Chap 6 About Emission

8/2/2019 Chap 6 About Emission

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Facts about emissions from motor vehicles

(based on H.Heywood Internal combustion engine fundamentals

and DieselNet website)

6.1 Complete combustion of hydrocarbon fuels

The vast majority of road transport in the world is powered by either gasoline (petrol) or

diesel fuel. Both of these fuels are derived from crude oil by using several refining processes

including distillation, reforming, cracking, polymerization and blending of different

compounds coming from different refining streams etc.

Regarding the chemical structure of gasoline and diesel fuel, both of them have two

elements in common: they both consist of carbon (C) and hydrogen (H), and are thus called

hydrocarbon (HC) fuels.

In addition to carbon and hydrogen, some of the so-called reformulated gasolines also

contain small amounts (typically about 2 mass-%) of oxygen (O2). The chemical composition of

reformulated gasolines has been especially selected to cause as low an impact as possible on

the environment. Fuels containing oxygen are also sometimes referred to as oxygenated

fuels. Oxygen in the fuel makes the combustion take place more effectively, especially under

certain conditions. From a theoretical point of view, it is not of great importance for the

reactions taking place, whether part of the oxygen needed for combustion originates in the

fuel or in the ambient air.

When the carbon (C) fraction of hydrocarbon fuel is combusted, the end product is carbon

dioxide (CO2). When the hydrogen (H) fraction of the fuel is combusted, the end product is

water (H2O). The following equations show the reactions:

C + O2

CO22H2 + O2 2H2O

The end products of the complete combustion of hydrocarbon fuels (CO2 and H2O) were for

a long time considered as totally harmless, since they are not toxic. However, recent findings

have revealed that carbon dioxide is the main contributor to the increase in the greenhouse

effect, causing global warming and climate change. Controlling CO 2 emissions and climate

change will probably be one of the greatest challenges ever faced by mankind.

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Internal combustion engines

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6.2 Real-world combustion products

In real conditions; that is, in the combustion chambers of engines, the process of combustion

is usually incomplete. This leads to the formation of unwanted components, in addition to

carbon dioxide and water, which affect air quality and cause harm both to human health and

to the environment.

The most important of these unwanted emission components (also called air quality

emissions), are carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and

particulate matter (PM). Of these four, particulates are solid, whereas the others are

gaseous.

These four compounds are referred to as the regulated emissions, since the emission

legislation sets limit values to these components. Under current European emission

legislation, CO, HC and NOx are regulated for gasoline powered vehicles, while all four are

regulated for diesel vehicles and engines.

In addition to the regulated components, the research literature on emissions also

recognizes the term unregulated emissions. This refers to emission components which cause

concern but are not regulated by the legislation. This group includes, for example, benzene,

1,3-butadiene, aldehydes and ultra-fine particulates.

Fig. 6.1. Division of different emission compounds

As mentioned above, CO2 has to be considered as a harmful emission component because of

its properties related to the greenhouse effect and global warming. Other emission

components contributing to this problem are, for example, methane (CH 4), the so-called CFC

Unregulatedemissions

- Carbon dioxide (CO2)

- Methane (CH4)

- CFC compounds

- Nitrous oxide (N2O)

Compounds not generallyregulated by legislation, butwhose detrimental properties areof interest among scientists.(E.g. benzene, 1,3-butadiene,aldehydes, fine particulates)

Tailpipe emission compounsregulated by legislation(CO, HC, NOX and PM).Also referred to as air qualityemissions (to differentiatefrom CO2)

Regulatedemissions

Greenhouse gasemissions

Mostly

local or

regional

problem

Global

problem


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Chapter 6. Facts about emissions from motor vehicles

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compounds (containing chlorine, fluoride and carbon) and nitrous oxide (N2O), whose popular

name is laughing gas). These compounds, as a group, are referred to as greenhouse gases

(GHG). Unlike regulated or unregulated emissions, which mostly affect the vicinity of the

emission source only (locally or regionally), the GHG emissions affect the whole atmosphere

regardless of the location of the emission source. The division between the three different

groups of emission compounds as described above is illustrated in Figure 6.1.

In the following four sections, each of the regulated emission components will be

discussed separately.

6.2.1 Carbon monoxide

Carbon monoxide (CO) is the product of incomplete combustion. It consists of a carbon atom

and an oxygen atom linked together. Usually it is formed due to lack of oxygen at least in

some parts of the combustion chamber. If the air-fuel mixture control system is not

functioning properly in the engine, there can be lack of oxygen throughout the combustion

chamber. If there is not enough oxygen available, the combustion takes place only partially,

and carbon from the fuel turns into carbon monoxide (CO) instead of carbon dioxide (CO 2) as

in the case of complete combustion.

In the case of gasoline engines (utilizing the so-called Otto-cycle), the air-fuel ratio is

controlled very strictly and is maintained constantly at the theoretically correct mixture in

almost all driving situations. The only exception occurs when a cold engine is started and

operated. Under these conditions it is usually necessary to enrich the mixture in order to

ensure the start-up and smooth operation of the engine before it is warmed up.

Under these conditions carbon monoxide emissions are high. They can be reduced,

however, after a cold start, providing the two following requirements are met: the

enrichment of the air-fuel ratio in the engine is turned off, and the temperatures of the

catalytic converter and the lambda sensor are high enough.

Engine and vehicle manufacturers are pursuing enrichment strategies which enrich the

mixture by as small an amount as possible. And they are trying to make the enrichment

period as short as possible. In addition, the catalytic exhaust after treatment device

manufacturers are working in order to find catalyst chemistry that will have as low a light-offtemperature as possible, meaning that the conversion (oxidation) of CO and hydrocarbons in

the catalyst would start as early as possible after a cold start. Typically, the light-off

temperature is in the range of 150 to 250 C. Ageing of the catalyst may increase this

temperature close to 300 C.

Figure 6.2 presents CO concentration measurement results for a European subcompact

gasoline-powered car (2003 model) with a 1.6 liter gasoline engine. Test temperature was -7

C. The drive cycle used in this test was the current European official emission test drive

cycle, also known as the New European Drive Cycle (NEDC) or "EC2000" cycle, which has been

implemented since the Euro 3 regulations came into effect in 2000.


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Essential in this test cycle is that the engine of the test vehicle and the emission sampling

are both started simultaneously. In previous legislation stages (up to the Euro 2 regulations),

the engine was started 40 seconds before the emission measurement began, allowing most of

the emissions to dissipate in the atmosphere without detection.

In Figure 6.2, cumulative CO emission and CO concentration measured from raw

(undiluted) exhaust are presented as a function of the distance driven.

