26 Tarun Singh

8/14/2019 26 Tarun Singh

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EMISSION CONTROL


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SOURCE OF EMISSION

Emissions from a fuel-driven motor vehicle usually come from four

sources: the fuel tank, the carburetor, the crankcase, and the

exhaust system.

The term emission normally refers to the pollution produced by a

light vehicle during normal use. Emission control systems are

designed to limit the pollution caused by the harmful products of

storing and burning fuel.


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The fuel tank and carburetor allow fuel to evaporate and escape

to the atmosphere. These are called evaporative emissions.

The crankcase and exhaust system emit pollutants directly fromthe engine into the atmosphere. They are caused when

hydrocarbons, lead compounds, and oxygen and nitrogen from

the air, are burned in the combustion chamber.


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COMBUSTION

Approximately 60% of emissions from an uncontrolledvehicle enginecome from the exhaust - a result of combustion of the fuel and the air.

It is a regulated requirement to reduce

these emissions. Some vehicles use

devices or systems that control the

combustion process itself, while others

treat the resulting exhaust gases.

Both Fuel injected and Carbureted engines

meet emission standards by maintaining

accurate mixture control over a full range of

engine conditions. To achieve this, most

fuel systems require an air supply atconstant temperature.


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One simple control system uses a temperature-sensitive valve inside

the air cleaner. It operates a flap that blends the hot air with cool air, so

that the intake and fuel delivery mechanism receives air at 104 degrees

Fahrenheit or about forty degrees Celsius, regardless of outside air

temperature. Maintenance of this temperature assists vaporization ofthe fuel, particularly when the engine is cold.

To reduce this effect the throttle positioned and dashpot slow down the

rate of closure of the throttle plate. This allows more time for air to enter

the manifold, and for the fuel to vaporize, before the throttle is

completely closed.Electronically managed fuel injection systems use sensors and catalytic

converters to control the combustion process and the air-fuel ratio

supplied to the engine at all times.


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COMBUSTION CHAMBER DESIGN

Combustion chamber design can affect the combustion process, and the

level of emissions. Designs that increase gas flow rate and promotevaporizations, distribute fuel more evenly in the chamber.

Combustion chamber design can affect the

combustion process also, and therefore the

level of emissions.

Designs that increase gas flow rate, and

promote vaporization, distribute the fuel more

evenly in the combustion chamber.


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Quenching of the combustion flame can occur in zones in the combustion

chamber where surface temperatures are low. The flame temperature dropsso low in these areas that the flame goes out, or is quenched. Fuel left

unburned in these zones is then exhausted, as hydrocarbon and carbon

monoxide emissions.

If the spark plug is positioned so that the flame front travels evenly through

the combustion chamber, combustion is more complete.

Gas flow rate, and volumetric efficiency, can be improved by using 2 intake

valves in each cylinder. The effective port opening is increased, and the gas

flow rate increases.

Changing valve timing also alters the combustion process. Reducing valve

overlap reduces the scavenging effect. It also reduces hydrocarbon emission.


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EMISSION CONTROL

A positive crankcase ventilation system flushes vapors from thecrankcase into the intake manifold, to join with the inlet air-fuel mixture.

Once there, the vapors are drawn into the engine for burning.

Early vehicles vented the fuel tank

through the filler cap into the

atmosphere. Some of the fuel inthe tank would vaporize. Some

vapors escaped from the filler

cap, some from the carburetor.

Non-vented filler caps are designed to stop the exit of vapors. A

vacuum relief valve can relieve low pressure in the tank when the

temperature drops. This will also stop the tank from collapsing if its

internal pressure falls below atmospheric pressure.


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A vapor line is connected to the vapor space in the tank, or the liquid

vapor separator. It carries fuel vapors from the tank to a storage volume.

This vapor line can incorporate check valves. If the vehicle is tilted too far

from the horizontal, they stop liquid fuel entering the storage volume.

