................................................................. 23

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Emission Sensors control............................................................................................................... 24
Classification of Sensors ............................................................................................................ 24
Oxygen sensor ........................................................................................................................... 25

Exhaust Gas Temperature Sensor ................................................................................................. 26
Soot (PM) Sensors ......................................................................................................................... 27
Thermal Anemometer Air Flow Sensors........................................................................................ 27
Emission standards........................................................................................................................ 28

European emission standards ................................................................................................... 28
United States emission standards ............................................................................................. 28
Stringency Levels ........................................................................................................................... 28
References..................................................................................................................................... 29

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Abstract:

Emission control system, in automobiles, means employed to limit the discharge of noxious gases
from the internal-combustion engine and other components. There are three main sources of
these gases: the engine exhaust, the crankcase, and the fuel tank and carburetor. The exhaust
pipe discharges burned and unburned hydrocarbons, carbon monoxide, oxides
of nitrogen and sulfur, and traces of various acids, alcohols, and phenols. The crankcase is a
secondary source of unburned hydrocarbons and, to a lesser extent, carbon monoxide. In the fuel
tank and (in older automobiles) the carburetor, hydrocarbons that are continually evaporating
from gasoline constitute a minor but not insignificant contributing factor in pollution A variety of
systems for controlling emissions from all these sources have been developed.

Introduction:

To control exhaust emissions, which are responsible for two-thirds of the total engine pollutants,
two types of systems are used: the air-injection system and the exhaust gas recirculation (EGR)
system, In EGR a certain portion of exhaust gases are directed back to the cylinder head, where
they are combined with the fuel-air mixture and enter the combustion chamber. The recirculated
exhaust gases serve to lower the temperature of combustion, a condition that favors lower
production of nitrogen oxides as combustion products (though at some loss of engine efficiency).
In a typical air-injection system, an engine-driven pump injects air into the exhaust manifold,
where the air combines with unburned hydrocarbons and carbon monoxide at a high temperature
and, in effect, continues the combustion process. In this way, a large percentage of the pollutants
that were formerly discharged through the exhaust system are burned (though with no additional
generation of power).

for additional combustion is the catalytic converter, consisting of an insulated chamber containing
ceramic pellets or a ceramic honeycomb structure coated with a thin layer of metals such as
platinum and palladium. As the exhaust gases are passed through the packed beads or the
honeycomb, the metals act as catalysts to induce the hydrocarbons, carbon monoxide, and
nitrogen oxides in the exhaust to convert to water vapor, carbon dioxide, and nitrogen. These
systems are not completely effective: during warm-up, the temperatures are so low that
emissions cannot be catalyzed. Preheating the catalytic converter is a possible solution to this
problem; the high-voltage batteries in hybrid cars, for example, can provide enough power to heat
up the converter very quickly.

In the past, gasoline fumes evaporating from the fuel tank and carburetor were vented directly
into the atmosphere. Today those emissions are greatly reduced by sealed fuel-tank caps and the
so-called evaporative control system, in operation, fuel-tank vapors flow from the sealed fuel tank
to a vapor separator, which returns raw fuel to the tank and channels fuel vapor through a purge
valve to the canister. The canister acts as a storehouse; when the engine is running, the vapors
are drawn by the resultant vacuum from the canister, through a filter, and into the combustion
chamber, where they are burned.

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Improvements in combustion efficiency are effected by computerized control over the whole
process of combustion. This control ensures the most efficient operation of the systems described
above. In addition, computer-controlled fuel-injection systems ensure more precise air-fuel
mixtures, creating greater efficiency in combustion and lower generation of pollutants.

