1 of 12 6. Emission Control Theory Support Automotive – Engine Performance Topics covered in this presentation: Types of Emissions Emission Control Devices.

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Topics covered in this presentation:

Types of Emissions Emission Control Devices

Emission Control

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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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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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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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Inlet

Outlet

Steel shell

Catalyst honeycomb

Reduction converter

Catalytic Converter

A catalytic converter removes the harmful gases that exit the tailpipe.

Oxidization converter

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).

A three-way converter contains honeycomb coated with platinum, palladium and rhodium to form oxidization and reduction converters.

The reduction converter converts oxides of nitrogen (NOX) into nitrogen (N2) and oxygen (O2).

The conversion process produces temperatures upto 1600°F.

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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 flowIntake manifold

EGR valve

Throttle plate Ported vacuum

TVV

Exhaust Gas Recirculation (EGR) System

The system uses an EGR valve that can be either vacuum and/or electronically controlled.

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.

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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Meteringorifice

Exhaust gas

Intakemanifold

Vacuum output

EVR duty cyclecontrol signal

Pressure voltage signals

EGR flow

Exhaustpressure

IntakevacuumDPFE sensor

ECU

EVR

EGR valve

Electronic EGR Components

In an electronic system, the ECU uses data from sensors to control EGR valve operation.

Vehicles that conform to OBD II regulations must be fitted with feedback sensors (DPFE) to confirm 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.

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Electronic Evaporative Emissions Control

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.

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.

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.

High pressurerelease Cap

Air dome

Fuel outlet

Vent line

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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.

VacuumFuel vapourAirPurge

line

Fuel tank Charcoal canister

Non-vented cap

Vacuum line

Intake manifold

Throttle plateRoll over valve/vapor separator

Purge valveVent line

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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'.

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.

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

Blowby

Fresh air mixes with blowby gases in the crankcase

Vapors pass through thePCV valve and hose

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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.

At engine idle speed, maximum vacuum defeats spring pressure and the plunger moves to the other end of the valve, allowing minimal vapor flow.

At normal engine speeds, lower vacuum levels allow the plunger to move to a central position and maximum vapor flow occurs.

To manifold

Valve

Spring

From crankcase

= Vapor

Seal seat