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UNIT III ENGINE EXHAUST EMISSION CONTROL

Formation of NOx, HC/CO mechanism , Smoke and

Particulate emissions, Green House Effect , Methods

of controlling emissions , hree !a" catal"tic con#erterand Particulate ra$, Emission %HC,CO, NO and

NOx ,& measuring e'ui$ments, Smoke and Particulate

measurement, (ndian )ri#ing C"cles and emission

norms

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Pollution Control

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Pollution

* Air pollution is the introduction intothe atmosphere of chemicals, particulates, or biological materials thatcause discomfort, disease, or deathto humans, damage other livingorganisms such as food crops, or

damage the naturalenvironment or built environment.

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Pollutants in Exhaust Gases ofI.C. Engine

* The exhaust gases of IC engineshave following pollutants

*!drocarbons* Carbon "onoxide #C$%

* &itrogen $xide #&ox%

* Particulates

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!drocarbons in 'I engine

* !drocarbons formed b! incompletecombustion of fuel.

* The (uantit! of un ) burnt h!drocarbons

depend upon the turbulence andcombustion chamber design.

* The oil *lm and deposit on c!linderwalls absorb fuel during inta+e andcompression and fuel vapour isdesorbed into the c!linder during theexpansion and exhaust.

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!drocarbons in CI Engine

* The diesel fuel component contain highermolecular weights on average than the '.I.engine fuel, resulting in higher boiling andcondensing temperature. C Particles condense

on the surface of the solid carbon soot generatedduring combustion.

* - ratio is heterogeneous causes local spot ofrich and lean mixture. The fuel mixture do not*nd ox!gen to react causes in / completecombustion.

* small amount of li(uid fuel is trapped at the tipof the in0ector no11le when fuel in0ection stop.

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Carbon "onoxide #C$%

* Carbon monoxide is an odorless, colorless and toxicgas.

* C$ ormed as a result of cold 2ame reaction and richfuel ratio in combustion chamber local de*cienc! of

ox!gen which causes incomplete combustion create C$.* The percentage of C$ increases in Idle range and

decreases with the speed. In a passenger car C$percentage has been found to be as high as 34 with therich mixture and 5.674 with near stiochiometric

mixture.

* The complete emission of C$ is not possible. 8here as9.74 C$ should be considered as reasonable goal

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&itrogen $xide #&ox%

* In '.I engine if ignition spar+ isadvanced the c!linder temperaturewill be increased and more &$x will

be produced.

* In C.I. engine with dividedcombustion chamber and indirect

in0ection tends to generate higherlevel of &$x.

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Particulate

* In '.I. Engine particulates arelead, organic particulatesincluding soot and sulphates.

* uel containing 'ulphur whichoxidi1ed within engine c!linder

form '$6.* :eaded fuel emit lead

compounds. 'ootemissions#;lac+ smo+e% Is aresult of rich mixture.

* In C.I. engine, carbonaceous

material #'oot% which someorganic compounds have beenabsorbed. "ost particulatesgenerate due to incompletecombustion of fuel.

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E

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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 viewpointof its odor, its photochemical smog, and from the

standpoint of its having a carcinogenic effect.

The products of photochemical smog cause wateringand burning of the eyes, and affect the respiratory

system, especially when the respiratory system is

marginal for other reasons.

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HYDROCARBON EMISSIONS FROM SI ENGINES The most widel! accepted causes for h!drocarbonemissions in exhaust gases of spar+ ignition enginesare-5.lame (uenching at the combustion chamber walls,leaving a la!er of unburned fuel)air mixture ad0acent tothe walls.

6. Crevices in the combustion chamber, small volumeswith narrow entrances, which are *lled with theunburned mixture during compression, and remainsunburned after 2ame passages, since the 2ame cannot

propagate into the crevices. The main crevice regionsare the spaces between the piston, the piston rings andthe c!linder walls. The other crevice regions are thethreads around the spar+ plug, the space around theplug centre electrode, crevices around the inta+e and

exhaust valve heads, and the head gas+et crevice.

