5. emission formation and control

8/12/2019 5. Emission Formation and Control

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Automotive Emissions and Control

technology

Dr. Rui Chen

Department of Aeronautical & automotive Engineering

Loughborough University


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There are twoprinciple types of atmospheric pollution

Lon!on fog results from smo"e an! fumes originating from the

combustion of hy!rocarbon#base! fuel. The primary ingre!ients

are suspended carbon particulates and sulphur dioxide.

Automobile contributes little to it.

Los Angeles smog$ characterise! by the %bron clou!'. (ne of

the primary concerns about smogis its o)one content$ hich

causes eye irritation$ coughing$ etc.

()one *(+, is forme! from the combination of o-i!es of

nitrogen *(-,$ ith unburne! hy!rocarbons */Cs,$ or volatile

organic compoun!s *0(Cs,$ in the presence of sunlight.

What is smog?


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+

Pollutants

Products

2222

Combustion

PMsHCsNOxCO

...HNOCO

AirFuel

+++

+++++

+

Automotive Emissions


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Fig. 1-1 Spark ignition engine emissions for different fuelair e!ui"alent ratios

SI Engine Emissions


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Fig. 1-2 Summar# of pollutant formation mec$anisms in a

direct%in&ection compression engine during premixed and

mixing controlled combustion p$ases

CI Engine Emissions


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SI Engine Emission Control


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Emission Controls in the 4567s

/Cs vente! from the cran"case accounte! for as much as278 of the /Cs emissions from 4567 vintage automobile.Positive crankcase valve P!C" systemis use! to recyclecran"case vente! /Cs into the engine inta"e.

To control /Cs originating in the fuel tan" an! thecarburettor$ evaporation control system ECS"as!evelope! prior to 4537 using a canister containingactivate! charcoal$ hich control further 278 of /Csemissions.

9reheat of Carburettor Air 0aporise fuel !rops for col! start. During arm#up$ a portion of inta"e air is arme! by

e-haust manifol!. :y mi-ing this arm air ith ambient air$the air temperature entering the engine can be controlle!.

Prior to catalytic converters


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Control of


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(-i!ation converter

Control C( an! /Cs emissions but unable to re!uce (-.

Dual converter systems

Re!ucing catalyst is mounte! upstream of o-i!i)ing catalyst

Engine operates slightly rich to provi!e re!ucing e-haust


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(verall reaction Reaction2/C ? C( ? 2(- ? (2 /2( ? +C(2 ? 2

(-i!ation */C an! C(,

2C( ? (2 2C(2

1/C ? (2 2/2( ? 1C(2

Re!uction *(-,

1( ? 1C( 22 ? 1C(2

1/C ? 47( 2 ? 2/2( ? 1C(2

C( ? /2( C(2 ? /2

2( ? /2 2/+ ? 2/2(

2/C ? +/2( C( ? C(2 ? 1/2

#hree$way catalytic converter #WC"


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Fig. 1-7 Con"ersion efficiencies of catal#st s#stems

A t#pical airfuel ratio perturbation for suc$ a s#stem is2'.(

#WC conversion e%%iciency


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Fig. 1-8 )esponse of specific fuel consumption and po*er output toc$anges in airfuel ratio

E%%ects on engine per%ormance


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Fig. 1-10 +ig$t%off temperatures of different catal#sts

Catalyst &ight$o%%


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To important re@uirements of a catalyst system are That it shoul! be !urable$ ith a life of say ;7$777"m *7$777miles,

That it shoul! start or"ing as soon as possible after the engine has

starte!

As a catalyst ages$ its performance changes in several ays

>ts light#off temperature rises

>ts conversion efficiency ill fall

>ts response to !ifferent components in the e-haust ill change

Catalyst performance !eteriorates mechanism

9oisoning of the catalyst !e#activation of the catalytic material

through !eposits. *lea!e! fuel$ sulphate !eposits$ a!!itives in thelubricant,.

Bailure of the substrate


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Due to fuel enrichment at lo temperatures.

9otential metho!s to re!uce col!#start emissions

uic"ly heat the converter above a threshol! reaction

temperature of +7oC.

Develop a catalyst ith a much loer threshol! temperature$hich is more !ifficult an! consumes more time.

Technologies

Close#couple! or manifol! converters

Electrically heate! catalysts

E-haust gas ignition through manifol! reactions or an in#line

burner using a!!itional fuel.

/y!rocarbon trap retain /Cs !uring col!#start an! release

in arm operation.

Cold$start


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Table 1-1 US federal emissions limits (grams of pollutant per mile)

Model #ear CO HC NOx Solution

,- /0 /./ 1. Pre%control

,-0(,-0

12/

.,1.(

.(1.,

)etarded ignition3 t$ermal reactors3 ex$aust gasrecirculation 456)7

,-0' ,' ,.' 1., Oxidation catal#st

,-00 ,' ,.' 2.( Oxidation catal#st and impro"ed 56)

,-/( 0 (., 2.( 8mpro"ed oxidation catal#st and t$ree%*a# catal#sts

,-/, 0 (., ,.( 8mpro"ed t$ree%*a# catal#st and support materials

Emission control summary


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CI Engine Emission Control


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4;

E-haust temperatures of !iesel engines are loer than gasoline

engines *about 177oC,

egligible C( emissions.

(- is relatively high an! nee!s to be re!uce!.

