ME6016 ADVANCED I.C ENGINES UNIT III

UNIT III - POLLUTANT FORMATION AND CONTROL

FORMATION OF POLLUTANTS
 There are some unburned or partially burned hydrocarbons in the
exhaust.
 The amount is insignificant from an energy standpoint, but it is
objectionable from the viewpoint of its odour, its photochemical smog,
and from the standpoint of its having a carcinogenic effect.
 The products of photochemical smog cause watering and burning of the
eyes, and affect the respiratory system, especially when the respiratory
system is marginal for other reasons.
26 December 2017 ME 6016 ADVANCED IC ENGINES 2

HYDROCARBON EMISSIONS FROM SI ENGINES
 The most widely accepted causes for hydrocarbon emissions in exhaust gases of spark
ignition engines are:
1. Flame quenching at the combustion chamber walls, leaving a layer of unburned fuel-air
mixture adjacent to the walls.
2. Crevices in the combustion chamber, small volumes with narrow entrances, which are
filled with the unburned mixture during compression, and remains unburned after flame
passages, since the flame cannot propagate into the crevices. The main crevice regions
are the spaces between the piston, the piston rings and the cylinder walls. The other
crevice regions are the threads around the spark plug, the space around the plug centre
electrode, crevices around the intake and exhaust valve heads, and the head gasket
crevice.

3. The oil film and deposits on the cylinder walls absorb fuel during intake
and compression, and the fuel vapour is desorbed into the cylinder during
expansion and exhaust.
4. Incomplete combustion, either partial burning or complete misfire,
occurring when the combustion quality is poor, e.g. during engine
transients when air-fuel, exhaust gas recirculation, and spark timing may
not be adequately controlled.

• All these processes, except misfire, result in unburned hydrocarbons close to the
combustion chamber walls. Mixing of unburned hydrocarbons with the bulk cylinder
gases occurs during expansion and the exhaust blowdown processes. During the
blowdown process a high concentration of hydrocarbons is released from the cylinder
through the exhaust valve.
• During the exhaust stroke the piston pushes most of the remaining fraction of the
cylinder mass with its high hydrocarbon concentration into the exhaust.
• The residual gases in the cylinder thus contain a high concentration of hydrocarbons.
• Unburned hydrocarbons are thus exhausted in two pulses, the first peak is obtained
with the exhaust blowdown and the second occurs towards the end of the exhaust
stroke.

Hydrocarbon emissions from CI engines
 The CI engines operate with an overall fuel-lean equivalence ratio,
therefore they emit only about one-fifth of the hydrocarbon emissions of
an SI engine. The following are the major causes for hydrocarbon
emissions in the exhaust of CI engines:
1. The diesel fuel contains components of higher molecular weights on
average than those in a gasoline fuel, resulting in higher boiling and
condensing temperatures.
 This causes some hydrocarbon particles to condense on the surface of the
solid carbon soot generated during combustion.
 Most of this is burned as mixing continues and the combustion process
proceeds but a small amount is exhausted out of the cylinder.

2. The air-fuel mixture in a CI engine is heterogeneous with fuel still being added
during combustion. It causes local spots to range from very rich to very lean and
many flame fronts exist at the same time unlike the homogeneous air-fuel mixture of
an SI engine that essentially has one flame front.
 Incomplete combustion may be caused by undermixing or overmixing.
 With undermixing, in fuel-rich zones some fuel particles do not find
enough oxygen to react with, and in the fuel-lean zones some local spots
will be too lean for combustion to take place properly.
 With overmixing, some fuel particles may be mixed with burned gases
and it will therefore lead to incomplete combustion.

3. A small amount of liquid fuel is often trapped on the tip of the injector
nozzle even when injection stops. This small volume of fuel is called sac
volume.
 This sac volume of liquid fuel is surrounded by a fuel-rich environment
and therefore it evaporates very slowly causing hydrocarbon emissions in
the exhaust.
4. CI engines also have hydrocarbon emissions for some of the same
reasons as SI engines do, e.g. flame quenching, crevice volume, oil-film
and deposits on the cylinder wall, misfiring, etc.

Carbon Monoxide (CO)
 Carbon monoxide is toxic. The hemoglobin in the blood, which carries oxygen to the different parts of
the body, has a higher affinity for carbon monoxide than for oxygen. The percent carboxy hemoglobin
gradually increases with time to an equilibrium value which depends upon the carbon monoxide
concentrations.
 Carbon monoxide is generated in an engine when it is operated with a fuel-rich equivalence ratio as
there is not enough oxygen to convert all carbon to carbon dioxide. For fuel-rich mixtures, CO
concentrations in the exhaust increase steadily with the increasing equivalence ratio. The engine runs
rich when it is started or when it is accelerated under load. For fuel-lean mixtures, CO concentrations
in the exhaust are very low and are of the order 10-3 mole fraction.
 Poor mixing, local rich regions, and incomplete combustion create some CO. The SI engines often
operate close to stoichiometric at part load and operate fuel rich at full load. Under these conditions,
the CO emissions are significant. However, CI engines operate well on the lean side of stoichiometric
and therefore produce very little CO emissions.

