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ME2041 Advanced Internal Combustion Engines

Department of Mechanical Engineering, St. Joseph’s College of EnUnit I

Syllabus:

• Air-fuel ratio requirements ,

• Design of carburettor –fuel et si!e an" #enture

si!e,

• Stages of combustion-normal an" abnormal

combustion,

• $actors a%ecting &noc&,• Combustion chambers,

• 'ntro"uction to thermo"(namic anal(sis of S'

Engine combustion process.

Unit I SPARK IGNITION ENGINES




Unit II

Syllabus:

• Stages of combustion-normal an" abnormal

combustion

• $actors a%ecting &noc&,

• Direct an" 'n"irect inection s(stems,• Combustion chambers,

• )urbo charging ,

• 'ntro"uction to )hermo"(namic Anal(sis of C'

Engine Combustion process.

Unit II COMPRESSION IGNITION ENGINES

Department of Mechanical Engineering, St. Joseph’s College of En




Unit III

Syllabus:

• $ormation of *+ , CC+ mechanism ,

Smo&e an" /articulate emissions,

• 0reen ouse E%ect ,

• Metho"s of controlling emissions ,

• )hree 1a( catal(tic con#erter an" /articulate

)rap,

• Emission 2C,C+, *+ an" *+ , 3 measuring

equipments, Smo&e an" /articulate

measurement,

• 'n"ian Dri#in C cles an" emission norms

Unit III ENGINE EXHAUST EMISSION CONTROL





Unit IV

Syllabus:

• Alcohols , 4egetable oils an" bio-"iesel, 5io-gas,

*atural 0as , 6ique7e" /etroleum 0as

,("rogen ,

• /roperties , Suitabilit(, Engine Mo"i7cations,

/erformance ,

•Combustion an" Emission Characteristics of S'an" C' Engines using these alternate fuels.

Unit IV ALTERNATE FUELS





Unit V

Syllabus:

• omogeneous Charge Compression 'gnition

Engine, 6ean 5urn Engine, Strati7e" Charge

Engine, Surface 'gnition Engine , $our 4al#e an"

+#erhea" cam Engines,

• Electronic Engine Management, Common 8ail

Direct 'nection Diesel Engine, 0asoline Direct

'nection Engine ,

• Data Acquisition S(stem –pressure pic& up,

charge ampli7er /C for Combustion an" eat

Unit V RECENT TRENDS





Unit I

• Carburetion )he process of formation of combustible air-fuelmi9ture, b( mi9ing correct amount of fuel an" airin a "e#ice calle" carburetor, before it enters theengine c(lin"er.• $actors A%ecting Carburetion

:. Carburetor Designhas in;uence on "istribution of air-fuel mi9ture to

c(lin"ers.

<. Ambient Air con"itionAmbient pressure an" temperature in;uence the e=cienc(

of carburetion. igher ambient temperature increases the

#apori!ation rate of fuel forming a homogeneous mi9ture.>. $uel Characteristics

E#aporation characteristics 2in"icate" b( "istillation cur#e3is critical for carburetion? presence of #olatile C also isimportant for quic& e#aporation





Unit I

@. Engine Spee" an" 6oa"

• At higher engine spee", the carburetion time is less causingstrain on carburetor to "eli#er uniform mi9ture in a short time?thus pro#ision of #enturi has to be such that the carburetion is"one e=cientl( at higher pressure "rops

• igher loa"s 1ill "eman" richer mi9ture an" lo1er loa" leanermi9tures.• )(pes of Air-$uel Mi9tures

:. Chemicall( Correct Mi9tureStoichiometric or balance" chemical mi9ture in 1hich air ispro#i"e" to completel( burn the fuel? the e9cess air factoris unit(

<. 8ich Mi9ture

$uel is in e9cess of 1hat is require" to burn the fuelcompletel(. )he e9cess air factor is less than unit(.

>. 6ean Mi9tureAir is in e9cess of 1hat is require" to burn the fuelcompletel(. )he e9cess air factor is greater than unit(.





Unit I

• 8ange of Air-$uel 8atio in S' Engines

B: 2rich3 to :B:2lean3 ? )he stoichiometric #aluefor gasoline is :@B:, )he S' engine 1ill not run fortoo rich or too lean mi9tures.

