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DEVELOPMENTOFANAIRCYCLEENVIRONMENTALCONTROLSYSTEMFORAUTOMOTIVE
APPLICATIONS
Athesis
Presentedto
thefacultyofCaliforniaPolytechnicStateUniversity
SanLuis
Obispo
InPartialFulfillmentof
theRequirementsfortheDegreeof
MasterofScienceinMechanicalEngineering
by
ChristopherJ.Forster
December2009
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2009
ChristopherJ.Forster
ALLRIGHTSRESERVED
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APPROVAL
PAGE
TITLE: DEVELOPMENTOFANAIRCYCLEENVIRONMENTALCONTROLSYSTEMFORAUTOMOTIVE
APPLICATIONS
AUTHOR: ChristopherJamesForster
DATESUBMITTED:
CommitteeChair: Dr.PatrickLemieux
CommitteeMember: Dr.ChrisPascual
CommitteeMember: Dr.KimShollenberger
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iv
Abstract
DevelopmentofanAirCycleEnvironmentalControlSystemforAutomotiveApplications
ChristopherJamesForster
Mechanical
Engineering
Department
CaliforniaPolytechnicStateUniversity,SanLuisObispo
Anaircycleairconditioningsystem,usingatypicalautomotiveturbochargerasthecoreofthe
system,wasdesignedandtested. Effectsonengineperformancewerekepttoaminimumwhile
providingthemaximumamountofcoolingpossibleandminimizingweightandspace
requirements. Ateststandutilizingshopcompressedairwasdevelopedtomeasurecomponent
performance. Anunmodifiedautomotiveturbochargerwastestedinitiallyasabaselineina
ReversedBraytonCycleaircoolingsystem. Oncethebaselinewasestablished, anotherair
cyclemachine,assembledfromcommercialturbochargercomponentschosenindividuallyto
optimizetheirperformanceforcoolingpurposes,wastestedtoimprovetheoverallcycle
efficiency. Finally,oncetheaircycleairconditioningsystemwasoptimized,itwastestedonan
engineto
simulate
more
realistic
operating
conditions
and
performance.
The
shop
air
test
stand
experimentsshowedapeakdryairrated(DAR)coefficientofperformance(COP)of0.38anda
DARcoolingcapacityof0.45tonsforthebaselineturbocharger,andapeakDARCOPof0.73
andDARcoolingcapacityof1.5tonsfortheoptimizedsystemwithamodifiedturbocharger.
TheonenginetestingwaslimitedduetoathrustbearingfailureintheACM. However,thedata
collectedatlowerengineloadandspeedindicatesaDARCOPof0.56andaDARcooling
capacityof0.72tons. Onenginetestingwasplannedtoincludeoperatingpointswherethe
stockturbochargerwasutilizingturbinebypasstolimitboostpressure. Whileitwasn'tpossible
tocontinuetesting,itisexpectedthatDARCOPandcoolingcapacitywouldhaveincreasedat
higherengineloadandspeed,whereturbinebypassoperationtypicallyoccurs.
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v
Acknowledgements
IwouldliketothankDr.PatrickLemieuxforhissupportandkeepingmeontaskthroughoutthis
project. IwouldalsoliketothankDr.GlenThorncroftandJimGerhardtfortheirhelpwith
instrumentationandlabequipmenttroubleshooting.
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vi
TableofContents
Nomenclature
.................................................................................................................................
ix
ListofTables................................................................................................................................... xi
ListofFigures................................................................................................................................. xii
Chapter1:Introduction................................................................................................................... 1
Chapter2:Background.................................................................................................................... 4
2.1SimpleCycle........................................................................................................................... 5
2.2TwowheelBootstrapCycle................................................................................................... 6
2.3ThreewheelBootstrapCycle................................................................................................. 7
2.4ProjectGoals.......................................................................................................................... 7
2.5COPDefined......................................................................................................................... 10
2.6PreviousworkperformedatQueensUniversity,Belfast.................................................... 11
2.7TheoreticalACMPerformance............................................................................................. 12
Chapter3ExperimentalApparatus,Procedures,andConditions................................................. 19
3.1ShopairTestConfiguration................................................................................................. 19
3.2OnengineTestingConfiguration......................................................................................... 23
3.3ACM
Turbine
Compressor
Matching
...................................................................................