Types of emissions | Pollutants of vehicle emissions:

 Nitrogen oxides (NOx)
 Fine Particulate Matter (PM2.5)
 Volatile organic compounds (VOCs)
 Carbon Monoxide (CO)
 Sulphur Dioxide (SO2)
 Hydrocarbons (HC)
 Air Toxics
 Coolants

History of emissions:

Throughout the 1950s and 1960s, various federal, state and local governments in the United
States conducted studies into the numerous sources of air pollution. These studies ultimately
attributed a significant portion of air pollution to the automobile, and concluded air pollution is
not bounded by local political boundaries. At that time, such minimal emission control regulations
as existed in the U.S. were promulgated at the municipal or, occasionally, the state level. The
ineffective local regulations were gradually supplanted by more comprehensive state and federal
regulations. By 1967 the State of California created the California Air Resources Board, and in
1970, the federal United States Environmental Protection Agency (EPA) was established. Both
agencies, as well as other state agencies, now create and enforce emission regulations for
automobiles in the United States. Similar agencies and regulations were contemporaneously
developed and implemented in Canada, Western Europe, Australia, and Japan.

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Emissions Diagram:

These air pollutants (HC-CO-NOx) are responsible for a number of adverse environmental
effects such as photochemical smog, rising mercury, acid rain, death of rain forests, health
hazards and reduced atmospheric visibilit.

Cause of emission Studying:

The apparent cause of this calamity is air pollution, which in the minds of many, is produced
primarily by gas-powered vehicles. Alas, the problem isn't that simple. While car are indeed big
air pollutants
Global warming endangers our health and threatens other basic human needs. Some impacts
such as record high temperatures, rising seas, and severe flooding and droughts are already
increasingly common.
The principal emissions from motor vehicles (by volume) are greenhouse gases, which
contribute to climate change. In vehicles, the principal greenhouse gas is carbon dioxide (CO2),
but vehicles also produce the greenhouse gases nitrous oxide and methane. Not all vehicles
have the same impact though. The vehicle's level of CO2 emissions is linked to the amount of
fuel consumed and the type of fuel used.

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The ingredients of air pollution

Cars and trucks produce air pollution throughout their life, including pollution emitted during
vehicle operation, refueling, manufacturing, and disposal. Additional emissions are associated
with the refining and distribution of vehicle fuel.

Air pollution from cars and trucks is split into primary and secondary pollution. Primary
pollution is emitted directly into the atmosphere; secondary pollution results from chemical
reactions between pollutants in the atmosphere. The following are the major pollutants from
motor vehicles:

Particulate matter (PM). These particles of soot and metals give smog its
murky color. Fine particles — less than one-tenth the diameter of a human
hair — pose the most serious threat to human health, as they can penetrate
deep into lungs. PM is a direct (primary) pollution and a secondary
pollution from hydrocarbons, nitrogen oxides, and sulfur dioxides. Diesel
exhaust is a major contributor to PM pollution.

Hydrocarbons (HC). These pollutants react with nitrogen oxides in the
presence of sunlight to form ground level ozone, a primary ingredient in
smog. Though beneficial in the upper atmosphere, at the ground level
this gas irritates the respiratory system, causing coughing, choking, and
reduced lung capacity.

Nitrogen oxides (NOx). These pollutants cause lung irritation and weaken
the body's defenses against respiratory infections such as pneumonia and
influenza. In addition, they assist in the formation of ground level ozone
and particulate matter.

Carbon monoxide (CO). This odorless, colorless, and poisonous gas is
formed by the combustion of fossil fuels such as gasoline and is emitted
primarily from cars and trucks. When inhaled, CO blocks oxygen from the
brain, heart, and other vital organs. Fetuses, newborn children, and
people with chronic illnesses are especially susceptible to the effects of
CO.

Sulfur dioxide (SO2). Power plants and motor vehicles create this
pollutant by burning sulfur-containing fuels, especially diesel. Sulfur
dioxide can react in the atmosphere to form fine particles and poses the
largest health risk to young children and asthmatics.

Hazardous air pollutants (toxics). These chemical compounds have been
linked to birth defects, cancer, and other serious illnesses. The
Environmental Protection Agency estimates that the air toxics emitted

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from cars and trucks — which include Benzene, acetaldehyde, and 1,3-
butadiene — account for half of all cancers caused by air pollution.

