University of PitestiFaculty of Mechanical Engineering and TechnologyMaster IAMD II

COMBUSTION ENGINE VEHICLE EXHAUST EMISSIONS

Supervisor: prof. PhD. IVAN Florian

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Student: BICA CornelSUMMARY:

1. COMPOSITION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 1.1. Exhaust gas components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 1.1.2. Intake and exhaust components of combustion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 1.1.3. Description of exhaust gas components . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42. EMISSION CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . ..5 2.1. Emission control strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Reduction in consumption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2.2.1. Aerodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 2.2.2. Weight savings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.3. Engine management system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.4. Engine and gearbox optimisation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.5. Fuel tank purging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.6. Exhaust gas recirculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 2.2.7. Positive Crankshaft Ventilation (PCV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3. Exhaust gas treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3.1. Catalytic converter (petrol engine) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3.2. Catalytic converter (diesel engine) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.3.3. Air Injection System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153. MEASUREMENT METHODS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..16 3.1. Performance control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 3.2. Measuring methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 3.2.1. Implementation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.2. Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .17 3.2.3. Driving cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184. STANDARDS FOR EXHAUST EMISSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215. ANALYZERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . ..22 5.1. Flame ionization detector – FID. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 5.1.1. Operating principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 5.1.2. Advantages and disadvantages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 5.1.3. Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 23 5.1.4. Description of a generic detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..23 5.2. Nondispersive infrared sensor – NDIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 5.2.1. Principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . …24 5.2.2. Measurement of CO using NDIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.3. Chemiluminescent Analyzer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 5.4. Paramagnetic Oxygen analyzers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.4.1. Measurement Principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.4.2. Interference Gas Compensation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.5. Opacimeters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . ..28 5.5.1. Principle of Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 5.5.2. Sampling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 5.5.3. Evaluation of measurement sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 5.5.4. Determination of PM Emission Mass from Smoke Concentration. . . . . . . . . . . . . . . . . . . . . . .30

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5.5.5. 10-15 Mode Running Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .. . . .. . . .. . . . . . . . . .31 5.5.6. Testing while Driving through an Urban Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .31

1. COMPOSITION1.1. Exhaust gas components

1.1.1. Summary

In the discussions on the constitution of motor vehicle exhaust emissions, the same terms are used repeatedly: carbon dioxide, nitrogen oxide, particulate matter or hydrocarbons. In this connection, mention is rarely made of the fact that these substances constitute only a fraction of total exhaust gas emissions.

Therefore,the approximate composition of the exhaust emissions of diesel and petrol engines before describing the individual exhaust gas components.

Fig1.Composition of exhaust emissions of petrol engines

Petrol engines may also emit small quantities of sulphur dioxide SO2 .

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Fig2.Composition of exhaust emissions of diesel engines

1.1.2. Intake and exhaust components of combustion

The following diagram shows a summary of the intake and exhaust components of the combustion cycle which takes place in the engine.

Fig 3.Intake and exhaust gas components

1.1.3. Description of exhaust gas components

N2 – Nitrogen is a non-flammable, colourless and odourless gas. Nitrogen is an elementary constituent of the air we breathe (78% nitrogen, 21% oxygen, 1% other gases), and is transported into the combustion chamber in the intake air. The largest proportion of the nitrogen induced is again discharged in pure form in the exhaust gases. Only a small proportion of the nitrogen combines with oxygen O2 to form oxides of nitrogen NOx .

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O2 – Oxygen is a colourless, odourless and tasteless gas. It is the primary constituent of the air we breathe (21%). Oxygen, like nitrogen, is drawn in through the air filter.

H2O – Water is partly induced by the engine (atmospheric humidity) or occurs during low-temperature combustion (warm-up period). Water is a harmless exhaust gas component.

CO2 - Carbon dioxide is a colourless, non-flammable gas. It is produced by the combustion of fuel containing carbon (e.g. petrol, diesel). Carbon combines with oxygen induced into the engine.The debate on climatic change (global warming) has increased public awareness to the subject of CO2 emissions. Carbon dioxide CO2 depletes the ozone layer which protects the earth against the sun's UV rays (greenhouse effect).

CO - Carbon monoxide results from the incomplete combustion of combustibles containing carbon. It is colourless, odourless, explosive and highly toxic. Carbon monoxide prevents red blood corpuscles (erythrocytes) from transporting oxygen. Even a relatively low concentration of carbon monoxide in the air we breathe is fatal. In normal concentrations in the open, carbon monoxide will oxidise to carbon dioxide CO2 within a short period of time.

NOx - Nitrogen oxides are compounds of nitrogen N2 and oxygen O2 (z. B. NO, NO2, N2O, etc.). Nitrogen oxides are produced by high pressure, high temperature and a surplus of oxygen in the engine during the combustion cycle. Several oxides of nitrogen are harmful to health. Action taken to reduce fuel consumption has, unfortunately, often led to a rise in nitrogen oxide concentrations in exhaust emissions because a more effective combustion process generates higher temperatures. These high temperatures in turn mean higher nitrogen oxide emission.