25
3.4PrimaryCompressorResizingforACMoperation............................................................... 25
Chapter4:Results,Conclusions,andFutureWork....................................................................... 28
4.1ResultsandDiscussionfromUnmodifiedGT1241ShopAirTestStand.............................. 28
4.2ResultsandDiscussionfromModifiedGT1244ShopAirTestStand................................... 31
4.3ResultsandDiscussionfromGT1244OnEngineTesting.................................................... 38
4.4ComparisonofACMtoR134aSystems............................................................................... 39
4.5Conclusion............................................................................................................................ 42
4.6FutureWork......................................................................................................................... 44
References..................................................................................................................................... 46
AppendixAUncertaintyAnalysis................................................................................................ 47
A.1CompressorEfficiency......................................................................................................... 47
A.2ACMMassFlowRate........................................................................................................... 49
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A.3CompressorPower.............................................................................................................. 50
A.4TurbinePower..................................................................................................................... 50
A.5CoolingCapacity.................................................................................................................. 50
A.6TurbineEfficiency................................................................................................................ 51
A.7IntercoolerEffectiveness..................................................................................................... 51
A.8IntercoolerPressureDrop................................................................................................... 52
A.9NumericalUncertaintyPropagationAnalysis...................................................................... 52
AppendixBDerivationofEquationsforAircycleAnalysis......................................................... 53
B.1IsentropicCompressorPowerRequirement....................................................................... 53
B.2IsentropicTurbinePower.................................................................................................... 56
B.3BearingLosses...................................................................................................................... 59
B.4Isentropic
Efficiency
.............................................................................................................
60
B.4.1CompressorIsentropicEfficiencyMeasurement.......................................................... 60
B.4.2TurbineIsentropicEfficiencyMeasurementwithBearingLossesCombined..............60
B.4.3TurbineIsentropicEfficiencyMeasurementwithoutBearingLossesCombined.........61
B.5CompressorDischargeTemperature................................................................................... 63
B.6CorrectedCompressorFlowRate........................................................................................ 64
B.7CorrectedCompressorSpeed.............................................................................................. 64
B.8TurbineDischargeTemperature.......................................................................................... 64
B.9CorrectedTurbineFlowRate............................................................................................... 65
B.10CorrectedTurbineSpeed................................................................................................... 66
B.11DryAirRatedTemperature............................................................................................... 66
AppendixC CompressorTurbineMatchingProcess................................................................... 66
AppendixD DetailedCalibrationProcedure................................................................................ 71
AppendixE SensorCalibrationCharts......................................................................................... 74
E.1PressureTransducerCalibration...................................................................................... 74
E.2Laminar
Flow
Element
and
Differential
Pressure
Transducer
Calibration
.......................
75
E.3ThermocoupleCalibration............................................................................................... 78
AppendixF PerkinsDieselPerformance,StockTurbocharger.................................................... 79
AppendixG PerkinsDieselPerformance,VNTTurbocharger...................................................... 83
AppendixH SandenR134aCompressorPerformanceChart....................................................... 87
AppendixI ACMPerformancePredictionCodeinMatlab......................................................... 88
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viii
AppendixJ ACMPerformancePredictionCodeinEES.............................................................. 143
AppendixK ACMSinglePointPerformanceComparisoninEES............................................... 147
AppendixL ACMComponentEfficiencyVariationSimulation.................................................. 150
AppendixM ACMPostprocessingCodeinMatlab................................................................... 153
