aurt304666a repair and replace emission control...

AUR30405 CERTIFICATE III IN AUTOMOTIVE MECHANICAL TECHNOLOGY

AURT304666A Repair and replace emission control systems

LEARNER WORKBOOK

© Commonwealth of Australia 2011

ISBN: 978-1-876838-45-4

This document is available under a “Free for Education” licence for educational purposes – see http://www.aesharenet.com.au/FfE2 for details.

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AURT304666A Repair and replace emission control systems1

Elements.........................................................................................1About the workbook........................................................................1Assessment....................................................................................3Skills Recognition............................................................................4Access and equity...........................................................................4Before you start..............................................................................4

Personal safety 5Activity 1........................................................................................7

Types and causes of emissions 9Emissions........................................................................................9Forms of pollution...........................................................................9Why do we need emission control systems?.................................11Normal combustion.......................................................................12Sources of emissions....................................................................13Emissions from petrol engines......................................................14Government legislation – light vehicles........................................17Emissions from diesel engines......................................................18Government legislation – diesel vehicles......................................20Activity 2......................................................................................21

Evaporative emission control systems 27Components of the evaporative system.......................................28Operation of the evaporative system............................................29Activity 3......................................................................................35Activity 4......................................................................................39Activity 5......................................................................................41

Crankcase emission controls 43Crankcase ventilation system.......................................................43PCV valve......................................................................................45Activity 6......................................................................................49Activity 7......................................................................................53Activity 8......................................................................................55

Exhaust emission control systems 57Combustion chamber design........................................................57Activity 9......................................................................................61

The Exhaust Gas Recirculation system (EGR)...............................65Activity 10....................................................................................71Activity 11....................................................................................75Catalytic converters......................................................................77Activity 12....................................................................................81Testing a catalytic converter........................................................85Activity 13....................................................................................87Particulate emissions in diesel engines.........................................89Activity 14....................................................................................91Emission Control Information label...............................................93Activity 15....................................................................................95Testing exhaust emissions............................................................97Conducting an exhaust gas analyser test.....................................99Activity 16..................................................................................101

Glossary 103

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AURT304666A Repair and replace emission control systemsThis unit covers the competence required to carry out repairs to emission control systems.

The unit includes identification and confirmation of work requirement, preparation for work, repair of emission control systems and associated components and completion of work finalisation processes, including clean-up and documentation.

Elements1. Prepare to undertake repair of emission control system

2. Repair and replace emission control systems and/or associated components

3. Prepare vehicle/ equipment for delivery to customer after repair is completed.

About the workbookThis workbook is designed to assist you in gaining underpinning knowledge and developing practical skills to achieve the competency standard Repair and Replace Emission Control Systems.

This workbook contains:

information

questions

practical activities

directions to use additional resources.

The workbook is divided into stages. At the end of a stage, you will see an icon (picture with a meaning) asking you to check your answers and/or practical activities with your trainer. This helps the trainer to monitor your progress.


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What do the icons mean?An icon is a picture with a meaning. In the workbook, these icons tell you something about:

what to do next (activity, check your answers, watch a video clip) or

the text (this is a safety warning).

Complete an activity

Check your answers with your trainer

Watch this video clip

Safety warning


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AssessmentTo meet the assessment requirements for this competency standard you must demonstrate the following:

Knowledge of:

Emission system types and components.

Operation of emission control systems, sub-assemblies and components.

Motor vehicle emissions and their effect on the environment.

The relationship between system faults and symptoms.

Testing procedures.

Service, repair and adjustment principles.

OH&S and statutory legislation.

Practical ability to:

Access, interpret and apply technical information.

Use correct tools and equipment in a safe manner.

Remove and replace emission control system components.

Test, inspect and evaluate emission systems and components.

Repair and adjust emission control systems.

Maintain customer records.


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Skills Recognition You may already have knowledge and skills for all (or part) of this competency standard. If you believe you can demonstrate that you already have the skills and knowledge required, talk to your trainer about applying for Skills Recognition.

This is also known as Recognition of Prior Learning (RPL), Recognition of Current competence (RCC), or simply Recognition.

Skills Recognition is a process for gaining credit for those skills and knowledge gained through work experience, formal training or other life experience.

Access and equityIn training, access and equity means ensuring that people with differing needs and abilities have the same opportunities to successfully gain skills, knowledge and experience through education and training. It is about removing barriers and providing the supports people need to access, participate and achieve, irrespective of their age, disability, colour, race, gender, religion, sexuality, family responsibilities or location.

For students with disabilities, training organisations may make adjustments to ensure equal opportunity. Reasonable adjustments are designed to minimise the disadvantage experienced by learners with a disability and can include administrative, physical or procedural modifications.

Before you startThe purpose of this learning resource is to help you develop the knowledge and skills necessary to carry out service and repairs to emission control systems and associated components.

Before you start this workbook, you should have a good understanding of the following:

Operating principles of two-stroke, four-stroke, spark ignition and compression ignition engines.

Operating principles of carburettors, electronic fuel injection systems, diesel fuel injection systems and engine management systems.

Operating principles of exhaust systems.


NOTE: If you believe you could benefit from support to help you overcome a barrier to participation, you should speak to your trainer or the person in your RTO responsible for access and equity.

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Personal safetyHere are the key safety practices you should follow during this unit:

Wear safety clothing and Personal Protective Equipment (PPE) as required by OH&S regulations.

Make sure the wheels are chocked and protective guard covers are used when you are working on vehicles.

Keep clear of any hot and moving components.

Use safety stands which are positioned correctly when raising a vehicle for inspection or repair.

If using a hoist, lift the vehicle correctly and use the safety catches.

Make sure there is enough ventilation when engines are running. Exhaust gas from a running engine contains carbon monoxide and can be lethal in a confined space.

Figure 1: Ventilate work areas


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Activity 1

Question 1What safety precautions should you take before you inspect or work on a vehicle?

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Question 2What safety precautions should you take when working near running engines?

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Question 3What safety precautions should you take when raising a vehicle for inspection?

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Ask your trainer to check your results before proceeding.


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Trainer Signature: .............................................................. Date: .......................


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Types and causes of emissionsEmissionsAn emission is something that comes out.

