Carburetion and Fuel Injectors

7/29/2019 Carburetion and Fuel Injectors

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1

1

Internal combustion Engines:

Carburetor, Fuel injection, valve timing

Dr. Primal Fernando

[email protected]: (081) 2393608

CarburetorsandFuelinjection Fuelinjection isasystemformixingfuelwithairinaninternalcombustion

engine.Ithasbecometheprimaryfueldeliverysystemusedingasolineautomotiveengines,havingalmostcompletelyreplacedcarburetorsinthelate

1980s.

ThecarburetorwasinventedbyKarlBenz(founderofMercedesBenz)in1885andpatentedin1886.

Carburetorsweretheusualfueldeliverymethodforalmostallgasoline(petrol)

2

fuelledenginesupuntilthelate1980s,whenfuelinjectionbecamethepreferredmethodofautomotivefueldelivery.IntheU.S.market,thelastcarburetedcarswerethe1990Oldsmobile CustomCruiser,BuickEstateWagon,andSubaruJusty,andthelastcarburetedlighttruckwasthe1994Isuzu.Elsewhere,Ladacarsusedcarburetorsuntil1996.Amajorityofmotorcyclesstillusecarburetorsduetolowercostandthrottleresponseproblemswithearlyinjectionsetups,butasof2005,manynewmodelsarenowbeingintroduced withfuelinjection.Carburetorsarestillfoundinsmallenginesandinolderorspecializedautomobiles,suchasthosedesignedforstockcarracing.

Afuelinjectionsystemisdesignedandcalibratedspecificallyforthetype(s)offuelitwillhandle.Mostfuelinjectionsystemsareforgasolineordieselapplications.

3

GasReviewNovember1913

Usedontractors,boats,andstationaryengines,includingtheWaterlooBoyandModelDtractors

GasReviewSeptember1917

4

Well,letsseeifwecanfigureitout

CarburetorTheory

ItsallduetoAirPressure(orlackthereof)

Closetosealevelpressureis14.7psi

Airhasweight 88lbsina12x12x8ftroom

Vacuumisapressurelessthan14.7psi

Oftenmeasuredininchesofmercury

5

14.7psi~30inHg

Asengineruns,intakestrokescreate

vacuumorlowerairpressureinmanifold

Normal~10psi(~20inHg)

Withthrottleplateopen,carburetorthroat

exposedtomanifoldpressure

CarburetorTheory

Venturi

Whatisit?

WindblowingindowntownChicago

alwaysstrongerinthesmallerareasbetween2

6

buildings Rivercurrents

alwaysfasterinanarrower,shallowerplacethandeep,widepools


2/22

2

CarburetorTheory

7

CarburetorsoperateontheventurieffectTheventuriisanarrowingofthebore

CarburetorTheory

Whatcausesairflowthroughcarburetor?

Intakestrokeofpistoncreatesvacuum

Intakevalveopen,transmitsvacuumtothrottleplate

Positionofthrottleplatedeterminesairflow

8

Open fullflow lowmanifoldvacuum

Air(at~atmosphericpressure)flowsfromair cleanerside,throughventuri,pastthrottleplate,throughmanifoldandintakevalve,intocylinder

ModelArunningat975rpmflowsabout70cfm (cubicfeetperminute)

Asairflowsthroughventuri,pressuredecreasesinventuri BernoullisLawtellsusasAreadecreases,velocityincreasesand Asvelocityincreases,pressuredecreases

CarburetorTheory

9

rpressureon ue n ow sa ways~a mosp er cAspressuredifferencebetween1)fuelinbowland2)attipofnozzle(locatedinventuri)increases,fuelflowincreasesfromnozzle Throttleopens,moreairflow,greater P,morefuelflow Throttlecloses,lessairflow,less P,lessfuelflow

Importantfactors AmountofvacuumcreatedbyintakestrokeLessvacuumif Intakevalveguidesleakair Exhaustvalveleaksair

CarburetorTheory

10

Pistonringsleakair Manifoldgasketleaksair PositionofthrottleplateDeterminesairflowthroughcarburetor DeterminesdifferenceinpressureonfuelinbowlandattipofnozzleinventuriGreaterdifference morefuelflow

CarburetorTheory

Tofurtherregulatethemixture,twoairregulatorsorbutterflyvalvesarealsoadded:

Theserestricttheamountofairflowthroughthecarburetoreithermanuallyorautomatically.

11

sac on ecreases epoweran spee an therichnessofthemixturewithintheengine.

Throttlevalvesrestrictairmovementatallspeedsandaregenerallymanuallycontrolled.

Chokevalvesrestrictairmovementatstartuptoallowforarichermixtureandcanbemanuallyorautomaticallyengaged.