SO2 - Sulphur dioxide is a colourless, pungent and non-flammable gas. Sulphur dioxide causes respiratory illness, but only occurs in very low concentrations in exhaust gases. Sulphur dioxide emission can be curbed by reducing the sulphur content in the fuel.

Pb – Lead has been completely eliminated from motor vehicle exhaust emissions. 3000 t were still released into the atmosphere in 1985 by the combustion of leaded fuel. Lead in fuel prevents engine knock, which is caused by spontaneous ignition, and had a damping effect on the valve seats. By using environmentally-friendly additives in unleaded fuel, it is now possible to largely preserve knock resistance.

HC – Hydrocarbons are unburnt fuel components which occur in the exhaust emissions after incomplete combustion. Hydrocarbons (HC) occur in a variety of forms (e.g. C6H6, C8H18) and each has different effects on the human organism. Some hydrocarbons irritate the sensory organs while others are carcinogenic (e.g. benzene).

Particulate matter PM is mainly produced by diesel engines. Research into the effects of particulate matter on the human organism is still inconclusive.

2. EMISSION CONTROL 2.1. Emission control strategies

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Fig 4. Typical emission control systemPre-combustion:

•BETTER MIXTURE PREPARATION , DISTRIBUTION & FUEL METERING •Introduction of tuned intake manifold •Intake manifold heating •Replacement of carburetor with MPFI (multi point electronic fuel injection)

•GASOLINE REFORMULATION •INTRODUCTION OF ALTERNATIVE FUELS

•Natural gas (cng & lng) •Liquefied petroleum gas (lpg) •Ethanol •Methanol •Hydrogen

In-cylinder (combustion chamber design mods):•REDUCTION IN COMPRESSION RATIO •MODIFICATION IN COMBUSTION CHAMBER GEOMETRY

•Smaller combustion chamber surface volume •Reduction in crevice volume •Reduce quench areas in combustion chamber •Centrally location of spark plug • Hemispherical combustion chamber is best in this regard

•VARIABLE VALVE TIMING •EMPLOYING HIGH ENERGY/DUAL IGNITION SYSTEM •RETARDATION OF IGNITION TIMING •INCREASE IN IDLING SPEED

Post combustion:

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•PCV (POSITIVE CRANK CASE VENTILATION SYSTEM) •EGR (EXHAUST GAS RECIRCULATION SYSTEM) •CATALYTIC CONVERTER •AIR INJECTION SYSTEM

Lean burn operation (GDI):With the rising emphasis on controlling CO2 emissions (which is a green house gas) and on fuel

economy, it is essential to operate the engines on fuel lean mixtures. gasoline direct injection (gdi) engines have been developed by different manufactures which work on the principle of charge stratification (lean mixture operation). In these engines, the fuel burns more efficiently with less pollutant emission of CO,HC and CO2 and with lower fuel consumption. The fuel consumption is lowered up to 30% compared to the stoichiometric combustion . These engines can operate very lean overall; the air-fuel ratio near the spark plug is nearly stoichiometric or slightly fuel rich while the other parts of the combustion chamber are provided with very lean air-fuel ratios.

2.2. Reduction in consumption

Nowadays, the development of individual automotive technologies alone is not enough to reduce certain exhaust gas components and fuel consumption. The answer, therefore, is to look at vehicles as an integral whole and match all the automotive components to one another. Taking this holistic approach to vehicle development as a basis, three main exhaust emission control strategies can be defined:- Reduction of consumption- Exhaust gas treatment- Performance monitoring

The following sections will explain these terms and what action they entail.

2.2.1. AerodynamicsThe drag coefficient of aerodynamic vehicle shapes is low. Lower drag means lower fuel

consumption. In the past few decades, Volkswagen has succeeded in reducing the drag coefficient of its vehicles to less than 0.30 from over 0.45. This is a major step forward especially when you consider that approximately 70% of input power is required to overcome the aerodynamic drag when travelling at 100 kph.

Fig 5. Aerodynamic tunnel

2.2.2. Weight savingsSafety standards and rising comfort levels offset weight savings. However, weight savings are

necessary in order to reduce fuel consumption. Take the Audi A8/A2 (Space Frame) and the Lupo 3L TDI for example. In these vehicles, lightweight materials (aluminium, magnesium) are used in body construction.

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Fig 6.Audi light weight Space Frame

2.2.3. Engine management systemToday's engine management systems have the ability to influence all controllable components

(final control elements) of an engine. This means that all signals from the sensors (e.g. engine speed, air mass, charge pressure) are evaluated in the engine control unit and form control values for the controllable components (e.g. fuel injection quantity, injection timing, ignition advance angle). As a result, the engine can be controlled as a factor of load and the combustion process can be optimised.