AppendixN PerkinsDieselPostprocessingCodeinMatlab..................................................... 175
AppendixO PerkinsPostprocessingComparisoninMatlab..................................................... 213
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ix
Nomenclature
P1C Compressorinletpressure
P2C Compressordischargepressure
P1T
Turbineinlet
pressure
P2T Turbinedischargepressure
T1C Compressorinlettemperature
T2C Compressordischargetemperature
T1T Turbineinlettemperature
T2T Turbinedischargetemperature
PRC Compressorpressureratio
PRT Turbinepressureratio
cp Specificheatcapacity
NC Physicalcompressorspeed
CorrectedcompressorspeedNT Physicalturbinespeed CorrectedturbinespeedWC Physicalcompressormassflowrate CorrectedcompressormassflowrateWT Physicalturbinemassflowrate Correctedturbinemassflowrate CompressorPower TurbinePowerR Gasconstant
UniversalgasconstantM Molecularweighth Specificenthalpy
Greek: RatioofspecificheatsAcronyms:
ACM Aircyclemachine
BSFC
Brakespecific
fuel
consumption
CFM Cubicfeetperminute
DAR Dryairrated
SCFM Standardcubicfeetperminute
LFE Laminarflowelement
CHRA Centerhousingrotatingassembly
CI Compressionignition
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x
SI Sparkignition
COP Coefficientofperformance
VE Volumetricefficiency
EGT Exhaustgastemperature
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xi
ListofTablesTable2.1Ambientconditionsfortheoreticalperformancemodel............................................... 15Table2.2Tabulateddatafromparametricstudyofperformanceanalysisforarelativehumidityof50%............................................................................................................................. 17Table4.1OperatingConditionsforsinglepointcomparisonoftheoreticalandactualperformance.................................................................................................................................. 38Table4.2Resultsofsinglepointcomparisonoftheoreticalandactualperformance..................38Table4.3ACMcomponentweightbreakdown............................................................................. 40TableA.1MeasurementUncertaintyBasedonCalibrationInstrumentation............................... 47TableA.2ValuesusedincalculatinguncertaintyinACMcompressorefficiencycalculations.....49TableA.3Conditionsforevaluatinguncertaintyinmassflowrate............................................... 49TableA.4ConditionsforevaluatinguncertaintyinACMcompressorpower............................... 50
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xii
ListofFiguresFigure1.1PvdiagramforanOttoCycle......................................................................................... 3
Figure2.1Simpleaircyclemachineschematic............................................................................... 5
Figure2.2Bootstrapaircyclemachineschematic.......................................................................... 6
Figure2.3
On
engine
two
wheel
bootstrap
schematic.
..................................................................
9
Figure2.4ComparisonoftheReverseBraytonAirCoolingCycleandtheBraytonCycle............14
Figure2.5ParametricstudyofACMperformanceforacompressorwith60%efficiencyand
varyinglevelsofturbineefficiencyandheatexchangereffectiveness......................................... 16
Figure2.6ParametricstudyofACMperformanceforacompressorwith80%efficiencyand
varyinglevelsofturbineefficiencyandheatexchangereffectiveness......................................... 16
Figure3.1Shopairtestingconfiguration...................................................................................... 19
Figure3.2PhysicalACMteststandusingshopair........................................................................ 21
Figure3.3Onenginetestingconfigurationschematic.................................................................. 23
Figure3.4Primaryenginecompressormatchingprocesswithanengineoperatingpointof
1600rpmandfullload.................................................................................................................... 26
Figure3.5PrimaryenginecompressormatchwiththePerkinsdieselboostcurveandthe
targetboostcurvewiththeACMoperating.................................................................................. 27
Figure4.1DryairratedCOPfortheunmodifiedGT1241turbocharger. Datapointsin
Figures4.14.3haveaonetoonecorrespondence...................................................................... 29
Figure4.2DryairratedACMcoolingcapacity. DatapointsFigures4.14.3havea
onetoonecorrespondence.......................................................................................................... 29
Figure4.3IntercoolereffectivenessvariationwithmassflowrateintheGT1241ACMwith
theelectricfan. DatapointsFigures4.14.3haveaonetoonecorrespondence....................... 30
Figure4.4DryairratedCOPforthemodifiedGT1244turbocharger. Datapoints
Figures4.44.5haveaonetoonecorrespondence...................................................................... 32
Figure4.5DryairratedACMcoolingcapacity. DatapointsFigures4.44.5havea
onetoonecorrespondence.......................................................................................................... 32
Figure4.6IntercoolereffectivenessvariationwithACMmassflowrateusingtheelectricfan.
DatapointsFigures4.44.5haveaonetoonecorrespondence.................................................. 33
Figure4.7DryairratedCOPforthemodifiedGT1244turbocharger. Datapoints
Figures4.74.9haveaonetoonecorrespondence...................................................................... 34
Figure4.8DryairratedACMcoolingcapacity. DatapointsFigures4.74.9havea
onetoonecorrespondence.......................................................................................................... 35
Figure
4.9
Intercooler
effectiveness
variation
with
ACM
mass
flow
rate.