Greenhouse gases. Motor vehicles also emit pollutants, such as carbon

dioxide, that contribute to global climate change. In fact, cars and trucks

account for over one-fifth of the United States' total global warming

pollution; transportation, which includes freight, trains, and airplanes,

accounts for around thirty percent of all heat-trapping gas emissions.



Oxygen. The next gas is oxygen (O2). There is about 21%oxygen in the 2
atmosphere, and most of this oxygen should be “used up” during the

Ocombustion process to oxidize all the hydrogen and carbon (hydrocarbons)
in the gasoline. Levels of O2 should be very low (about 0.5%). High levels

of O2, especially at idle, could be due to an exhaust system leak.

Emission Control Types:

There are mainly three types of vehicle emission control they are
 Air injection.
 Catalytic converter.
 Exhaust gas recirculation(EGR).
 Evaporative emission control (EVAP).
 Positive Crank Ventilation (PCV).

Air injection | Secondary Air Injection (SAI):

Secondary air injection systems pump outside air into the exhaust stream so unburned fuel can
be burned, Early systems have a belt-driven air pump.

Newer aspirated systems use the vacuum created by an exhaust pulse to pull air into the pipe.
The latest systems use an electric motor to pump air, these systems are critical for the life of the
catalytic converter.

The system injects the correct amount of air using inputs like coolant temperature
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History
Secondary air injection (commonly known as air injection) is a vehicle emissions control strategy
introduced in 1966, wherein fresh air is injected into the exhaust stream to allow for a fuller
combustion of exhaust gases.



Parts and Operation
The SAI pump, also called an AIR pump, a smog pump, or thermactor pump, is mounted at the
front of the engine and can be driven by a belt from the crankshaft pulley. It pulls fresh air in
through an external filter and pumps the air under slight pressure to each exhaust port through
connecting hoses or a manifold. The typical SAI system includes the following components: _ A
belt-driven pump with inlet air filter (older models)

1. An electrically driven air pump (newer models)
2. One or more air distribution manifolds and nozzles
3. One or more exhaust check valves
4. Connecting hoses for air distribution
5. Air management valves and solenoids on all newer applications

With the introduction of NOx reduction converters (also called dual-bed, three-way converters,
or TWC), the output of the SAI pump is sent to the center of the converter, where the extra air
can help oxidize unburned hydrocarbons (HC)and carbon monoxide (CO) into water vapor (H 2 O)
and carbon dioxide (CO 2). The computer controls the airflow from the pump by switching on and
off various solenoid valves.



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AIR DISTRIBUTION MANIFOLDS AND NOZZLES
The secondary air-injection system sends air from the pump to a nozzle installed near each
exhaust port in the cylinder head. This provides equal air injection for the exhaust from each
cylinder and makes it available at a point in the system where exhaust gases are the hottest. Air
is delivered to the exhaust system in one of two ways:
1. An external air manifold, or manifolds, distributes the air through injection tubes with
stainless-steel nozzles. The nozzles are threaded into the cylinder heads or exhaust manifolds
close to each exhaust valve. This method issued primarily with smaller engines.
2. An internal air manifold distributes the air to the exhaust ports near each exhaust valve
through passages cast in the cylinder head or the exhaust manifold. This method issued mainly
with larger engines.
EXHAUST CHECK VALVES
All air-injection systems use one or more one-way check valves to protect the air pump and other
components from reverse exhaust flow. A check valve contains a spring-type metallic disc or reed
that closes under exhaust back pressure. Check valves are located between the air manifold and
the switching valve(s). If exhaust pressure exceeds injection pressure or if the air pump fails, the
check valve spring closes the valve to prevent reverse exhaust flow.