Fig 7.Engine management control loop

2.2.4. Engine and gearbox optimisation

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Engine and gearbox construction has a major bearing on vehicle fuel efficiency. In engines, for example, modern injection systems are important for fuel-efficient combustion:- Pump injector-technology used in the diesel (TDI)- Direct injection in the petrol engine (FSI)

In the gearbox, it is necessary to adapt the gear ratios to the size and weight of the vehicle. In addition, 6-speed gearboxes are now in use. They allow the engine to operate in its optimal RPM range most of the time to obtain the best fuel economy.

2.2.5. Fuel tank purgingTo prevent petrol vapour (hydrocarbons) from escaping into the environment, the evaporated

petrol from the fuel tank is accumulated in an activated charcoal canister and combusted in a controlled manner.

A charcoal canister is used to trap the fuel vapors. The fuel vapors adhere to the charcoal, until the engine is started, and engine vacuum can be used to draw the vapors into the engine, so that they can be burned along with the fuel/air mixture. This system requires the use of a sealed gas tank filler cap. This cap is so important to the operation of the system, that a test of the cap is now being integrated into many state emission inspection programs.

Today with the use of sealed caps, redesigned gas tanks are used. The tank has to have the space for the vapors to collect so that they can then be vented to the charcoal canister. A purge valve is used to control the vapor flow into the engine. The purge valve is operated by engine vacuum.

One common problem with this system is that the purge valve goes bad and engine vacuum draws fuel directly into the intake system. This enriches the fuel mixture and will foul the spark plugs. Most charcoal canisters have a filter that should be replaced periodically. This system should be checked when fuel mileage drops.

Fig 8.Fuel tank purging(purge canister)

Electronic Evaporative Emissions Control:- Vent line connects to charcoal canister, via roll over/vapour separator valve.- Charcoal canister stores fuel vapours.- Purge valve controls vapour removal into inlet manifold, via purge line. - Purge valve operated by vacuum (shown) and/or ECU.-

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Fig 9.Electronic evaporative emissions control

2.2.6. Exhaust gas recirculation In modern engines, the exhaust gas recirculation system is used firstly to reduce engine air intake and, secondly, to utilise the positive effect of the exhaust gas on the combustion process in defined driving situations.

Fig 10. Exhaust Gas Recirculation

The purpose of the exhaust gas recirculation valve (EGR) valve is to meter a small amount of exhaust gas into the intake system; this dilutes the air/fuel mixture so as to lower the combustion chamber temperature. Excessive combustion chamber temperature creates oxides of nitrogen, which is a major pollutant. While the EGR valve is the most effective method of controlling oxides of nitrogen, in it's very design it adversely affects engine performance. The engine was not designed to run on exhaust gas. For this reason the amount of exhaust entering the intake system has to be carefully monitored and controlled. This is accomplished through a series of electrical and vacuum switches and the vehicle computer. Since EGR action reduces performance by diluting the air /fuel mixture, the system does not allow EGR action when the engine is cold or when the engine needs full power.

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Fig 11.EGR flow

2.2.7. Positive Crankshaft Ventilation (PCV) Combustion gases leak past piston rings, into crankcase - blowby. Modern vehicles use a PCV system to remove gases to be burnt in the inlet manifold. Older vehicles vented gases into atmosphere. PCV system operation is regulated by a PCV valve Uses manifold vacuum to clean blow-by gases from crankcase. Needs a breather tube for fresh air. Needs a pcv valve to regulate the amount of gases entering the intake manifold.

Fig 12.PCV operationPCV operation:

The purpose of the positive crankcase ventilation (PCV) system, is to take the vapors produced in the crankcase during the normal combustion process, and redirecting them into the air/fuel intake system to be burned during combustion. These vapors dilute the air/fuel mixture, they have to be carefully controlled and metered so as not to affect the performance of the engine.

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PCV Valve: Spring loaded valve that is shut when engine is off. At idle, maximum vacuum defeats spring pressure and minimal crankcase vapours flow. At normal engine speeds, plunger moves to a central position and maximum vapours flow.

Fig 13.PCV Valve

REGULATING THE PCV VAPOR FLOW

Amount Condition

Manifold Vacuum

Blow-by Gases

Idle High Vacuum

Small Volume

High Speed

Low Vacuum

Large Volume

2.3. Exhaust gas treatment2.3.1. Catalytic converter (petrol engine)

Nowadays, the exhaust gases of petrol engines are treated by catalytic converters. The catalytic cleaning process is controlled by the engine control unit. The lambda probe signals to the engine control unit the oxygen content in the exhaust gases, and the engine control unit adjusts the fuel/air mixture to a ratio of lambda=1.