Fig. 6.2. CO concentration and cumulative CO emission from a subcompact 1.6 liter gasoline car inthe official European test cycle at ambient temperature of -7 C. (VTT)

Figure 6.2 shows that the CO concentration in exhaust has been high, between 4 to 6%,

during the first 250 meters of driving. This is caused by the cold-start enrichment period.

Timewise, this means about 75 seconds from engine start-up. (there is an idle period of 11

seconds at the beginning of the test cycle before actual driving starts). After about 250

meters of driving, the CO concentration has decreased dramatically. This is due to the fact

that the fuel mixture enrichment has been turned off, and the air-fuel ratio has become

stoichiometric (lambda = 1). When a mixture (or a ratio) is stoichiometric, it means that the

engine receives exactly the correct amount of fuel corresponding to the amount of air

available. Under these conditions, there is just enough air for complete combustion.

However, the CO concentration has still been around 0.5% between about 300 meters and

350 meters of driving. This indicates that the mixture has been stoichiometric, but that the

catalytic converter temperature has not been high enough for effective CO conversion.

CO * EC2000 @ -7 C

0.088

0.217

0.279

0

10

20

30

40

50

60

70

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Trip length [km]

Cumulativeemissio

n[g]

0

2

4

6

8

10

12

14

Concentration[%]

Koe # 22470; Mini Cooper 2D-RC31/247

CO-pstkertym50 % kertymst, km90 % kertymst, km95 % kertymst, km

CO-tilavuusosuus

Cumulative CO emission

50 % accumulated

90 % accumulated

95 % accumulated

CO concentraton

CO * EC2000 @ -7 C

0.088

0.217

0.279

0

10

20

30

40

50

60

70

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Trip length [km]

Cumulativeemissio

n[g]

0

2

4

6

8

10

12

14

Concentration[%]

Koe # 22470; Mini Cooper 2D-RC31/247

CO-pstkertym50 % kertymst, km90 % kertymst, km95 % kertymst, km

CO-tilavuusosuus

Cumulative CO emission

50 % accumulated

90 % accumulated

95 % accumulated

CO concentraton


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After about 350 meters of driving (about 90 seconds from engine start), the temperature

in the catalytic converter has apparently reached a sufficiently high level, because at that

stage the CO concentration dropped to almost negligible values.

The concentration trace has risen a few times after reaching the close-to-zero values for

the first time. This is probably due to slight enrichment periods in the engine operation

during the acceleration of the vehicle.

The red curve in Figure 6.2 (cumulative CO emission in grams) and the driving distances in

meters associated with it, show that almost all of the total CO emission is generated during

the first quarter of a kilometer of driving. For example, 95% of the CO from the whole test

distance (4.052 km) has been generated after 279 meters of driving.

Typically, carbon monoxide emissions from diesel engines are relatively low. This is due to

the fact that diesel engines always run on excess air, meaning that the air-fuel ratio, also

known as the lambda value, is all the time much greater than one. This results in fairly

complete combustion of carbon, since there is usually enough air and oxygen available in all

parts of the combustion chamber under most driving conditions.

Carbon monoxide is an insidious poisonous gas that can cause death very easily. It cannot

be smelled, seen or tasted, but it binds itself to the hemoglobin of the blood forming

carboxyhemoglobin, which prevents the blood circulation system from transporting oxygen to

the tissues of the body.

Persons with heart disease are especially sensitive to carbon monoxide poisoning and may

have chest pain if they breathe CO while exercising. Infants, elderly persons and individuals

with respiratory diseases are also particularly sensitive. Carbon monoxide can affect healthy

individuals, impairing their exercise capacity, visual perception, manual dexterity, learning

functions and ability to perform complex tasks. (EPA 1). The content of CO in air and the time

of exposure are the critical factors concerning how serious the consequences might be when a

human being is exposed to carbon monoxide.

Figure 6.3 indicates, for example, that exposure of one hour to breathing air containing

over 600 ppm of CO can cause death.


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Fig. 6.3 Effect of CO on human body at different concentrations and exposure times (Bartlett)

Carbon monoxide can usually be detected in ambient air around areas where there is

heavy traffic. CO concentration is typically at its highest during rush hours and/or if the

weather is cold there are several cars around starting cold engines. The area of influence of

CO is usually limited, causing mostly local problems, since carbon monoxide is oxidized to

carbon dioxide in the atmosphere fairly quickly. It has to be emphasized that a vehicle should

never be started in a closed garage, and no exhaust gas should ever be allowed to enter the

interior of a vehicle.

6.2.2 Hydrocarbons (HC)

Hydrocarbons in the exhaust are uncombusted or only partially combusted components of the

fuel. They contain hydrogen and carbon. Hydrocarbon pollution results when unburned or

partially burned fuel is emitted from the engine as exhaust, and also when fuel evaporates

directly into the atmosphere. Hydrocarbons are often also referred to as volatile organic

compounds (VOC).

Hydrocarbon compounds found in the exhaust can be aldehydes (CmHn-CHO), ketones

(CmHn-CO) or different carboxylic acids (CmHn-COOH) (Bosch, 2003). Because the

temperature in the engine is high, the hydrocarbon chains may crack due to the heat, and

they can also reconnect to form new kinds of compounds. These reactions may even continue

in the tailpipe. If the fuel travels through the engine completely unburned, hydrocarbons in

the form of CmHn (as in the fuel) are generated.

Hydrocarbons are typically formed in the engine under conditions similar to those

producing carbon monoxide. If there is a lack of oxygen in the combustion chamber,

hydrocarbon emissions increase. A typical case for this is the cold engine enrichment period.


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Furthermore, the formation of unburned hydrocarbons can result from unvaporized fuel

droplets or from a liquid-state fuel layer on the surfaces of the combustion chamber. The

composition of the fuel has, of course, an effect on the hydrocarbon formation. Small isolated

spots in the combustion chamber, such as around the tip of the spark plug or between the

piston and the cylinder wall (above the first piston ring), may generate hydrocarbon emissions

because of a lack of oxygen locally.

As in the case of CO, the catalytic converter has to reach the light-off temperature in

order to be able to convert (oxidize) hydrocarbons into less harmful compounds. The light-off

temperature for hydrocarbons can be higher than for carbon monoxide, and it usually

increases as the converter gets older.

In principle, evaporative hydrocarbon emissions are always released into the atmosphere

when hydrocarbon fuel is poured from one container into another. In many gasoline stations,

a suction device is used nowadays to collect at least part of the hydrocarbon fumes escaping

from the vehicle fuel tank while it is being refilled.