Carburetortypes

VenturitypeCarburetor

P+1/2V2 =Constant

Bernoulli Effect:

Valve StemFuel Inlet

Throttle Plate

Air/Fuel Mixture To Engine

Atomized Fuel

12

Ref. Obert

Constant level ismaintained in bowl -as

float moves down,valve stem moves down,allowing more fuel intobowl, float moves up andcloses valve

Float

Metering Orifice

Choke Plate

FuelNozzle

Inlet Air

Bowl

Venturi


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3

% BoreOpen0 0.0

10 1.514 3.017 4.424 8.630 13.4

13

33 16.141 25.045 29.360 50.075 75.084 90.090 100

%Boreopen= b(1 cos)x100BoreOpenisdifferencebetween

boresizeandareaofthrottleplate

b=radiusofboresize

TheThrottle

Thethrottleisarounddiscmountedonashaftbeyondthemainfuelnozzleinthe

14

carburetor.

Itregulatestheamountofairfuelmixtureenteringthecylinder.

TheChoke

Thechokeisarounddiscmountedonashaftlocatedattheintakeendofthecarburetor.

Sincecoldfuelishardtovaporize,thechokeisusedduringcoldenginestartstoprovidearichmixturetothe

15

car uretorinor ertogett eenginestarte .

NaturalDraftCarburetor

Thiscarburetorisusedwherethereislittlespaceontopofthe

16

engine. Theairhorizontallyintothemanifold.

UpdraftCarburetors

Thistypeisplacedlowontheengineanduseagravityfedfuelsupply. Inother

17

words,thetankisabovethecarburetorandthefuelfallstoit.

DowndraftCarburetors

Thiscarburetoroperateswithlowerairvelocitiesandlargerpassages. Thisisbecausegravityassiststheairfuelmixtureflowtothecylinder.

18

Thedowndraftcarburetorcanprovidelargevolumesoffuelwhenneededforhighspeedandhighpoweroutput.


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4

DiaphragmCarburetors

Thistypedoesnothaveafloat,ratherthedifferencebetweenatmosphericpressureandthevacuumcreatedintheengine

ulsatesaflexibledia hra m.

19

Thepulsationofthediaphragmtakesplaceoneveryintakeandcompressionstroke.

MixtureRequirements

Engineinductionandfuelsystemmustprepareafuelairmixturethatsatisfiestherequirementsoftheengineoveritsentireoperatingregime.

20

gives

1. requiredpoweroutput

2. withlowestfuelconsumption

3. consistentwithsmoothandreliableoperation

21 22

CalculationofAirfuelRatio

ot

2out

outoutoutoutin

2in

inininin gZ2

hmWQgZ2

hmWQ

in

2

inininot

2

outoutoutinoutoutin gZ

2hmgZ

2hmWWQQ

Energybalanceforasteadyflowsystem

23

Generalform

in

2in

ininot

2out

outout gZ2

hmgZ2

hmWQ

Note:Intheaboveequation,heatinputtothesystemandworkoutputfromthesystemispositive(+)andheatoutputfromthesystemandworkinputtothesystemisnegative().


in

2in

ininot

2out

outout gZ2

hmgZ2

hmWQ

in

ininot

outout gZhgZhwq

22

22

Applyingthesteadyflowenergyequationto

24

1

21

12

22

222

gZhgZhwq

Here,q andwaretheheatandworktransfersfromtheentrancetothethroatandh andv standforenthalpyandvelocityrespectively.Ifweassumereversibleadiabaticconditions,andthereisnoworktransfer,q=0,w=0,andifapproachvelocityv10weget

sectionsAAandBBperunitmassflowofair:


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5


20

22

12

hh

212 2 hhv

writecanwehenceTch

getwegasperfectabetoassumedisairIf

25

212 2 TTcv p

k

k

k

k

p

pTTT

p

p

T

Tthen

isentropicbetothroattoinletfromflowAssume

1

1

2121

1

1

2

1

2

1


k

k

ppTTT

1

1

2121 1

212 2 TTcv p

k

k 1

26

pp

Tcv1

212 12

Bythecontinuityequationwecanwritedownthetheoreticalmassflowrateofair

222111

.

vAvAma

where A1 and A2 are the crosssectional areas at the air inlet (point 1)and venturi throat (point 2).


k

k

pp

pTcv

1

1

212 12

222111

.

vAvAma

(velocity)

27

To calculate the mass flow rate of air at the throat, we have assumed theflow to be isentropic till the throat so the equation relating p and v (or) can be used.

kk vpvp 2211 kkpp

2

2

1

1

k

p

p1

1

212

(specificvolume)


k

k

pp

pTcv

1

1

212 12

222111

.

vAvAma

1

28

k

p

p

1

212

k

k

p

k

a

p

pTcA

p

pm

1

1

212

1

1

21

.

12


k

k

p

k

a

p

pTcA

p

pm

1

1

212

1

1

21

.

12

For a perfectgas we have 1

11

RT

p

29

k

k

p

k

ap

pTcA

RT

p

p

pm

1

1

212

1

1

1

1

2.

12

rearrangingtheaboveequationwehave

k

k

k

pap

p

p

pc

TR

pAm

1

1

2

2

1

2

1

12.

2


k

k

k

pap

p

p

pc

TR

pAm

1

1

2

2

1

2

1

12.