Data
points
Figures4.74.9haveaonetoonecorrespondence...................................................................... 35
Figure4.11Pvdiagramforfourstrokegasolineengine.............................................................. 41
FigureA.1UncertaintyinACMcompressorefficiencyduringtypicaloperatingconditions.........48
FigureB.1Compressorcontrolvolumeanalysis............................................................................ 53
FigureB.2Turbinecontrolvolumeanalysis................................................................................... 56
FigureB.3Bearingsystemcontrolvolumeanalysis....................................................................... 59
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xiii
FigureC.1GT1244compressorperformancemap........................................................................ 67
FigureC.2GT1244turbineperformancemap............................................................................... 67
FigureD.1Thermocouplemeasurementnoise(prefiltered)beforeandaftershielding
thewires........................................................................................................................................ 72
FigureD.2Temperaturemeasurementoutputafteroversamplingandaveraging...................... 72
FigureE.1
MAP
sensor
calibration
chart.
.......................................................................................
74
FigureE.2 ThisschematicshowstheconfigurationoftheLFE,differentialpressure
transducer,andresistor................................................................................................................. 75
FigureE.3Laminarflowelementcalibrationcurve.DataisprovidedbyMeriamProcess
Technologies.................................................................................................................................. 76
FigureE.4Differentialpressuretransducerandresistorcombinedcalibration........................... 77
FigureE.5Laminarflowelementsetupcalibration....................................................................... 78
FigureF.1BSFCcontourmapusingthestockturbocharger.......................................................... 79
FigureF.2VEcontourmapusingthestockturbocharger............................................................. 79
FigureF.3Intercoolereffectivenesscontourmapusingthestockturbocharger......................... 80
FigureF.4
Pressure
differential
between
the
exhaust
and
intake
manifolds.
(P_int
P_exh)
......
80
FigureF.5Engineturbochargercompressorefficiency................................................................. 81
F.6Engineturbochargerturbineefficiency................................................................................... 81
F.7Enginefuelmassflowrate....................................................................................................... 82
FigureG.1BSFCcontourmapusingtheVNTturbocharger........................................................... 83
FigureG.2VEcontourmapusingtheVNTturbocharger.............................................................. 83
FigureG.3IntercoolereffectivenesscontourmapusingtheVNTturbocharger.......................... 84
FigureG.4differentialbetweentheexhaustandintakemanifolds.(P_int P_exh)....................84
FigureG.5Engineturbochargercompressorefficiency................................................................ 85
FigureG.6Engineturbochargerturbineefficiency........................................................................ 85
FigureG.7Enginefuelmassflowrate........................................................................................... 86
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1
Chapter1:Introduction
Automotiveairconditioningsystemsareintheprocessofundergoingsomemajorchangesdue
toenvironmentalconcerns. Thenewchangesaretopreventglobalwarming,inadditionto
ozonedepletion. Thesechangestendtohavenegativeimpactsonairconditioningperformance
duetoashiftinrefrigerantselectioncriteria,frommaximumcoefficientofperformance(COP)
tolifecycleenvironmentalimpactofthesystem.Thenewcriteriaconsidersdesignsthathave
lowerCOPbutmaystillhavelessoverallnegativeimpactontheenvironmentthroughoutthe
lifecycleofthesystem. Someoftheotherconsiderationsinselectingarefrigerant,arethe
systemweight,manufacturingcosts,refrigeranttoxicity,andeffectsofpotentialleaks. Looking
intothefuture,additionalchangestoautomotiveairconditioningsystemsarelikely,anduseof
arefrigerantthatisnaturallyavailableanddoesnotneedtoberetrofittedisconvenient.
Aircyclemachines(ACM)convenientlyuseairastherefrigerantandhavethepotentialto
provideconvenientairconditioningforhighperformancevehicles,whereweightisata
premium. AtypicalACMcanconsistofacompressor,heatexchanger,andcoolingturbine,
whichissuppliedwithpressurizedair. Themaincomponentsofanaircyclecoolingsystemare
thecompressionprocess,heatremoval,andcontrolledexpansion. Thecoolairfromtheturbine
outletcanberouteddirectlyintothepassengercabin.
Inracingapplicationsairconditioningisasecondaryconsiderationinvehicledesign,andoften
notused
due
to
weight
and
power
requirements.
Any
amount
of
cooling
that
can
be
provided
withoutlossinengineperformanceandminimalweightincreaseisconsideredtobean
improvement. Ableedaircontrolconfigurationisbestsuitedtoracingapplicationsbecausethe
amountofcoolingrequiredisnotset,anycoolingprovidedisbeneficial. Thebleedair
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2
configurationrequiresaforcedinductionsystemastheprimarysourceofcompressedairfor
theReverseBraytonCycletooperate. Thisconfigurationwillworkwitheitherasupercharged
orturbochargedsystem. Thelatterispreferredtominimizetheparasiticpowerlossonthe
enginecausedbytheACMoperation.