The properties of the fuel also affect the evaporative hydrocarbon emissions. The vapor

pressure of gasoline should be kept as low as possible to minimize evaporative emissions. This

is the task of the fuel refiner. A drawback of low vapor pressure is that it can result in poor

cold starting properties of the fuel. However, blending gasoline with some oxygen-containing

compound (e.g. ethers like MTBE or ETBE or alternatively with alcohol) may result in equal

cold-start properties as before, even though the vapor pressure of the fuel is lowered.

Gasolines of this kind, the so-called oxygenated gasolines, have been used in some heavily

trafficked areas of the industrialized countries since the early 1990s.

Hydrocarbon emissions are mostly gaseous compounds, but they may also take the form of

tiny particles or droplets. Hydrocarbons include many toxic compounds that cause cancer and

other adverse health effects. Hydrocarbons also react with nitrogen oxide in the presence of

sunlight to form ozone, a serious air pollutant in major cities across the world. Ground-level

ozone, in turn, is the primary constituent of smog (EPA 2).

Hydrocarbons come from a great variety of industrial and natural processes. In typical

urban areas, a significant part of hydrocarbons come from road transportation and also from

non-road mobile sources such as construction vehicles. Traditional 2-stroke engines,

lubricated by oil blended in the fuel, are gross-emitters of hydrocarbons. This is caused bythe fact that the lubrication oil consists of heavy long-chained hydrocarbons which do not

combust well. This results in extremely high hydrocarbon emissions from small 2-stroke

engines that are used for mopeds, snowmobiles, chain saws, garden equipment etc.

6.2.3 Nitrogen oxides (NOx)

Nitrogen oxides are not end-products but side-products of fuel combustion, since the

constituents of nitrogen oxides (nitrogen and oxygen) do not originate from fuel but from

ambient air.


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Nitrogen oxides (NOx) is the generic term for a group of highly reactive gases, all of which

contain nitrogen and oxygen in varying amounts. The most significant oxides of nitrogen are

nitrogen oxide (NO) and nitrogen dioxide (NO2). Many of the nitrogen oxides are colorless and

odorless. However, one common pollutant, nitrogen dioxide (NO 2) along with particles in the

air can often be seen as a reddish-brown layer over many urban areas.

Nitrogen oxides form when fuel is burned at high temperatures, as in a combustion

process. The primary man-made sources of NOx are motor vehicles, electric utilities and

other industrial, commercial and residential sources that burn fuels. NOx can also be formed

naturally.

Nitrogen oxides can be controlled in gasoline engines by utilizing the three-way catalyst

which, through the chemical reduction process, converts NOx into nitrogen, carbon dioxide

and water. In diesel engines, which run on an excess amount of air, three-way catalyst

technology cannot be utilized. However, the means of controlling NOx emissions in diesel

engines include retarding injection timing, using exhaust gas recirculation (EGR) and utilizing

new catalytic reduction technology like the SCR (selective catalytic reduction) catalyst, which

uses urea solution as a reductant.

The adverse effects of NOx in the atmosphere include smog formation. Smog is formed

when NOx and volatile organic compounds (VOCs) react in the presence of sunlight. Children,

people with lung diseases such as asthma, and people who work or exercise outside are

susceptible to the adverse effects of NOx such as damage to lung tissue and reduction in lung

function. Ozone can be transported by wind currents and cause health impacts far from

original sources. Millions of people live in areas that do not meet the health standards for

ozone. Other impacts from ozone include damaged vegetation and reduced crop yields.

NOx and sulfur dioxide (SO2) react with other substances in the air to form acids (nitric and

sulfuric acid), which fall to earth as rain, fog, snow or dry particles. Some may be carried by

wind for hundreds of kilometers. Acid rain damages buildings and historical monuments as

well as cars, and also causes lakes and streams to become acidic and unsuitable for many fish

(EPA 3). NOx also reacts with ammonia, moisture, and other compounds to form nitric acid

and related particles. Human health concerns include effects on breathing and the respiratory

system, damage to lung tissue, and premature death.


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Fig. 6.4 Annual amount of NOx emissions (kilotons per year) in Europe in 1995 (People)

One member of the NOx group, nitrous oxide or N2O, is a greenhouse gas. It accumulates in

the atmosphere with other greenhouse gases causing a gradual rise in the earth's

temperature. This will lead to increased risks to human health, a rise in the sea level, and

other adverse changes to plant and animal habitats.

In the air, NOx reacts readily with common organic chemicals and even ozone, to form a

wide variety of toxic products, some of which may cause biological mutations. Examples of

these chemicals include the nitrate radical, nitroarenes, and nitrosamines. Nitrate particles

and nitrogen dioxide can block the transmission of light, reducing visibility especially in urban

areas. The map in Figure 6.4 (above) shows the annual NOx emission in kilotons in different

parts of Europe in 1995.

6.2.4 Particulates (PM)

Particulates, also known as particles or particulate matter (PM), are solid exhaust

components while, as mentioned above, the compounds (CO, HC and NOx) are in the gaseous

state. Particulate emissions are regulated by law for diesel engines, but it seems evident

that, in the future, they will be regulated for gasoline engines, too. This will happen most

likely for at least direct-injected gasoline engines.


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Particulates are formed especially in diesel engines, in which the air-fuel mixture is not

homogenous, meaning that close to the fuel spray nozzles there is less air available for

combustion than at the outer edges of the combustion chamber. The mixture in diesel

engines is lean, meaning that there is, on average, always excess air available in the

combustion chamber compared to the amount of air needed for complete combustion.

However, due to the heterogeneity of the mixture, close to the fuel injector nozzles lack of

sufficient amounts of air may be encountered locally.

Lack of air is one of the main contributors to particulate formation. To limit particulate

formation in diesel engines, the amount of fuel injected has to be limited at low engine

speeds. This, of course, reduces the torque. The use of turbochargers, the very newest types

of which are equipped with electronically controllable vanes (also called variable geometry

turbochargers), has made it possible, along with increased amounts of air available, to

increase the amount of fuel sprayed at low engine speeds, thus increasing the low-rpm torque

without increasing particulate formation.

The actual composition of particulates varies according to the engine and driving

conditions, fuel composition etc., but basically they are formed from an uncombusted carbon

core which is surrounded by fuel and lubricant originated hydrocarbons, water and some

miscellaneous compounds. If the fuel contains sulfur, this too is found in particulates. The

size of particulates can also vary, with typical diesel particulate sizes ranging from 0.01 to 1

m. (Neste)

The most recent research has shown that particulates are also generated in gasoline

engines. This is especially true in the case of direct injection gasoline engines, which are

gaining popularity all the time due to their improved fuel economy. However, the particulate

size in gasoline engine exhaust is very small, which leads to considerably lower total

particulate mass emissions compared to those from diesel engines.