2

Since the fluid flowing in the intake is air, we can put in theapproximate values of R = 287 J/kgK, cp = 1005 J/kgKand k = 1.4 at 300K.

30

1

12

.

1

2.

1

2

1

12.

1562.0

1562.0

T

pA

p

p

p

p

T

pAma

71.1

1

2

43.1

1

2

p

p

p

pwhere


6/22

6


1

12

71.1

1

2

43.1

1

2

1

12.

1562.0

1562.0

T

pA

p

p

p

p

T

pAma

71.1

1

2

43.1

1

2

p

p

p

p

31

Here, pressure p is in N/m2, area A is in m2,and temperature Tis in K.If we take the ambient temperature T1 = 300Kand ambient pressurep1 = 10

5 N/m2, then2

.

8.901 Ama

Above equation gives the theoretical mass flow rate of air. The actualmass flow rate, can be obtained by multiplying the equation by thecoefficient of discharge for the venturi, Cd,a.

.

.

,

a

aad

m

mC

1

12,

.

1562.0

T

pACm ada

The coefficient of discharge and area are both constant for a givenenturi hus


71.1

1

2

43.1

1

2

p

p

p

p

32

1

1.

T

pma

Sincewehavetodeterminetheairfuelratio,wenowcalculatethefuelflowrate.

1

1.

T

pma

Thefuelisaliquidbeforemixingwiththeair,itcanbetakentobeincompressible.

WecanapplyBernoullisequationbetweentheatmosphericconditionsprevailing atthetopofthefuelsurfaceinthefloatbowl


33

whichcorrespondstopoint1andthepointwherethefuelwillflowout,attheventuri,whichcorrespondstopoint2.

Fuel flow will take place because of the drop in pressure at point 1due to the venturi effect.

(Constant)C gz2VP 2

2

22

2

2

1

21

1

1

22 gz

VP

gz

VP

or

1

1.

T

pma Fuel flow will take place because of

the drop in pressure at point 1 dueto the venturi effect.

2

22

2

21

21

1

1

22gz

VPgz

VP

2

22

2

2

1

1

2gz

VPP


34

(1)

(2)gzVPP f

ff

2

2

21

where f is the density of the fuel in kg/m3, Vf is the velocity of the fuel

at the exit of the fuel nozzle (fuel jet), and z is the depth of the jet exitbelow the level of fuel in the float bowl. This quantity must always be

above zero otherwise fuel will flow out of the jet at all times. The valueof z is usually of the order of 10 mm.

gzVpp f

ff

2

2

21

From above equation we can obtain an expression for the fuel velocity atthe jet exit as

gzpp

Vf212


35

f

Applyingthecontinuityequationforthefuel,wecanobtainthetheoretical massflowrate,

gzppA

VAm

fff

ffff

21

.

2

where Af is the exit area of the fuel jet in m2. If Cd,f is the

coefficient of discharge of the fuel nozzle (jet) given by

.

.

,

f

f

fd

m

mC

.

21, 2 gzppACm ffffdf


36

Since .

.

f

a

m

m

F

A

Fuel

Air

gzppTp

A

A

C

C

F

A

ffffd

ad

211

12

,

,

21562.0

1

12,

.1562.0

TpACm ada

71.1

1

2

43.1

1

2

p

p

p

p


7/22

7


k

k

k

p

ad

ap

p

p

pc

TR

pACm

1

1

2

2

1

2

1

12,.

2 .


1

11

RT

p

11

1 1

Tp

R

11

1 1

Tp

R

37

k

k

k

padap

p

p

pc

R

p

p

RACm

1

1

2

2

1

21

1

12,

.

2

k

k

k

padap

p

p

pc

R

pACm

1

1

2

2

1

2112,

.

2


.


k

k

k

padapp

ppc

RpACm

1

1

2

2

1

2112,

.

2

k

k

kc12

.

1

.

c

R

c

cRcc

pp

v

vp

38

padappR

pACm1

2

1

2112, 2

1

1

k

k

R

c

ck

p

p

k

k

k

adap

p

p

p

k

kpACm

1

1

2

2

1

2112,

.

1

2


.


k

k

k

adap

p

p

p

k

kpACm

1

1

2

2

1

2112,

.

1

2

39

gzppAC

p

p

p

p

k

kpAC

m

m

ffffd

k

k

k

ad

f

a

21,

1

1

2

2

1

2112,

.

2

1

2


gzppAC

p

p

p

p

k

kpAC

m

m

ffffd

k

k

k

ad

f

a

21,

1

1

2

2

1

2112,

.

2

1

2

40

k

k

k

ffffd

ad

f

a

p

p

p

p

k

k

gzpp

p

A

A

C

C

m

m1

1

2

2

1

2

21

12

1

12

,

,

.

1

21 pppa Ifweput 1

1

21

p

p

p

pa

and


k

k

k

ffffd

ad

f

a

p

p

p

p

k

k

gzpp

p

A

A

C

C

m

m1

1

2

2

1

2

21

12

1

12

,

,

.