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Example on SAI

Catalytic converter

A catalytic converter is an emissions control device that converts toxic gases and pollutants in
exhaust gas to less toxic pollutants. It provides an environment for a chemical reaction wherein
toxic combustion by products are converted to less-toxic substances.
Catalytic converters located in vehicles exhaust system. Often near the engine’s exhaust manifold
(the part that joins the vehicles exhaust to the engine). Catalytic converters are far more efficient
when hot, hence why they are located close to the engine where it is of a higher temperature.
The optimal working temperature of a catalytic converter is between 350 to 400 degrees Celsius,
as shown in figure below.

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History
The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert
in catalytic oil refining.
Houdry first developed catalytic converters for smoke stacks called “cats” for short,
In the mid-1950s, he began research to develop catalytic converters for gasoline engines used on
cars, Catalytic converters were further developed by a series of engineers including John J.
Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic
converter in 1973
1975 onwards started use these catalytic converters in fuel engines vehicles
Three-way catalyst technology, introduced in the 1980s, made it also possible to control NOx
emissions.

Parts and Operation
 In chemistry, a catalyst is a substance that causes or accelerates a chemical reaction
without itself being affected.
 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.
 Vehicular emissions produce the CO, HC and NOx these emissions are reduced by using
catalytic converters.
 The two-way oxidation catalytic converter that are reduces the effect produced by CO,
HC.
 The three-way oxidation catalytic converter that are reduces the effect produced by CO,
HC and NOx,
 catalytic converters are play a major role in reduction of emission produced by the
vehicles.

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The converter substrate contains small amounts of rhodium, palladium, and platinum. These
elements act as catalysts. As mentioned, a catalyst is an element that starts a chemical reaction
without becoming a part of, or being consumed in, the process. In a three-way(catalytic) converter
(TWC) all three exhaust emissions (NO x, HC, and CO) are converted to carbon dioxide (CO 2) and
water (H 2 O). As the exhaust gas passes through the catalyst, oxides of nitrogen (NO x) are
chemically reduced (that is, nitrogen and oxygen are separated) in the first section of the catalytic
converter. In the second section of the catalytic converter, most of the hydrocarbons and carbon
monoxide remaining in the exhaust gas are oxidized to form harmless carbon dioxide (CO 2) and
water vapor (H 2 O). Acceptable exhaust emissions.

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CONVERTER USAGE
A catalytic converter must be located as close as possible to the exhaust manifold to work
effectively. The farther back the converter is positioned in the exhaust system, the more the
exhaust gases cool before they reach the converter. Since positioning in the exhaust system
affects the oxidation process, vehicle manufacturers that use only an oxidation converter
generally locate it underneath the front of the passenger compartment. Some vehicles have used
a small, quick heating oxidation converter called a reconverted or a pup (mini) converter that
connects directly to the exhaust manifold outlet. These have small catalyst surface area close to
the engine that heats up rapidly to start the oxidation process more quickly during cold engine
warm-up. For this reason, they were often called light-off converters (LOCs).

CATALYTIC CONVERTER PERFORMANCE

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CATALYTIC CONVERTER EFFICIENCY CHART

CATALYTIC CONVERTER TYPES
1. Two-way catalytic converter
2. Three-way catalytic converter

Two-way
A two-way (or “oxidation”) catalytic converter has two simultaneous tasks:

 Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
 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 converters.

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Three-way
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:

 Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
 Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
 Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: 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 (or liquefied petroleum gas
(LPG)), 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

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all 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.

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Diesel engines
For compression-ignition (i.e., diesel engines), the most commonly used catalytic converter is the
Diesel Oxidation Catalyst (DOC). This catalyst uses O2 (oxygen) in the exhaust gas stream to
convert CO (carbon monoxide) to CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water)
and CO2. These converters often operate at 90 percent efficiency, virtually eliminating diesel odor
and helping to reduce visible particulates (soot). These catalysts are not active for NOx reduction
because any reductant present would react first with the high concentration of O2 in diesel
exhaust gas.
Reduction in NOx emissions from compression-ignition engines has previously been addressed by
the addition of exhaust gas to incoming air charge, known as exhaust gas recirculation (EGR). In
2010, most light-duty diesel manufacturers in the U.S. added catalytic systems to their vehicles to
meet new federal emissions requirements. There are two techniques that have been developed
for the catalytic reduction of NOx emissions under lean exhaust conditions – selective catalytic
reduction (SCR) and the lean NOx trap or NOx adsorbed. Instead of precious metal-containing NOx
absorbers, most manufacturers selected base-metal SCR systems that use a reagent such as
ammonia to reduce the NOx into nitrogen. Ammonia is supplied to the catalyst system by the
injection of urea into the exhaust, which then undergoes thermal decomposition and hydrolysis
into ammonia. One trademark product of urea solution, also referred to as Diesel Emission Fluid
(DEF).