Formation of CO in IC Engines
 Formation of CO is well established.
 Locally, there may not be enough O2 available for complete oxidation and some of the carbon in the
fuel ends up as CO.
 The amount of CO, for a range of fuel composition and C/H ratios, is a function of the relative air-fuel
ratio.
 Even at sufficient oxygen level, high peak temperatures can cause dissociation.
 Conversion of CO to CO2 is governed by reaction
HCOOHCO  2

Formation of Carbon Monoxide

Air/Fuel Ratio Vs Carbon Monoxide Concentration

Formation of CO in CI Engines
 The mean air-fuel mixture present in the combustion chamber per cycle is far leaner
in the diesel engine than in the SI engine.
 Due to a lack of homogeneity of the mixture built up by stratification, however,
extremely “rich” local zones are exist.
 This produces high CO concentrations that are reduced to a greater or lesser extent
by post-oxidation.
 When the excess-air ratio increases, dropping temperatures cause the post-
oxidation rate to be reduced.
 The reactions “freeze up”.
 However, the final CO concentrations of diesel engines therefore are far lower than
in SI engines.
 The basic principles of CO formation, however, are the same as in SI engine.

Sources of CO formation
 Over mixing of fuel
 Occurs in conventional diesel combustion
 Due to low peak combustion temperature
 Associated with lean combustion during ignition delay period
 Under mixing of fuel
 Product of rich premixed combustion
 CO fails to mix with sufficient O2 to complete oxidation
 CO formation is function of chemical kinetics
 Rate of oxidation of CO is slow as compared to other hydrocarbons
 Thus CO lags behind in oxidation even with the presence of O2

Oxides of Nitrogen (NOx)
• The oxides of nitrogen tend to settle on the haemoglobin in the blood. The most undesirable toxic
effect of oxides of nitrogen is their tendency to join with the moisture in the lungs to form dilute nitric
acid. NOx is one of the primary causes of photochemical smog (smoke + fog). Smog is formed by the
photochemical reaction as follows:
 NO2 + energy from sunlight NO + O + Smog
 Monoatomic oxygen reacts with O2 to form ozone (03) as follows:
 O + O2 = O3
• Ozone is harmful to lungs and other biological tissues. It is harmful to crops and trees. It reacts with
rubber, plastics and other materials causing damage.
• Most of the oxides of nitrogen comprise nitric oxide (NO), a small amount of nitrogen dioxide (NO2)
and traces of other nitrogen oxides. These are all grouped together and the group is called NOx.
• NOx is mostly formed from atmospheric nitrogen. There are a number of possible reactions that form
NO. NO forms in both the flame front and the post flame gases.

FORMATION OF POLLUTANTS
• N, O, OH are formed from the dissociation of N2, O2 and H2O vapour at high temperatures that exist in
the combustion chamber (2500-3000 K).
• The higher the combustion reaction temperature, the more diatomic nitrogen (N2) will dissociate to
monatomic nitrogen (N) and more NOx will be formed.
• At low temperatures, a very small quantity of NOx is created. The flame temperature is maximum at the
stoichiometric equivalence ratio (0 = 1.0) but maximum NOx, is formed slightly at a lean equivalence
ratio (0 = 0.95). At this condition the flame temperature remains very high but excess oxygen helps in the
formation of more NOx. The most important engine variables that affect NOx emission are the fuel/air
equivalence ratio, the burned gas fraction (EGR and residual gas fractions) and combustion duration
within the cylinder. NOx is reduced in modem engines with fast-bum combustion chambers.
• If ignition spark is advanced, the cylinder temperature will be increased and more NOx will be
produced. CI engines with divided combustion chambers and indirect injection (DI) tend to generate
higher levels of NOx.
Some of the NO forming reactions are:

PARTICULATES
• The particulates from SI engines are lead, organic particulates including soot and sulphates. Gasoline may
contain some sulphur, which is oxidized within the engine cylinder to form SO2.
• is oxidized to SO3 which combines with water to form a sulphuric acid aerosol.
• Leaded gasolines emit lead compounds. Soot emissions (black smoke) can result from combustion of overly
rich mixtures. In properly adjusted spark-ignition engines, soot in the exhaust is not a significant problem.
• Diesel particulates consist mainly of combustion generated carbonaceous material (soot) on which some
organic compounds have been absorbed.
• Most particulates are generated in the fuel rich zones within the cylinder during combustion due to
incomplete combustion of fuel hydrocarbons; some particulate matter is contributed by the lubricating oil.
• These are undesirable odorous pollutants. Maximum particulate emissions occur when the engine is under
load. At this condition, maximum amount of fuel is injected to obtain maximum power from the engine. It
results in a rich mixture and poor fuel economy.
• At temperatures above 500°C, soot particulates appear as clusters of a large number of solid carbon spheres
with individual diameters of about 15 to 30 nm.