1

21 pppa 1

1

21

p

p

p

pa

41

1

2

1

1

2

2

1

2

2

1

12

,

,

.

1

1

p

p

p

p

p

p

k

k

gzp

p

A

A

C

C

m

m

k

k

k

fa

a

fffd

ad

f

a


1

2

1

1

2

2

1

2

2

1

12

,

,

.

1

1

p

p

p

p

p

p

k

k

gzp

p

A

A

C

C

m

m

k

k

k

fa

a

fffd

ad

f

a

42

gzpp

AA

CFA

fa

a

f

a

ffd

ad

2

,

,

2

1

1

2

1

1

2

2

1

2

11

p

p

p

p

p

p

k

k

k

k

k


8/22

8

if we take T1 = 300K and p1 = 105 N/m2 then

gzppAA

C

C

F

A

ffffd

ad

21

2

,

,

28.901

The coefficient of discharge represents the effect of all deviations fromthe ideal onedimensional isentropic flow. It is influenced by many


43

factors of which the most important are:

1.Fluidmassflowrate,2.Orificelengthtodiameterratio,3.Orificeareatoapproacharearatio,4.Orificesurfacearea,5.Orificesurfaceroughness,6.Orificeinletandexitchamfers,7.Fluidspecificgravity,8.Fluidviscosity,and9.Fluidsurfacetension.

Airfuelrationeglectingcompressibilityofair

Ifweassumeairtobeincompressible,thenwecanapplyBernoullisequationtoairflowalso.Sinceinitialvelocityis

assumedzero,wehave

2221 vpp

Thus

44

2aa

Thus

a

ppv

212 2

Applyingthecontinuityequationforthefuel,wecanobtainthetheoreticalmassflowrate,

21222.

2 ppACAm aaa

where A2 is the venturi in m2. If Cd,a is the coefficient of discharge of the

venturi given by.

45

.,

a

aad

m

C

then .

212,

.

2 ppACm aada

Since .

.

f

a

m

m

F

A

Fuel

Air

gzpp

pp

A

A

C

C

F

A

ff

a

ffd

ad

21

212

,

,

ppACA aad 212,

46

gzpp ffffd 21,

Ifweassumez=0,then

f

a

ffd

ad

A

A

C

C

F

A

2

,

,

The equivalence ratio, (ratio between stoichiometric airfuel ratio to actual air fuel ratio)

AA

F

A

s 6.14

112 k

gzp

p

A

A

C

C

F

A

fa

a

f

a

ffd

ad

2

,

,

Typicalvalueforagasolineengine

47

2

1

2,

, 1

a

f

a

ff

ad

fds

p

gz

A

A

C

CF

A

FF

1

2

1

2

1

2

11

p

p

pp

pp

k

k

kk

2

1

2,

,1

a

f

a

ff

ad

fds

p

gz

A

A

C

CF

A

Theeffectsofequivalenceratiovariations

Mixturerequirementatfullload:Completeutilizationofairtoobtainmaximumpower,wideoperationofthrottle,richofstoichiometricmixtures,1.1.

Mixturerequirementatpartloads:Partthrottle,diluteair

48

mixturewithexcessairorexhaustedgasrecycled(EGR)(improvesthefuelconversionefficiency).

Theequivalentratioofthemixturedeliveredbyanelementarycarburetorisnotconstant.


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9

ACA


1

2

1

1

2

2

1

2

2

1

12

,

,

.

1

1

p

p

p

p

p

p

k

k

gzpp

AA

CC

mm

k

k

k

fa

a

fffd

ad

f

a

49

gzpACF fa

a

f

a

ffd ,

,

2

1

1

2

1

1

2

2

1

2

11

p

p

p

p

p

p

k

k

k

k

k

50

CarburetorPerformance

Figureshowstheperformanceofanelementarycarburetor.ThetopgraphshowsthevariationofCd,a andCd,f and withtheventuripressuredrop(typicallyvarywithpressuredrop).For pa fgz,thereisnofuelflow.Oncefuelstartstoflow,thefuelflowrateincreasesmore

51

rap y an ea r owra e. ecar ure or e versamixtureofincreasingequivalenceratioastheflowrateincreases.z istypicallyorderof10mm.Usuallyfuellevelinthefloatchamberisheldbelowthefueldischargenozzletopreventthefuelspillagewhentheengineisinclinedtohorizontal.

Thedeficienciesofaelementarycarburetor

1. Atlowloadsthemixturebecomesleaner;theenginerequiresthemixturetobeenrichedatlowloads.

2. Atintermediateloads,themixtureequivalenceratioincreasesslightlyastheairflowincreases.Theenginerequiresanalmostconstantequivalenceratio.

3. Astheairflowapproachesthemaximumwideopenthrottle

52

value,theequivalenceratioremainsessentiallyconstant.However,themixtureequivalenceratioshouldincreaseto1.1orgreatertoprovidemaximumenginepower.

4. Theelementarycarburetorcannotcompensatefortransientphenomenaintheintakemanifold.Norcanenrichthemixtureduringenginestartingandwarmup.