Emissions from motor vehicles are the gases that come out of their engines when they burn fuel and air. They are considered to be a major cause of air pollution.

For this reason, vehicle manufacturers are required to reduce emissions so that their vehicles meet specified government standards. To achieve this, engines have been made more fuel efficient and have various control devices fitted.

Forms of pollutionThere are two general forms of pollution caused by motor vehicles:

pollution from evaporation

pollution from combustion.

Pollution from evaporationLiquid fuel is an extremely volatile liquid. It takes only a little heat from the engine or from the atmosphere to make it evaporate. The petrol vapour then floats into the air, polluting it.

Pollution from combustionCombustion is when air and fuel combine and burn in the engine. The harmful chemicals left over after the combustion process are then discharged through the exhaust into the atmosphere, polluting the air.


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The main chemicals

AIR

Oxygen (O) 20% Nitrogen (N) 80%

FUEL

A mixture of hydrogen (H) and carbon (C) called

hydrocarbons (HC) +

Figure 2: Mixing air and fuel

The air (oxygen & nitrogen) joins with the fuel (hydrocarbons) in the engine. The air and fuel is burnt (combustion). A range of gases are produced called exhaust gases:

Carbon monoxide (CO)

Carbon dioxide (CO2)

Oxides of nitrogen oxygen (NOy)

Oxygen (O2)

Unburnt fuel (HCs).

Figure 3: Producing exhaust gases


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Why do we need emission control systems?If combustion was a perfect process, there would be nothing left over afterwards, and we would have less need for emission control systems.

The emissions would be water, carbon dioxide and heat. Unfortunately this is not possible.

Figure 4: Perfect combustion


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Normal combustionNormal combustion produces many more emissions and these must be controlled with emission systems.

The emissions that must be controlled are:

Hydrocarbons HC

Oxides of nitrogen NOx

Carbon monoxide CO

Figure 5: Normal combustion


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Sources of emissionsPollution or emissions from motor vehicles come from the following sources:

%? System? How?

60% Exhaust From combustion

30%. Crankcase From combustion and blow-by

10% Fuel tanks and carburettors By evaporation

Figure 6: Source of emissions

Watch this video: Source of emissions


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Emissions from petrol enginesHydrocarbons (HC)Hydrocarbon emissions can come from:

1. Unburnt fuel in exhaust gases

2. Evaporating fuel from the fuel tank and fuel system

3. Crankcase vapours or blow by gases.

Watch this video: Hydrocarbons via the exhaust

Unburnt fuel in exhaust gases can be a result of:

- Cold combustion temperature

- Mixture too rich in air or fuel

- Mixture too lean

- Cylinder misfiring or improper mixture burning

- Worn or faulty injector – EFI or diesel

- Worn or faulty diesel fuel injection pump

- Severely blocked air filter element.

Evaporated fuel (HC) is emitted into the atmosphere from the fuel tank and carburettor vents especially with:

- A full tank of fuel and a vehicle left in the sun

- Older vehicles with fuel tanks and carburettor vented to the atmosphere

- An incorrect fuel tank cap fitted to newer vehicles

- Fuel system leaks

- Older vehicles with carburettor flooding problems.

Crankcase vapours or blow by gases are a mixture of combustion gases and fuel vapour. These gases have leaked past worn piston rings and have escaped into the crankcase.


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Leaner air / fuel mixtureMore air in the mixtureGood for combustion Less carbon monoxide

More carbon monoxide

Richer air / fuel mixtureMore fuel in the mixture Not enough air for complete combustion

Very lean air / fuel mixtureToo much air in the mixture

More unburnt fuel (HC)Reduced power and throttle response of engines

Carbon monoxide (CO)Carbon monoxide occurs during combustion when there is not enough oxygen (air), for complete combustion.

Carbon monoxide levels increase as the air/fuel mixture is enriched.

Carbon monoxide levels decrease when a leaner air/fuel mixture is burnt.

Watch this video: Carbon monoxide


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Oxides of nitrogen (NOx)The air we use for burning fuel is made up of 50% nitrogen (N2) and 20% oxygen (O2). Oxygen burns, but nitrogen does not burn.

When combustion temperatures get very hot (above 180°C), the nitrogen combines with oxygen to form oxides of nitrogen (NOx).

Conditions which increase the formation of oxides of nitrogen (NOx) include:

moderate engine load

high combustion temperature.

High temperatures can be caused by:

increased compression ratios.

over advanced ignition timing.

severely retarded ignition timing

mixtures slightly leaner than ideal (14.7:1) during moderate load operation.

Watch this video: Oxides of nitrogen


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Government legislation – light vehiclesThe main method used in Australia for reducing vehicle emissions has been the introduction of tighter emission standards for new vehicles through the Australian Design Rules (ADRs). Australia has had vehicle emission standards in place for petrol vehicles since the early 1970s and these have been progressively (bit by bit) tightened over the past 30 years.

What are the ADRs?The ADRs set the legal standards that each vehicle model is required to meet, prior to (before) their first supply to the market. The ADRs set standards for emissions, noise and fuel consumption labelling.

What are the emission ADRs?The emission ADRs are performance standards which specify (state exactly) the maximum (highest) levels of emissions permitted (allowed) under a specified test.

They do not require the use of particular technology, but from 1986 vehicle manufacturers had to fit catalytic converters to light petrol vehicles in order to meet new emission limits.

How much have allowed emissions changed?A summary of the emission standards which have applied to petrol engined cars since 1972 through to 2010 can be viewed at. http://www.infrastructure.gov.au/roads/environment/impact/emission.aspx

This table compares emissions allowed in 1976 with what is allowed from 2008.

YEAR HC maximum CO maximum NOx maximum

1976 2.1 g/km 24.2 g/km 1.9 g/km

2008 0.1 g/km 1.0 g/km 0.08 g/km

The ADRs also give guidelines for 6 tests for petrol vehicles:

1. Exhaust emissions after a cold start

2. Carbon monoxide emission test at idling speed

3. Emissions of crankcase gases

4. Evaporative emissions from vehicles with positive-ignition engines

5. Endurance test for durability of pollution control devices

6. Average exhaust emissions of carbon monoxide and hydrocarbons after a cold start at low ambient temperature.

7.


http://www.infrastructure.gov.au/roads/environment/impact/emission.aspx

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Emissions from diesel enginesA variety of different combustion deposits are formed when diesel fuel is burned.