Particulates
 A high concentration of particulate matter (PM) is manifested as visible smoke in the exhaust gases.
 Particulates are any substance other than water that can be collected by filtering the exhaust,
classified as:
 Solid carbon material or soot.
 Condensed hydrocarbons and their partial oxidation products.
 Diesel particulates consist of solid carbon (soot) at exhaust gas temperatures below 500oC, HC
compounds become absorbed on the surface.
 In a properly adjusted SI engines soot is not usually a problem .
 Particulate can arise if leaded fuel or overly rich fuel-air mixture are used.
 Burning crankcase oil will also produce smoke especially during engine warm up where the HC
condense in the exhaust gas.

• As the temperature decreases below 500°C during expulsion, the particles become coated with HC and with traces
of other components.
• The words particulates and soot are often used synonymously, but there is a difference in nature between these two
emissions.
• Dry soot is usually the carbon that is collected on a filter paper in the exhaust of an engine.
• The unit of measurement of soot is usually the Bosch Smoke Number, which is assessed by the reflectance of a filter
paper on which the soot has been collected.
• Particulates contain more than simply the dry soot; they are the soot particles on which the other compounds, often
the polycyclic aromatic hydrocarbons (PAH), have condensed.
• The PAH compounds have a tendency to be carcinogenic.
• The level of particulates increases with the sulphur content in the fuel. Particulates are measured by trapping the
particles on glass-fibre filter papers placed in a dilution tunnel, and then weighing the quantity.

Particulate composition of diesel engine exhaust

Mechanism of Formation of Particulates (soot)
 The soot formation process is very fast.
 10 – 22 C atoms are converted into 106 C atoms in less than 1 ms.
 Based on equilibrium the composition of the fuel-oxidizer mixture soot ,
formation occurs when x ≥ 2a (or x/2a ≥ 1) in the following reaction:
)()2(
2
2 22 sCaxH
y
aCOaOHC yx 

 Experimentally it is found that the critica C/O ratio for onset of soot formation
is between 0.5 and 0.8.
 The CO, H2, and C(s) are subsequently oxidized in the diffusion flame to CO2
and H2O via the following second stage.
OHOHCOOsCCOOCO 2222222
2
1
)(
2
1

Any carbon not oxidized in the cylinder ends up as soot in the exhaust!

NOx Formation in I.C. Engines
 Three chemical reactions form the Zeldovich reaction are:
Forward rate constants:
 
 
 Tk
Tk
Tk
f
f
f
/450exp101.7
/4680exp108.1
/38370exp108.1
10
,3
7
,2
11
,1



Zelodvich reaction is the most significant mechanism of NO formation in IC engines.

MEASUREMENT OF POLLUTANTS
• The measurement of exhaust emissions is very important for the control
of air pollution from IC engines.
• CO concentrations are measured by infrared absorption,
• NO concentrations are measured by chemi-luminescence and
• Unburned HC are measured by flame ionization detector.

Non-dispersive Infra-red (NDIR) Analyzer
• The NDIR analyzers are used for measuring the concentrations of carbon
monoxide and carbon dioxide. This device is based on the principle that
the infrared energy of a particular wavelength, peculiar to a certain gas,
will be absorbed by that gas. The infrared energy of other wavelengths
will be transmitted by that gas.
• Carbon dioxide absorbs infrared energy in the wavelength band of 4 to 4.5
microns (m) and transmits the energy of the surrounding wavelengths.
The carbon monoxide absorption band is between 4.5 and 5 microns (gm).

Non-dispersive Infra-red (NDIR) Analyzer
• Nitric oxide (NO) has also a weak absorption band, allowing it to be analyzed by NDIR, but lack of
sensitivity and interference by water vapour do not give high accuracy with low concentrations.
• A schematic arrangement of the IR analyzer is shown in Figure.
• A wideband infrared radiation source consists of a heated wire, which is placed in a quartz tube
mounted in the source block.
• Radiation from the source is reflected within the mounting block and passes out of a symmetrical pair of
rectangular apertures as two parallel beams into the two separate cells a sample cell and a reference cell.
• These cells are internally highly polished and gold plated to ensure high transmission of radiation.
• After passing through these cells the infrared radiation is received in two separate detector cells, which
are full of the gas whose concentration is to be measured.

• The two detector cells contain equal amounts of this gas and are separated by a flexible diaphragm.
• The sample cell is a flow-through tube that receives a continuous stream of the mixture of gases to be
analyzed.
• When the particular gas to be measured is present in the sample, it absorbs the infrared radiation at its
characteristic wavelengths. The percent of radiation absorbed is proportional to the molecular
concentration of the component of interest in the sample.
• The sample cells may be divided by quartz windows into various lengths to give different ranges of
sensitivity.
• The quartz windows do not absorb infrared energy in the region of interest. Low concentrations are best
measured by longer cells so that more molecules of interest are present.
• The unused sample cells are generally flushed with a non-infrared absorbing gas such as oxygen or
nitrogen, or with a gas free of the components being measured, e.g. fresh air for carbon monoxide
analyzers.