• Mi9ture 8equirements at Di%erent EngineCon"itions


)he air fuel ratio a%ects the po1er output an"bra&e speci7c fuel consumption of the engine as

sho1n in the $igure:.

/o1er+utput2&3

5S$C2&g&h3

/o1er

5S$C

A$ratio




Unit I

• Mi9ture 8equirements at Di%erent EngineCon"itions 2Cont".3


• )he mi9ture correspon"ing to ma9imum outputon the cur#e is calle" best po1er A$ mi9ture,1hich is richer than the stoichiometric mi9ture.

• )he mi9ture correspon"ing to ma9imum 5S$C onthe cur#e is calle" best econom( mi9ture, 1hich

is leaner than the stoichiometric mi9ture.• )he actual A$ ratio requirement for an

automati#e carburetor falls in > rangesB

'"ling 2rich3

Cruising 2lean3 igh /o1er 2rich3




Unit I



'"ling

A$8atio

)hrottle+pening

:

<>

@

!"

#"

Cruising

/o1er

$igure <. A$ 8atio 4s )hrottleopening




Unit I



'"ling 8ange 2:-<3• During i"ling, engine operates at no loa" an" close" throttle.

• )he engine requires rich mi9ture for starting at i"ling.

• 8ich mi9ture is require" to compensate for the charge "ilution"ue to e9haust gases from the combustion chamber.

• Also, the amount of fresh charge a"mitte" is less "ue to smallerthrottle opening.

• E9haust gas "ilution pre#ents e=cient combustion b( re"ucingthe contact bet1een the fuel an" air particles.

• 8ich mi9ture impro#es the contact of fuel an" air b( pro#i"ing

e=cient combustion at i"ling con"itions.• As the throttle is opene" further, the e9haust gas "ilution

re"uces an" the mi9ture requirement shifts to the leaner si"e.




Unit I



Cruising 8ange 2<->3• $ocus is on fuel econom(.

• *o e9haust gas "ilution.

• Carburetor has to gi#e best econom( mi9ture i.e.. 6ean mi9ture.

igh /o1er 8ange 2>-@3• As high po1er is require", a""itional fuel has to be supplie" to

achie#e rich mi9ture in this range.

• 8ich mi9ture also pre#ents o#erheating b( re"ucing the ;ametemperature an" c(lin"er temperature.




Unit I

• /rinciple of +peration of Simple Carburettor





Unit I Department of Mechanical Engineering, St. Joseph’s College of En

• /rinciple of +peration of Simple Carburettor• )he carburettor 1or&s on 5ernoullis principleB the faster air

mo#es, the lo1er its static pressure, an" the higher its "(namicpressure.

• )he throttle 2accelerator3 lin&age "oes not "irectl( control the;o1 of liqui" fuel. 'nstea", it actuates carburettor mechanisms1hich meter the ;o1 of air being pulle" into the engine. )hespee" of this ;o1, an" therefore its pressure, "etermines theamount of fuel "ra1n into the airstream.

• A simple carburetor consists of a ;oat chamber, fuel "ischargeno!!le, a metering ori7ce, a #enturi a throttle #al#e an" cho&e.

• )he ;oat an" nee"le #al#e maintain the fuel le#el

• $uel strainer is use" to trap "ebris from the fuel an" pre#entcho&ing of the fuel no!!le. 't is remo#e" perio"icall( for cleaning.

• During suction stro&e air is "ra1n through the #enturi.

• 4enturi accelerates the air causing a pressure "rop.





• /rinciple of +peration of Simple Carburettor• )his pressure "rop pro#i"es #acuum necessar( to meter the air-

fuel mi9ture to the engine manifol".• $uel is fe" to the fuel "ischarge et, the tip of 1hich is locate" at

the throat of the #enturi

• /ressure "rop is proportional to the throttle opening or loa" onthe engine.

• )hrottle #al#e achie#es go#erning of S' engine b( #ar(ing the A$ratio. 't is a butter;( #al#e locate" after the #enturi tube. henthe loa" is less, the throttle is in near close" position an" if theloa" is high throttle is full( opene".