The type of product formed depends on engine design, engine power output and working load. The most complete combustion of the fuel leads to a major reduction in the formation of toxic substances.

Complete combustion is supported by:

controlling the air/fuel mixture.

precision in the injection process

optimum air/fuel mixture turbulence.

Figure 7: Diesel vehicle

Diesel combustion produces water (H2O) and carbon dioxide (CO2).The following substances are also produced in relatively low concentrations:

Carbon monoxide (CO).

Unburnt hydrocarbons (HC).

Oxides of nitrogen (nox).

Sulphur dioxide (SO2).

Sulphuric acid (H2SO4).

Soot particles (particulates).

When a diesel engine is cold, the exhaust gas emissions include unburnt hydrocarbons, which we notice as white or blue smoke and the strong smell of aldehydes.


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ParticulatesParticulates are solid or semi-solid particles of carbon in the exhaust gas and can sometimes be seen as black smoke.

Carbon is formed due to:

incomplete combustion

slow cold engine operation

high engine oil consumption.

Particulate emission is considerably higher from diesel engines than from petrol engines.

Watch this video: Particulates


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Government legislation – diesel vehiclesThere are also Australian Design Rules (ADRs) which control emissions from light duty and heavy duty diesel engines.

These rules have applied since 1995. From 2006 the latest Euro 4 standards have applied. The ADR sets out the emission limits, their timetable for adoption, and the tests which must be used to check emissions.

The most recent version is the National Environment Protection Measure (Diesel Vehicle Emissions) 2001, amended (updated) in 2009.

How much have allowed emissions changed?This table compares emissions allowed in 1996 with what is allowed in 2011.

YEAR CO maximum HC maximum NOx maximum Particulate matter maximum

1996 4.5 g/kWh 1.1 g/kWh 8.0 g/kWh 0.36 g/kWh

2011 1.5 g/kWh 0.46 g/kWh 2.0 g/kWh 0.02 g/kWh

Figure 8: A page from the National Environment Protection Measure (Diesel Vehicle Emissions) 2001


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Activity 2

Answer the following questions.

Question 1Name the two general forms of air pollution caused by motor vehicles.

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Question 2What do these words mean?

Evaporation _______________________________________________________________________

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Combustion _______________________________________________________________________

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Question 3Name the sources of emissions.

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Question 4What are hydrocarbons (HC)?

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Question 5Name the three sources of hydrocarbon emissions.

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

Question 6Name six causes of unburnt fuel in exhaust gases.

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

4. _______________________________________________________________________________

5. _______________________________________________________________________________

6. _______________________________________________________________________________

Question 7Name five sources of evaporated fuel emissions.

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

4. _______________________________________________________________________________

5. _______________________________________________________________________________


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Question 8How is carbon monoxide (CO) produced?

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Question 9a) What factors cause carbon monoxide levels to increase (go up)?

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b) What factors cause carbon monoxide levels to decrease (go down)?

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Question 10What effects will very lean mixtures have on emissions and engine power?

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Question 11How are oxides of nitrogen (NOx) produced?

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Question 12Name four conditions that will increase the formation of oxides of nitrogen (NOx).

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

4. _______________________________________________________________________________


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Question 13Name the three requirements for complete combustion in a diesel engine.

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

Question 14Name the eight substances produced in diesel engine exhaust emissions.

1. _______________________________________________________________________________

2. _______________________________________________________________________________

3. _______________________________________________________________________________

4. _______________________________________________________________________________

5. _______________________________________________________________________________

6. _______________________________________________________________________________

7. _______________________________________________________________________________

8. _______________________________________________________________________________

Question 15What causes particulate emissions?

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Question 16Tick the correct answer

Particulate emission is considerably higher from diesel engines than from petrol engines?

r True

r False?

Question 18In a diesel engine, how is complete combustion supported?

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Trainer Signature .............................................................. Date .......................


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Evaporative emission control systemsThere are three main types of emission control systems used:

1. Evaporative controlsPrevents fuel vapour (gas) from the fuel tank and fuel system escaping to the atmosphere.

2. Crankcase ventilationPrevents crankcase emissions escaping to the atmosphere.

3. Exhaust emission controlsReduces the products of combustion before they are emitted (sent out) to the atmosphere in exhaust gases.

The evaporative emission control system consists of:

Fuel tank – provides vapour space at the top of tank.

Fuel cap - with vacuum relief valve.

Charcoal canister – stores the fuel vapours from the tank and carburettor when the engine is stopped.

Air vent solenoid valve – opens the vent between the carburettor float bowl and the canister when the ignition switch is on.

Purge valve no. 1 – located on the top of the charcoal canister, it opens and closes the vapour passage (purge line) between the canister and the intake manifold.

Purge valve no. 2 – also located on top of the canister, this valve is in the fuel tank vent line. It opens and closes the vent according to fuel tank pressure.

Liquid vapour separator.


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Components of the evaporative system

Figure 9: Carburettor evaporative system

Figure 10: Evaporative emission controls


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Operation of the evaporative systemTo prevent evaporating fuel going to the atmosphere:

the fuel storage compartments (carburettors and fuel tanks) must be sealed

a temporary storage area for evaporated fuel must be provided

the temporary storage area must be flushed out regularly.

Faulty evaporative emission control systems can result in:

fuel odours

fuel leakage

fuel tank collapse (due to vacuum build up)

excess fuel tank pressure

rough engine idle (due to excess fuel vapours).

Watch this video: Hydrocarbons


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The charcoal canisterIn warm weather, fuel evaporates from the carburettor (if fitted) and fuel tank in a vehicle. This is vented or piped into the charcoal canister (also called the carbon canister).

The charcoal canister contains activated carbon (a special kind of charcoal). This temporarily absorbs (soaks up like a sponge) the evaporating fuel vapour and prevents it from escaping into the atmosphere.

Once the engine is operating above idle, throttle ported vacuum draws fresh air through the canister which pushes the fuel vapour into the intake system where it is burnt in the combustion chamber. This process is called purging (pushing out bad substances).