• The reference cell is sealed and is physically identical to the sample cell. It is filled with an inert gas
(usually nitrogen) which does not absorb the infrared energy of the characteristic wavelength of the
species of interest.
• The radiant energy, after passing through the cells, heats the gas in the corresponding chamber of the
detector. Since no radiant energy is absorbed in the reference cell, the corresponding chamber in the
detector is heated more and its pressure becomes higher than that in the other chamber.
• This pressure differential causes the diaphragm to move and vary the capacitance. Therefore, the
variation in the capacitance is proportional to the concentrations of the species of interest in the exhaust
sample.
• The radiation from the source is interrupted by a rotating two-bladed shutter driven by a synchronous
motor.
• The shutter is placed between the infrared source and the cells.

• When the shutter blocks the radiation, the pressure in the two compartments of the detector is equal
because there is no energy entering either of the chambers of the detector.
• This allows the diaphragm to return to its neutral position. As the shutter alternatively blocks and
unblocks the radiation, the diaphragm fluctuates causing the capacitance to charge cyclically.
• This sets up an ac signal, which is impressed on a carrier wave provided by a radio-frequency oscillator
(amplifications of ac signals have better drift-free characteristics than the amplifications of dc signals).
Additional electronic circuitry in the oscillator unit demodulates and filters the resultant signal.
• This signal is then amplified and rectified to a de signal which is measured by a meter or recorder. The
final dc signal is a function of the concentration of the species of interest in the exhaust sample.

• To set the zero point, a non-infrared-absorbing gas, e.g. dry air, is passed through the instrument. For the
other points on the scale, calibrating gases with known concentrations are passed through the analyzer.
• An error in the NDIR readings may arise if the exhaust sample contains other species that can absorb
radiation at the same frequencies that the gas in the detector will absorb.
• In order to minimize this interference, a large concentration of the interfering gas is placed in the filter
cells.
• The analyzer zero is then set with this large concentration of the interfering gas.

FLAME-IONIZATION DETECTOR (FID)
• Some hydrocarbons have an infrared absorption at 3.4 microns, but some others, notably aromatics,
have almost none. Only about 50 % of exhaust hydrocarbons is measured by NDIR, therefore, this
method is not suitable for the measurement of HC concentrations.
• The flame ionization detector is mainly used to measure the unburned hydrocarbon concentrations in the
exhaust gases. It is based on the principle that pure hydrogen-air flames produce very little ionization,
but if a few hydrocarbon molecules are introduced the flames produce a large amount of ionization. The
ionization is proportional to the number of carbon atoms present in the hydrocarbon molecules.
• A schematic arrangement of the instrument is shown in Figure. It consists of a burner assembly, an
ignitor, an ion collector and electric circuitry. The burner consists of a central capillary tube.

• Hydrogen, or a mixture of hydrogen and nitrogen, enters one leg of the capillary tube and the sample
enters through another leg. The length and bore of the capillary tubes are selected to control the flow
rates. The mixture of H2 - N2 - C„H,„ then flows up the burner tube.
• The air required for combustion is introduced from around the capillary tube.
• The combustible mixture formed in the mixing chamber is ignited by a hot wire at the top of the burner
assembly and a diffusion flame stands at the exit to the burner tube.
• An electrostatic field is produced in the vicinity of the flame by an electric polarizing battery.
• This causes the electrons to go to the burner jet and the positive ions go to the collector.

• The collector and the capillary tube form part of an electric circuit.
• The flow of ions to the collector and the flow of electrons to the burner complete the electrical circuit.
• The dc signal produced is proportional to the number of ions formed and the number of ions is
proportional to the number of carbon atoms in the flame.
• The dc signal generated is attenuated by a modulator and then fed to an ac amplifier and a demodulator.
• The signal is then recorded on a meter. The meter is calibrated directly in amount of hydrocarbon
concentrations.
• To calibrate, the samples of known concentration of hydrocarbons are fed to the instrument and the
meter readings are adjusted accordingly.

CHEMILUMINESCENCE ANALYZERS (CLA)

• The chemilutilinescent analyzer measures the nitric oxide (NO) concentrations. This technique is based
on the principle that NO reacts with ozone (03) to give some NO2 in an electronically excited state.
These excited molecules on decaying to the ground state emit red light (photons) in the wavelength
region from 0.6 gm to 3 gm, i.e.
• NO + 03 NO2* + 02
• NO2* --> NO2 + hv
• where h is Planck's constant and v represents a photon of light.
• The oxides of nitrogen (NO„) from the engine exhaust comprise mainly a combination of nitric oxide
(NO) and nitrous oxide (NO2).
• By converting any exhaust NO2 to NO in a thermo-catalytic converter before supplying the exhaust gas
to the analyzer, the value of total nitrogen oxides (N0x) can be obtained.