• )he cho&e #al#e is locate" bet1een the entrance an" #enturithroat. 't is also of butter;( t(pe. hen cho&e is partl( close", alarge pressure "rop occurs at the #enturi throat, 1hich pro#i"es arich mi9ture b( in"uction of large amount of fuel as require""uring i"ling or high loa" con"itions. Cho&e #al#es are springloa"e" to pre#ent e9cessi#e cho&ing an" are sometimesautomaticall( controlle" b( thermostat.

• $or pro#i"ing rich mi9ture "uring i"ling, an i"ling a"ustment ispro#i"e". 't has an i"ling passage an" i"ling port.





• /rinciple of +peration of Simple Carburettor• )he s(stem operates at starting an" shuts o% 1hen <FG throttle

opening is reache".• *ormal #enturi "epression is not su=cient to pro#i"e rich

mi9ture "ue to lo1er throttle opening. 5ut this lo1 pressurecauses fuel rice in i"ling passage an" it is "ischarge" throughi"ling port "o1nstream of the throttle #al#e.

• )he i"ling air blee" suc&s some air for mi9ing 1ith the i"ling fuelan" #apori!es the mi9ture. )he a""itional fuel-air suppl( ma&esthe mi9ture rich for i"ling.

• Simple carburettor has the "ra1bac& of pro#i"ing rich mi9ture1ith increasing throttle opening.





• Compensating s(stems in Carburettors• $or part loa" con"itions, the carburettor must suppl( economic

air-fuel ratio mi9ture. )he main metering s(stem 1ill not satisf(this requirement. )he follo1ing compensating s(stems are use"to achie#e thisB

• Air 5lee" Jet

• Compensating Jet

• Emulsion )ube• 5ac& Suction Control Mechanism

• Au9iliar( Air 4al#e

• Au9iliar( Air /ort

• Altitu"e Compensating De#ice





• Compensating s(stems in Carburettors

Air 5lee" Jet• 't contains an air blee" to the main

no!!le.• Air ;o1 through the blee" passage

is restricte" b( ori7ce.• hen engine is not operating the

blee" passage is 7lle" 1ith fuel.• hen the engine starts the fuel

from the blee" passage is"isplace" b( air ;o1 from theori7ce.

• )he air an" fuel form an emulsionat the tip of the blee" passage.

• )his causes faster "eli#er( of fuel"ue to lo1 #iscosit( an" fuel"ischarge" rises.

• )hus uniform mi9ture ratio is

supplie".






Compensating Jet• )he purpose of this is to ma&e the

mi9ture leaner as the throttleopens progressi#el(.

• An a""itional et calle"compensating et is pro#i"e" 1ith

the main et.• )his et is also connecte" to the

fuel 1ell an" the fuel is metere"through compensating ori7ce.

• As the throttle opening increasesthe main et ma&es the mi9turericher b( a""ing more fuel.

• )he compensating et ma&es themi9ture leaner proportionatel(. )hetotal mi9ture 1ill ma&e A$ ratioconstant.

•hen the main et is lean,compensating et is rich.






Emulsion )ube• 't is also &no1n as submerge" et

"e#ice.• ere, the main metering et is &ept

at a le#el <H mm belo1 the fuelle#el in ;oat chamber.

• )he et is calle" submerge" et. )he et is place" in a 1ell that has holese9pose" to atmosphere.

• hen the throttle openingincreases, the holes in the 1ell areunco#ere" causing a""itional fuelan" air to enter the air-fuel stream,causing the faster A$ mi9ture"eli#er( "uring part loa" operation.






5ac& Suction Control Mechanism• 'n this "e#ice, the top of the fuel

chamber is connecte" to air entr(b( means of a large #ent line 7tte"1ith a control #al#e.

• )he secon" line connects the fuel

;oat chamber to #enturi throat #iaa metering ori7ce.

• hen the control #al#e is opene",the pressure in ;oat chamber is p:

an" the throat pressure is p< 1hich

is lo1er than p:. )his causes thefuel to ;o1. hen the #al#e isclose", there is no "i%erence inpressure an" hence no fuel ;o1.