There is evidence, however, that the smallest particulates might pose the greatest danger

to human health, since the smaller the particle is, the further into the respiratory system it

can penetrate. Small particles could find their way deep into the sensitive parts of the lungs

and cause or worsen respiratory disease such as emphysema and bronchitis, and aggravate

existing heart disease (EPA 4). This fact will probably have the consequence that in the

future, also direct injection gasoline engines will be incorporated under particulate emissionregulations.

There is every reason to believe that diesel exhaust particulates can cause cancer,

although studies on humans do not provide sufficient evidence as yet. In performing these

kinds of studies, the difficulty is to prevent the test persons from being exposed to other

cancer-causing substances. In any case, numerous research results indicate elevated lung

cancer rates in occupational groups exposed to diesel exhaust.

In 1998, the California Air Resources Board (CARB) formally listed diesel particulates as a

toxic air contaminant. Extensive scientific literature demonstrates that exposure to diesel

exhaust increases the risk of developing lung cancer and creates other, non-cancer, health

problems, as well.


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6.3 Evaporative emissions

In addition to combustion originated emissions (tailpipe emissions), evaporative emissions are

also generated from motor vehicles. Evaporative emissions are hydrocarbons, or volatile

organic compounds (VOC), that dissipate to the atmosphere from the vehicle's fuel system.

Generally, efforts at the reduction of evaporative emissions include the capturing of

vented vapors from within the vehicle, but also the reduction of emissions released to the

atmosphere when refueling vehicles or whenever liquid hydrocarbon fuels are transferred

from one container to another.

To control the evaporative emissions in modern vehicles, vapors from the fuel tank are

channeled through canisters containing activated carbon instead of being vented to the

atmosphere, as was the case with carbureted engines. The vapors are adsorbed within the

canister, which feeds them into the inlet manifold of the engine. When the vehicle is running,

the vapors are desorbed from the carbon, drawn into the engine and burned.

Evaporative emissions of passenger cars have to be measured as a part of the type

approval procedure, and the result of the test has to be below legislative limit values before

a new car model may enter the market.

Evaporative emissions are measured using the co called SHED-test. When conducting the

shed test, the test vehicle is parked inside a special measuring device, called "a shed", like a

small garage, the airspace of which is completely sealed and isolated from the surrounding

atmosphere. After keeping the vehicle in the shed a certain amount of time at a controlled

and certified temperature, the hydrocarbon concentration of the air inside the shed is

analyzed. The current limit is 2 grams of HC per hour, which may amount to an evaporation of

one liter of gasoline in a month (Wikipedia).

6.4 History of emission legislation

Emission legislation specifies the maximum amount of pollutants allowed in exhaust gasesdischarged from a vehicle or an engine. The first emission standards in the world were

initiated in California. The rationale behind the decisions in California was that air quality

was worsening alarmingly in the South Coast Air Basin, where the city of Los Angeles is

located. Already in the late 1950s, tailpipe emissions from motor vehicles were identified as

key contributors to the ambient air pollution problems encountered.

The gasoline-powered vehicles of those days utilized carbureted engines, the air-fuel ratio

of which varied within a wide range of mixtures in different driving conditions producing

plenty of carbon monoxide, hydrocarbons and nitrogen oxides. Needless to say, the vehicles

had no emission after treatment.


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The city of Los Angeles was heavily trafficked already in those days, and it is surrounded

by mountains which hinder the air from moving around. This phenomenon makes the pollution

from the cars stay in the air and not dilute and dissolve in the atmosphere.

The high population density and substantially large number of vehicles (for the time) in

that relatively small area combined with the given climatic conditions, made the air quality

so bad that legislative measures had to be taken.

Subsequently, in 1964, the State of California became the first region to issue regulations

stating maximum allowable emission levels for all 1966 and later model year new cars (EPA

5). A separate administrative office, the California Air Resources Board (CARB), was founded

at the same time.

The other states of the USA joined California by regulating emissions from motor vehicles

soon after that. In 1966, a very similar statute was passed by the US Congress covering new

cars from 1968 onwards. The next major milestone was passing of the Clean Air Act in 1970,

which established the Environmental Protection Agency (EPA), and gave it the jurisdiction to

control motor vehicle emissions. (Laurikko, 1998)

The first stages of emission regulations limited only carbon monoxide and hydrocarbons. In

response to this, the first catalytic converters appeared in 1975, having only the capability of

oxidizing CO and HC.

The character and adverse effects of NOx and particulates were not realized until several

years later. The next major milestone was reached in 1981, when the USA also began

regulating nitrogen oxides. Subsequently, three-way catalyst technology, capable of oxidizing

CO and HC while simultaneously also reducing NOx, was introduced in 1981.

In Japan, the emission legislation was initiated in 1967, when CO regulation for gasoline

passenger cars came into force. Hydrocarbon regulation began in Japan in 1970, and NOx

regulation in 1975. Since 1981, Japanese emission limit values have been 8 % below the levels

when no limitations were in force. (Minato, 2005)

In Europe, the first laws regulating vehicle emissions were initiated in 1970, when the

European Economic Community (EEC) passed its first directive (70/220/EEC) on the subject.

Already before that, the Inland Transport Committee (ITC), part of the United Nations

Economic Commission for Europe (UN/ECE), had established an expert forum, the Group of

Reporters on Pollution and Energy (GRPE), to collaborate internationally and report on thematter to the Working Party No 29 (WP.29), which deals with the regulations related to the

construction of motor vehicles. (Laurikko, 1998).

Since the original Directive in 1970, several Adaptations and Amendments have been

adopted. The limit values have been lowered step by step, and also the test method

designation has changed several times.

6.5 Emission legislation today


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Today, emissions from internal combustion engines are regulated in dozens of countries

throughout the world. Their regulatory authorities usually apply American, Japanese or

European emission regulations to some degree, although the most recent and most stringent

steps are not enforced in all cases.

The regulated diesel emissions include:

Carbon monoxide (CO)

Hydrocarbons (HC), regulated either as total hydrocarbon emissions (THC) or as non-

methane hydrocarbons (NMHC). One combined limit for HC + NOx is sometimes used

instead of two separate limits.

Nitrogen oxides (NOx), composed of nitric oxide (NO) and nitrogen dioxide (NO2). Other

oxides of nitrogen which may be present in exhaust gases, such as N2O, are not regulated.

Diesel particulate matter (PM), measured by gravimetric methods (meaning mass

determination). Sometimes diesel smoke opacity measured by optical methods is also

regulated.

Emissions are measured over an engine or vehicle test cycle which is an important part of

every emission standard. Usually, light-duty vehicles are tested as complete vehicles on a

chassis dynamometer, and heavy-duty engines are tested as engines-only in an engine

dynamometer.