5. Theelementarycarburetorcannotadjusttochangesinambient

airdensity(dueprimarilytochangesinaltitude).

ModernCarburetorDesign

Thechangesrequiredintheelementarycarburetorsothatitprovidestheequivalenceratiorequiredatvariousairflowratesareasfollows.

1. Themainmeteringsystem mustbecompensatedtoprovideaconstantleanorstoichiometricmixtureover20to80%oftheairflowrange.

2. Anidlesystemmustbeaddedtometerthefuelflowatidleandlightloadstoprovidearichmixture.

3. Anenrichmentsystem mustbeprovidedsothattheenginecangetarichmixtureaswideopenthrottleconditionsisapproachedandmaximumpowercanbeobtained.

53

4. Anacceleratorpump mustbeprovidedsothatadditionalfuelcanbeintroducedintotheengineonlywhenthethrottleissuddenlyopened.

5. Achoke mustbeaddedtoenrichthemixtureduringcoldstartingandwarmuptoensurethatacombustiblemixtureisprovidedtoeachcylinderatthetimeofignition.

6. Altitudecompensation isnecessarytoadjustthefuelflowwhichmakesthemixturerichwhenairdensityislowered.

7. Increaseinthemagnitudeofthepressuredropavailableforcontrollingthefuelflowisprovidedbyintroducingboostventuris(Venturisinseries)orMultiplebarrelcarburetors(Venturisinparallel).

Twocommonmethodsusedtoachieveaboveare

Boostventuris

Doubleventurisystem,multipleventuris.

54

Multiplebarrelcarburetors

Twobarrelcarburetorsusuallyconsistsoftwosinglebarrelcarburetorsmountedinparallel.


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10

Fuelinjectionsystems

Gasolinefuelinjection Injectthefuelintotheengineintakesystem

Requiredoneinjectorpercylinder

Therearebothmechanicalandelectronicinjectorsystems Increasedpowerandtorque,uniformfueldistribution,rapidengine

responsetothrottleposition,precisecontrolofequivalenceratio

Dieselfuelinjection

55

FuelsprayedincylindernearTDC

Atomization,vaporization&mixingdelayignition

Ignitionoccurswhereverconditionsright

Combustionratecontrolledbyinjectioncharacteristics(injectionrate,sprayangle,injectionpressure,nozzlesizeandshape),chambershape,mixturemotion,&turbulence

Glowplugmaybeusedtoaidcoldstarting

Poweroutputcontrolledonlybyamountoffuelinjected

MeritsofFuelInjectionintheSIEngine

AbsenceofVenturi NoRestrictioninAirFlow/HigherVol.Eff./Torque/Power

HotSpotsforPreheatingcoldaireliminated/Denserairenters ManifoldBranchPipesNotconcernedwithMixturePreparation

(MPI)

BetterAccelerationResponse(MPI)

56

FuelAtomizationGenerallyImproved

UseofGreaterValveOverlap

Use of Sensors to Monitor Operating Parameters/Gives AccurateMatching of Air/fuel Requirements: Improves Power, Reducesfuel consumption and Emissions

PreciseinMeteringFuelinPorts

PreciseFuelDistributionBetweenCylinders(MPI)

LimitationsofPetrolInjection HighInitialCost/HighReplacementCost

IncreasedCareandAttention/MoreServicingProblems

RequiresSpecialServicingEquipmenttoDiagnoseFaultsandFailures

SpecialKnowledgeofMechanicalandElectricalSystemsNeededtoDiagnoseandRectifyFaults

InjectionEquipmentComplicated,DelicatetoHandleandImpossibletoServicebyRoadsideServiceUnits

57

ContainMoreMechanicalandElectricalComponentsWhichMayGoWrong

IncreasedHydraulicandMechanicalNoiseDuetoPumpingandMeteringofFuel

Very Careful Filtration Needed Due to Fine Tolerances of Metering andDischarging Components

More Electrical/Mechanical Power Needed to Drive Fuel Pump and/orInjection Devices

More Fuel Pumping/Injection Equipment and Pipe Plumbing Required May be Awkwardly Placed and Bulky

GasolineFuelInjectionSystemComponents

1. ElectricFuelPump

2. FuelAccumulator MaintainsFuelLinePressureWhenEngineisShutOffandQuietnesstheNoiseCreatedbytheRollerCellPump

3. FuelFilter APleatedPaperorLintoffluffTypePlusStrainer

4. PrimaryPressureRegulator MaintainsOutputDeliveryPressuretobeAbout5Bar

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5 PushUpValve PreventsControlPressureCircuitLeakage.

ItisaNonreturnValvePlacedatOppositeEndofPressureRegulator

6. Fuel Injection Valve Valves are Insulated in Holders to Prevent FuelVapor Bubbles Forming in the Fuel Lines Due to Engine Heat.

ValvesOpenatabout3.3BarandSprayFuel.

ValveOscillatesAbout1500cyclespersecondandsoHelpsinAtomization

GasolineFuelInjection

InSIenginestheairandfuelareusuallymixedtogetherintheintakesystempriortoentrytotheenginecylinder.