• )hus the control #al#e achie#es the"esire" air fuel ratio "uring part

loa" operation.






Au9iliar( Air 4al#e• hen the engine is not in

operation, the pressure p: acting

on the #al#e is ambient. )hepressure p< acting at the #enturi is

negati#e 2#acuum3. )his pressure"i%erential lifts the au9iliar( #al#eagainst the spring tensile force.

• A""itional air is thus infuse" in theair-fuel mi9ture pre#enting richmi9ture "uring part loa" operation.






Au9iliar( Air /ort• 'f the butter;( #al#e is opene",

a""itional air passes through thisport, re"ucing air ;o1 through#enturi. )hus pressure "i%erentialis comparati#el( smaller. )hus fuel

"ra1n is re"uce" to compensatefor loss in "ensit( of air at highaltitu"es.






Altitu"e Compensation De#ice• )his 1as use" in high altitu"e car "ri#ing an" for aircrafts.• At high altitu"es, air "ensit( "ecreases an" hence engine

po1er output is a%ecte".• A$ ratio is a%ecte" at high altitu"es as carburettors are

"esigne" to operate on sea le#el.

• )o compensate for the change in air "ensit(, fuel ;o1 has tobe re"uce" from the calibrate" #alue at sea le#el.

• A mi9ture control s(stem comprising a nee"le #al#e, 1hichrestricts fuel ;o1 in proportion to altitu"e change acts as analtitu"e compensating "e#ice.





• Calculation of A$ ratio for a Simple Carburettor• 6et be the "i%erence in height bet1een the tip of the no!!le

an" fuel le#el in the ;oat chamber•

21,C C

21, p p

ρ

- /ressures at inlet an" e9it

- Air "ensit(

- Air #elocities at inlet an" e9it

Z

Appl(ing 5ernoulli’s Equation across the #enturi,

ρ ρ

2

2

21

2

1

22

pC pC +=+

As,

21 C C ⟨⟨

ρ ρ

2

2

21

2

pC p+=





• Calculation of A$ ratio for a Simple Carburettor

ρ pC ∆= 22

Mass ;o1 rate of air through the #enturi,

; AC C m d a ρ = ;2

ρ

ρ p

AC m d a

∆= p AC m d a ∆= ρ 2

Similarl( Mass ;o1 rate of fuel,

; f f f d f C AC m f ρ = )(2 Zg p AC m f f f d f f

ρ ρ −∆=

Due to the

"i%erence inle#el bet1een tipof et an" fuelle#el in chamber

A$ ratio is,

)()(2

2

Zg p

p

A

A

C

C

Zg p

p

A

A

C

C

m

m

f f f d

d

f f f d

d

f

a

f f ρ ρ

ρ

ρ ρ

ρ

−∆

∆=

−∆

∆=

here , A- area of #enturi, Af – Area of fuel et, ρf – "ensit( of fuel





• Combustion in S' Engines

• Combustion is the process of o9i"ation of fuel resulting intothe release of energ( equi#alent to calori7c #alue of fuel.Energ( release" in combustion is in the form of heat.

• Combustion process in spar& ignition engine has requirementof the• mixture of fuel and air in right proportion

• mechanism for initiation of combustion process and• stabilization and propagation of ame for complete

burning• $or complete combustion of e#er( fuel there is chemicall(

correct fuel-air ratio also calle" stoichiometric fuel-air ratio.• )his fuel air ratio ma( be rich or lean "epen"ing upon the

proportion of fuel an" air present in mi9ture. 'n S' engine this

fuel air ratio generall( #aries bet1een : B I to : B >F 1ith leanmi9ture at : B >F an" rich mi9ture at : B I.• Stoichiometric fuel-air ratio is aroun" : B :@ to : B :H for

h("rocarbon fuel. )he e9treme #alues of fuel-air ratiopermissible in S' engine on both rich an" lean en"s put limitsas lower ignition limit’ and ‘upper ignition limit’.





• Combustion in S' Engines

• Varying fuel-air ratio is required in S engine "ue to #ar(ingloa"s on engine bet1een no loa" to full loa" on engine. )heratio of actual fuel-air ratio to stoichiometic fuel-air ratio isgi#en b( equi#alence ratio’ or relati#e fuel-air ratio’.