Regulatory test procedures are necessary to verify and ensure compliance with the various

standards. These test cycles are supposed to create repeatable emission measurement

conditions and, at the same time, simulate real driving conditions of a given application.

Analytical methods that are used to measure particular emissions are also regulated by the

standards.

Emission cycles are a sequence of speed and load conditions performed on a chassis or

engine dynamometer. Emissions measured on vehicle (chassis) dynamometers are usuallyexpressed in grams of pollutant per unit of traveled distance, e.g., g/km. Emissions measured

according to an engine dynamometer test cycle are expressed in grams of pollutant per unit

of mechanical energy delivered by the engine, typically g/kWh.

Depending on the character of speed and load changes, cycles can be divided into steady

state cycles and transient cycles. Steady state cycles are a sequence of constant engine speed

and load modes. Emissions are analyzed for each test mode. Then the overall emission result

is calculated as a (weighted) average from all test modes. In a transient cycle the vehicle

(engine) follows a prescribed driving pattern which includes accelerations, decelerations,

changes of speed and load, etc. Transient cycles usually represent real-world driving better.


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The final test results can be obtained either by analysis of exhaust gas samples collected

in plastic bags over the duration of the whole cycle, or by electronic integration of a fast

response, continuous emission measurement.

Regulatory authorities in different countries have not been unanimous in adopting emission

test procedures. Consequently, many types of test cycles are in use. Since exhaust emissions

depend on the engine speed and load conditions, specific engine emissions which were

measured on different test cycles may not be comparable, even if they are expressed or

recalculated in the same units of measurement. This should be kept in mind when comparing

emission standards from different countries.

Tailpipe emission standards are usually implemented by government ministries responsible

for the protection of the environment, such as the EPA (Environmental Protection Agency) in

the USA. In Europe, the legislation is set by the European Union Directives. The duty to

comply with these standards is on the equipment (vehicle or engine) manufacturer. Typically

all equipment has to be emission certified before it is released to the market. (Dieselnet 1)

6.6 Emission testing stages

In most cases, tailpipe emission legislation requires the emissions of a vehicle or an engine to

be tested at several stages over the whole of the lifetime of a product model. The emissions

usually have to be controlled at three different stages. These are:

type approval

conformity of production

in-use compliance

Type approval (or certification) testing means that the manufacturer brings a new vehicle

or engine model to an emission testing facility and has its product tested according to the

appropriate legislative testing methods. This usually happens when the new model is in itsprototype stage, and the actual production has not started yet.

The purpose of the type approval testing is to provide evidence that the manufacturer of

the product is capable of designing and building a vehicle or an engine that complies with the

current appropriate emission standards. If this is proven, the new product may enter the

market.

Conformity of production (COP) testing is performed for vehicle or engine units, taken

randomly from the production line, to provide evidence that the manufacturer of the product

is capable of producing units, the emissions of which are sufficiently alike with the unit

having been type approved, meaning that they are manufactured in mass-produced with

sufficient exactitude.


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In-use compliance testing is performed for vehicles having been in use for a certain

amount of time. The purpose of this type of testing activity is to make sure that the emission

level of the vehicle does not increase dramatically along with vehicle aging, but stays within

the given range of deterioration.

In-use compliance testing may be implemented for randomly selected vehicles, or in many

cases for every vehicle in use, usually in conjunction with the legally required (annual)

technical inspection. In the USA this type of testing is called the "smog check".

In most cases, in-use compliance testing is performed using simpler measuring methods

than are utilized in type approval and COP testing. This means that usually no chassis

dynamometer is used, but the emissions are measured from an unloaded engine.

6.7 European regulations for light-duty vehicles

6.7.1 General

In Europe, and typically elsewhere, the type approval emission testing of light-duty vehicles

(passenger cars and vans up to 3500 gross vehicle weight) is carried out as complete-vehicle

testing using a road-simulation chassis dynamometer. A simple type of chassis dynamometer,

one which is capable of performing power measurements, is not suitable for emission testing,

since the emission test cycle consists of variable driving speeds. Variable speeds require that

the dynamometer has to feature the inertia-simulation capability, because the vehicle inertia

has to be accounted for when the speed is increasing or decreasing.

The exact road resistance values of the vehicle being tested have to be known based on

calculations and/or road-testing results. These values are then programmed into the chassis

dynamometer to simulate actual driving. The settings of the dynamometer can be checked by

performing a coast-down test on the dynamometer and comparing the results to the

corresponding values measured on a flat road under non-windy conditions.

The emissions are collected over the test using a device called constant volume sampler

(CVS). This device dilutes the exhausts gases with ambient air and measures the volume of

the diluted exhaust. Dilution is used to prevent the moisture in the exhaust condensing andcausing trouble in the analyzers. Another reason is to simulate normal conditions: the exhaust

coming out of the tailpipe is diluted with ambient air anyway.

Constant volume sampler vacuums a fixed pre-adjusted volume of the mixture of exhaust

and dilution air. This means that when the engine load is low and a small amount of exhaust

is generated, more dilution air is sucked through the system, whereas when the exhaust flow

is high, the flow of dilution air is low. This principle makes it possible to measure the

emissions (concentration multiplied by exhaust amount) over a transient test cycle without

knowing the actual concentrations and exhaust flow rates at each moment.

Figure 6.5 illustrates the complete test set-up for a type approval emission test for a

passenger car. Part of the diluted exhaust collected and measured by the CVS system is


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collected in sample bags with a plastic coating called tedlar. Samples are taken from both

diluted exhaust and from the dilution air. When calculating the final results, the possible

emissions originating from the dilution air can thus be eliminated.

Fig. 6.5 Test set-up for a type approval emission test (VTT)

After performing the test, the collected samples are analyzed, and the results are calculated

according to the measured exhaust volume, measured concentrations and densities of the

emission compounds, and distance driven. The final results are then expressed as grams per

kilometer (g/km).

The test conditions, like temperature and humidity, have to be controlled, recorded and

checked that they are within the limits set by the Directives. For example, because high

amounts of moisture in the intake air lowers combustion temperature and also NOxformation, humidity of the test cell has to be controlled and recorded.

When calculating the NOx result, a correction factor calculated from the test conditions is

used. If the humidity of the test cell is high, the correction factor for NOx is greater than 1,

because high humidity has lowered the amount of NOx generated. Under low humidity

conditions, however, high levels of NOx have been generated because of the elevated

combustion temperature, and in this case the value of the NOx correction factor is below 1.

The factor corrects the NOx result as if to represent average humidity conditions.