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Acceptable exhaust emissions include the following:

Advantages and Disadvantages of Catalytic converter
Advantages
Reduce the amount of harmful pollution produced by the vehicles

 Faster reactions
 Easy replaceable
Disadvantages
Decreased horsepower-engine uses more energy for the converter
 Catalyst require some time to start its action
 they are very expensive to get

Test by Back Pressure on Catalytic converter

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EXHAUST GAS RETURN (EGR)

The Exhaust Gas Recirculation (EGR) system's purpose is to reduce NOx emissions that contribute
to air pollution. The first EGR systems were added to engines in 1973, and today most engines
have an EGR system.
If the EGR system is functioning properly, it should have no noticeable effect on engine
performance. But if the EGR system is leaking or inoperative, it can cause drivability problems,
including detonation (knocking or pinging when accelerating or under load), a rough idle, stalling,
hard starting, elevated NOx emissions and even elevated hydrocarbon (HC) emissions in the
exhaust.
Exhaust gas recirculation reduces the formation of NOX by allowing a small amount of exhaust
gas to "leak" into the intake manifold. The amount of gas leaked into the intake manifold is only
about 6 to 10% of the total, but it's enough to dilute the air/fuel mixture just enough to have a
"cooling effect" on combustion temperatures. This keeps combustion temperatures below 1500
degrees C (2800 degrees F) to reduce the reaction between nitrogen and oxygen that forms NOx.

EXHAUST GAS RETURN CROSS SECTION

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EGR SYSTEM OPERATION

Since small amounts of exhaust are all that is needed to lower peak combustion temperatures,
the orifice through which the exhaust passes are small. EGR is usually not required during the
following conditions because the combustion temperatures are low:

 During idle speed
 When the engine is cold
 At wide-open throttle (WOT) (Not allowing EGR allows the engine to provide extra power

when demanded. While the NOx formation is high during these times, the overall effect
of not using EGR during WOT conditions is minor)

The level of NOx emission changes per engine speed, temperature, and load. Many systems use
a cooler to reduce the temperature of the exhaust gases before they enter the intake manifold.
The cooler the exhaust gases, the more effective they are at reducing the formation of NOx.

POSITIVE AND NEGATIVE BACK PRESSURE EGR VALVES

Some vacuum-operated EGR valves used on older engines are designed with a small valve inside
that bleeds off any applied vacuum and prevents the valve from opening:



Positive back pressure EGR valves

These EGR valves require a positive back pressure in the exhaust system. At low engine speeds
and light engine loads, the EGR system is not needed, and the back pressure in it is also low.
Without enough back pressure, the EGR valve does not open even though vacuum may be present
at the EGR valve.

Negative back pressure EGR valves

On each exhaust stroke, the engine emits an exhaust “pulse.” Each pulse represents a positive
pressure. Behind each pulse is a small area of low pressure. Some EGR valves react to this low-
pressure area by closing a small internal valve, which allows the EGR valve to be opened by
vacuum.





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pressure-type vacuum-controlled EGR will operate:
1. Vacuum must be applied to the EGR valve itself. The vacuum source can be ported vacuum

(above the throttle plate) or manifold vacuum (below the throttle plate) and byte
computer through a solenoid valve.
 Exhaust back pressure must be present to close an internal valve inside the EGR to allow
the vacuum to move the diaphragm.