• Appropriate fuel-air ratio is maintaine" in S' engines throughcarburettor’ 2the fuel metering s(stem3.





• Stages of Combustion in S' Engines






Combustion in S' engine ma( be "escribe" to be occurring infollo1ing signi7cant phaseB2i3 preparation phase(•) !fter compression of fuel-air mixture in cylinder the high

temperature spar" is deli#ered by spar" plug in the compresse"fuel-air mi9ture. )emperature at the tip of spar& plug electro"ema( go e#en more than :F,FFFKC at the time of release ofspar&.

(•) Spar&les release" ha#e su=cientl( high temperature to initiatethe combustion of fuel. $or complete combustion of fuel mereinitiation of combustion "oes not ser#e the purpose instea" asustainable combustion process is require".

(•) After setting up of combustion, a sustainable ;ame front or;ame nuclei is nee"e" so that it procee"s across the combustionspace to ensure complete combustion. )hus, this phase in 1hichspar& is 7rst release" follo1e" b( setting up of sustainable;ame front is calle" Lpreparation phase an" ma( consumearoun" :FK of cran& angle rotation.






• Cran& angle rotation consume" in Lpreparation phase "epen"supon the spee" of engine, constructional feature of c(lin"er,piston, location of spar& plug, strength of spar&, characteristics offuel, fuel-air ratio etc.

• /reparation phase is sho1n to occur from a’ to ‘b’ with small ornegligible pressure rise as initially rate of burning is #er( small.

2ii3 $lame /ropagation /hase(•) After sustainable combustion ;ame is set up, then the ;ame

nuclei get scattere" "ue to e9cessi#e turbulence in combustionspace causing pressure to rise from b’ to ‘c’.

(•) $his phase of combustion "epen"s upon the turbulence insi"e

c(lin"er, strength of combustion nuclei, fuel-air ratio, strength ofspar&, c(lin"er geometr(, fuel properties etc.

(•) )his phase of combustion is calle" as L;ame propagation phasean" is accompanie" b( the e9cessi#e pressure rise. $lamepropagation phase shoul" also be as small as possible.






2iii3After 5urning /hase(•) After the ma9imum amount of fuel-air mi9ture is burnt, the

resi"ual gets burnt after the piston has mo#e" across the )DC.(•) )his last phase is terme" as Lafter burning phase an" occurs

"uring the e9pansion stro&e.

(•) ence, it can be summarise" that the complete combustion in S'engine occurs in three "istinct !ones i.e. preparation phase, ;amepropagation phase an" after burning phase.

(•) 'n or"er to ha#e complete combustion in smallest possible timethe ;ame propagation phase an" preparation phase shoul" beshortene".

(•) +ut of total "istance tra#elle" in combustion space in 7rst phasei.e. /reparation phase about :FG of combustion space length isco#ere" in about <F–>FG of total time for combustion.

d d l b i i






• $lame propagation phase is sprea" in about NFG of combustionspace length an" is co#ere" in OF–IFG of total time ofcombustion.

• After burning’ occurs in less than :FG of combustion space in lessthan :FG of total combustion time.

• Abnormal Combustion

• Combustion ma( also sometimes occur abnormall(. LAbnormalcombustion is sai" to occur 1hen combustion begins insi"e thec(lin"er on its’ o1n before the stipulate" time for it.

• )his abnormal combustion ma( be "ue to pre-ignition 2i.e. ignition

of fuel e#en before spar& plug ignites it3 or auto-ignition 2i.e.'gnition of fuel "ue to hot spots in the combustion space li&e #al#eseats, spar& plug3 an" results in uncontrolle" pressure rise.

• Abnormal combustion is also terme" as "etonation or &noc&ingan" can be felt b( er&( operation of engine, e9cessi#e noise,re"uce" po1er output etc

ME2041 Ad d I l C b i E i





• $actors a%ecting &noc&

• $uel

A lo1 self ignition temperature’ fuel promotes &noc&.• 'n"uction pressure'ncrease of pressure "ecreases S') an" increases in"uction time? ten"enc(of &noc& increases. Eg. At full throttle &noc& ten"s to occur more.