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Fig 14.Lambda control loop

The catalytic converter is able to clean the exhaust gases at a temperature of approximately 300 degrees C or higher and needs a certain amount of time to heat up after a cold start. To shorten the warm up phase and clean exhaust gases more quickly, primary catalytic converters are used in modern exhaust systems. They are located near to the exhaust manifold. They are normally small in size, and so reach their operating temperature more quickly.

The catalytic cleaning processes involves two chemical reactions:1. Reduction - Oxygen is withdrawn from the exhaust gas components.2. Oxidation - Oxygen is added to the exhaust gas components (secondary combustion).

Fig 15.Catalytic process

Three-Way Catalytic ConverterAs the exhaust gases flow through the catalyst, the NO reacts with the CO, HC and H2 via a

reduction reaction on the catalyst surface. NO+CO→½N2+CO2 , NO+H2 → ½N2+H2O, and others The remaining CO and HC are removed through an oxidation reaction forming CO2 and H2O

products (air added to exhaust after exhaust valve). A three-way catalysts will function correctly only if the exhaust gas composition corresponds to

nearly (±1%) stoichiometric combustion.- If the exhaust is too lean – NO are not destroyed - If the exhaust is too rich – CO and HC are not destroyed A closed-loop control system with an oxygen sensor in the exhaust is used to determine the

actual A/F ratio and used to adjust the fuel injector so that the A/F ratio is near stoichiometric.

Effect of Mixture Composition

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Fig 16.Mixture composition effectEffect of TemperatureThe temperature at which the converter becomes 50% efficient is referred to as the light-off

temperature. The converter is not very effective during the warm up period of the engine.

Fig 17.Temperature effectEfficiency

Require near stoichiometric combustion for effective conversion of all three pollutants ,CO and HC conversion efficiency drop for rich mixtures,NOx conversion efficiency drops for lean mixtures.Exhaust gas oxygen sensor(Zirconia,ZrO2 based)essential to keeping the Air/fuel ratio in window of optimum conversion efficiency for all three.

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Fig 18.The “Window”

2.3.2. Catalytic converter (diesel engine)The diesel engine operates with a surplus of oxygen in the fuel/air mixture. Therefore, oxygen

content need not be controlled by the lambda probe, and an oxidation catalytic converter undertakes the task of catalytic cleaning by using the high residual oxygen level in the exhaust gas.

This means that catalytic exhaust gas treatment is not controlled in the diesel engine and that the oxidation catalytic converter can only convert oxidisable exhaust gas components. As a result, the concentrations of hydrocarbons (HC) and carbon dioxide (CO) are substantially reduced. However, the nitrogen oxide components in the exhaust gas can only be reduced by design improvements (e.g. combustion chambers and injection systems).

Fig 19.Main constituents of particulate matter(PM)

The particulate matter typically emitted by a diesel engine comprises a core and several attached components, of which only the hydrocarbons (HC) are oxidised in the oxidation catalytic converter. The residues of the particulate matter can only be collected by special particulate filters.Flow through oxidation catalyst(two-way catalytic convertor)for reduction of CO and VOC(80%),and PM SOF(20-30%),does not retain PM.

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Fig 20.Flow through Two Way Catalyst

2.3.3. Air Injection System-Forces air into exhaust ports to burn excess hydrocarbons. -Air pump provides a supply of pressurized air, via air injection manifold. -Diverter valve stops air flow under deceleration. -Check valve stops hot exhaust gases coming back up air hose. Since no internal combustion engine is 100% efficient, there will always be some unburned fuel in the exhaust. This increases hydrocarbon emissions. To eliminate this source of emissions an air injection system was created. Combustion requires fuel, oxygen and heat. Without any one of the three combustion cannot occur. Inside the exhaust manifold there is sufficient heat to support combustion, if we introduce some oxygen than any unburned fuel will ignite. This combustion will not produce any power, but it will reduce excessive hydrocarbon emissions. Unlike in the combustion chamber, this combustion is uncontrolled, so if the fuel content of the exhaust is excessive, explosions that sound like popping will occur. There are times when under normal conditions, such as deceleration, when the fuel content is excessive. Under these conditions we would want to shut off the air injection system. This is accomplished through the use of a diverter valve, which instead of shutting the air pump off diverts the air away from the exhaust manifold. Since all of this is done after the combustion process is complete, this is one emission control that has no effect on engine performance. The only maintenance that is required is a careful inspection of the air pump drive belt.

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Fig 21. Air Injection System

3. Measurement methods3.1. Performance control

You will already be familiar with the performance control of all automotive components and systems relevant to exhaust emissions under the term "On-Board Diagnosis”. This concept was coined in

California in 1988. The European variant of this diagnosis concept is called "Euro On-Board Diagnosis (EOBD)” and is required by the government for homologating new vehicles of the automobile industry since the start of 2000.