Figure 11: Charcoal canister

Watch this video: Charcoal canister


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Fuel tanksFuel tanks have room to store and condense the vapour rising from the fuel surface.

The tank has an overfill-limiting pipe. Once the fuel reaches the lower end of the pipe, air cannot escape back up the filler neck. This stops more fuel being added, and provides the required vapour space.

Figure 12: Overfill limiting pipe

Fuel tank vents can have more than one vent pipe. This depends on the location and shape of the tank in the vehicle. These pipes are generally connected to a common vent, situated above the fuel tank.

When there is more than one pipe, at least one of these pipes will be above the fuel level, regardless of the vehicle position. This has 2 purposes:

4. Vents the tank

5. Prevents fuel from syphoning through the vent pipe.

Watch this video: Fuel tanks and lines


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Fuel tank capThe fuel tank cap is fitted with a vacuum relief valve.

As fuel is consumed, a vacuum or negative pressure is created in the fuel tank. When the pressure in the fuel tank falls below atmospheric pressure, this valve opens and allows air to enter the fuel tank. This prevents the tank from buckling.

Figure 13: Fuel tank cap

Liquid vapour separatorSome systems have a ‘condense tank’ or a liquid vapour separator above the fuel tank. This acts as a trap to prevent liquid fuel reaching the carbon canister. The canister will be damaged if liquid fuel enters the canister.

Figure 14: Liquid vapour separator


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Electronic Fuel Injection (EFI) operationThe evaporative control system for EFI engines is similar to the system used on carburetted engines, except that a solenoid-operated purge valve is used.

The purge valve is situated between the intake manifold and charcoal canister. It is operated by the Electronic Control Unit (ECU), which controls all engine management functions.

The ECU keeps the purge valve closed so that fuel vapour is not drawn into the intake manifold:

when the engine coolant temperature is low

during engine idle.

The ECU opens the purge valve so the canister is purged - the stored vapour enters the inlet manifold and is burnt in the engine:

at normal engine operating temperature

during normal driving conditions.

Figure 15: Evaporative emission system


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Activity 3


Question 1How do evaporative emission controls reduce emissions?

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Question 2Label the diagram below to show the major components of the evaporative emission control system.

Figure 16: Evaporative emission system


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Question 3Which two system components will emit fuel vapour?

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Question 4Which system component is used to soak up fuel vapours?

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Question 5Label the diagram below to show where the canister connections are fitted to on a vehicle.

Figure 17: Charcoal canister


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Question 6Briefly describe how the charcoal canister works.

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Question 7Describe how the fuel level is limited in the fuel tank.

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Question 8State two functions of fuel tank vents.

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Question 9What is the function of a liquid vapour separator in a fuel tank?

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Question 10Is liquid fuel allowed to reach the charcoal canister? Why?

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Question 11What is the function of the vacuum relief valve in the fuel tank cap?

__________________________________________________________________________________

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Question 15How is the purge valve operated on an EFI evaporative control system?

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Question 16During which operating conditions will the purge valve be open on an EFI system?

__________________________________________________________________________________

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Trainer Signature .............................................................. Date .......................


42 © Commonwealth of Australia 2011

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Activity 4

Step 1Ask your trainer to nominate a vehicle/model relevant to your trade area.

Step 2Obtain the relevant workshop manual, training material, resources for that vehicle/unit.

Step 3

Find the vehicle/model in the reference/resource material.Locate all the components of the evaporative emission control system.Study the operation of the evaporative emission control system and its components.

Step 4When you feel you are ready, call your trainer and explain the operation of the evaporative emission control system and its components on the vehicle.




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Activity 5

For this activity, your teacher will select the charcoal canister and the type of test for you to complete.

Step 1Your trainer will nominate a charcoal canister and type of function test for you to complete.

Step 2Obtain the relevant workshop manual, training material, resources for the charcoal canister selected.

Step 3Write down in point form below the manufacturer’s test procedure for this type of canister.

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Step 4

Fill in the table below after checking the charcoal canister and lines.

Component Serviceable? Comment

Defective fuel tank cap

Leaking charcoal canister valves

Deteriorated or leaking canister valves

Blocked filter pads

Fuel and vacuum leaks

Purge valve operation




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Crankcase emission controlsCrankcase ventilation systemWhen the engine is operating, a small amount of gas escapes the piston rings and enters the crankcase. These are called blow-by gases. These gases contain harmful pollutants (unburnt hydrocarbons) that can cause contamination of the engine oil and contribute to air pollution.

The engine has to be ventilated for 2 reasons:

to remove blow-by gases from the crankcase

to prevent pressure from building up in the crankcase.

These blow-by gases are controlled by the PCV (Positive Crankcase Ventilation) system.

The PCV system supplies clean air to the crankcase and, at the same time, removes gases (HCs) that are harmful to both the engine and the atmosphere.


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Operation of the PCV system Filtered air is drawn into the rocker cover and into the engine where it mixes with the

blow-by gases.

The gases are drawn from the crankcase through the Positive Crankcase Ventilation valve (PCV) and into the intake manifold.

The gases are now burnt as part of the normal combustion process.

Figure 18: PVC system for a carburetted system

Gases within the crankcase increase as the engine wears, and the pistons and rings allow more blow-by to escape.

Similar systems are used both on carburettor and EFI engines.


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PCV valveThe PCV valve controls the flow of air and crankcase gases into the intake manifold, to ensure the gases will not affect the engine operation.

PCV closedThe PCV valve is closed:

when the engine is not running to assist starting

it is forced closed during a backfire condition to reduce the chance of an explosion in the crankcase.

Figure 19: PCV valve, closed position


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PCV restricted flowDuring idle or deceleration, the high manifold vacuum pulls the PCV plunger inward, to restrict the flow of crankcase gas drawn into the intake manifold. Only a small amount of flow is allowed to enter the manifold as so that excess air will not affect the idle speed.

Figure 20: PCV valve, restricted position

PCV large flowAt cruising and high speed, the reduced manifold vacuum allows the plunger to be moved outwards by the spring force. This allows a larger flow of air through the PCV valve.

Figure 21: PCV valve, large flow


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At high speed, the crankcase pressure forces the blow-by gases to reverse flow through the air cleaner housing into the air inlet stream.