• A schematic arrangement of the chemiluminescent instrument is shown in Figure. The vacuum pump controls the pressure in the
reaction chamber and draws ozone and the exhaust sample. The ozone is produced by an electric discharge in oxygen at low
pressure.
• An NO2-to- NO converter is also shown in the diagram. An arrangement is made by using a bypass line, so that it may be possible
to measure only the NO concentrations or NO + NO2, i.e. NOx concentrations in the combustion engine exhaust.
• A mixture of a gas sample and ozone enters a reaction chamber (reactor) which is maintained at a very low absolute pressure.
The reaction of the ozone and nitric oxide when heated under vacuum at 600°C produces some electronically excited molecules
of NO2.
• The electronically excited molecules on decaying, emit light. The light can readily be detected accurately by a photo- multiplier.
• The signal is then amplified and fed to a recorder. Many parameters affect light emission in the reactor, it is therefore essential to
calibrate the analyzer regularly.
• Pure nitrogen may be used for zero setting. The zero control is adjusted until the digital voltmeter reads zero, the nitrogen gas is
then disconnected and a standard NO / N2, mixture is connected.
• The NO/NOx, switch is set to 'NO' mode and the span control is used to adjust the NO reading to correspond with the standard.
For the NOx reading the NO/NOx, function switch is pressed to initiate the NOx mode.

MEASUREMENT OF PARTICULATES
 A dilution tunnel is used to measure the amount of particulate present in
the exhaust gas from the diesel engine. In the dilution tunnel, the exhaust
gases are diluted with ambient air to a temperature of 52°C or less, and a
sample stream from the diluted exhaust is filtered to remove the
particulate material.
 The particulate is trapped after dilution because the particulate gets
condensed over the filter at this temperature. The amount of particulate
trapped is obtained by weighing the filter before and after the experiment.

MEASUREMENT OF EXHAUST SMOKE
 Smoke-meters are used to measure the intensity of exhaust smoke.
Smoke-meters may measure either the relative quantity of light that
passes through the exhaust gas (Hartridge smoke-meter), or the relative
smudge left on a filter paper (Bosch smoke-meter).

HARTRIDGE SMOKE-METER
 It is based on the principle that the intensity of a light beam is reduced by smoke which is a measure of
smoke intensity. A schematic diagram to illustrate the principle of this smoke-meter is shown in Figure.
 Light from a source is passed through a standard length of a tube where the exhaust gas sample is
continuously supplied from the engine and at the other end of the tube the transmitted light is measured
by a photo-electric cell.
 The photoelectric cell converts the light intensity to an electric signal, which is amplified and recorded
on a meter. The intensity of smoke is expressed in terms of smoke density. It is defined as the ratio of
electric output from the photoelectric cell when an exhaust sample is passed through the tube to the
electric output when clean air is supplied.

BOSCH SMOKE-METER
• It is based on the principle that when a certain quantity of exhaust gas passes through a fixed filter
paper, some smoke smudge is obtained on it, which is a measure of smoke intensity.
• A schematic diagram to illustrate the principle of this instrument is shown in Figure.
• A fixed quantity of the exhaust gas from the engine is introduced into a tube, where it passes through a
fixed filter paper. Depending upon the smoke density, some quantity of smudge is deposited on the filter
paper, which can be evaluated optically.
• A pneumatically-operated sampling pump and a photoelectric unit are used for the measurement of the
intensity of smoke smudge on the filter paper.

Euro and Bharat Norms
 What are Emission Norms?
 Emission norms are prescribed CO (Carbon Monoxide), HC (Hydrocarbons)
and NOX (Nitrous oxide) levels set by the government which a vehicle would
emit when running on roads. All the manufacturers need to implement the
same for vehicles being manufactured from the date of implementation.

What are Euro Norms?
 Euro norms refer to the permissible emission levels for both petrol and diesel
vehicles, which have been implemented in Europe. However in India, the
government has adopted the Euro norms for available fuel quality and the method of
testing.
 Chronology of Euro Norms = operational year = vehicle type
 • EURO-1 = 1993 = for passenger car
 • EURO-II = 1996 = for passenger car
 • EURO-III = 2000 = any vehicle
 • EURO-IV = 2005 = any vehicle
 • EURO-V = 2008 = for heavy good vehicle

Euro v/s Bharat norms: Transition to Bharat norms
 The first Indian emission regulations were idle emission limits which became
effective in 1989. These idle emission regulations were soon replaced by mass
emission limits for both petrol (1991) and diesel (1992) vehicles, which were
gradually tightened during the 1990’s. Since the year 2000, India started
adopting European emission and fuel regulations for four wheeled light-duty
and for heavy-dc. Indian emission regulations still apply to two- and three-
wheeled vehicles. On October 6, 2003, the National Auto Fuel Policy was
announced, which envisaged a phased program for introducing Euro 2 - 4
emission and fuel regulations by 2010. Current requirement is that all
transport vehicles carry a fitness certificate that is renewed each year after
the first two years of new vehicle registration.