Faults which impair the emission behaviour of a vehicle are indicated by self-diagnosis fault warning lamp K83. Faults and various other items of information can be read out at the diagnosis interface using a generic OBD visual display unit or Vehicle Diagnostic, Testing and Information System VAS 5051.

Fig 22.Malfunction Indicator Lamp (MIL)

WORKING OF OBD:- Uses information from sensors to judge the performance of the emission controls

- These sensors do not directly measure emissionsEXAMPLE OF HOW OBD WORKS:- Fuel system pressure control- Fuel pressure sensor measures how well pressure is controlled- Manufacturer correlates pressure control error to corresponding emission increase- OBD system is calibrated to turn on MIL when pressure is outside limits

BENEFITS OF OBD :- Encourages design of durable emission control systems- Aids diagnosis and repair of complex electronic engine controls- Helps keep emission slow by identifying emission controls in need of repair- Works for life of the vehicle

3.2. Measuring methods3.2.1. Implementation

For homologation purposes, the exhaust emissions of a vehicle are determined on a roller dynamometer by using a prescribed measuring system. For this purpose, a defined driving cycle is implemented on the roller dynamometer and the measuring system records the quantity of exhaust gas components. Type approval must be performed by the automobile industry before it brings a new vehicle onto the market.

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Fig 23. Roller dynamometer

3.2.2. Function- The driving cycle is executed on the roller dynamometer.- While this cycle is under way, the main blower induces exhaust gas together with the filtered ambient air in a steady air mass flow. This means that the amount of air-exhaust gas mixture induced stays constant. When the vehicle produces higher exhaust emissions (e.g. during an acceleration phase), less ambient air is induced. When the vehicle produces lower exhaust emissions, more ambient air is drawn in.- A constant quantity of this air-exhaust gas mixture is withdrawn continuously and pumped into one or more collecting bags.- The collected exhaust components are measured, referred to the total distance covered and output in grammes per kilometre.

3.2.3. Driving cyclesEurope: NEDC (New European Driving Cycle) with 40-second lead timeThis driving cycle was introduced in 1992 and will be replaced by a modified cycle on Jan. 1, 2000.

A striking feature of this driving cycle is the 40-second lead time before measurement of the exhaust emissions begins. This lead time can also be described as a "warm-up period".

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Fig 24. NEDC with 40-second lead time

Characteristics:Cycle length: 11,007 kmAverage speed: 33.6 kphMaximum speed: 120 kph

Europe: NEDC without 40-second lead timeWhen the EU III exhaust emission standard came into effect on Jan.1, 2000, the 40-second lead

time was eliminated from the current driving cycle. The measuring cycle begins as soon as the engine is started. The elimination of the lead time intensifies the measuring method because allowance is made in the test results for all exhaust components produced after a cold start while the catalytic converter heats up.

Fig 25. NEDC without 40-second lead time19

Characteristics:Cycle length: 11,007 kmAverage speed: 33.6 kphMaximum speed: 120 kph

USA: FTP 75 driving cycleEuropean exhaust emission limits are frequently compared with US exhaust emission limits

because the USA has played a precursory role in the statutory reduction of exhaust emissions. However, the following comparison of driving cycles shows that it is not possible to draw a direct comparison.

Besides, test results in Europe are specified in grammes per kilometre (g/km) while test results in the USA are specified in grammes per mile (g/mile).

Fig 26. FTP 75 driving cycleCharacteristics:

Cycle length: 17.8 kmAverage speed: 34.1 kphMaximum speed: 91.2 kph

To highlight the differences between the European NEDC and the US FTP 75 driving cycle, the two curves are shown superimposed in the following diagram. The two cycles differ in respect of test duration, top speed, average speed, speed intervals and start-up phase.

The start-up phase in the FTP 75 driving cycle in particular is more intensive than in the NEDC cycle because the vehicle can be driven at higher speeds after a cold start while the catalytic converter isheating up.

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Fig 27. NEDC and US FTP 75 driving cycle

4. STANDARDS FOR EXHAUST EMISSIONS

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Fig 28. Emission limits5. ANALYZERS

5.1. Flame ionization detector - FID22

A flame ionization detector (FID) is a scientific instrument that measures the concentration of organic species in a gas stream. It is frequently used as a detector in gas chromatography. Standalone FIDs can also be used in applications such as landfill gas monitoring and fugitive emissions monitoring in stationary or portable instruments.

5.1.1. Operating principle The operation of the FID is based on the detection of ions formed during combustion of organic compounds in a hydrogen flame. The generation of these ions is proportional to the concentration of

organic species in the sample gas stream. Hydrocarbons generally have molar response factors that are equal to number of carbon atoms in their molecule, while oxygenates and other species that contain heteroatoms tend to have a lower response factor. Carbon monoxide and carbon dioxide are not detectable by FID.