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FORMATION OF POLLUTANTS>. Incomplete combustion, either partial burning or completemis*re, occurring when the combustion (ualit! is poor, e.g.during engine transients when air)fuel, exhaust gasrecirculation, and spar+ timing ma! not be ade(uatel!controlled.

*ll these processes, except mis*re, result in unburnedh!drocarbons close to the combustion chamber walls. "ixingof unburned h!drocarbons with the bul+ c!linder gases occursduring expansion and the exhaust blow down processes.?uring the blowdown process a high concentration ofh!drocarbons is released from the c!linder through theexhaust valve.

*?uring the exhaust stro+e the piston pushes most of theremaining fraction of the c!linder mass with its highh!drocarbon concentration into the exhaust.

* The residual gases in the c!linder thus contain a high

concentration of h!drocarbons.*

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FORMATION OF POLLUTANTSHydrocarbon emiion !rom CI en"ine The CI engines operate with an overall fuel)lean e(uivalence ratio,therefore the! emit onl! about one)*fth of the h!drocarbon

emissions of an 'I engine. The following are the ma0or causes forh!drocarbon emissions in the exhaust of CI engines-

5.The diesel fuel contains components of higher molecular weightson average than those in a gasoline fuel, resulting in higher boiling

and condensing temperatures.

This causes some h!drocarbon particles to condense on thesurface of the solid carbon soot generated during combustion.

"ost of this is burned as mixing continues and thecombustion process proceeds but a small amount is exhausted outof the c!linder.

6. The air)fuel mixture in a CI engine is heterogeneous with fuelstill being added during combustion. It causes local spots to range

from ver! rich to ver! lean and man! 2ame fronts exist at the same

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FORMA#ION OF $O%%AN#SHydrocarbon emiion !rom CI en"ine

Incomplete combustion ma! be caused b! under)mixing or over)mixing.

8ith under)mixing, in fuel)rich 1ones some fuel particles do not*nd enough ox!gen to react with, and in the fuel)lean 1onessome local spots will be too lean for combustion to ta+e place

properl!.

8ith over)mixing, some fuel particles ma! be mixed with burnedgases and it will therefore lead to incomplete combustion.

=. small amount of li(uid fuel is often trapped on the tip of thein0ector no11le even when in0ection stops. This small volume offuel is called sac volume. This sac volume of li(uid fuel is surrounded b! a fuel)richenvironment and therefore it evaporates ver! slowl! causing

h!drocarbon emissions in the exhaust.

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FORMA#ION OF $O%%AN#SCarbon "onoxide #C$%

Carbon monoxide is toxic. The haemoglobin in the blood, which

carries ox!gen to the di

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FORMA#ION OF $O%%AN#S$xides of &itrogen #&$x%

* The oxides of nitrogen tend to settle on the haemoglobin in the

blood. The most undesirable toxic e

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Some of the NO forming reactions are:

* N, O, O are formed from the dissociation of N!, O! and !O vapour at high

temperatures that exist in the combustion chamber "!#$$%&$$$ '(.

* The higher the combustion reaction temperature, the more diatomic nitrogen "N!( will

dissociate to monatomic nitrogen "N( and more NOx will be formed.

* )t low temperatures, a very small *uantity of NOx is created. The flame temperature is

maximum at the stoichiometric e*uivalence ratio "$ + .$( but maximum NOx, is formed

slightly at a lean e*uivalence ratio "$ + $.-#(. )t 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 fuelair e*uivalence ratio, the burned gas fraction "/01 and residual gas fractions( and combustion duration within the

cylinder. NOx is reduced in modem engines with fast%bum combustion chambers.

* 2f ignition spar3 is advanced, the cylinder temperature will be increased and more NOx

will be produced. 42 engines with divided combustion chambers and indirect injection

"52( tend to generate higher levels of Nox.

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* This causes the electron go to the burner 0et and positive ions go on collector. The2ow of ion on collector and the 2ow ofelectron to the burner complete electricalcircuit.

* The ?.C. signal produced is proportional tothe number of ion formed and the numberof ion is proportional to the carbon atom in2ame. The ?.C. signal modulated and fedto ampli*er and demodulator.

* The signal recorded on a meter.

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Catal!tic Converter

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Catal!tic Converter

* The main aim of catal!tic converter is toconvert the harmful gases into the harmlessgases.