The crankcase emission system also reduces engine oil contamination during cold engine operation. This helps extend engine oil quality between services.

Some small engines use a specially sized restrictor hole (orifice) in the intake manifold instead of a PCV valve to control crankcase gas flow.

Checking a PVC valveA faulty PCV system can cause:

Poor idling

Excessive crankcase pressure resulting in oil leaks.

There are several test procedures for PCV valves. Refer to manufacturer’s instructions if required.

To check a PCV valve:

Remove the valve

With the vacuum line still connected start the engine

Place finger over the end of the valve - a vacuum or a sucking should be felt.

If no vacuum or sucking is felt, valve or valve line is blocked or faulty.

Figure 22: Checking the PCV valve

Watch this video: Crankcase emission control


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Activity 6


Question 1What is the function of a crankcase ventilation system?

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Question 2 Label the diagram below to show the major crankcase ventilation system components.

Figure 23: PVC system for a carburetted system


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Question 3What are ‘blow-by gases’?

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Question 4Which harmful emission can be found in the crankcase?

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Question 5Where does the crankcase get ‘fresh air’ from?

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Question 6What substances are mixed with the fresh air and then drawn out of the crankcase?

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Question 7 What happens to the pollutants after they leave the crankcase?

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Question 8What position is the PCV valve in:

when the engine is not running

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during idle or deceleration

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at cruising and high speed

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Question 9What happens if blow-by gases exceed the PCV valve flow rate?

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Question 10What can be used on small engines to control PCV valve flow other than a PCV valve?

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Activity 7

Step 1Ask your trainer to nominate a vehicle.

Step 2Obtain the relevant workshop manual, training material, resources for the vehicle/model nominated.

Step 3Find the vehicle/model in the references/resource material.Locate all the components of the crankcase ventilation system.Study the operation of the Crankcase Ventilation System and its components.

Step 4When ready, call your trainer and explain the operation of the crankcase ventilation system and its components.




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Activity 8

Ask your trainer to nominate a vehicle.

Step 1On a vehicle nominated by your teacher complete and inspection of PCV valve and related components and complete this chart.

Components Serviceable? Comment

PCV valve

PCV valve vacuum hose and clamps

PCV sealing thread and grommets

Valve pass test


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Step 2Write the manufacturer’s test procedure for the PCV valve for the vehicle nominated.

__________________________________________________________________________________

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__________________________________________________________________________________

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__________________________________________________________________________________

__________________________________________________________________________________

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Exhaust emission control systemsEmissions from the exhaust system account for approximately 60% of the total emissions from a motor vehicle. Exhaust emissions are more complex than evaporative emissions.

If complete combustion occurred, the oxygen (O) in the air would combine with the hydrogen (H) in the fuel to form water (H2O). The oxygen in the air would also combine with the carbon (C) in the fuel to form carbon dioxide (CO2).

However, ideal complete combustion does not occur within the engine. Some hydrocarbons (HC) remain after combustion and carbon monoxide (CO), a more harmful gas, is produced instead of CO2.(carbon dioxide)

Manufacturers have changed engine designs to improve the combustion of the fuel/air mixture and reduce exhaust emissions.

Combustion chamber designThe design of the combustion chamber can influence the amount of fuel that remains unburnt.

Burning of the air/fuel mixture starts at the spark plug and moves across the chamber, consuming the air and fuel as it goes. Most fuel particles are completely burnt but some are not, and contribute to pollution if not controlled.


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Wedge-shaped combustion chambersIn a wedge-shaped combustion chamber, burning starts at the spark plug at the side of the combustion chamber and moves across the chamber.

This design has a large quench area which is a relatively cool section. This reduces the temperature of the burning fuel and so prevents the chance of detonation.

Having the quench area is a disadvantage as far as emissions are concerned. The cooler area allows particles of unburnt fuel to collect on its surface. These particles are exhausted as hydrocarbons and increase the emissions of the engine.

Figure 24: A wedge-shaped combustion chamber


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Hemispherical combustion chambersA hemispherical combustion chamber has the spark plug located in the centre. This enables burning to occur in all directions. The benefits of this shape for emission output are:

There are no quench areas so the temperature of the burning fuel is higher and combustions is more complete.

There is less surface area so fewer particles of unburnt fuel collect.

The hemispherical shape creates swirl during the intake stroke, so that the fuel remains vaporised and burns more completely.

Figure 25: A hemispherical combustion chamber

Watch this video: Combustion chamber design


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Quench areasThe quench area is a zone in the combustion chamber where the piston top dead centre is very close to the cylinder head. Because the piston and cylinder head is cooler than the unburned part of the fuel – air mixture which is called end gas detonation is quenched or reduced. However, the process does form unburned hydrocarbons

Engine cooling systems are designed to maintain uniform high operating temperatures of these components, which improves combustion and reduces emissions that are produced by this action.

Valve overlapValve overlap is a certain period in which both the intake and exhaust are partially open. The intake is starting to open while the exhaust is not yet closed.

It can be altered on some engines to reduce the scavenging effect of the intake charge. This causes any unburnt hydrocarbons to remain in the combustion area where they are burnt rather than being exhausted as HC fuel emissions

Ignition timingIgnition timing is when the spark coming from the spark plugs ignites the air – fuel mixture at the correct moment determined by the manufacturer of the engine. Often this is a few degrees before top dead centre (BTDC).

Spark advance is required to obtain the maximum efficiency from the air/fuel charge. However sometimes, at idle and slower speeds or when the engine is cold, a slightly retarded spark will reduce emissions.

EFI and engine management systems (ECUs) are programmed to provide the optimum ignition settings for all conditions.


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Activity 9


Question 1State two ways in which exhaust emissions can be reduced

1. _______________________________________________________________________________

__________________________________________________________________________________

2. _______________________________________________________________________________

__________________________________________________________________________________

Question 2What is the advantage of wedge shape combustion chambers?

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Question 3What is the disadvantage of wedge shape combustion chambers?

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Question 4What are the advantages of hemispherical combustion chambers?

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Question 5How do hemispherical combustion chambers help fuel vaporisation?

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Question 6What is a ‘quench area’ in a combustion chamber?