• Engine Spee"6o1 engine spee" 1ill gi#e lo1 turbulence an" lo1 ;ame #elocit( an" hence&noc& ten"enc( is more.

• 'gnition )imingA"#ancing ignition timing increases pea& pressure an" promotes &noc&.

• Compression 8atioigh compression ratio increases c(lin"er pressures an" increases theten"enc( for &noc&.

• Combustion Chamber Design/oor "esign results in long ;ame path, lo1 turbulence an" insu=cientcooling all of 1hich increase &noc& ten"enc(.

• C(lin"er Cooling/oor c(lin"er cooling increases the temperature an" hence the chances of&noc& temperature’ fuel promotes &noc&.

ME2041 Ad d I t l C b ti E i





• Combustion Chambers





Unit I

THERMOD$NAMIC ANAL$SIS OF SI ENGINECOM%USTION

5ecause combustion occurs through a ;ame propagationprocess, the changes instate an" the motion of the unburne" an" burne" gas are muchmore comple9than the i"eal c(cle anal(sis.

)he gas pressure, temperature an" "ensit( changes as a resultof changes in #olume "ue to piston motion.During combustion, the c(lin"er pressure increases "ue to therelease of the fuelschemical energ(.

As each element of fuel-air mi9ture burns, its "ensit( "ecreasesb( about a factor of four. )his combustion-pro"uce" gas e9pansion compresses theunburne" mi9ture ahea" of the ;ame an" "isplaces it to1ar"the combustion chamber 1alls.

)he combustion-pro"uce" gas e9pansion also compresses thoseparts of the charge 1hich ha#e alrea"( burne", an" "isplacesDepartment of Mechanical Engineering, St. Joseph’s College of En

%u&n'( an( Unbu&n'( Mi)tu&' Stat's





Unit I


During the combustion process, the unburne" gas elementsmo#e a1a( from the spar& plug? follo1ing combustion,in"i#i"ual gas elements mo#e bac& to1ar" the spar& plug.$urther, elements of the unburne" mi9ture 1hich burn at"i%erent times ha#e "i%erent pressures an" temperatures ust

prior to combustion, an" therefore en" up at "i%erent statesafter combustion. )he thermo"(namic state an" composition of the burne" gas is,therefore, non-uniform.A 7rst la1 anal(sis of the spar&-ignition engine combustion

process enables us toquantif( these gas states.or& transfer occurs bet1een the c(lin"er gases an" the piston2to the gas before )C? to the piston after )C3.







Unit I


eat transfer occurs to the chamber 1alls, primaril( from theburne" gases.At the temperatures an" pressures t(pical of spar&-ignitionengines it is a reasonable appro9imation to assume that the#olume of the reaction !one 1here combustion is actuall(

occurring is a negligible fraction of the chamber #olume e#enthough the thic&ness of-the turbulent ;ame ma( not benegligible compare" 1ith the chamber "imensions.ith normal engine operation, at an( point in time or cran&angle, the pressure throughout the c(lin"er is close to uniform.

)he con"itions in the burne" an" unburne" gas are then"etermine" b( conser#ation of mass B







Unit I


)he conser#ation of energ(B

1here 4 is the c(lin"er #olume, m is the mass of the c(lin"ercontents, # is the speci7c #olume, xb is the mass fractionburned, Uo is the internal energ of the c(lin"er contents

at some reference point 0 , u is the s!eci"c internal energ,# is the 1or& "one on the piston, an" P is the heat transfer tothe 1alls. )he subscripts u and b denote unburned andburned gas !ro!erties, res!ectivel$

%he 1or& an" heat transfers areB

here is the instantaneous heat-transfer rate to the chamber1alls.







Unit I


Qseful results can be obtaine" b( assuming that the burne" an"unburne" gases are "i%erent i"eal gases, each 1ith constantspeci7c heats. i.e.

Combining these eqns.







i


)he abo#e equations ma( be sol#e" to obtain

'f 1e no1 assume the unburne" gas is initiall( uniform an"un"ergoes isentropic compression, then

D f M h i l E i i S J h’ C ll f E


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