Evaporative emission control (EVAP)

On older EVAP systems, the tank is vented by a spring-loaded valve inside the gas cap. On newer
vehicles, it is vented through the EVAP canister.

PURPOSE AND FUNCTION

The purpose of the evaporative emission control system is to trap and hold gasoline vapors, also
called volatile organic compounds (VOCs). The evaporative control (EVAP) system includes the
charcoal canister, hoses, and valves. These vapors are routed into a charcoal canister, then into
the intake airflow, where they are burned in the engine instead of being released into the
atmosphere.

EVAP SYSTEM COMPONENTS:

The major components of the evaporative emission control system include:

Fuel tank, which has some expansion space at the top so fuel can expand on a hot day without
overflowing or forcing the EVAP system to leak.

Gas cap, which usually contains some type of pressure/vacuum relief valve for venting on older
vehicles (pre-OBD II), but is sealed completely (no vents) on newer vehicles (1996 & newer).

Liquid-Vapor Separator, located on top of the fuel tank or part of the expansion overflow tank.
This device prevents liquid gasoline from entering the vent line to the EVAP canister. You do not
want liquid gasoline going directly to the EVAP canister because it would quickly overload the
canister's ability to store fuel vapors. The liquid-vapor separator is relatively trouble-free. The
only problems that can develop are if the liquid return becomes plugged with debris such as rust
or scale from inside the fuel tank; if the main vent line becomes blocked or crimped; or if a vent
line develops an external leak due to rust, corrosion, or metal fatigue from vibration.

EVAP Canister, this is a small round or rectangular plastic or steel container mounted
somewhere in the vehicle. It is usually hidden from view and may be in a corner of the engine
compartment or inside a rear quarter panel

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Positive Crank Ventilation (PCV)

This process of gases leaking past the rings is called blowy, and the gases form crankcase vapors.
These combustion by-products, particularly unburned hydrocarbons(HC) caused by blowy, must
be ventilated from the crankcase.
However, the crankcase cannot be vented directly to the atmosphere because the hydrocarbon
vapors add to air pollution.
Positive crankcase ventilation (PCV) systems were developed to ventilate the crankcase and
recirculate the vapors to the engine’s induction system so they can be burned in the cylinders.
PCV systems help reduce HC and CO emissions.
All systems use the following:
1. PCV valve or calibrated orifice, or orifice and separator.
2. PCV inlet air filter plus all connecting hoses.

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PCV CHECK VALVE OPERATION

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Emission Sensors control

Classification of Sensors

Various types of soot sensors, also known as particulate matter or PM sensors, are used for the
control and diagnostics of emission systems utilizing diesel particulate filters (DPF). Soot sensors
have been developed for two main types of applications:

Estimation of the amount (mass) of the soot accumulated in a diesel particulate filter, to utilize
accurate DPF regeneration strategies.
DPF failure detection which may result in excess PM emissions, to trigger an OBD fault signal.
An accurate estimate of a DPF soot mass allows devising a proper regeneration strategy (how
often, when to start or stop a regeneration), while inaccurate estimates result in unsuitable
regeneration timing. If the soot mass is over-estimated, too-frequent (excessive) regenerations
take place, resulting in unnecessary fuel consumption penalty and rapid system wear-out,
amongst other adverse effects. Conversely, under-estimating a DPF soot mass may cause

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excessive regeneration exotherms inside a DPF, inducing rapid aging, wash coat loss or DPF
deterioration, or even a total DPF failure.
The other area of soot sensor application has been driven by advances in OBD regulations,
especially those adopted by the California ARB/US EPA, as well as by the EU OBD requirements.