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Question 7What is the function of the cooling system in relation to quench areas?

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Question 8Why do some manufacturers alter valve overlap on their engines?

__________________________________________________________________________________

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Question 11Why is spark advance used?

__________________________________________________________________________________

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Question 12When and why would a slightly retarded spark be used?

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Question 13Describe how optimum ignition settings are achieved on EFI engines.

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The Exhaust Gas Recirculation system (EGR)An EGR system returns a controlled amount of exhaust gas into the intake manifold at cruising speeds. This lowers the combustion temperature and reduces NOx emissions from the exhaust.

When the flow control valve (EGR valve) is opened, exhaust gas is carried into the intake manifold by either a small external pipe or an internal port.

The vacuum port for EGR operation is situated above the throttle valve, so no EGR flow occurs at idle. EGR is used to reduce combustion temperature, so it would cause rough running if used at idle speed.

Figure 26: Exhaust gas system


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Operation of the EGR SystemIn a cold engine, combustion temperatures are too low for NOx formation. A thermal valve prevents vacuum acting on the EGR valve until the engine reaches operating temperature (approximately 55°C).

At warm or hot cruising speeds, the EGR valve is opened to allow exhaust gas into the intake manifold. It provides up to 10% of non-combustible mixture, which dilutes the air/fuel mixture. This reduces the heat during combustion and reduces NOx emissions.

During acceleration or heavy load operation, manifold vacuum is too low to operate the EGR valve so it stays closed. If EGR was used during heavy load conditions, it would dilute the air/fuel mixture, lower the combustion temperature, and reduce engine power.


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Thermo Valve The thermo valve in the cooling system prevents the EGR system from operating until the engine reaches operating temperature.

The thermo valve is a bimetal (two metals) valve that acts like a vacuum switch.

Figure 27: Thermo valve

When the engine is cold, the thermo valve remains closed. It cuts off vacuum from the EGR valve which in turn remains closed.

When coolant temperature reaches approximately 60°C, the thermo valve opens, allowing vacuum from the throttle body port to pass through the thermo valve to reach the EGR valve diaphragm.

Vacuum on the top side of the diaphragm will open the valve to allow some exhaust gases to pass from the exhaust manifold to the inlet manifold and into the combustion chambers.


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Modulator control of EGR systemsSome EGR systems use a vacuum modulator unit to control the vacuum signal sent to the EGR valve.

The vacuum modulator unit is sensitive to exhaust system back pressure. It bleeds out the EGR vacuum supply until a specified exhaust back pressure is achieved (at moderate engine load).

During moderate load conditions, the exhaust system will build up enough back pressure so that the internal bleed is closed off. The modulator then allows throttle ported vacuum to open the EGR valve.

At light cruising load there is very little exhaust system back pressure. So when throttle ported vacuum is applied to the modulator, the vacuum bleeds off to the atmosphere through the modulator vent and the EGR valve remains closed.

By venting the modulator at differing throttle body ports, EGR operation can be controlled depending on a combination of throttle valve opening angle and exhaust back pressure.

Some carburetted engines use an oxidation type catalytic converter which cannot reduce NOx emissions. An EGR system is used to control NOx emissions but is only required during moderate load conditions.

Electrical control of EGR systemsEGR valve operation can also be controlled by an emission control computer which is a part of the engine management system.

The control computer or engine management system may:

operate a solenoid in the EGR vacuum line so that EGR operation only occurs during pre-programmed conditions

use an EGR valve position sensor to sense how far the EGR valve is opened, and supply an input signal of the valve’s position to the ECU (Electronic Control Unit). The ECU then uses this signal to pulse the EGR solenoid for the correct amount of exhaust gas recirculation.


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Checking an EGR valveThe ERG valve can be tested for correct operation using a hand vacuum pump.

If accessible on the engine, it can be checked by feel. When the engine is at normal operating temperature, the diaphragm should retract during acceleration, and return during deceleration.

However many EGR valves are not accessible and must be checked by the engine management diagnostic procedure. If you need to conduct further testing of the EGR valve, refer to manufacturer’s procedures.

Figure 28: EGR valve

Watch this video: Emission EGR


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Activity 10


Question 1What does the term ERG mean?

__________________________________________________________________________________

Question 2What is the function of an exhaust gas recirculation (EGR) system?

__________________________________________________________________________________

__________________________________________________________________________________

Question 3Label the components in this diagram of the EGR system.


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Figure 29: Exhaust gas system

Question 4Which harmful emission is reduced by using EGR action?

__________________________________________________________________________________

Question 5Why is the EGR valve not open at engine idle?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 6Why is the EGR system not used during cold engine operation?

__________________________________________________________________________________

__________________________________________________________________________________

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Question 7Is the EGR vacuum port situated above or below the throttle valve?

__________________________________________________________________________________

Question 8How does the thermo valve operate?

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Question 9If the EGR system operated during acceleration or heavy load, what would be the effects on engine performance?

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Question 10Vacuum modulators are fitted to some EGR systems. Briefly, how do they work?

__________________________________________________________________________________

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__________________________________________________________________________________

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Activity 11

Step 1

Ask your trainer to nominate a vehicle/model.

Step 2

Obtain the relevant workshop manual, training material, resources for the vehicle/model nominated.

Step 3

Locate the vehicle/model in the references/resource material.

Identify the components of the EGR system.

Study the operation of the EGR system.

Step 4

When ready, call your trainer and:

Name all the components of the EGR system

Explain the operation of the EGR system.

Step 5

On a vehicle nominated by your teacher complete an inspection of the EGR valve and related components and complete this chart.

Component Serviceable? Comment

EGR valve vacuum lines & valves

EGR valve exhaust pipes & gaskets

Electrical wires, connectors & switches

Engine management or scan tool test


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Step 6

For the vehicle nominated write the manufacturer’s test procedure here.

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Catalytic convertersCatalytic converters are fitted into the vehicle’s exhaust system.

They contains catalysts that promote a chemical reaction with the exhaust gases, which reduce the amount of harmful pollutants that are emitted to the atmosphere (hydrocarbons, carbon monoxide, and nitrous oxides).

Figure 30: Catalytic converter in the exhaust system

The catalytic converter consists of a stainless steel shell with a ceramic honeycomb core inside.