A storage device is used to store the fuel vapors. The fuel tank breathes

through this storage device. Some vehicles use the engine crankcase.

When the temperature of the fuel in the tank increases, fuel vapors are

forced along the vent line, past a liquid check valve, and into the

crankcase.

When the engine starts, the Positive Crankcase Ventilation systemflushes vapors out of the crankcase and into the intake manifold where it

joins with the inlet air-fuel mixture. Once in the inlet manifold, the vapors

are drawn into the engine where combustion can convert them into

carbon dioxide and water vapor.


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CATALYTIC CONVERSION

Maintaining the stoichiometric ratio is necessary for a catalytic converter to

operate efficiently. It receives all the engine's exhaust gases, andchemically converts remaining pollutants to less harmful substances.

Modern petroleum based fueled

vehicles are fitted with three-way

catalytic converters. 3-way

converters convert hydrocarbonsand carbon monoxide to water and

carbon dioxide, as well as convert

the oxides of nitrogen, nitric oxide

and nitrogen dioxide, back into

harmless nitrogen and oxygen

molecules.

The converter uses two different types of catalysts to reduce the

pollutants: a reduction catalyst and an oxidation catalyst.


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When a nitric oxide or nitrogen dioxide molecule comes into contact with the

coating, it strips the nitrogen atom out of the molecule and retains it. This

frees up the one or two oxygen atoms in the molecule which combine in pairs

to form molecules of oxygen.

The nitrogen atoms bond with other nitrogen atoms that are retained in the

catalyst and form molecules of nitrogen. So two molecules of nitric oxide

become one molecule each of nitrogen and oxygen, or two molecules of

nitrogen dioxide become one molecule of nitrogen and two molecules of

oxygen.

The exhaust gases then flow over the oxidation catalyst in the converter. This

has the effect of reducing any unburned hydrocarbons and carbon monoxide

by oxidizing them over the platinum and palladium coating. This aids the

reaction of the carbon monoxide and hydrocarbons with any remaining

oxygen in the exhaust gas.

Each carbon monoxide molecule combines with an oxygen molecule to make

one less harmful carbon dioxide molecule. Because of strict emission

requirements, vehicles with a 3-way catalytic converter have a feedback

system, called looping.


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CLOSED LOOP

A closed loop is part of a feedback system that collects information on how a

system is operating & feeds that information back to affect how the system isworking.

This vehicle has a cruise control unit to

help it maintain a set speed. When it falls

below it, a computer sends a signal that

moves the throttle linkage and increasesthe fuel reaching the engine, and speed.

It has the opposite effect when the

vehicle exceeds the set speed. A cruise

control unit that continually monitors the

system is called a closed loop system.

A closed loop system in an engine exhaust system can monitor the amount

of oxygen in exhaust gases, to maintain a constant air-fuel ratio.


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REGULATED EMISSION

Air pollutants are classified as either primary or secondary contaminants.

Typically the regulated emissions are carbon monoxide, hydrocarbon, nitrogen

oxides and particulate matter.

A primary air contaminant, such as carbon

monoxide gas, or particles of unburned fuel, is

added to the atmosphere as a by-product of

burning gasoline in an internal combustion

engine.

Secondary emissions are emitted as gasesand can combine with other airborne

substances to form particles once in the

atmosphere.

Air contaminants can be divided into gases and

particulates.Particulates, often referred to as Particulate Matter, or PM, are tiny particles

of solid or liquid suspended in the air. They are graded in a size range from

10 nanometers to 100 micrometers in diameter. Particulates of less than 10

micrometers are dangerous to humans because they can be breathed and

reach the lungs. Smaller particles also tend to stay airborne longer than

larger particles, which settle more quickly.


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CRANKCASE EMISSION CONTROL

A PCV valve, controlled by manifold pressure, regulates gas flow

between the crankcase and the inlet manifold. With the engine off, thevalve is closed. Air cannot enter the inlet manifold. This allows theengine to start.