 Emission requirements for light road vehicles have existed in the EU (European Union) since the early 1970s,
while the first requirements for heavy vehicles came in at the end of the 1980s. Requirements have been
repeatedly tightened over the years, a process that is ongoing. Today, vehicle emissions are controlled under two
basic frameworks: the “Euro standards” and the regulation on carbon dioxide emissions. The “Euro standards”
regulate emissions of nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), particulate matter (PM),
and particle numbers (PN). There are separate regulations for light vehicles (under 3.5 tonnes) and heavy-duty
vehicles. The standards for both light and heavy vehicles are designated “Euro” and followed by a number
(usually Arabic numerals for light vehicles: Euro 1, 2, 3..., and Roman numerals for heavy vehicles: Euro I, II, III...).
Compliance is determined by running the vehicle or the engine in a standardised test cycle. Non-compliant
vehicles cannot be sold in the EU, but new standards do not apply to vehicles already on the roads. Euro
standards also exist for two and three-wheeled vehicles (motorcycles and mopeds) and for engines for non-road
machinery. The regulation on carbon dioxide (CO2) emissions is more recent and so far only covers passenger
cars and vans. There are as yet no limits for CO2 emissions from heavy-duty vehicles. The carbon dioxide
directive differs from the Euro standard in that compliance is not required for a single vehicle but for the
weighted performance of the entire fleet produced by a manufacturer (or a group of manufacturers) in a year.

Euro standards for light vehicles
 The light category of vehicles covers road vehicles under 3.5 tonnes, i.e. both
passenger cars and light commercial vehicles such as vans. Standards vary depending
on whether the vehicle uses petrol or diesel, as well as on the class of the vehicle
within the broader light-duty vehicle category. The first Euro standard, Euro 1
(91/441/EEC) entered into force in 1992-93, and these requirements forced
manufacturers to install three-way catalytic converters in petrol vehicles. Since then,
the emissions limits have been progressively tightened, and the standards have
subsequently been updated several times. Most recently, a regulation adopted in
December 2006 (715/2007/EC) established the currently applicable Euro standards.
The Euro 5 standard applies to the approval of new vehicles as of September 2009,
and to the sale of all new vehicles as from January 2011, while the Euro 6 standard
will apply from September 2014 (new approvals) and September 2015 (all sales)
onwards.26 December 2017 ME 6016 ADVANCED IC ENGINES 55

 The standards for light vehicles are defined by driving distance, and expressed in milligrams per
kilometre (mg/km). The limit values for light commercial vehicles are generally slightly higher than for
passenger cars and are dependent on the weight class – the heavier the vehicle, the higher the
permissible emissions. The main effect of the Euro 5 standard has been to reduce the amount of
particulate matter (PM) emitted from diesel engines by 80 per cent, while also tightening NOx
emission requirements. The main change contained within the Euro 6 standard is the further
reduction of NOx emissions from diesel engines to a level closer to that currently required of petrol
engines. Also new is a standard for particle numbers (PN). The number limit will prevent the
possibility that the tougher mass limit for PM is met using technologies (such as “open filters”) that
would enable a high number of ultra-fine particles to pass. Prior to Euro 5, particulate matter from
petrol engines was not regulated, as emissions are low compared to diesel engines. However, some
direct-injection petrol engines can create PM emissions of a level comparable to diesel engines, and
under the Euro 5 and 6 standards the same limit of 5mg/km is imposed on both diesel and direct-
injection petrol engines.

 The Commission had originally proposed a Euro 5 limit of 200 mg/km for NOx
emissions from diesel engines, which was reduced to 180 mg/km in
negotiations between the Parliament and Council. However, this level of
reduction limit does generally not require the use of NOx after-treatment
technologies. Further reductions to 80 mg/km under the Euro 6 standard in
2014 will likely require such technologies to be fitted.
 The future Euro 6 standard is still substantially weaker than standards
currently in force in the United States. There, the so-called Tier II standards
limit fleet average NOx emissions close to 40 mg/km (70 mg/mile) for both
diesel and petrol engines. The Tier II standards have already been in force for
several years in California and several other states.

 Under the current framework, large personal vehicles with a weight of over 2.5
tonnes – that is, sports utility vehicles (SUVs) – are subject to the less strict rules
applicable to vans. While the Commission had proposed to close this concession
under the Euro 5 standard, a compromise between the Parliament and the Ministers
extended it until September 2012. From this date, SUVs are subject to the same
limits as other personal vehicles. New legislation on durability was introduced along
with the Euro 3 and 4 standards, making manufacturers responsible for the
emissions from light vehicles for a period of five years or 80,000 km (Euro 3) and five
years or 100,000 km (Euro 4), whichever comes first. Euro 5 and 6 standards
maintain the five year or 100,000 km durability requirement for ‘in-service
conformity’, but require an extended durability of five years or 160,000 km in the
durability testing of pollution control devices for type approval.

Euro standards for heavy vehicles
 The first EU directive to regulate emissions from heavy vehicles, i.e. road
vehicles heavier than 3.5 tonnes, came in 1988 (88/77/EEC). Before that there
had been a common standard within the UN Economic Commission for Europe
(ECE R49).
 The Euro I standards for medium and heavy engines were introduced in 1992–
93 (91/542/EC). The same directive also laid down standards for Euro II, which
took effect in 1995–96. Another directive (1999/96/EC) was adopted in 1999
giving standards for Euro III (2000), IV (2005) and V (2008). In 2013 the Euro VI
standard (defined in regulation 595/2009) will be put in to effect.