Ratioofairtofuel 15:1

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Fuelisinjectedtotroughindividualinjectorsfromalowpressurefuelsupplysystemintotheintakeport.

IndirectInjection

AlsoCalledManifoldInjectionorSinglePointInjection(SPI)orThrottleBodyInjection(TBI)

InjectorUsuallyUpstreamFromThrottle(AirIntakeSide)orInSomeCasesPlacedontheOppositeSide

PressuresareLow 2to6Bar.MaybeInjectedIrrespectiveofIntakeProcess

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CostWouldbeLow

Has Same Air and Fuel Mixing and Distribution Problems asCarburetor but Without Venturi Restriction so Gives HigherEngine Volumetric Efficiency

Higher Injection Pressures Compared to Carburetion Speeds upAtomization of Liquid Fuel


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SemidirectInjection AlsoCalledPortInjectionorIndirectMultipointInjection(IMPI)or

SimplyMultipointInjection(MPI)

InjectorsPositionedinEachInductionManifoldBranchJustinFrontofInletPort

InjectionatLowPressure(26Bar)

NeedNotBeSynchronizedWithEngineInductionCycle

FuelCanBeDischargedSimultaneouslytoEachInductionPipeWhere

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itisMixedandStoredUntilIVO

NeedNotBeTimed RequiresLowDischargePressures InjectorsNotExposedtoCombustionProductssoComplexityReduced LessCost

No Fuel Distribution Difficulties Since Each Injector Discharges DirectlyInto Its Own Port and Mixture Moves a Short Distance Before EnteringCylinder

Induction Manifold Deals Mainly With Only Inducted Air So BranchPipes Can Be Enlarged and Extended to Maximize Ram Effect

DirectCylinderInjection AlsoCalledDirectMultipointInjection(DMPI)orGasolineDirect

Injection(GDI)

InjectionMaybeDuringIntakeorCompressionProcess

IncreasedTurbulenceRequired ToCompensateForShorterPermittedTimeFor

Injection/Atomization/MixingInjectionPressureMustBeHigher

MoreValveOverlapPossibleSoFreshAirCanBeUtilizedFor

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InjectorNozzleMustBeDesignedForHigherPressureandTemperatureSoMustBeMoreRobustandWillBeCostlierThanOtherTypes

PositionandDirectionofInjectionAreImportant NoOnePositionWillBeIdealForAllOperatingConditions

AirandFuelMixingIsMoreThoroughinLargeCylindersThanInSmallCylindersBecauseDropletSizeistheSame

CondensationandWallWettinginIntakeManifoldEliminatedButCondensationOnPistonCrownandCylinderWalls

GasolineFuelInjectionInjectortypes

Mechanicalinjectionusinganinjectionpumpdrivenbytheengine.

Mechanical,driveless,continuousin ection.

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Electronicallycontrolleddrivelessinjection.

FuelInjection (electronic,multiport)

Monitored EngineOperating Conditions:

Manifold PressureEngine Speed

Air TemperatureCoolant Temperature

Acceleration

COMPUTERTRIGGER

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50 psi typical

INJECTOR DRIVE UNIT

Pressure Regulator Fuel Filter

FuelPump

FUEL TANK

Injectors

ELECTRONICFUELINJECTION

Strictemissionstandardsrequireprecisefueldelivery

Computersusedtocalculatefuelneeds

EFIveryprecise,reliable&costeffective

EFIprovidecorrectA/Fratioforallloads,speeds,&temp

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ranges

TheFuelInjector

Electromechanicaldevice

Enginerpmdetermineswheninjectoropens

Howlongitstaysopendeterminedby:

Enginetemp

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Throttlepos.

O2sensorvoltage


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ThrottleBodyInjection(TBI)

Firstinjectionunitused

HousingsimilartoCarb

One or two

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injector

Oneortwooftheseunitsmountedtointakemanifold

FIG 6-40 CLASS

LOWPRESSUREFUELINJECTOR

1316psioperatingpressure

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a sty epintle

Easilyreplaceable

MultiPortFuelInjection

Oneinjectorpercylinder

Mountsinintakemanifold,spraysdirectlyatintakevalve

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individually (SFI)

RamTuningfordenseraircharge

LowerA/Ftemps

Leanermixtureduringwarmup

FuelPressureRegulator

Locatedatendoffuelrail

Maintainsconstantpressureatinjectors

Internalchambercontainsadiaphragm Pressurizedfuelononeside

Manifoldvacuum&springtensiononother

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Manifoldvacuumpullsupondiaphragm,meteringfuelthatisreturnedtotank

Excessfuelpressurecanovercomespringtension,allowingfueltoreturntotank

Increasesinmanifoldpressurecausesspringtensiontopushdiaphragmdown,blocking

returnline,increasingpressureinrail.


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Vacuum hoseconnection Fuel rail


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Fuelreturn


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Dieselengine(CI)

Theliquidfueljetatomizesintodropsandentrainsair;evaporatesfuelvapormixeswithairairtemperatureandpressureareabovethefuelsignitionpoint.Afterashortdelayautoignitionstarts.