6.7.2 Performing the test

J.Lauri kko'96

Chassis dyno

Dyno anddriver's aid

control

Driver'said

display

Chassis DynoControl

CVS-system

Samplebags

Dilution Air

UndilutedSample

(optional)

DilutedExhaust

Printout

Storage

Calculations anddata acquisition

Gasanalysis

COCO

HCNOx

2

Exhaust evacuation

Dilutionair

Rawexhaust


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The test cycle in the European test type consists of periods of steady acceleration, steady

speed and steady deceleration. The test is divided into two parts representing urban and

extra-urban driving. The maximum speed in the urban part is 50 km/h and in the extra urban

part is 120 km/h. The duration of the test is 1180 seconds (19 min 40 seconds), and the

distance driven is 11.007 kilometers. Average speed is 33.6 km/h (Figure 6.6). The engine and

emission measurement are both started simultaneously at the beginning of the test.

The New European Driving Cycle

0

20

40

60

80

100

120

140

0 200 400 600 800 1000 1200

time [s]

speed[km/h]

Fig. 6.6 The new European driving cycle

The cycle has been used as such from the beginning of the Euro 3 regulations, which

became effective in the year 2000. Before that, an extra idling period of 40 seconds was

applied before the emission sampling started. Needless to say, the old procedure was not a

realistic method of determining the amount of emissions, because the highest concentrations

right after cold start were not accounted for. Before 1991, only the urban part (the first 780

seconds) of the test was used.

During the test, the driver drives the vehicle just like s/he would drive it on the road.

S/he has a computer screen, called a driver's aid, which shows him or her the required speed

and use of gears. The driving cycle is programmed as a graphic curve in the system, and the

actual driving speed measured by the dynamometer is presented to the driver as a moving dot

on the screen. The driver's responsibility is to keep the dot on top of the speed curve by

moving the accelerator pedal as little and as slowly as possible.

The urban part of the test cycle consists of four elementary cycles (195 seconds). In each

of the elementary cycles, the car is accelerated from zero three times (Figure 6.7).

During the first acceleration, only first gear is used, the speed is increased to 15 km/hfollowed by a steady speed phase before bringing the speed back to zero for the next idle


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period. During the second acceleration, first gear is used up and till 15 km/h, when the gear

is switched to second, and the speed is increased to 32 km/h before slowing down. During the

third acceleration, after first and second gears, third gear is used from a speed of 32 km/h

upwards.

ECE 15 urban cycle

0

10

20

30

40

50

60

70

0 30 60 90 120 150 180

time [s]

speed

[km/h]

Fig. 6.7 Elementary cycle of the urban part of the European test cycle

In the extra-urban part of the test, constant speeds of 70 km/h, 50 km/h, 70 km/h, 100

km/h and, briefly, 120 km/h are used.

A lot of experience is required for the driver to be able to follow the required speed curve

exactly enough. Usually, a beginner driver overacts and moves the gas pedal too much when

correcting the speed that has drifted out of the required value.

As already mentioned, the cycle designation also determines the gears that the driver is

supposed to use. The gear changing pattern is the same for all light-duty vehicles, which

means that it can be more suitable for the gear ratios of some vehicles than those of others.

On the other hand, the gear changing pattern of the designated emission and fuel

consumption test cycle may be one of the factors the vehicle manufacturer considers, whenselecting the gear ratios.

In the case of automatic transmission, the gear selector is set to "D" position, and the

driver allows the selection of gears to happen automatically.

The acceleration and deceleration rates of the test cycle are quite low. As such, the cycle

does not represent actual aggressive driving of today very well. In most real-world driving

situations the speed changes are faster, and constant speed is used only seldom.

Before a vehicle can be tested, the fuel in the tank has to be replaced by a designated

test fuel. Also, the vehicle has to be driven on the dynamometer according to certain

procedures during the day preceding the actual test. This is called preconditioning the

vehicle.


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The need for preconditioning the vehicle is due to the fact that the light-off temperature

and general functioning of the catalytic converter may vary depending on the type of use the

vehicle has experienced just before the test. For example, if the vehicle has been used only

for short cold-running periods preceding the test, the catalytic converter would be sooty and

would not function efficiently. On the other hand, if the vehicle has been used only for long

high-speed motorway driving before the test, the catalytic converter would be exceptionally

clean and effective at the time the test begins. The preconditioning of the vehicle evens out

these differences.

After the preconditioning of the vehicle is completed, the vehicle is soaked(i.e., left to

stand) under controlled temperature conditions for a certain amount of hours (in practice,

overnight). The engine is then not started until next day, at the very moment when the actual

test begins. As a result, type approval emission testing takes quite a long time. If something

goes wrong, the preconditioning has to be re-done, and the vehicle soaked overnight again.

6.7.3 Limit values

Over the years, the Directives have established several sets of limit values, which have

become stricter and stricter each time a new set of values has been issued. Figure 6.8

illustrates the development of the limit values from 1970, when the first limit values were

published, until today. It can be seen that current limit values for passenger cars are roughly

3 to 5 % compared with the typical values before limitations.

Fig. 6.8 Development of the European limit values for passenger cars

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

CO

HC

NOx

0

10

20

30

40

50

60

70

80

90

100

Psttaso[%]

Vuosi

Pstlaji

CO

HC

NOx

100% = taso ennen mryksi (=ECE15/00)

Summa

HC+NOx >

CO

HC

NOx

< 5%

< 5%

< 3%

Emissionlevel[%]

Year

100 % = The level before regulations(=ECE 15/00)

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

CO

HC

NOx

0

10

20

30

40

50

60

70

80

90

100

Psttaso[%]

Vuosi

Pstlaji

CO

HC

NOx

100% = taso ennen mryksi (=ECE15/00)

Summa

HC+NOx >

CO

HC

NOx

< 5%

< 5%

< 3%

Emissionlevel[%]

Year

100 % = The level before regulations(=ECE 15/00)


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Numerical values for the limit values from the Euro 1 stage onwards are presented in Table

6.1. It can be seen that the Euro 3 CO limit value for gasoline cars (2.30 g/km) is higher than

the preceding corresponding Euro 2 value (2.2 g/km). This seems strange, since, usually a

new standard is lower than the old one. The explanation for this is the change in the test

method. As already mentioned, until the introduction of the Euro 2 stage, the engine was

idling for 40 seconds before the measurement started. When Euro 3 became effective, all the

exhaust was collected right from the very start-up of the engine. This makes the Euro 3 CO

regulation much tighter than the old one, even though the numerical limit value is higher.

6.7.4 Cycle beating

The expression cycle beating refers to a way of calibrating an engines emission control

system in such a way that the emissions are low for the load conditions present during theofficial emission test cycle, but can be much higher when the engine is operating outside of

the load/engine speed range used in the test.