* The catal!tic converter converts harmful

gases li+e &$x, C and C$ into compoundsli+e &6, 6 and C$6.

* hodium is used as reducing catal!st forconverting &$x in the exhaust has into

nitrogen and ox!gen.* Platinum and Palladium are used asoxidation catal!st which changes C andC$ into 8ater and C$6.

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T!pes of Catal!tic Converter

* Two 8a! Catal!tic Converter

+ 8hich is used to control onl! C$ and Cemission b! oxidation.

* Three 8a! Catal!tic Converter

+ 8hich control C$ and C b! oxidationas well as &$x b! reduction.

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Two Way Catalytic Converter

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* It consist c!lindrical unit li+e silencer andit is installed into the exhaust s!stem of avehicle such as motor c!cle, car etc.

* Inside the c!lindrical tube there is hone!comb structure of ceramic or metal.8hich will be coated with alumina basedmaterial with second coat of preciousmetals li+e platinum, palladium or

rhodium.* this second coating serves as a catal!stwhich causes the chemical reaction ofexhaust gases with coating material.

Th 8 C l i

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Three 8a! Catal!ticConverter

* This is installed in the exhaust linebetween manifold and muDer.

* The converter have mesh or

hone!comb metal construction inside.

* The catal!st is coated on mesh orhone!comb.

* It is commonl! used in petrol engines.

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* 'tage 5 / eduction Catal!st- + The exhaust gases are *rst sent over the reduction catal!st #which is

made of platinum and rhodium%. It converts oxides of nitrogen #&$x%

to nitrogen #&6% and ox!gen #$6%. The following reactions ta+e placewhen the exhaust gases pass over the reduction catal!st.

+ 6&$ &6 B $6

+ 6&$6 &6 B 6$6

+ The reduction catal!st simpl! rips o< nitrogen and ox!gen from theoxides of nitrogen. s !ou might +now, nitrogen and ox!gen areharmless gases while oxides of nitrogen are reall! harmful to theenvironment.

* 'tage 6 / $xidation Catal!st- + Exhaust gases that are free of oxides of nitrogen #&$x% are then sent

over the oxidation catal!st #made of platinum and palladium%. The

oxidation catal!st coverts carbon)monoxide #C$% and h!drocarbons#C% in the gases into carbon)di)oxide #C$6% and water #6$%.

+ The following reactions ta+es place when the exhaust gases passover the oxidation catal!st-

+ 6C$ B $6 6C$6

+ C B $6 C$6 B 6$


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PARTICULATES* The particulates from 'I engines are lead, organic particulates including

soot and sulphates. Gasoline ma! contain some sulphur, which isoxidi1ed within the engine c!linder to form '$6.

* is oxidi1ed to '$= which combines with water to form a sulphuric acidaerosol.

* :eaded gasolines emit lead compounds. 'oot emissions #blac+ smo+e%can result from combustion of overl! rich mixtures. In properl! ad0ustedspar+)ignition engines, soot in the exhaust is not a signi*cant problem.

* ?iesel particulates consist mainl! of combustion generatedcarbonaceous material #soot% on which some organic compounds havebeen absorbed.

* "ost particulates are generated in the fuel rich 1ones within the

c!linder during combustion due to incomplete combustion of fuelh!drocarbonsF some particulate matter is contributed b! the lubricatingoil.

* These are undesirable odorous pollutants. "aximum particulateemissions occur when the engine is under load. t this condition,

maximum amount of fuel is in0ected to obtain maximum power from theengine. It results in a rich mixture and poor fuel econom!.


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PARTICULATES

* )s the temperature decreases below #$$64 during expulsion, the particles become coated with 4and 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.

* 5ry 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 7osch Smo3e Number, which is assessed by the

reflectance of a filter paper on which the soot has been collected.

* 8articulates contain more than simply the dry soot9 they are the soot particles on which the other

compounds, often the polycyclic aromatic hydrocarbons "8)(, have condensed.

* The 8) compounds have a tendency to be carcinogenic.

* The level of particulates increases with the sulphur content in the fuel. 8articulates are measured by

trapping the particles on glass%fibre filter papers placed in a dilution tunnel, and then weighing the

*uantity.