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Dieselfuelinjectionsystemconsistsof

1. Injectionpump

2. Deliverypipes

3. Fuelinjectornozzles

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THEDIESELFUELSYSTEM

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InjectionPumpusuallymechanical drive

Beltsandrollersnotgood,usegearsandchains

Notespilllinefrominjector,pump,separator

FuelInjectionSystems

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GeneralCharacteristics

Pumprunsatenginespeed

ControlsQuantityANDtimingofinjection

Maxfuellimitedbysmokelimit

Howdoestimingvarywithload?

IgnitiondelayisSHORTER(higherdensity)BUT:

Althoughignitiondelayisshorted,stillneedmoreadvancetoensureallfuelisburntduringstroke

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Timingvarieswithloadandspeed

Timingaccurateto1o crankangle

Atmaxloadfuelvarianceamongcylindersshouldbelessthan3%otherwisepowerlimitedbysmokyexhaustofrichestcyl.

Apumpaintsosimple!

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Layoutofconventionalfuelsystem

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InLinePumps(mostcommon)asetofcamdrivenplungers(oneforeachcylinder)

Drivenfromcrankspeed

Multilobecam Thisexampleusesrack,notlever

Rackrotatesplungerassy andcontrolsflow

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drivenbyrotatingweightsactingagainstaspring(likemechanicaladvanceondistributor)

Fueltrappedintheplungerisforcedthroughacheckvalveintotheinjectionline.Theinjectionnozzlehasoneormoreholesthroughwhichthefuelissprayedtocylinder.

PlungerDesign TraditionalInjectionPump

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Plungerforcesfuelthroughfitting

RotatingLevercontrolshowmuchspills back levercontrolsfuelflow(nothrottle)

Allrunbycamdrivenbycrank

Plungers

Operation:

Plungermovesupandblocksinlet

Fuelisallowedtoescapethroughspillport(noticehelical

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Reminderoffuelforcedoutoutletport

Strokeisconstantbydeliveryvariedbyrotation

RotaryPump

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Muchlesscomplicatedbutlowerpressures

Fewmovingparts

Fedbytransferpump

Meteringthroughgovernormechanism rotorslides

Pressurizationviaslidingpistons

TypicalRotaryPump

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FuelInjectors

Nozzletypedictatesperformance

SingleHole

GoodforID

1mmhardtoclog

Multihole

Bettermisting

Easyclogassize >0.1mm

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Clogscausedbydecompofleakedfuel

Differentialpressurescauseopening

Noteneedledesign pressureOPENSnozzle

Differentialpressures

f(needlediametervs.seatdiameter)

Springclosing

Hardertoopenthantokeepopen

Smallerseatcontactareaandstrongspringenhancesealing,eliminatedribble

Dribbleleadstoemissionsanddeposits

Timing sets

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Gear sets

Cam and crank rotate in opposite directions Noisy if not free of burrs Helical and spur cut gears

Timing sets

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Timing chains Single and double roller Tensioners

PintleNozzle

Excellentdisbursement,providesconicalspraypattern

LooksSimilartothatusedinCISsystems

OpensUPWARD

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xce en c ogres s ance

MoreInjectorConsiderations Auxholetobleedexcessfuelandpreventdeposits

4VHeads:Upside

Vf Up

Central injector position

Downside

Less swirl

More nozzle holes for ood disbursion/combustion, as

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small as 0.1 mm Nozzlescooledbyfuel

Coolingimportanttomaintaintolerancesandsealing

SprayPatternCritical!AspectRatioof28

LargerAspectRatio morepenetration

LargerAspectratio Smallercone

Atomizationupw velocity,butrestrictspenetrationaswell

PilotInjection

SmallAmountoffuelearlytoinitiateflamefront

Allowsforlargeadvance

Eliminatesknockandcorrespondingproblemsassociatedwithhighpeakpressuresandwaveimpingement

2SpringSpecialinjectorneededfor2modeoperation

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ElectronicUnitInjection

ElectronicUnitInjection

SolenoidControlled

Sofastpilotinjectioncanbeused

Expensivetoproduce

Widelyusedinheavytruck

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whereemissionsandeconomyarecritical

ControlledjustlikeSIEFI

VariationisHEUI

MovingComponents

Valves

Intake:opentoadmitairtocylinder(withfuelinOttocycle)

Exhaust:opentoallowgasestoberejected

Camshaft&Cams

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Usedtotimetheadditionofintakeandexhaustvalves

Operatesvalvesviapushrods&rockerarms

Valve trains

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OHV (overhead valve)Pushrod configurationMany reciprocating partsHigher valve spring pressure required

Compact engine size compared to OHC

Valve trains

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OHC (overhead cam)Fewer reciprocating partsReduced valve spring pressure required

Higher RPM capabilityCylinder head assemblies are taller

Valve trains

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Cam-in-head

No pushrodsUse rocker arms

ValveLocations

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Combustion process: stratified chargeCombustion process: stratified charge

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jet guided wall guided inlet air guided

ChargeStratification

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CombustionChamberDesigns

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CombustionChamberDesign

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CLASSIFICATIONOFINTERNALCOMBUSTIONENGINES

Cooling

1. DirectAircooling

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.

