Topics covered in this presentation:

1
Emission Control

• Topics covered in this presentation
• Types of Emissions
• Emission Control Devices

2
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.

3
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.

4
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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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
upto 1600F.
Oxidization converter
Reduction converter
Steel shell
6
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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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.
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.
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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.
Vehicles that conform to OBD II regulations must
be fitted with feedback sensors (DPFE) to confirm
valve operation.
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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.
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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.
11
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.
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.
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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.
Spring
To manifold
From crankcase
Seal seat
At engine idle speed, maximum vacuum defeats
spring pressure and the plunger moves to the
other end of the valve, allowing minimal vapor
flow.
Valve
At normal engine speeds, lower vacuum levels
allow the plunger to move to a central position
and maximum vapor flow occurs.