Fig 29.Schematic of FID

5.1.2. Advantages and disadvantagesAdvantages

Flame ionization detectors are used very widely in gas chromatography because of a number of advantages.• Cost: Flame ionization detectors are relatively inexpensive to acquire and operate.• Low maintenance requirements: Apart from cleaning or replacing the FID jet, these detectors require no maintenance.• Rugged construction: FIDs are relatively resistant to misuse.• Linearity and detection ranges: FIDs can measure organic substance concentration at very low and very high levels, having a linear response of 10^6.

Disadvantages Flame ionization detectors cannot detect inorganic substances. In some systems, CO and CO2 can be detected in the FID using a methanizer, which is a bed of Ni catalyst that reduces CO and CO2 to methane, which can be in turn detected by the FID. Another important disadvantage is that the FID flame oxidizes all compounds that pass through it; all hydrocarbons and oxygenates are oxidized to carbon dioxide and water and other heteroatoms are

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oxidized according to thermodynamics. For this reason, FIDs tend to be the last in a detector train and also cannot be used for preparatory work.

5.1.3. Operation In order to detect these ions, two electrodes are used to provide a potential difference. The positive electrode doubles as the nozzle head where the flame is produced. The other, negative electrode is positioned above the flame. When first designed, the negative electrode was either tear drop shaped or angular piece of platinum. Today, the design has been modified into a tubular electrode, commonly referred to as a collector plate. The ions thus are attracted to the collector plate and upon hitting the plate, induce a current. This current is measured with a high-impedance picoammeter and fed into an integrator. The manner in which the final data is displayed is based on the computer and software. In general, a graph is displayed that has time on the x-axis and total ion on the y-axis.

The current measured corresponds roughly to the proportion of reduced carbon atoms in the flame. Specifically how the ions are produced is not necessarily understood, but the response of the detector is determined by the number of carbon atoms (ions) hitting the detector per unit time. This makes the detector sensitive to the mass rather than the concentration, which is useful because the response of the detector is not greatly affected by changes in the carrier gas flow rate.

5.1.4. Description of a generic detectorThe design of the flame ionization detector varies from manufacturer to manufacturer, but the

principles are the same. Most commonly, the FID is attached to a gas chromatography system. The eluent exits the GC column (A) and enters the FID detector’s oven (B). The oven is needed to make sure that as soon as the eluent exits the column, it does not come out of the gaseous phase and deposit on

the interface between the column and FID. This deposition would result in loss of eluent and errors in detection. As the eluent travels up the FID, it is first mixed with the hydrogen fuel (C) and then with the oxidant (D). The eluent/fuel/oxidant mixture continues to travel up to the nozzle head where a positive bias voltage exists (E). This positive bias helps to repel the reduced carbon ions created by the flame (F) pyrolyzing the eluent. The ions are repelled up toward the collector plates (G) which are connected to a very sensitive ammeter, which detects the ions hitting the plates, then feeds that signal (H) to an amplifier, integrator, and display system. The products of the flame are finally vented out of the detector through the exhaust port (J).

Fig 30. NGA 2000 FID Burner

5.2. Nondispersive infrared sensor - NDIR

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A nondispersive infrared sensor (or NDIR) sensor is a simple spectroscopic device often used as gas detector. It is called nondispersive because wavelength which passes through the sampling chamber is not pre-filtered instead a filter is used before the detector.

5.2.1. Principle The main components are an infrared source (lamp), a sample chamber or light tube, a wavelength sample chamber, and gas concentration is measured electro-optically by its absorption of a specific wavelength in the infrared (IR). The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas, typically nitrogen. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Ideally other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector to compensate for interfering components. For instance, CO2 and H2O often initiate cross sensitivity in the infrared spectrum. As many measurements in the IR area are cross sensitive to H2O it is difficult to analyse for instance SO2 and NO2 in low concentrations using the infrared light principle. The IR signal from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal. In the NDIR analyzer the exhaust gas species being measured is used to detect itself. This is done by selective absorption. The infrared energy of a particular wavelength or frequency is peculiar to a certain gas in that the gas will absorb the infrared energy of this wavelength and transmit the infrared energy of other wavelengths.

5.2.2. Measurement of CO using NDIR The absorption band for carbon monoxide is between 4.5 and 5 microns. So the energy absorbed at this wavelength is an indication of concentration of CO in the exhaust gas. The NDIR analyzer consists of two infrared sources, interrupted simultaneously by an optical chopper. Radiation from these sources pass in parallel paths through a reference cell and a sample cell. Exhaust gas from the tailpipe of the engine/vehicle is passed through the sample cell during the measurement of exhaust emissions. The reference cell is filled with an inert gas, usually nitrogen, which does not absorb the infrared energy for the wavelength corresponding to the compound being measured.