To sources of /Cs emissions Aroun! the perimeter of the reaction )one there is a mi-ture

that is too lean to burn.

The fuel retaine! in the no))le


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ER !isplaces o-ygen$ so only a limite! amount can be use! ina !iesel engine before there is insufficient o-ygen for thorough

combustion.

ER in !iesel engines has only about half the effect that occurs

ith stoichiometrically operate! engines.

>n the engine$ the stoichiometry is unaffecte!$ an! there is

a significant increase in the heat capacity of the mi-ture.

>n contrast$ ER riches the mi-ture in a !iesel engine$ an!

has less effect on the heat capacity.

Therefore$ the mechanism for (- re!uction by ER is not

obvious$ but has been eluci!ate! by some e-periments in

hich the !ilution$ chemical an! thermal effects have been

isolate! for the C(2present in ER.

Exhaust 'as (e$circulation


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)*x catalyst+

Diesel engines operate ea"$ so for (- re!uction$ thesystems hich potentially useful for lean#burn (- re!ucing

catalyst can be use!.

/oever$ the levels of sulphur in the !iesel have to be less

than 7.78 by mass. This is because an o-i!ation catalyst

oul! lea! to the formation of sulphur trio-i!e an! thencesulphuric aci!. This in turn oul! lea! to sulphate !eposits

that oul! bloc" the catalyst. .

Particulates catalyst+

9articulates can be o-i!ise! by a catalyst incorporate! into

the e-haust manifol!.

/oever$ it has to be operating above its light#off

temperature.

Diesel engines have comparatively cool e-haust$ catalysts

!o not necessarily attain their light#off temperature. .

A%ter #reatments


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Criteria+ two con%licting demands" Efficiency ith hich the 9F is actually collecte!

:ac"#pressure in the e-haust system.

Critical topic , Sel%$regeneration+

/o to !eal ith the progressive buil!#up of 9F insi!e the

filter. The ignition temperature of 9F is 7#677o

C$ but theengine e-haust is 277#77oC.

To groups of regeneration metho!s Catalytic regeneration catalytically re!uce ignition temperature

Thermal regeneration electric heater$ burner

Fulti pulse fuel in=ection e.g. 4stto control the start of heat release

2n!to pro!uce the :FE9

+r!to increase the e-haust temperature

-iesel Particulate .ilters


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(2is a strong o-i!ant for o-i!ising carbon. CRT chemical reactions

( ? 4G2(2(

2

2( (2? 4G2

2

(2? C ( ? C(

Continuously$regenerating trap C(#"


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9articulate traps are filters thatre@uire temperatures of about 7#

677oC for soot o-i!ation.

Electrically heate! regenerative

particulate traps have trapping

efficiencies of about ;78.

An o-i!ation catalyst an! soot

filter can be combine! in a

single enclosure as shon.

o-i!ises C($ /C$ an! (- to

(2 The (

2is then responsible for

o-i!ising the particulates in the

soot filter.Fig. 1-12 An oxidation catal#st and soot filter assembl# for use in diesel

Particulate traps


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Emissions -evelopment Europe

/

/0/1

/0/2

/0/3

/0/4

/0/5

/0/6

/ /01 /02 /03 /04 /05 /06

)*x g7km"

Particulate8atter

g7km"

Euro 4 Combustion

System 7 E'(

-P.-e)*x

#echnology and7or 9CCI

Euro 3


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Catalyst -P.Engine

#urbine


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#he growing importance o% a%ter$treatment technology in meeting emissions

legislation


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C*2$ #he .orgotten Pollutant?


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9oint C5C AC5M Monitoring

8ntroduction

of some

models *it$

,2(gCO2km

:erification of

intermediate target.

)e"ie* of potential

for additional CO2

reductions to*ards

,2(g CO2km b#

2(,2

Central

AC5A

commitment

,(gCO2km

Startingpoint; ,/'g

CO2km in

,--'

120g C2!"m

2((( 2((1 2((/ 2(,2

#he ACEA Commitment


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0ehicle 0ehicle mass a re!uction in vehicle mass results in !irect

improvement

Transmission high gear ratioH automate shaft manualtransmissionH constantly variable transmission.

Aero!ynamics re!uce aero!ynamic !ragH lo rollingresistance tyres

Engine

Briction re!uctionH combustion chamber optimisationHvariable valve timingH high pressure common rail in=ectionHD>

Engine !onsi)ing vehicle average poer re@uirement ismerely 41.3"I

A!vance! combustion concepts Lean burn$ D>$ CA>G/CC>

/ybri! poertrain system

E%%ects on %uel economy


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Bast burnt chamber !esigns to increase turbulence of the

airGfuel mi-ture are re@uire!.

Fig. 1-#


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asoline !irect in=ection *D>, technology offers the potential to achievethe specific output of engine$ yet ith fuel economy that is comparableto !iesel engines.

Bor such engine$ the airGfuel mi-ture nee!s to be in a stratifie! mo!e.

The (- emission nee!s to re#treate! by e-haust catalysts

# Lean#burn (- re!ucing catalysts

# De#(- technologies

#


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Lean burn$ high ER$

lo combustion

temperature$ therefore

lo (- emission

un#throttle! engine

control strategy coul!

be employe!

negligible cycle#to#cycle

variations

very lo soot emissions

can be achieve!

Advanced CAI 7 9CCI Combustion

5. emission formation and control

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