 The way in which the emission standards for heavy road vehicles in the EU
have been stiffened over the years is shown in table. There are different
standards for compression ignition engines (diesels) and positive ignition
engines (gas and petrol), however among heavy-duty vehicles there is only a
tiny fraction that does not run on diesel. The standards for heavy-duty
vehicles are defined by energy output (g/kWh) and cannot be directly
compared with the standards for light vehicles where standards are defined by
distance. The present Euro V standard differs from Euro IV in its stricter
emission requirement for NOx. Euro VI is a step forward towards global
harmonisation since the limit values are similar to those of the United States,
where the limit for NOx is 0.27 g/kWh and the limit for PM is 13 mg/kWh.

 The Euro VI regulation also includes an ammonia (NH3) concentration limit of
10 parts per million (ppm) for both compression ignition and positive ignition
engines. In June 2011 a particle number (PN) limit was defined for diesels, in
addition to the mass limit (582/2011). A corresponding limit for positive
ignition engines is yet to be defined. The Commission also have the right to
define a maximum limit for the NO2 component of NOx emissions in future
implementing regulation. In “traditional” diesel engines the NO2 content in
the total NOx emissions is about 5 per cent. Modern engines may, however,
bring this share up to 50 per cent, strongly depending on the technology used.

CO2 standards
 Within the context of the EU’s commitment to reducing greenhouse gas
emissions, limits on CO2 emissions from cars have long been discussed. As
early as 1994, Angela Merkel, then environment minister in Germany,
proposed to cap car CO2 emissions at 120 g/km from 2005.3 However, the
first binding limits for CO2 emissions from vehicles were only agreed in 2009,
when the EU set a legally binding CO2 standard for new cars (443/2009). In
May 2011 a similar EU legislation for vans was passed (510/2011). Since there
is currently no after-treatment technology that can reduce CO2 emissions
from road vehicles, the standards can also be seen as fuel efficiency standards.

Bharat Stage Emission Standards
 Bharat Stage emissions standards are emissions standards instituted by the Government of the
Republic of India that regulate the output of certain major air pollutants (such as nitrogen oxides
(NOx), carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), sulfur oxides (SOx)) by
vehicles and other equipment using internal combustion engines. They are comparable to the
European emissions standards. India started adopting European emission and fuel regulations for
four-wheeled light-duty and for heavy-duty from the year 2000. For two and three wheeled vehicles,
the Indian emission regulations are applied. As per the current requirement, all transport vehicles
must carry a fitness certificate which is to be renewed each year after the first two years of new
vehicle registration. The National Fuel Policy announced on October 6, 2003, a phased program for
implementing the EU emission standards in India by 2010. The implementation schedule of EU
emission standards in India is summarized in Table. Some of the important emission standards.

Overview of the emission norms in India
 1991 - Idle CO Limits for Gasoline Vehicles and Free Acceleration Smoke for Diesel Vehicles, Mass Emission
Norms for Gasoline Vehicles
 1992 - Mass Emission Norms for DieselVehicles.
 1996 - Revision of Mass Emission Norms for Gasoline and Diesel Vehicles, mandatory fitment of Catalytic
Converter for Cars in Metros on Unleaded Gasoline.
 1998 - Cold Start Norms Introduced.
 2000 - India 2000 (Eq. to Euro I) Norms,Modified IDC (Indian Driving Cycle), Bharat Stage II Norms for Delhi.
 2001 - Bharat Stage II (Eq. to Euro II) Norms for All Metros, Emission Norms for CNG & LPG Vehicles.
 2003 - Bharat Stage II (Eq. to Euro II) Norms for 11 major cities.
 2005 - From 1 April Bharat Stage III (Eq. to Euro III) Norms for 11 major cities.
 2010 - Bharat Stage III Emission Norms for 4-wheelers for entire country whereas Bharat Stage - IV (Eq. to Euro
IV) for 11 major cities. Bharat Stage IV also has norms on OBD (similar to Euro III but diluted)

Emission norms for passenger cars ( Petrol)
Norms CO( g/km) HC+ NOx)(g/km)
1991Norms 14.3-27.1 2.0(Only HC)
1996 Norms 8.68-12.40 3.00-4.36
1998Norms 4.34-6.20 1.50-2.18
stage
2000 norms
2.72 0.97
Bharat stage-II 2.2 0.5
Bharat Stage-III 2.3 0.35(combined)
Bharat Stage-IV 1.0 0.18(combined)

Emission Norms for 2/3 Wheelers ( Petrol)
Norms CO ( g/km) HC+ NOx (g/km)
1991 norms 12-30 8-12 (only HC)
1996 norms 4.5 3.6
stage
2000 norms
2.0 2.0
Bharat stage-II 1.6 1.5
Bharat Stage-III 1.0 1.0