The cells of the honeycomb core have a coating of alumina, impregnated with special metals — platinum, palladium, or rhodium. These metals provide the catalyst that produces the reaction with the exhaust gases.


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Figure 31: Catalytic converter

The honeycomb core is used because:

it allows a free gas flow through the converter

It provides a large area of contact between the exhaust gas and the surface of the catalyst, where the reaction occurs.

Catalytic converters can be TWO WAY or THREE WAY converters.

Two way converterTwo way, or oxidising, converters use palladium and platinum as a catalyst.They convert hydrocarbons (HC) and carbon monoxide (CO) to water (H2O) and carbon dioxide (CO2).,which are less harmful.

Figure 32: 2 way converter

Two way catalytic converters do not react with NOx, so the engine still requires an EGR system to control NOx emissions.


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Three way converterThree way converters use an extra catalyst of rhodium. It reacts with and reduces the NOx in the exhaust gases.

The three way converter needs an ECU and fuel injection to accurately control the fuel air ratio so the converter will operate efficiently

Figure 33: 3 way converter

In some EGR systems, air is injected into the exhaust system before the catalytic converter to supply ‘secondary air’. The additional oxygen helps promote the reaction with NOx in the converter.

Exhaust manifold catalytic converterThis type of converter is attached directly to the exhaust manifold, usually on smaller capacity engines.

On some vehicles, this converter can be used with a second catalytic converter further along the exhaust system.

Figure 34: Manifold catalytic converter

Watch this video: Catalytic converter


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Activity 12


Question 1What is the function of a catalytic converter?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 2Fill in the labels on the diagram below.

Figure 35: Catalytic converter

Question 3Describe the construction of a catalytic converter.

__________________________________________________________________________________

__________________________________________________________________________________

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Question 4What is the advantage of using a honeycomb core in the catalytic converter?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 5What are the catalyst chemicals used in a two way catalytic converter?

__________________________________________________________________________________

__________________________________________________________________________________

Question 6Why might an EGR system be used in conjunction with a two way catalytic converter?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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Question 7How does a three-way catalytic converter controls NOx emissions.

__________________________________________________________________________________

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__________________________________________________________________________________

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Question 8Why do some EGR systems inject air into the exhaust system before the catalytic converter?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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Testing a catalytic converterGenerally catalytic converters are trouble-free. The main reasons a converter will fail are:

physical damage e.g. hit a rock

partially or fully blocked - usually caused by excessive amounts of fuel entering the catalytic converter. This extra fuel causes high internal temperatures that can melt the converter core, leading to restricted (reduced) flow and performance.

contaminated core caused by:

- coolant from leaking head gasket

- excessive oil from worn engine piston rings coating converter core surface.

A converter failure is often the result of another fault i.e. excessive fuel. So when replacing a damaged converter you also need to locate and repair the fault that caused the converter to fail.

There are a number of ways to test a converter. Vehicles with engine management systems can diagnose a catalytic converter fault. Refer to manufacturer’s procedure for details.


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Temperature testing a catalytic converterYou can test converter operation by checking the temperature of the inlet and outlet of the converter. If the converter is working correctly, the catalytic reaction will make the exhaust outlet temperature higher than the inlet.

How to test the catalytic converter:

Warm the vehicle up to operating temperature

Run engine at 1500 rpm

Test the inlet and outlet temperatures of the converter with an infra red thermometer. Remember - the converter and exhaust will be extremely hot.

The inlet temperature should be cooler than the outlet temperature by approximately 200-500C.

Figure 36: Temperature sensors

Catalytic converters operate at temperatures of 5000C and above. Avoid touching hot exhaust components.


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Activity 13

Step 1

Ask your trainer to nominate a vehicle/model.

Step 2

Obtain the relevant workshop manual, training material, resources for the vehicle/model nominated.

Step 3

Using the references/resource material:

Locate the catalytic converter

Identify the type of catalytic converter

Study the manufacturer’s test procedures for the converter.

Step 4

List the manufacturer’s test procedures for the catalytic converter you will test.

__________________________________________________________________________________

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__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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Step 5

On a vehicle nominated by your teacher, complete an inspection of the catalytic converter and related components.Then complete this chart.

Component Comment

Physical damage to converter

Rattle test

Engine management test results

Restricted exhaust gas flow

Converter temperature test Input temp Output temp




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Particulate emissions in diesel enginesDiesel particulate filters (DPF)Changes to new car emission legislation will make particulate filters on diesel engines much more wide spread.

What are particulates in the exhaust?Anything solid in the exhaust gas is called particulate matter (PM). It includes things such as carbon soot.

Carbon soot is in the exhaust gas due to incomplete combustion of the fuel. Slow warm up and cold engine conditions increase the particulate matter.

Figure 37 Diesel particulate filter

How do particulate filters work?A diesel particulate filter (DPF) traps the carbon soot of the exhaust, a bit like the dustbag in a vacuum cleaner.

However, instead of emptying or cleaning the filter, the diesel particulate filter operates at a very high temperature and the carbon soot is burnt off.

This is called regeneration and it is either passive or active.

Particulate filters can be incorporated (included) into the catalytic converter. However, some vehicles have the particulate filter separate from the catalytic converter.


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Passive regenerationWhen the particulate filter reaches sufficient temperature (5600C) during normal operation, the carbon soot is burnt off. This is called the passive regeneration cycle.

Active regenerationIn some driving conditions, the exhaust temperature may not reach a high enough temperature to burn off the soot, so the ECU must control the process. This is called active regeneration.

The ECU directs small increases in fuel delivery or adjustments to fuel injection timing to raise the exhaust gas temperatures. This rise in temperature will burn and clean out the accumulated carbon soot.

If the particulate filter accumulates excessive carbon soot, a dashboard warning light will illuminate and the vehicle will require attention by a dealer specialist.

Testing and maintenanceThe diesel particulate filter needs to be serviced and maintained to a strict schedule. Generally a fault with the filter will need to be repaired by the vehicle dealer or a specialist who has been trained to do this task using specialist equipment.


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Activity 14

Answer the following questions

Question 1What are diesel particulates?