While the engine is running, some gases from combustion leak betweenthe piston rings and the cylinder walls, down into the crankcase.

This leakage is called blow-by. Unburned fuel, and water fromcondensation, also find their way into the crankcase, and sump. Whenthe engine reaches its full operating temperature, the water and fuelevaporate. To prevent pressure build-up, the crankcase must beventilated.

A valve called a PCV valve, regulates gas flow between the crankcase

and the inlet manifold. It is controlled by the pressure in the manifold.

With the engine off, the valve is closed, and air cannot enter the inlet

manifold. This allows the engine to start.


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The system is designed to remove

more air than just blow-by, so theres a

fresh air intake, usually at the air

cleaner, to direct filtered air to the

crankcase. This intake is usually as far

as possible from the PCV valve.

Wide throttle openings produce

maximum blow-by. Gases that cant be

handled through the vacuum system,

are directed back through the inlet

connection to the air cleaner, wherethey join the carburetor intake air, and

are drawn into the cylinders for

burning.

A valve called a PCV valve, regulates gas flow between the crankcase

and the inlet manifold. It is controlled by the pressure in the manifold.

With the engine off, the valve is closed, and air cannot enter the inlet

manifold. This allows the engine to start.


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EGR VALVES

The EGR valve lets some exhaust gases pass into the intake system. During

combustion, these exhaust gases absorb heat. This lowers peak combustiontemperatures, and reduces formation of oxides of nitrogen.

If valve overlap is maintained, or even increased,

oxides of nitrogen can be reduced by an exhaust

gas recirculation, or EGR, valve, connected

between the exhaust port, or manifold, and theintake system.

If engine conditions are likely to produce oxides of

nitrogen, the EGR valve opens, letting some

gases pass from the exhaust, into the intake

system. During combustion, these exhaust gases

absorb heat from the burning air and fuel. This

lowers peak combustion temperatures, which

reduces the formation of the oxides of nitrogen.


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CONTROLING AIR FUEL RATIOElectronic fuel injection and engine management systems deal with emissions

more effectively than carbureted engines by more closely controlling the air-

fuel ratio entering each cylinder, and by ensuring the ignition timing matches

operating conditions.

The pulse air method uses the pulsations

of the exhaust gas to open and close a

reed valve. It admits air into the exhaust

manifold in short bursts. Air drawn from theair filter enters the exhaust manifold. This

method suits engines with 4 cylinders, or

less, because their exhaust pulsations are

further apart.

Electronic fuel injection and engine management systems deal with

emissions more effectively than carbureted engines by more closelycontrolling the air-fuel ratio entering each cylinder, and by ensuring the

ignition timing matches operating conditions.

Sensors around the engine send the ECU information about air-flow, coolant

temperature, throttle position and engine speed. The ECU uses this to set

fuel and ignition settings, from its programmed memory.


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CHARCOL STORAGE DEVICE

A charcoal canister can store large quantities of fuel vapor. It has connections for

the fuel tank vent line, the atmosphere, and the purge line, which carries the

vapors to the intake manifold.

When the engine is running, the action of the

piston during the intake strokes, creates a low-

pressure area in the inlet manifold. This can

be used to open a purge valve, which draws

fresh air into the bottom of the canister. The

air collects the vapour and directs it to the inlet

manifold where it is drawn into the engine and

burned. The purge valve is designed to

operate only at speeds well above idle.

If it operated at low speeds, the extra fuel vapours could upset the air-fuel

mixture, which could cause poor idling and rough running.


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ONBOARDDIAGONOSTICS

OBD systems

On-Board Diagnostic systems use the vehicle's computers to detect

problems with its emission components and other systems.

There are two different types of On Board

Diagnostic systems. OBD 1, which

operates under manufacturer standardsand OBD 2, which operates under a

standard set by the Society of Automotive

Engineers.

OBD I is a system that identifies faults in

the vehicles emission and power train.