Emission norms for Heavy diesel vehicles:
Norms CO
(g/kwhr)
HC
(g/kwhr)
Nox
(g/kwhr)
PM
(g/kwhr)
1991 Norms 14 3.5 18 -
1996 Norms 11.2 2.4 14.4 -
stage 2000
Norms
4.5 1.1 8.0 0.36
Bharat stage-II 4.0 1.1 7.0 0.15
Bharat Stage-III 2.1 1.6 5.0 0.10
Bharat Stage-IV 1.5 0.96 3.5 0.02

Emission control technology for vehicles
 Petrol-driven passenger cars
 A petrol engine without emission control produces large emissions of nitrogen oxides and unburnt hydrocarbons.
The technology that manufacturers have used to meet stiffer emission requirements is the three-way catalytic
converter. This consists of a ceramic material with microscopically small channels, coated with a very thin film of
precious metals. As the exhaust gases pass through the converter the hydrocarbons and carbon monoxide are
oxidised by the oxygen that is released when the nitrogen oxides are reduced to nitrogen (N2). The three-way
catalytic converter has been fitted to all petrol passenger cars sold in the EU since the start of the 1990s and has
become increasingly efficient as emission requirements have become stricter. The biggest problem is during cold
starts, since a certain temperature (300-400°C) has to be reached before the catalytic process starts to work.
Some models have pre-heating systems, while others collect some of the initial exhaust gases and heat them
before they pass through the catalytic converter.
 In the case of petrol engines that use an excess of air (known as lean-burn technology) the three-way catalytic
converter has no effect on emissions of NOx. Some manufacturers use a NOx trap to meet the standards. Petrol
vehicles with direct injection (GDI, FSI, SCi, etc.) produce relatively high emissions of PM, which means that these
may require special PM reduction as emission requirements are stiffened (see Diesel-driven passenger cars
below).

 Diesel-driven passenger cars
 The biggest air pollution problems associated with diesel vehicles are emissions of NOx and PM, both of which are higher than for petrol vehicles.
 NOx. Because a diesel engine works with an excess of air the three-way catalytic converter cannot be used to reduce emissions of NOx. Instead
Exhaust Gas Recirculation (EGR) has been the most widely used technology to reduce NOx emissions from diesel engines. The EGR technology
implies that some of the exhaust gases are recirculated through the combustion chamber. The addition of exhaust fumes lowers the combustion
temperature and reduces NOx formation. Less effective combustion and increased soot production are some disadvantages with the EGR
technology. There is also a limit to the extent that the EGR technology can reduce NOx (around 35 per cent), which means that further treatment
of exhaust gases is likely to be necessary in order to meet future standards. One further treatment method is to use a NOx adsorber, also known
as a NOx trap. It consists most commonly of the mineral zeolite, which adsorbs NO and NO2 molecules. After a few minutes the material gets
saturated and loses its ability to trap more NOx, so there is a need for periodic regeneration. One regeneration technique is to run combustion
with excess diesel for some seconds. The CO formed during this period will quite easily reduce the trapped NOx to N2. This method has been in
commercial use since 2008. Another method – although mainly applied to heavy vehicles – is selective catalytic reduction (SCR). This involves
reducing the nitrogen oxides to nitrogen gas in a catalytic converter with the aid of ammonia (injected as urea). The reduction efficiency
approaches 80–90 per cent. Disadvantages include the added operating cost of using urea, the possibility of increased ammonia emissions and
the loss of effect when the urea tank is empty. Some questions also exist regarding the durability of the technology. One advantage is that higher
levels of NOx can be permitted during the combustion process, which can consequently be better optimized for low fuel consumption.

 PM. The formation of particulates can be reduced to some extent by modifying the
combustion process. Smaller engines could meet Euro 4 requirements in this way.
But with the stiffened emission requirements of Euro 5, particulate filters are
required for all diesel engines. They consist of a ceramic matrix of silicon carbide,
perforated with microscopic channels. As the exhaust gases pass through, a large
proportion of particulates (90–99 per cent) stick to the walls of these channels. The
trapping of particulates means that the channels become blocked, and the filter
therefore has to be raised to a high temperature at regular intervals to burn off the
particulates. Various methods have been developed to achieve this combustion,
including a brief additional injection of fuel and a catalytic substance that reduces
the temperature required. One requirement for low particulate emissions is a fuel
with low sulphur content.

 Heavy vehicles
 Practically all heavy road vehicles have diesel engines. In common with diesel cars,
the emissions that are most important to reduce are NOx and particulates. In the
case of NOx the Euro V requirement for 2008 (max. 2 g/kWh) has in practice
compelled the use of SCR (see above) on all new heavy vehicles.
 Particulate reduction by means of filters is easier to solve for heavy diesel vehicles
than for light ones, since heavier vehicles have a higher exhaust temperature. This
makes the critical phase – burning off particulates from the filter – easier to achieve.
A particulate filter is often combined with an oxidation catalytic converter that
reduces the content of carbon monoxide and hydrocarbons in the exhaust gases.

ME6016 ADVANCED I.C ENGINES UNIT III

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