Oxygen sensor

Originally called a "Lambda Sensor" when it was first used in fuel-injected European cars, the
oxygen sensor monitors the level of oxygen (O2) in the exhaust so an onboard computer can
regulate the air/fuel mixture to reduce emissions. The sensor is mounted in the exhaust manifold
downpipe(s) before the catalytic converter or between the exhaust manifold(s) and the catalytic
converter(s). It generates a voltage signal proportional to the amount of oxygen in the exhaust.
The sensing element on nearly all oxygen sensors in use is a zirconium ceramic bulb coated on
both sides with a thin layer of platinum. The outside of the bulb is exposed to the hot exhaust
gases, while the inside of the bulb is vented internally through the sensor body or wiring to the
outside atmosphere.
When the air/fuel mixture is rich and there is little O2 in the exhaust, the difference in oxygen
levels across the sensing element generates a voltage through the sensor's platinum electrodes:
typically, 0.8 to 0.9 volts. When the air/fuel mixture is lean and there is more oxygen in the
exhaust, the sensor's voltage output drops to 0.1 to 0.3 volts. When the air/fuel mixture is
perfectly balanced and combustion is cleanest, the sensor's output voltage is around 0.45 volts.
The oxygen sensor's voltage signal is monitored by the onboard engine management computer
to regulate the fuel mixture. When the computer sees a rich signal (high voltage) from the oxygen
sensor, it commands the fuel mixture to go lean. When it receives a lean signal (low voltage) from
the oxygen sensor, it commands the fuel mixture to go rich. Cycling back and forth from rich to
lean averages out the overall air/fuel mixture to minimize emissions and to help the catalytic
converter operate at peak efficiency, which is necessary to reduce hydrocarbon (HC), carbon
monoxide (CO) and oxides of nitrogen (NOX) levels even further.

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Oxygen sensor performance can be checked
by reading the sensor's output voltage to
make sure it corresponds with the air/fuel
mixture (low when lean, high when rich).
The voltage signal can also be displayed as a
wave form on an oscilloscope to make sure
the signal is changing back and forth from
rich to lean and is responding quickly
enough to changes in the air/fuel ratio.

Exhaust Gas Temperature Sensor

In modern internal combustion engines, the knowledge of the exhaust gas temperature (EGT) is
necessary for the management and diagnosis of the exhaust gas after treatment system, as well
as for the protection of components that may be sensitive to thermal overloads.

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In the diesel engine, after treatment components that are often actively managed based on
exhaust gas temperature include diesel particulate filters (DPF) and NOx reduction catalysts
such as SCR catalysts and NOx adsorbed catalysts (NAC/LNT).
The following two exhaust gas temperature sensors are used to help the PCM control the DPF:

 EGT sensor 1 is positioned between the DOC and the DPF where it can measure the
temperature of the exhaust gas entering the DPF.

 EGT sensor 2 measures the temperature of the exhaust gas stream immediately after it
exits the DPF.

Soot (PM) Sensors

SOOT CATEGORIES In general, soot particles produced by diesel combustion fall into the
following categories
Fine. Less than 2.5 micron
Ultrafine. Less than 0.1 micron, and make up 80% to 95% of soot

Thermal Anemometer Air Flow Sensors

As technology, advanced, it became apparent that this approach had several disadvantages:
Moving parts (sensitive to contamination, decrease of restoring forces of springs)
No compensation for changing air densities (altitude, air temperature and pressure)
Long response time (the mechanical components represented a spring mass system with high
inertia)
In the early 1980s, an increasing number of sensor systems were introduced that utilized a new
measuring principle: thermal anemometry. Thermal anemometers utilize at least one electrically
heated sensor element—typically made of nickel or platinum—the ohmic resistance of which is
dependent on the temperature. When gas flows around the measuring element, heat is
transferred into the flow medium. A correlation exists between the gas velocity and heat

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dissipation—the higher the flow velocity, the higher the rate of heat dissipation—which allows
to determine the gas flow rate through measurement of the electrical resistance.
Thermal anemometer air flow sensors are also known as mass air flow (MAF) sensors, air flow
sensors (AFS) or air mass-flow sensors (AMS).