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Fig 31. Schematic diagram of NDIR

A closed container filled with only the compound to be measured works as a detector.The detector is divided into two equal volumes by a thin metallic diaphragm. When the chopper blocks the radiation, the pressure in both parts of the detector is same and the diaphragm remains in the neutral position. As the chopper blocks and unblocks the radiations, the radiant energy from one source passes through the reference cell unchanged whereas the sample cell absorbs the infrared energy at the wavelength of the compound in the cell. The absorption is proportional to the concentration of the compound to be measured in the sample cell. Thus unequal amounts of energy are transmitted to the two volumes of the detector and the pressure differential so generated causes movement of the diaphragm of the detector. This changes the capacitance between the diaphragm and a fixed probe, thereby generating an a.c. signal which is amplified and, after rectification to d.c. displayed on a meter.

5.3. Chemiluminescent Analyzer

Chemiluminescent is the emission of light energy resulting from a chemical reaction. If NO and O3 are brought together a chemical reaction takes place which produces NO2 in

activated state. Activated NO2 emits light NO + O3 → NO2 + O2 NO2 → NO2 + light emissions

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Fig 32. Schematic diagram of Chemiluminiscent Analyzer

To measure NO concentration the gas sample to be analysed is send to a reaction chamber, where it combines with ozone. The resulting chemiluminescent is monitored through an optical filter by a high sensitivity photomultiplier positioned at one end of the reactor.The filter photo multiplier combination responds to light in a narrow wavelength band unique to the above reaction. The output from the photo multiplier is linearly proportional to the NO concentration. To measure NOx concentration (i.e. NO plus NO2) the sample gas flow is diverted through an NO2-to-NO converter. The chemiluminescent response in the flow reactor to the converter effluent is linearly proportional to the NOx concentration entering the converter.

5.4. Paramagnetic Oxygen analyzers5.4.1. Measurement Principle

A sample gas is introduced from the sample gas inlet and divided into two streams in the ring-shaped sensor cell. An auxiliary gas is introduced from the auxiliary gas inlet and divided into two streams, A and B. Each stream meets the sample gas in the ring-shaped path and where stream B meets the sample gas, a magnetic field is created by a magnet. Two thermistors are installed in streams A and B, respectively, to determine the flow rates. When a sample gas contains oxygen, the oxygen is drawn into the magnetic field, thereby decreasing the flow rate of auxiliary gas in stream B. The difference in flow rates of two streams, A and B, which is caused by the effect of flow restriction in stream B, is proportional to the oxygen concentration of the sample gas. The flow rates are determined by the thermistors and converted into electrical signals, the difference of which is computed as an oxygen signal.

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This method provides fast response and resistance to vibration and shock. Furthermore, as the thermistors do not come in contact with sample gas, stable measurement is achieved over a long period of time without the effects of contamination and corrosion.

Fig 33. Flow schematic of Paramagnetic Oxygen Sensor Cell

5.4.2. Interference Gas Compensation The paramagnetic oxygen analyzers utilize the paramagnetic property of oxygen (the oxygen is drawn into a magnetic field) to measure the concentration of oxygen. However, gases other than oxygen have a little magnetism, although their magnetism is very low compared to oxygen. In actual measurement, background gas having magnetic susceptibilities may cause interference, affecting a measurement result. For example, if carbon dioxide (CO2) which has a lower magnetic susceptibility than nitrogen (N2), is passed through the cell, the analyzer will read a negative value. If the cell is tilted as shown in the figure, the flow rate of the auxiliary gas toward stream B’ will increase due to the higher density of CO2. This

will change the flow ratio, thereby canceling out the negative deviation. A change in the auxiliary gas flow ratio due to the magnetic susceptibility of background gas is cancelled out by a change in the auxiliary gas flow ratio due to the density difference which is generated by changing the cell angle. Thus, the interference can be compensated for.

Fig 34.Schematic of Paramagnetic Oxygen Sensor

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5.5. Opacimeters5.5.1. Principle of Measurement

Smoke meters that use light can be broadly classified into two types: a light reflecting type that measures smoke concentration based on changes in the reflectivity when light is shown on PM collected on a filter, and a light transmitting type (opacimeter) that measures smoke concentration based on the strength of the absorbed and scattered light when light is shown directly on the exhaust gas. The MEXA-130S uses the light transmission method, which also has a high sensitivity with respect toblue and white smoke. Figure above shows the principle of measurement of the MEXA-130S. The exhaust gas is drawn into the sample cell, and when the gas contains black smoke due to hightemperature fuel combustion and blue and white smoke due to unburned oil, unburned fuel and water, the visible light from the light source is attenuated due to absorption and scattering. The concentration of smoke is calculated from the amount of attenuation using the Lambert-Beer equation (Equation (1)). The result is expressed as an opacity N (%) given by Equation (2), or a light absorption coefficient k (m-1) given by Equation (3).