It has been superseded by OBD II, an enhanced On-Board diagnostic system

that identifies faults in the vehicles emission and power train and also tests

the vehicles operational system to determine faults that do not affect the

vehicles drive ability but may affect its safety or emission efficiency.


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DIAGONOSTIC TROUBLE CODE

The diagnostic trouble codes inform the technician of the computers opinion of

the location of a system fault.

Diagnostic trouble codes are generic, as are the names used to describe

components. Computers also communicate with each other using

standardized languages. Therefore, all non-manufacturer specific codes arethe same from each vehicle.


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Standardized languages also allow the manufacturer to provide specific

technologies to the vehicle in order to maintain a level of security in relation to

theft deterrent and vehicle immobilization.

The system reports that a fault exists by a Malfunction Indicator Lamp or MIL

located in the instrument cluster or by a scan tool connected to the vehicles

diagnostic plug.

The Malfunction Indicator Lamp also indicates, to the driver, that there is a

problem in the system. When a malfunction occurs, the Malfunction Indicator

Lamp will remain on until the system returns to normal or the fault is repaired

or rectified.

A Diagnostic Trouble Code or DTC is then placed in the computers memory.

The Diagnostic Trouble Codes inform the technician of the computers opinion

of the location of a system fault.

The Diagnostic Trouble Codes are used in conjunction with Flow Charts found

in the Manufacturers Service Manual, to assist technicians in determining the

likely cause of the failure.


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MONITORING EMISSION

Under the OBD II standard the vehicles computer monitors the emission

systems in two ways.

The first, is referred to as Continuous where major emission causing faults

such as Engine Misfire and incorrect Air/fuel mix are continually monitored.

The second is referred to as Non-continuous. This is where checks are

made only once each warm up cycle.

Each time the engine is started, the

computer checks components such as

the Oxygen sensor, catalytic converter

and other engine systems are

functioning correctly. If a fault is

detected the MIL is illuminated

indicating that the vehicle needs

attention.


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If the condition is intermittent and the faulty system operates normally, the MIL

will turn off after the vehicle has operated through three warm-up cycles, but

the Diagnostic Trouble Code will remain in the computer memory for a set

period.

If the fault does not reoccur within 40 drive cycles, the code will be

automatically erased but will remain logged in the computer memory as a

history code.


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EMISSION PROCEDURE

Checking & cleaning a PCV valve

Most modern vehicles have a PCV valve, which should be checked

periodically to make sure that it is not clogged with deposits from the

exhaust waste. The objective of this procedure is to show you how to check

and clean the PCV valve part of the emission control system.

Part 1. Preparation and safety

ObjectiveCheck and clean the PCV valve

part of the emission control

system.


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Whenever you perform a task in the workshop you must use personal

protective clothing and equipment that is appropriate for the task andwhich conforms to your local safety regulations and policies.

Among other items, this may include:

Work clothing - such as coveralls and steel-capped footwear

Eye protection - such as safety glasses and face masks

Ear protection - such as earmuffs and earplugs

Hand protection - such as rubber gloves and barrier cream

Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

PERSONAL SAFETY


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SAFETY CHECK

Always make sure that you wear the appropriate personal protection

equipment before starting the job. It is very easy to hurt yourself even

when the most exhaustive protection measures are taken.

Always make sure that your work area/environment is as safe as you

can make it. Do not use damaged, broken or worn out workshop

equipment.

Always follow any manufacturer's personal safety instructions to preventdamage to the vehicle you are working on.

Make sure that you understand and observe all legislative and personal

safety procedures when carrying out the following tasks. If you are

unsure of what these are, ask your supervisor.


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POINTS TO NOTE

When an engine is running, some of the air/fuel mixture and some of the

exhaust gases can squeeze past the piston rings in the cylinder and leak

into the crankcase. A method called "Positive Crankcase Ventilation" orPCV is commonly used to feed these gases back into the intake manifold

with the rest of the fuel/air mixture.

