Transcript No Slide Title

6. Emission Control
Theory Support
Automotive – Engine Performance
Emission Control
Topics covered in this presentation:
 Types of Emissions
 Emission Control Devices
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6. Emission Control
Theory Support
Automotive – Engine Performance
Emission Types
Vehicles are responsible for producing emissions that are harmful to the
atmosphere and the environment. Legislation has been introduced stating
that emissions must be reduced. The major emissions produced by a
vehicle are:
 Hydrocarbons (HC) are created
by unburned fuel entering the
atmosphere. They are either fuel
that has not combusted properly or
fuel vapor leaking from the fuel
bowl, filler pipe etc. HCs are
reactive and can cause illnesses.
 Oxides of Nitrogen (NOX) are
formed when nitrogen and oxygen
mix under high pressure and high
temperature (25000F). NOX can
cause eye and respiratory problems.
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6. Emission Control
Theory Support
Automotive – Engine Performance
Emission Types
 Carbon Monoxide (CO) is caused
by the incomplete combustion of
fuel. It is an invisible poisonous
gas that can be fatal if large
amounts are inhaled.
 Particulates are soot particles
caused by fuel additives. They are
particularly prominent with diesel
engines. 30% of the particles sink to
the ground while the other 70% can
be airborne for long periods of time.
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6. Emission Control
Theory Support
Automotive – Engine Performance
Emission Control Systems
Modern vehicles are fitted with emission control systems, designed to
reduce emissions. These include:
 A catalytic converter.
 Air injection (AIR) system.
 Exhaust gas recirculation (EGR) system.
 Evaporative emissions control (EVAP) system.
 Positive crankcase ventilation (PCV) system.
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6. Emission Control
Theory Support
Automotive – Engine Performance
Catalytic Converter
A catalytic converter removes the harmful gases that exit the tailpipe.
A three-way converter contains honeycomb coated with platinum, palladium
and rhodium to form oxidization and reduction converters.
The oxidization converter stores oxygen when the air/fuel mixture is lean. It
converts hydrocarbons (HC) into water (H2O) and carbon monoxide (CO)
into carbon dioxide (CO2).
Catalyst honeycomb
The reduction converter
converts oxides of
nitrogen (NOX) into
nitrogen (N2) and
oxygen (O2).
Outlet
Inlet
The conversion
process produces
temperatures up
to 1600°F.
Oxidization converter
Steel shell
Reduction converter
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6. Emission Control
Theory Support
Automotive – Engine Performance
Air Injection System
This system forces clean air into exhaust ports to ignite unburned fuel
(hydrocarbons), within the exhaust manifold. Some systems also force air
into a catalytic converter to
aid the conversion process.
Air is forced into the exhaust
ports by a vane type air pump,
via an air injection manifold.
Vacuum operated diverter
valve is used to stop air
flow during deceleration,
otherwise backfiring may
occur within the exhaust.
A check valve is placed
in the line to stop hot
exhaust gases traveling
back up the air hose.
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6. Emission Control
Theory Support
Automotive – Engine Performance
Exhaust Gas Recirculation (EGR) System
The EGR system reduces NOX emissions. It feeds inert exhaust gases back
into the intake manifold, where they dilute the air/fuel mixture, without
altering the air/fuel ratio. With less oxygen and fuel, combustion
temperatures (and therefore NOx levels) are lower.
EGR valve
Throttle plate
The system uses an
EGR valve that can be
either vacuum and/or
electronically controlled.
Early EGR valves were
operated by ported
vacuum. They did not
function until engine was
at operating temperature
and above idle speed.
Ported vacuum
TVV
Intake manifold
Exhaust gas flow
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6. Emission Control
Theory Support
Automotive – Engine Performance
Electronic EGR Components
In an electronic system,
the ECU uses data from
sensors to control EGR
valve operation.
The ECU calculates the
ideal quantity of exhaust
gas to recirculate (and
timing). This provides
optimum vehicle
efficiency with the least
amount of emissions.
Pressure voltage signals
EVR duty cycle
control signal
ECU
Vacuum output
DPFE sensor
EVR
Intake
vacuum
EGR valve
EGR flow
Vehicles that conform to
OBD II regulations must
be fitted with feedback
sensors (DPFE) to
confirm valve operation.
Exhaust
pressure
Metering
orifice
Intake
manifold
Exhaust gas
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6. Emission Control
Theory Support
Automotive – Engine Performance
Electronic Evaporative Emissions Control
Fuel produces vapors, if stored in a container that contains air. The rate at
which fuel vapor is produced increases with air temperature increase. Older
vehicles had vented fuel tanks and carburetors, allowing fuel vapors to enter
the atmosphere.
In a modern vehicle, the fuel system is
sealed and fuel vapors are stored and
then burned at an appropriate time,
along with the normal air/fuel mixture.
The fuel tank has a sealed cap
that may contain valves to
relieve fuel pressure and allow
air in. The tank contains an air
dome that allows for fuel
expansion and a vent line for
vapor removal.
Air dome
Fuel outlet
High pressure
release Cap
Vent line
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6. Emission Control
Theory Support
Automotive – Engine Performance
Electronic Evaporative Emissions Control
The vent line is fitted with a roll over/vapor separator valve to stop liquid fuel
entering the system (vehicle inversion). It connects to a charcoal canister
that stores vapors when the engine is switched off.
A purge valve is used to control vapor removal from the canister. Vapors are
drawn into the intake manifold via a purge line. On older vehicles the valve
is operated by ported vacuum (shown). On modern engines, the ECU
controls valve operation for optimum engine efficiency.
Vacuum line
Roll over valve/vapor separator
Throttle plate
Vent line
Non-vented cap
Purge
valve
Purge
line
Fuel tank
Charcoal canister
Intake manifold
Air
Fuel vapour
Vacuum
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6. Emission Control
Theory Support
Automotive – Engine Performance
Positive Crankshaft Ventilation (PCV)
Combustion produces high
pressure in a cylinder. Some of
the pressurized gas leaks past
the piston rings into the
crankcase, even on a new
engine and is known as 'blowby'.
Older vehicles had a breather
tube that vented these gases
into the atmosphere.
Fresh air enters through the air cleaner
Vapors pass into the intake manifold
Air flow
Modern vehicles are fitted with a
PCV system. Vacuum is used to suck
blowby out of the crankcase and into
the intake manifold to be burned.
Fresh air replaces the gases in the
crankcase. System operation is
regulated by a PCV valve.
Blowby
Vapors pass
through the
PCV valve
and hose
Fresh air mixes with blowby
gases in the crankcase
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6. Emission Control
Theory Support
Automotive – Engine Performance
PCV Valve
The PCV valve is a spring-loaded
device, with an engine specific
orifice size. The valve is sealed
shut when an engine is stopped to
prevent backfires.
At engine idle speed, maximum
vacuum defeats spring pressure
and the plunger moves to the
other end of the valve, allowing
minimal vapor flow.
Spring
= Vapor
To manifold
From
Seal seat crankcase
Valve
At normal engine speeds, lower
vacuum levels allow the plunger
to move to a central position and
maximum vapor flow occurs.
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