Fig 35. Principle of measurement

I =Io · e-kL=Io · ( 1-N/100) (1)N=(1-I/Io) · 100 (2)k = -1 /L · ln(1-N/100) (3)I0 : Light intensity when there is no smokeI : Light intensity when smoke existsL : Cell length (m)

5.5.2. SamplingThe MEXA-130S uses a sampling method that utilizes the exhaust gas pressure. With this method,

a special sampling pump is not needed and stable collection of exhaust gas, which is very changeable, is possible. Figure shows the cycle of the free acceleration method, which is a typical measurement method. A sampling probe is inserted into the tailpipe, and the engine is quickly accelerated with no load to produce smoke. The exhaust pressure causes the smoke to pass through the probe and into the sample cell. the engine is revved a set number of times, the smoke concentration is measured as the peak value of the output signal during acceleration. An opacimeter and the free acceleration method areused in combination in automobile service shops in Europe1), and it is anticipated that this will become an effective and convenient smoke measurement method for low-concentration smoke.

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Fig 36.Measurement Cycle of Free Acceleration Method

5.5.3. Evaluation of measurement sensitivity The next figure shows the time chart of the MEXA-130S output signal when an actual vehicle is run using the free acceleration method. A stable signal with sufficiently high S/N was obtained.

Fig 37. Time chart of smoke Measurement using Free Acceleration Method

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5.5.4. Determination of PM Emission Mass from Smoke Concentration The sensitivity of an opacimeter is normally calibrated at a light transmittance of 0% and 100% and the linearity verified with the optical filter whose transmittance is known. This means that the readings of an opacimeter are not directly calibrated using PM itself. In order to study the validity of determining the PM emission mass from the readings of an opacimeter, the authors conducted a comparison with the conventional filter method using an engine running test on a chassis dynamometer. The test vehicle was an RV vehicle equipped with a divided combustion chamber diesel engine. The main specifications are shown in the next Table.

First we ran the test vehicle on a chassis dynamometer at fixed speeds of 40, 60, 70, and 80 km/h, and measured the PM mass using the filter weighing method. We simultaneously measured the smoke concentration using the MEXA-130S. We may infer that the relation given in Equation (4) holds between the PM mass (MPM) obtained using the filter weighing method and the light absorption coefficient k obtained using the MEXA-130S.MPM = PM · k · Qex (4)MPM : PM mass[g/s]PM : PM density[g/s]k : Light absorption coefficient[m-1]C : Conversion coefficient[m]Qex : Flow rate of exhaust gas[L/s]

Next figure shows the test results. A good correlation is evident between the smoke concentration and the PM mass.

Fig 38. Relation of smoke concentration to emitted PM mass

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5.5.5. 10-15 Mode Running Test The amount of smoke emitted varies widely depending on the running state. We measured the change in smoke concentration along with other components in exhaust gas in 10-15 mode, a Japanese standard mode for exhaust gas testing. The next figure shows a time chart of vehicle speed and the quantities of HC, CO, and PM emitted. The PM mass was obtained by conversion from the smoke concentration using the approximation line of the previous figure. The emission of PM increases and decreases according to changes in vehicle speed, and the pattern resembles those of other components. The fact that we can observe an emission pattern that is very close to the expected pattern supports the possibility that the MEXA-130S is effective as a real time testing instrument for PM.

Fig 39.Emission pattern while running in 10-15 modes

5.5.6. Testing while Driving through an Urban Area Interest is growing in on-board measurement, whereby a test vehicle is equipped with a small analyzer and the exhaust gas is measured while actually driving through an urban area. Following HC, CO, and NOx testing2), the authors studied the possibility of on-board measurement of PM using the MEXA-130S. We equipped the test vehicle with a MEXA-130S Opacimeter, a Portable-type Total Hydrocarbon Analyzer (MEXA-1170HFID), and a Nitrogen Oxide Analyzer (MEXA-120NOx). We drove the vehicle through the suburbs of Kyoto and measured the exhaust gas. We also simultaneously recorded the output of an excess air ratio sensor and the outputs of various thermometers and humidity sensors. The results are shown in the next figure.The emitted mass of PM obtained using the MEXA-130S shows the same pattern of change corresponding to sudden acceleration and deceleration as THC, NOx, the excess air ratio, and fuel consumption. This indicates that the MEXA-130S can be used for PM measurement not only on a chassis dynamo but also in on-board measurement.

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Fig 40. Emission pattern during Urban-Area On-Board measurement

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REFERENCES:

1. www.howstuffworks.com2. www.dieselnet.in3. www.auto101.com4. www.wikipedia.com5. www.VW-AG.com6. www.tsi.com7. www.AVL.com8. www.teledyne-ml.com

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