Insteadof"wastegating",aprocessinwhichafractionoftheexhausttobypasstheturbine
stagetolimitcompressoroutletpressure,thecompressoroutletpressurecanbelimitedby
bleedingairthroughtheACM. Thishasareducedimpactonpowerconsumptionfromthe
enginebecausethepowerwouldhavegonetowasteifnotusedforcooling.
Avariablenozzleturbine(VNT)canbeusedtoachieveadesiredcoolingcapacitywhile
maintainingboostlevelswithincreasedprimarycompressorpowerrequirementsduringfull
ACMoperationbyvaryingturbinepower. Thisconfigurationcanbedesignedtoincreaseoverall
systemefficiencybyminimizinglowerlooplosses,whichisimportantforminimizingfuel
consumption. ThelowerlooplossescanbeseenonthePvdiagramoftheOttoCycle,inFigure
1.1. ThelowerlooponeithertheOttoorDieselCyclesrepresentsthenetpumpinglosses
inducedontheenginebytheexhaustandintakesystems. Thenetpowercanbedeterminedby
integratingthePvcurveforwardthroughtheintakeandexhauststrokes. Thesumofthe
signedareasresultsinthenetpowerconsumed. Anintakepressuregreaterthantheexhaust
backpressurewillresultinanegativepumpingloss,orincreasedenginepower.
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T
d
A
d
c
c
heVNTcontr
emonstrates
CMeffective
emonstratet
mponentst
nberedesi
olmethodw
thatthepri
lyinableed
hefeasibility
designanA
gnedtosupp
Figure1.1
asfoundtob
aryturboch
airconfigura
ofusingco
CMunit;and
orttheaddit
3
vdiagramfo
ethemostp
rgercansup
ion. Therea
merciallyav
,2)demonst
ionalairflow
ranOttoCycl
racticaltoi
plythenece
retwoobjec
ilableauto
ratethatan
requiredbyt
.
plementfor
saryairflow
ivesinthisp
otiveturboc
ngineturbo
heACM.
histesting,
ooperateth
roject;1)
harger
chargersyst
ndit
e
m
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Chapter2:Background
Aircycletechnologyhasbeeninusesincethe1940sinaircraftenvironmentalcontrolsystems
(ECS)[1]. Untilthenitwasconsideredcommerciallyunfeasibleduetoitsrelativelylow
coefficientofperformance(COP)comparedtootherrefrigerationmethodsavailable,namely
vaporcyclesystemsanddryice. Theappealthatmadeitaconsiderationforuseinaircraftis
thesizeandweightofatypicalACM. Inadditiontothis,thereisaconvenientsourceof
compressedaironboardalready,thejetenginescompressorstages. Forcomparablesystems,
intermsofcoolingcapacity,aircyclesystemscanreducespacerequirementsbyapproximately
25%andweightby50%[1]. Thisisimportantinracingandhighperformanceapplications
becauseenginebaysaretypicallyverytightonspace,andweightcandiminishaccelerationand
handling.Theincreasedweightcanbeespeciallydetrimentalinvehicleswithdownforcesince
theincreaseinweightdoesnotnecessarilyincreasethelateralloadcapabilitybyaproportional
amount.
Theaircyclemachineisbasedaroundtheconceptofacoolingturbine. Thisisthecommon
componentamongallofthevariousACMconfigurations,suchasthesimple,twowheel,or
threewheelbootstrapcycles. Thecoolingturbineoperatesbyprovidingacontrolledexpansion
ofair;anadiabatic,controlledexpansionrequirestheairtodoworkonitsboundariesto
provideanycoolingeffect. Theworkdoneontheturbinewheelistransmittedbytheshafttoa
compressororfantoutilizethispower. Thecompressorandfanaremethodsofdissipating
turbinepowertodousefulworkinthesystem.