MEASUREMENT OF POLLUTANTS

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MEASUREMENT OF POLLUTANTS

* The measurement of exhaust emissions is very important for the control of air pollution

from 24 engines.

* 4O concentrations are measured by infrared absorption,

* NO concentrations are measured by chemi%luminescence and

* nburned 4 are measured by flame ioni;ation detector.

Non-dispersive Infra-red (NDIR) Analyer

* The N521 analy;ers 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.

* 4arbon dioxide absorbs infrared energy in the wavelength band of < to

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* Nitric oxide "NO( has also a wea3 absorption band,

allowing it to be analy;ed by N521, but lac3 of

sensitivity and interference by water vapour do not givehigh accuracy with low concentrations.

* ) schematic arrangement of the 21 analy;er is shown in

=igure.

* ) wideband infrared radiation source consists of a heated

wire, which is placed in a *uart; tube mounted in the

source bloc3.* 1adiation from the source is reflected within the

mounting bloc3 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.* )fter 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.

Non-dispersive Infra-red (NIR! Ana"#$er

f ( !

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* The two detector cells contain e*ual 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 analy;ed.

* >hen 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 *uart; windows into

various lengths to give different ranges of sensitivity.

* The *uart; windows do not absorb infrared energy in the

region of interest. ?ow 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 analy;ers.


Non dispersive Infra red (NIR! Ana"#$er

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* The reference cell is sealed and is physically identical to the

sample cell. 2t 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.



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* >hen the shutter bloc3s the radiation, the pressure in

the two compartments of the detector is e*ual because

there is no energy entering either of the chambers ofthe detector.

* This allows the diaphragm to return to its neutral

position. )s the shutter alternatively bloc3s and

unbloc3s 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%fre*uency oscillator

"amplifications of ac signals have better drift%free

characteristics than the amplifications of dc signals(.

)dditional 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.

Non dispersive Infra red (NIR! Ana"#$er


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* To set the ;ero point, a non%infrared%absorbing

gas, e.g. dry air, is passed through the

instrument. =or the other points on the scale,

calibrating gases with 3nown concentrations

are passed through the analy;er.

* )n error in the N521 readings may arise if the

exhaust sample contains other species that canabsorb radiation at the same fre*uencies that

the gas in the detector will absorb.

* 2n order to minimi;e this interference, a large

concentration of the interfering gas is placed in

the filter cells.

* The analy;er ;ero is then set with this large

concentration of the interfering gas.


FLAME-IONI%ATION ETECTOR (FI!

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* Some hydrocarbons have an infrared absorption at

&.< microns, but some others, notably aromatics,

have almost none. Only about #$ @ of exhaust

hydrocarbons is measured by N521, therefore, this

method is not suitable for the measurement of 4

concentrations.

* The flame ioni;ation detector is mainly used to

measure the unburned hydrocarbon concentrations

in the exhaust gases. 2t is based on the principle that pure hydrogen%air flames produce very little

ioni;ation, but if a few hydrocarbon molecules are

introduced the flames produce a large amount of

ioni;ation. The ioni;ation is proportional to the

number of carbon atoms present in the hydrocarbon

molecules.

* ) schematic arrangement of the instrument is shown

in =igure. 2t consists of a burner assembly, an

ignitor, an ion collector and electric circuitry. The

burner consists of a central capillary tube.


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FLAME IONI%ATION ETECTOR (FI!

* ydrogen, or a mixture of hydrogen and

nitrogen, enters one leg of the capillary tube

and the sample enters through another leg. Thelength and bore of the capillary tubes are

selected to control the flow rates. The mixture

of ! % N! % 4A,A then flows up the burner

tube.

* The air re*uired 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.

* )n electrostatic field is produced in the vicinityof the flame by an electric polari;ing battery.

* This causes the electrons to go to the burner jet

and the positive ions go to the collector.

FLAME IONI%ATION ETECTOR (FI!

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* The collector and the capillary tube form part of

an electric circuit.

* The flow of ions to the collector and the flow ofelectrons 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 theflame.

* 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 meteris calibrated directly in amount of hydrocarbon

concentrations.