In many cases, the fuel injection system of a gasoline engine can be programmed so that

the air-fuel ratio (lambda value) is kept at the stochiometric value only at low load levels and

low engine speeds, which are the load conditions utilized during the emission test. Above this

range of engine operation, mixture enrichment is often used, and this leads to dramatically

increased CO and HC values in the exhaust.

This may not be known by the general public, who may believe that they can press down

on the accelerator pedal as hard as they want because the catalytic converter in the vehicleTable 6.1 Numerical values for the passenger car limit values in Europe (Dieselnet 2)


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will keep the emissions low. Unfortunately, this is not the whole truth. In many cases the

emissions burst up from the rated values when the vehicle is accelerated hard.

A Swedish study on this issue, conducted in 1998 (Kgeson, 1998), provides evidence for

the assumptions mentioned above. Figure 6.9 illustrates the maximum power values as a

function of engine speed for two passenger cars. There are two curves presented for both

vehicles. The continuous curve indicates the power measured with regular fuel injection

settings programmed by the manufacturer. The lower curve (dotted line) indicates the

maximum power, measured when the mixture was kept at the lambda = 1 value.

The differences between the continuous and dotted curves illustrate the margin in power

output between the rated power and the power achieved at a mixture setting giving the

lowest possible emissions. It can be seen that the car on the left is only able to reach very

low power at the setting optimized for emissions. This kind of behavior can be called cycle

beating. The car on the right performs much better in this respect.

In the late 1990s, several heavy-duty truck engine manufacturers in the USA were caught

out manipulating the engine operation to release low emissions only at the engine operating

points used in the test cycle. The exposure of this cycle beating activity led to penalties and

resulted in substantial negative publicity for the manufacturers involved.


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Fig. 6.9 Differences in power in two passenger cars when the air-fuel ratio is at the manufacturerssetting and when it was kept at lambda = 1 (Kgeson)

6.8 European regulations for heavy-duty vehicles

Unlike in the case of passenger cars and vans, which are tested as complete vehicles, the

emission certification tests for heavy-duty transportation vehicles are conducted as engine-

only tests on an engine dynamometer. Engines used in heavy-duty vehicles are mostly diesel

engines, but also the use of gaseous fuel powered engines is increasing because of

environmental reasons.

The reasons for engine-only testing are very practical. Firstly, large-scale chassis

dynamometers capable of handling heavy-duty vehicles are very rare, and secondly, the

heavy-duty engines are used in so many applications and variations of vehicles that the large

amount of combinations that should be tested would made the complete-vehicle testing

method too work-consuming and too costly.

In the case of heavy-duty vehicles, the same engine is typically used in vehicles with

different transmissions and final drives, different amounts and different types of axles,

different states of load, different wheelbases and different weights of the vehicle. It is self-

evident that the amount of possible combinations make complete-vehicle testing unthinkable.

Before the year 2000, the European certification test method for heavy-duty engines

utilized a steady-state type test cycle only. The test used was called the ECE-R49.

From the Euro 3 regulations onwards (i.e., after 2000), the ECE-R49 test was replaced by a

new steady-state test, called the ESC (European Steady Cycle). Also, an additional transienttype test, called ETC (European Transient Cycle), became at the Euro 3 level compulsory for


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engines having either advanced emission after-treatment systems (in other words, particulate

traps) and/or NOx catalysts. An oxidation catalyst was not considered an advanced after-

treatment system, so engines equipped with an oxidation catalyst were not required to take

the ETC test (Directive 1999).

From the Euro 4 level (2005) on, both steady-state (ESC) and transient type (ETC) tests

have to be passed before the certification for a heavy-duty engine is granted. Also, a smoke

opacity test (ELR, European Load Response) is required. This applies to all types of diesel

engines, regardless of their emission control systems. For gaseous fuel powered engines, only

the ETC test is required (Directive 1999).

6.8.1 The ECE-R49 test

The ECE-R49 test is a 13-mode test, where the engine is measured at idle and at five load

levels at two engine speeds. The idle is measured three times, which make the total amount

of measuring points equal to 13.

Table 6.2 presents the measuring points and the measuring sequence of the ECE-R49 cycle.

It can be seen that idle conditions are measured at the beginning, in the middle and at the

end of the test.

Table 6.2 Measuring points and test sequence of the ECE-R49 test (Dieselnet 3)

Figure 6.10 illustrates the measuring points of the ECE-R49 test. The numbers in the circles

represent the order of the measuring points, and the size of the circles visualize the

weighting factor of each point. The weighting factors are also marked next to the circles.


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Fig. 6.10 Schematic view of the test sequence of the ECE-R49 test (Dieselnet 3)

6.8.2 The ESC test

The ESC test is a modified form of the ECE-R49 test. It also has 13 modes, but there are 3

engine speeds instead of 2. Additionally, the lowest load level, 10 %, has been dropped. The

measuring points and the test sequence are presented in Table 6.3

Table 6.3 Measuring points and test sequence of the ESC test (Dieselnet 4)


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Figure 6.11 illustrates the measuring points of the ECS test. The numbers in the circles

represent the order of the measuring points, and the size of the circles show the weighting

factor of each point. The weighting factors are also marked next to the circles.

Fig. 6.11 Schematic view of the test sequence of the ESC test (Dieselnet 4)

In Figure 6.11 three additional points, to be determined by the certification personnel, are

marked. This means that the person in charge of the measuring procedure, has to select three

load points between engine speeds "A" and "C" and between load levels of 25 % and of 100 %

maximum. At these additional measuring points, the NOx concentration of the exhaust is

measured. This procedure has been set up in order to prevent the cycle beating discussed

earlier.


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The three engine speeds used in the ESC test are marked as "A", "B", and "C". The

determination of these points is presented in Figure 6.12. The speed "nlo" is the speed below

the speed producing maximum power (Pmax), at which the engine delivers 50 % of its

maximum (rated) power. The speed "nhi" is the speed above Pmax, at which the engine

delivers 70 % of its maximum power. The speed B is in the middle of the speeds nlo and nhi,

whereas the speed A is in the middle of the speeds nlo and B, and the speed C is in the

middle of the speeds B and nhi (Directive 1999). Mathematically this can be presented as

follows:

A = nlo + 25 % (nhi - nlo)

B = nlo + 50 % (nhi - nlo)

C = nlo + 75 % (nhi - nlo)

Fig. 6.12 Determination of the engine speeds in the ESC test (Directive)

The speed nref (=nlo + 95 % (nhi - nlo)) in Figure 6.12 is needed for the ETC test only, and

is not used in the case of the ESC test.

