26 Tarun Singh
Transcript of 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