* To calibrate, the samples of 3nown concentration

of hydrocarbons are fed to the instrument and the

meter readings are adjusted accordingly.


CHEMILUMINESCENCE ANAL&%ERS (CLA!

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* The chemilutilinescent analy;er measures the nitric oxide "NO(

concentrations. This techni*ue is based on the principle that NO reacts witho;one "$&( to give some NO! in an electronically excited state. These excited

molecules on decaying to the ground state emit red light "photons( in the

wavelength region from $.B gm to & gm, i.e.

* NO C $& NO!D C $!

* NO!D %%E NO! C hv

where ! is 8lanc3Fs constant and v represents a photon of light.

* The oxides of nitrogen "NOA( from the engine exhaust comprise mainly a

combination of nitric oxide "NO( and nitrous oxide "NO!(.

* 7y converting any exhaust NO! to NO in a thermo%catalytic converter before

supplying the exhaust gas to the analy;er, the value of total nitrogen oxides

"N$x( can be obtained.


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* ) schematic arrangement of the chemiluminescent instrument is shown in =igure. The

vacuum pump controls the pressure in the reaction chamber and draws o;one and the

exhaust sample. The o;one is produced by an electric discharge in oxygen at low pressure.* )n NO!%to% NO converter is also shown in the diagram. )n arrangement is made by using a

bypass line, so that it may be possible to measure only the NO concentrations or NO C NO!,

i.e. NOx concentrations in the combustion engine exhaust.

* ) mixture of a gas sample and o;one enters a reaction chamber "reactor( which is maintained

at a very low absolute pressure. The reaction of the o;one and nitric oxide when heatedunder vacuum at B$$64 produces some electronically excited molecules of NO!.

* 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. Gany parameters affect light emission in

the reactor, it is therefore essential to calibrate the analy;er regularly.

* 8ure nitrogen may be used for ;ero setting. The ;ero control is adjusted until the digital

voltmeter reads ;ero, the nitrogen gas is then disconnected and a standard NO N !, mixture

is connected.

* The NONOx, switch is set to FNOF mode and the span control is used to adjust the NO

reading to correspond with the standard. =or the NOx reading the NONOx, function switch

is pressed to initiate the NOx mode.


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dilution tunnel is used to measure the amount of particulate

present in the exhaust gas from the diesel engine. In the dilutiontunnel, the exhaust gases are diluted with ambient air to atemperature of 76C or less, and a sample stream from thediluted exhaust is *ltered to remove the particulate material.

The particulate is trapped after dilution because the particulate

gets condensed over the *lter at this temperature. The amount ofparticulate trapped is obtained b! weighing the *lter before andafter the experiment.

MEASUREMENT OF PARTICULATES

MEASUREMENT OF EXHAUST SMO'E

'mo+e)meters are used to measure the intensit! of exhaustsmo+e. 'mo+e)meters ma! measure either the relative (uantit!of light that passes through the exhaust gas #artridge smo+e)meter%, or the relative smudge left on a *lter paper #;oschsmo+e)meter%.

HARTRIGE SMO'E-METER

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HARTRIGE SMO'E METER

2t is based on the principle that the intensity of a light beam is reduced by

smo3e which is a measure of smo3e intensity. ) schematic diagram to

illustrate the principle of this smo3e%meter is shown in =igure.?ight 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, whichis amplified and recorded on a meter. The intensity of smo3e is expressed in

terms of smo3e density. 2t 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.

OSCH SMO'E-METER

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* 2t is based on the principle that when a certain *uantity of exhaust gas passes

through a fixed filter paper, some smo3e smudge is obtained on it, which is a

measure of smo3e intensity.

* ) schematic diagram to illustrate the principle of this instrument is shown in

=igure.

* ) fixed *uantity of the exhaust gas from the engine is introduced into a tube,

where it passes through a fixed filter paper. 5epending upon the smo3e density,

some *uantity of smudge is deposited on the filter paper, which can beevaluated optically.

* ) pneumatically%operated sampling pump and a photoelectric unit are used for

the measurement of the intensity of smo3e smudge on the filter paper.

OSCH SMO'E-METER

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aic unit 3 29 02 2016

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