3. LowHeatRejection(Semiadiabatic)engine.

Cooling system operation

Engine heat is transfered . . . through walls of the combustion chambers through the walls of cylinders

Coolant flows . . .

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o upper ra aor ose through radiator to water pump through engine water jackets through thermostat back to radiator

Cooling system operation

Fans increase air flow through radiator Hydraulic fan clutches Hydraulic fans consume 6 to 8 HP Electric fans

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Coolant (ethylene glycol) 50/50 mixture increases boiling point to 227F pressurizing system to 15 PSI increases to 265F

Coolant (propylene glycol) Less protection at the same temperatures Less toxic


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CIvs.SIEngines

SIenginesdrawfuelandairintothecylinder. Fuelmustbeinjectedintothecylinderatthedesiredtimeof

combustioninCIengines. AirintakeisthrottledtotheSIengine nothrottlinginCIengines.

CompressionratiosmustbehighenoughtocauseautoignitioninCIengines(CI:12to24),compressedtopressureabout4Mpa

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an empera urea ou . UppercompressionratioinSIenginesislimitedbytheauto

ignitiontemperature(SI:8to12). FlamefrontinSIenginessmoothandcontrolled. CIcombustionisrapidanduncontrolledatthebeginning. ThevalvetiminginbothCIandSIaresimilar.

Diesel: GasolinesDirtyCousin?

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HowisDieselDifferentfromGasoline?

Dieselisapetroleumbasedfuelwithahigherenergycontentthangasoline.

containsabout30%moreenergypergallonascomparedtogasoline.

Dieselisasaferfuelthangasolineorotheralternatives.

lessflammableandex losivethan asolineduetolower

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combustibility.

DieselisCheaperthanGasoline

CurrentCostofaGallonofGasolineandDiesel

Gasoline = $1.78

Diesel = $1.65

MisconceptionsAboutDiesel

ItsDirty

ItCausesalotofPollution

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IthasLimitedUses

BenefitsofDiesel

Awellmaintaineddieselengineusuallyemitslowerlevelsofcarbonmonoxide,hydrocarbonsandcarbondioxidethangasolineengines.

Betterfueleconomy,

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ncrease ura y or ongereng ne e.

ProblemswithOldDieselTechnologies

HighSulfurContentofFuel

HighNOx Emissions

HighParticulateMatterEmissions

TheBlackSmokeeveryonesees

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NoisyEngines


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SulfurContent

DieselfuelavailableintheU.S.currentlycontainsfrom340ppmofsulfurto140ppminCalifornia.

EuropeanStandardsaremuchlower

Aslowas10ppminGermanyandSweden

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NOx Emissions

HighcylinderpressureandtemperaturewithexcessiveairistherecipeformakingNOx Becauseofexcessairindieselengines,currentcatalyticcant

scruboutNOx

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ParticulateMatter

Unburnedfuelinthecompressionignitionprocessbecomessoot,apervasiveformofparticulatematter.

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CleanDiesel

Cleandieselisanevolutionarysystemsbasedprocessthatcombinesadvancementsindieselengines,cleanerburningfuelsandemissionscontrolsystem,allworkingandoptimizedtogether.

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WhatMakesDieselClean?

TheThreePillarsofCleanDieselTechnology:

cleanerburningfuels

stateoftheartengines

effectiveemissionscontrolsystems

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CleanerBurningFuels

ThenewestindieselfuelsiscalledUltralowSulfurDiesel(ULSD)

Ultralowsulfurdieselfuelisaspeciallyrefineddieselfuelthathasdramaticall lowersulfurcontentthan

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regulardieselandcanbeusedinanydieselenginejustlikeregulardieselfuel.

Today,thesulfurcontentofULSDrangesfrom15to30partspermillion.Regulardieselhasamaximumof500partspermillionofsulfur.


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HowDoesULSDHelp?

Reducessulfateemissions Allowstheuseofparticulatetrapsandcatalyticconverters

Lowersenginemaintenancecosts

Easytoconvertto

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Noretrofittingrequired

Onlycostsafewcentsmore

StateoftheArtEngines

NewEngineTechnologies ElectronicControls

CommonrailFuelInjection

VariableInjectionTiming

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ImprovedCombustionChamberConfiguration

Turbocharging

ComparisonofSIandCIEngines

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TypicalBrakeThermalEfficienciesofCIandSIEngines

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(portfuelinjection)

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Roger Krieger, GM R&D Center

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SummaryDieselEngines

Advantages:

Efficiency(mostefficientprimemover) Emissions(lowCO,CO2,gooddurability) Veryhightorqueandperformance

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sa van ages:

Emissions(morechallengingtocontrolNOx,particulates)

Highercost Heavier Noise(morechallengingtomakequiet)

Documents

Carburetion and Fuel Injectors