The limit values for the ESC test cycle are presented in Table 6.4 (Directive 1999). The

smoke opacity limit values in the ELR (European Load Response) test are also presented in the

rightmost column of the table.

Table 6.4 Limit values of the ESC (and the ELR) tests.


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Table 6.4 also shows a new vehicle category designation; that of EEV. The EEV, or

Environmentally Enhanced Vehicle, is a vehicle category that reaches lower emission values

than those required from every vehicle. This gives the governments of the countries of the

European Union the possibility to grant, for example, tax relief for vehicles that fulfill the

EEV designation. This is a way to make early (earlier than compulsory) purchasing of the best

possible emission control technology economically attractive for a new vehicle buyer.

6.8.3 The ETC test

The ETC test has been generated by collecting data from real-world driving. It simulates

urban, rural and motorway driving. The driving speed and engine conditions (speed and

torque) were recorded during an actual driving situation, and a certified emission cycle was

established on the basis of the results obtained. Figure 6.13 presents the time - driving speed

pattern that lies behind the ETC cycle.


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Fig. 6.13 The time - driving speed pattern behind the ETC test (Dieselnet 5)

Figure 6.14 shows the variation in engine speed during the ETC test. It can be clearly seen

that variations in engine speed are smaller in motorway than in rural or urban driving.

Fig. 6.14 The time - engine speed pattern of the ETC test (Dieselnet 5)

In Figure 6.15, the engine torque variation during the ETC test is shown. The torque varies

quite rapidly even at the motorway-simulating phase (end part of the test). It is also

noteworthy that the torque quite often reaches below-zero values. These phases in the test

cycle simulate engine braking situations. In real driving, engine braking occurs when the

vehicle is moving and the driver does not press the accelerator pedal, but the inertia

(movement) of the vehicle forces the engine to run.


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During the engine braking simulation stages in the ETC test, the engine dynamometer acts

like an electric motor and forces the test engine to rotate rather than absorbs power from it.

Fig. 6.15 The time - engine torque pattern of the ETC test (Dieselnet 5)

In terms of equipment needed for running the ETC test, the rapid variations in engine

speed and torque, as well as the requirement to simulate engine braking, make the use of a

so-called active engine dynamometer a must. The active type engine dynamometers are very

expensive devices that have extremely sophisticated computerized control systems and can

also deliver power (during engine braking simulations) in addition to absorbing it. An active

engine dynamometer at the Technical Research Center of Finland, capable of handling power

levels up to 400 kW, is illustrated in Figure 6.16.

Fig. 6.16 The active engine dynamometer for ETC testingat the Technical Research Center of Finland (VTT)


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Limit values for the ETC test are presented in Table 6.5. It has to be noted that instead of

limiting the total amount of hydrocarbons (HC, also abbreviated as THC), the hydrocarbon

limits for this transient type test are given as non-methane hydrocarbons (NMHC). The NMHC

value can be determined, for example, by measuring both the total hydrocarbon (THC) and

the methane (CH4) values and subtracting the methane proportion from the total value.

For the ETC test, in addition to the NMHC limit, there is also a separate limit value for

methane (CH4). The methane limit is applicable to natural gas engines only. Methane is the

main constituent of natural gas, so the amount of unburned methane has to be limited. This is

especially important because the methane molecule is fairly sturdy and it is more difficult to

oxidize in the catalytic converter than other hydrocarbon compounds. Usually, natural gas

engines utilize catalysts, the chemical composition of which is explicitly optimized for

methane oxidation.

Methane itself is not considered to be toxic or reactive. However, methane emissions

became more of an issue after it was realized that methane is a greenhouse gas trapping the

heat in the atmosphere like carbon dioxide (CO2), but at a rate about 20 times stronger.

Among the ETC test limit values, there are also separate values for the EEV vehicle

category discussed earlier in conjunction with the ESC test.

Table 6.5 Limit values of the ETC test


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6.8.4 The ELR test

The ELR engine test was introduced by the Euro 3 emission regulation, with effect from the

year 2000, for the purpose of smoke opacity measurement from heavy-duty diesel engines.

The test consists of a sequence of three load steps at each of the three engine speeds A

(cycle 1), B (cycle 2) and C (cycle 3), followed by cycle 4 at a speed between speed A and

speed C and a load between 10% and 100%, selected by the certification personnel. Speeds A,

B, and C are the same as in the ESC test, and they were defined earlier. The sequence of

dynamometer operation on the test engine is shown in Figure 6.17 (Dieselnet 6).

In the ELR test, the engine load is increased rapidly three times at each of the enginespeeds from 10 to 100 %, while the engine dynamometer keeps the engine speed constant. In

the ELR test, there are 3 designated engine speeds (cycles 1 to 3) and the fourth one (cycle

4). The purpose of cycle 4 is to prevent cycle beating. In cycle 4, both the engine speed and

the starting load level before increasing the load to 100 %, are to be selected by the testing

personnel. This makes it very difficult for the engine manufacturer to design the engine to

have good emissions performance only during the conditions existing in the known part of the

test cycle.

In the ELR test, smoke measurement values are continuously sampled during the test with

a frequency of at least 20 Hz. The smoke traces are then analyzed to determine the final

smoke values by calculation (Dieselnet 6).


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Figure 6.17 The ELR test

6.8.5 Conclusion

It is easy to see that steady-state testing does not represent real-world driving. Even in the

case of motorway driving at a relatively constant speed, the engine power varies all the time

because of wind conditions and the small inclinations (gradients) in the road, even though

they are not easily visible. This makes even steady-speed driving very transient in terms of

how the engine experiences it. Needless to say that driving in cities and in heavy traffic

provides even more transient conditions for the engine. Nevertheless, with the introduction

of a transient type test in the year 2000, emissions testing took a huge step forward in terms

of cycle correspondence to real-world conditions. In addition, the use of transient cycles

makes it more and more difficult for the manufacturer to commit cycle beating.

Review questions

1. What are the differences between the air quality emissions and greenhouse gas emissions?

2. What effects can CO, HC and NOx have on humans?

3. Why does a lean mixture contribute to the formation of PM in diesel engines?

4. How are the stochiometric ratio and the lambda value related?

5. What happens when the lambda value is greater than 1 in a) diesel engines, and b)gasoline engines?


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6. How effective do you think emission legislation has been in reducing emissions worldwide?

7. Can you suggest some other measures to reduce emissions worldwide?

8. What are the advantages and disadvantages of emissions testing in a laboratory and

testing under real driving conditions?

9. Why is laboratory testing used - in other words, why isnt all emission testing carried out

under actual road driving conditions?

Documents

Chap 6 About Emission