Most modern vehicles have a PCV valve, which should be checked

periodically to make sure that it is not clogged with deposits from the

exhaust waste. If it is not working properly, the engine may idle less

smoothly, the fuel efficiency will drop, and the oil will become contaminated

and less effective.


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PART-2 Step by Step Instruction

Locate the PCV valve

The PCV valve is usually located next to the valve cover of the engine, or

in the intake manifold. If you cannot identify it quickly, check with theworkshop manual.

Check PCV valve operation

Switch on the ignition and start the engine. With the engine idling, pinch

the hose attached to the PCV valve hard enough to shut off the supply of

air through it. If the valve is working correctly, the idle speed should drop

enough for you to be able to hear the change. Alternatively, remove thehose from the PCV valve attached to the valve cover, leaving the valve in

place, and putting your finger over the opening of the hose, you should

feel suction. Clean PCV valve and hose

Remove the hose and check that it is still pliable and not clogged with

sludgy deposits. If the hose cannot be cleaned easily by blowing some air

through it, then it should be replaced. Remove the PCV valve and inspect

it for deposits. If it can be taken apart, then you can clean it with PCV

solvent or lacquer thinners. If it cannot be dismantled but has restricted

operation because of sludge, then replace it with a new one of the same

type.


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SAFETY CHECK

If the vehicle is to be run inside the workshop use exhaust extraction hoses.

Output solenoids can be energized from the scan tool, activating

components without warning. It is imperative that the operator should follow

the service manual procedures.

Make sure that you understand and observe all legislative and personalsafety procedures when carrying out the following tasks. If you are unsure of

what these are, ask your supervisor.


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Whenever you perform a task in the workshop you must use personal

protective clothing and equipment that is appropriate for the task and whichconforms to your local safety regulations and policies. Among other items,

this may include:

Work clothing - such as coveralls and steel-capped footwear

Eye protection - such as safety glasses and face masks

Ear protection - such as earmuffs and earplugs

Hand protection - such as rubber gloves and barrier cream

Respiratory equipment - such as face masks and valve respirators

If you are not certain what is appropriate or required, ask your supervisor.

PERSONAL SFETY


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Points to noteMake sure that you follow service manual procedures for the vehicle you are

working on.

The standard procedure for retrieving codes for an OBD I vehicle, is toaccess the codes, write them down, clear the codes, start the vehicle and

recheck for any codes that reset.

The standard procedure for diagnosing an OBD II vehicle is different as it

requires that the codes should NOT be cleared until the vehicle is repaired.

Clearing the codes also clears all of the freeze frame data in the system that

is useful for the diagnosis process.

It may take several 'trips' for the code to reset, so with OBDII you must

complete the diagnosis process first before clearing the codes.

Always check for any applicable service bulletins when diagnosing computer

related problems, as they can provide valuable information about new faults

that emerge on vehicles as their operational characteristics change as the

vehicles get older.

P t 2 St b t i t ti


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Part 2: Step-by-step instruction

Connect the scan tool

Locate the scan tool access point and connect the scan tool using the

appropriate connector for the vehicle. Turn on the vehicle ignition. Turn on the

scan tool. Run the scan tool diagnostic program and navigate through each ofthe different systems in turn to access the diagnostic trouble codes from the

vehicles electronic control module. Note your findings for each vehicle system.

Check your findings

Look up what each code means and present the information to your supervisor.

Any fault indicated by the diagnostic trouble codes will need to be corrected

before you clear the codes.

Clear fault codes

To clear the fault codes from the vehicle, select the delete codes option on the

scan tool. Check that the codes have cleared, and turn off the vehicle ignition.

4. Recheck for fault codes

Turn on the vehicle ignition. Run the scan tool diagnostic program and navigate

through each system again to check the codes do not reactivate. If the fault

codes reactivate, take your findings to your supervisor. Turn off the vehicle

ignition Turn off the scan tool and disconnect from the access point

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