__________________________________________________________________________________

__________________________________________________________________________________

Question 2Where do diesel particulates come from?

__________________________________________________________________________________

__________________________________________________________________________________

Question 3Where are diesel particulate filters located?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 4How does a diesel particulate filter operate?

__________________________________________________________________________________

__________________________________________________________________________________

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Question 5When does the diesel particulate warning light operate?

__________________________________________________________________________________

__________________________________________________________________________________

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Question 6What is passive regeneration?

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 7What is active regeneration?

__________________________________________________________________________________

__________________________________________________________________________________

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Emission Control Information labelIn 2005, the Australian Federal Government introduced regulations to control emissions called Australian Design Rules (ADR) 79/02 Emission Control for Light Vehicles.

One of the things this required was for manufacturers to attach an Emission Control Information Label in a visible position in the vehicle engine compartment.

The label must state engine specifications and adjustments including:

Idle speed

Ignition timing

Idle air/fuel mixture setting procedures and value

The transmission position during tune up

Any accessories which should be in operation (ADR 79/02).

Figure 38: Emission Control Information label


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Activity 15

Answer the following questions

Question 1Where is the emission control information label located?

__________________________________________________________________________________

Question 2State the specifications given on the label in Figure 28 for service personnel.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 3State any recommendations given on the label in Figure 28 about adjusting the idle mixture (CO%).

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Question 4On the nominated vehicle locate the emission control information label and state its exact location below.

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Testing exhaust emissionsAn exhaust gas analyser is used to measure the emissions of the vehicle exhaust before they enter the catalytic converter. They can test between two and five different exhaust gas emissions.

The five exhaust gases that can be analysed are:-

1. Hydrocarbons (HC)

2. Carbon monoxide (CO)

3. Carbon dioxide (CO2)

4. Oxides of nitrogen (NOX)

5. Oxygen (O2).

Figure 39: Gas analyser


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Reasons for performing an exhaust gas testThere are two reasons for performing an exhaust gas test.

1. Engine performance

Exhaust gas measurement can be useful in diagnosing engine condition, engine management and fuel injection faults etc.

Some typical exhaust readings are:

HC 200 ppm or less

ppm = parts per million

CO 2% or less

O2 0%-2%

CO2 12%-15% or higher

NOX less than 100 ppm

2. Emission compliance

Exhaust gas measurement indicates if the engine and the emission devices are functioning correctly for emission compliance.

Some typical exhaust readings are:

HC 30-50 ppm or less

CO 4% or less

O2 0%-2%

CO2 12%-15% or higher

NOX less than 100 ppm

The test results can be compared with the vehicle manufacturer’s specifications and the Environmental Protection Authority (EPA) standards to check that the exhaust outputs meet emission standards.


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Conducting an exhaust gas analyser testFollowing is a typical procedure for operating an analyser. However, there are many different types of gas analysers available so you should always refer to manufacturer’s instructions.

STEP DONE

1. Run the engine until it reaches operating temperature.

2. Connect the analyser to the proper voltage supply.

3. Allow the analyser to warm up and perform the calibration function.

4. Connect the analyser probe to the exhaust outlet.

5. Hold the engine speed at 2500 rpm (revolutions per minute), and record the emissions readings.

6. Allow the engine to return to idle and record the emissions readings.

Compare the readings with manufacturer’s specifications and Environmental Protection Authority (EPA) standards. See your workshop supervisor if the workshop does not have it available.

If the measured exhaust gases are outside the acceptable level, refer to the manufacturer’s diagnosis procedure for further instructions.

Figure 40 Analyser measuring exhaust gases

Operating the engine in a confined space or without proper exhaust gas extraction can cause death from breathing exhaust gases. Do not carry out this test unless it is safe to do so.


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Activity 16

1. Your teacher will nominate a vehicle.

2. Locate the procedure and specifications for an exhaust emissions test in the gas analyser operation instructions and the manufacturer’s manual.

3. Carry out an exhaust emissions test.

4. Fill in the chart below as you go.

GASES

IDLE 2500 RPM

Vehicle specifications Your results Vehicle

specifications Your results COMMENTS

HC(hydrocarbons)

CO(carbon monoxide)

CO2

(carbon dioxide)

O2

(oxygen)




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GlossaryWORD MEANING

activated carbon A special kind of charcoal

absorbed Soaked up like a sponge

accumulated Gathered, collected over some time

advanced Moved forward

amended updated

bimetal (say by-metal) Made of two metals

buckling Bending out of shape

canister A container

compression Pressing on something

concentration How strong a mixture is

condense When a gas turns back into a fluid

confined Closed in, a small space

consumption use

contamination pollution

deceleration Slowing down

deposits Something left over

detonation Explosion

emissions What comes out of something

emitted Sent out

evaporate When surface liquid turns into vapour (a gas of droplets)

hemispherical A half globe shape

illuminate Light up


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WORD MEANING

incorporated Included, built into

insufficient / sufficient Not enough/ enough

internal Inside

lethal Deadly, can kill you

maximum The most, the biggest, the highest

moderate Medium

optimum Close to perfect

orifice Hole

particulates A small piece of something, a particle. Can sometimes be seen as black smoke in the exhaust gas.

permitted allowed

precautions An action taken in advance to protect against possible danger

pollution Poisons in the air, water or earth

pollutants Things which cause pollution

ported vacuum Engine vacuum drawn from an opening (or port) ahead of the throttle

prior to before

progressively bit by bit

purging To remove impurities. In this case, stored fuel vapour is the impurity and it is pushed into the intake system where it is burnt in the combustion chamber.

quench area A cooler area

ratio The amount of two things compared eg the ratio of petrol to air in a fuel mixture

regeneration Renew, make new again

restrict Limit, make smaller


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WORD MEANING

retarded Slowed down

scavenging Collecting and removing (exhaust gases)

situated Placed, located

source Where something comes from

specify state exactly

specified government standards

Standards set by government

sufficient/ insufficient Enough/ not enough

swirl Air or gas blowing around

temporarily For a while, not forever

syphoning Being sucked up

turbulence Being thrown around or mixed up

vapour gas

vented Flows out of a hole in the container

ventilation Fresh air

volatile How easily a substance turns from liquid to vapour/gas

wedge- shaped


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