Emission standards

European emission standards
United States emission standards

In the United States, emissions standards are managed by the Environmental Protection Agency
(EPA) as well as some U.S. state governments. Some of the strictest standards in the world are
formulated in California by the California Air Resources Board (CARB).

European emission standards define the acceptable limits for exhaust emissions of new vehicles
sold in EU and EEA member states. The emission standards are defined in a series of European
Union directives staging the progressive introduction of increasingly stringent standards.

Stringency Levels

TLEV: Transitional Low-Emission Vehicle: More stringent
for HC than Tier 1.
LEV: (also known as LEV I): Low-Emission Vehicle, an
intermediate California standard about twice as stringent
as Tier 1 for HC and NOx.
ULEV: (also known as ULEV I): Ultra-Low-Emission Vehicle. A stronger California standard
emphasizing very low HC emissions.
SULEV: Super-Ultra-Low-Emission Vehicle. A California standard even tighter than ULEV,
including much.
ZEV: Zero-Emission Vehicle. A California standard prohibiting any tailpipe emissions. The ZEV
category is largely restricted to electric vehicles and hydrogen-fueled vehicles. In these cases,
any emissions that are created are produced at another site, such as a power plant or hydrogen
reforming center, unless such sites run on renewable energy.

PZEV: Partial Zero-Emission Vehicle.

ILEV: Inherently Low-Emission Vehicle- a vehicle certified to meet the transitional low-emission
vehicle standards established by the California Air Resources Board (CARB).

AT-PZEV: Advanced Technology Partial Zero-Emission Vehicle. If a vehicle meets the PZEV
standards and is using high-technology features, such as an electric motor or high-pressure
gaseous fuel tanks for compressed natural gas, it qualifies as an AT-PZEV. Hybrid electric vehicles

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such as the Toyota Prius can qualify, as can internal combustion engine vehicles that run on
natural gas (CNG), such as the Honda Civic GX.
Europe has its own set of standards that vehicles must meet, which includes the following tiers:
Euro I (1992–1995)
Euro II (1995–1999
Euro III (1999–2005)
Euro IV (2005–2008)
Euro V (2008_)
Vehicle emission standards and technological advancements have successfully reduced pollution
from cars and trucks

References

 Air injection and Catalytic converters by Matthew Whitten Brookhaven College
 AUTOMOTIVE FUELAND EMISSIONS CONTROL SYSTEMSTHIRD EDITION James D.

Halderman Jim Linder Catalystor.
 https://www.dieselnet.com/tech/catalysts.php-gives introduction, background
 http://www.ecmaindia.in/emission-control-technology
 http://www.carparts.com/classroom/emission.htm-gives the emissions control devices.
 http://auto.howstuffworks.com/coal-rollers3.htm-gives a emission by vehicle
 Mechteacher.com-gives information about the three-way catalytic converter
 http://www.telegraph.co.uk/news/uknews/road-and-rail-

transport/11881954/Volkswagen-emissions-scandal-Which-other-cars-fail-to-meet-
pollution-safety-limits.html
 "Transport Environment.org Transport & Environment, Bulletin - News from the
European Federation for Transport and Environment, No146, March 2006, WHO adds
pressure for stricter Euro-5 standards" (PDF). Retrieved 2011-02-02.
 https://www.dieselnet.com/tech/sensors.php
 Norton, H., 1989. “Transducer fundamentals”, Handbook of Transducers. Englewood
Cliffs, NJ: Prentice Hall, 1989, Ch. 2

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 Carstens, S., 2001. “Auslegungskriterien von Abgastemperatursensoren”, Auto &
Elektronik, 4/2001

 McGee, T.D., 1991. “Principles and Methods of Temperature Measurement”, John Wiley
and Sons, New York, 1988

 Khalek, I.A., Premnath, V., 2015. “Particle Sensor Performance & Durability for OBD
Applications”, Proceedings from the 19th ETH Conference on Combustion Generated
Nanoparticles, Zurich, June 28 - July 2,
2015, http://nanoparticles.ch/archive/2015_Khalek_PR.pdf

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