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2
T
D
t
e
t
t
f
a
p
h
T
.1Simple
hemainadv
ecreasedco
emainjete
changerwit
mperature
rbineforex
n. Theturb
retwo
comp
owerderived
eatexchang
hefactthatt
Cycle
ntagetousi
ponentnu
gineistypic
hhigheffecti
spossible.
ansion. The
inepowerco
nentsto
co
fromtheair
reffectivene
hesimplecy
Figure2.1Sim
gthesimple
bersreduce
allyinthera
venesstoge
ncetheairi
powerprod
rrespondsto
lingthe
air;
flowreduces
ssbyincreas
leutilizesaf
5
pleaircycle
aircyclesys
weightands
geof4006
theaircool
cooledbyt
cedbythet
theenthalp
)Heat
rejec
enthalpyan
ingtheairflo
ananddoes
achineschem
em,asthen
pacerequire
0oF. Thisair
ddowntoa
eheatexch
urbineistran
changeint
ionfrom
the
airtemper
overthec
notrelyonly
atic.
ameimplies,
ments. The
isthenpasse
sclosetothe
nger,itisint
smitted,by
eairpassing
ACMinterc
ture. Thefa
ldsideofth
onramairf
issimplicity.
ircomingfr
dthrougha
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roducedinto
irectdrive,t
throughit.
oler;2)
Turb
helpsimpr
heatexcha
rcoolingthe
m
eat
the
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here
ine
ve
ger.
heat
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e
a
f
2
T
in
a
t
c
t
p
changerall
pplicationsw
bricationre
.2Two-w
hemostnoti
steadofafa
nddoesnot
rbinedischa
ncernsabo
rbinewheel
ressureratio
wsittoprov
iththeinten
uiredforma
eelBoot
F
eablediffer
n,andaseco
rovidecooli
rgetempera
tfreezingth
itself,itcan
acrossthetu
idecoolingw
ofusingtyp
nufacturing
trapCycl
igure2.2Boot
ncesfromth
ndheatexch
gwhilethe
ures. Thetu
moistureo
uilduptoa
rbineandde
6
hiletheplan
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ndinstalling
e
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esimpleair
anger. Whil
ircraftissta
rbinedischar
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ionary,itdo
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esprovidesi
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ntsbecause
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ughtohave
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bin,reducin
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the
gthe
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Theairisdrawnfromoneofthemainenginecompressorstagesandcooledthroughaprimary
heatexchanger,justasthesimplecycledoes. Next,thecoolerairentersthesecondary
compressorstage. Thisprovidesanotherpressurerisetofurthercompressandheattheair.
Thepowerrequiredbythesecondarycompressortoaccomplishthistaskisprovidedbythe
coolingturbine. Theairexitingthesecondarycompressorstageiscooledbyanotherheat
exchangerbeforeenteringtheturbine. Theturbineinthebootstrapconfigurationreceivesair
atapproximatelythesametemperatureasthesimplecycle,butatasignificantlyhigher
pressureratioacrosstheturbine. Thisishowthebootstrapaircyclemachineisabletoprovide
lowerturbinedischargetemperaturesthanthesimplecycle.
2.3Three-wheelBootstrapCycle
Thethreewheeledbootstrapcycleisessentiallythesameasthetwowheeledassemblywith
theadditionofafanmountedonthesameshaftastheACMcompressorandturbineorgear
drivenfromtheshaft. Thefanensuresadequateairflowonthecoldsideoftheintercooler,but
itwillconsumepowerfromtheturbineandreducethepressureratioacrossthecompressor.
ThisconfigurationrequiresoneoffdesignandfabricationofACMcomponentsthatarenot
readilyavailablewithautomotiveparts.
2.4ProjectGoals
ThegoalofthisprojectistodemonstratethatanACMairconditioningunitcanbe
manufacturedfromexistingautomotiveturbochargercomponentsandprovideacceptable
coolingwith
aminimal
performance
penalty.
There
are
many
choices
for
ACM
configuration,
butsomeofthemlendthemselvesmoreeasilytoautomotiveapplicationsthanothers.
Thesimplecyclehasfewcomponents,buttheturbochargercompressorwouldhavetobe
replacedbyafan. Thisrequiresasignificantamountoffabricationanddoesnotmeetthegoal
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ofusingexistingautomotiveturbochargercomponents. Usingafanmountedontheturbine
shaftrequiresductingthatmaybedifficulttopackageinacarenginebay.
Thethreewheelbootstrapconfigurationmakesforanicelypackagedrotatingassembly. The
mainconcernwiththissetupisthemanufacturingandbalancingofacomplicatedrotating
assembly. Thisrequiresextensivemodificationtoaturbochargerandisnotappropriatefor
meetingthegoalsofthisproject.
Thetwowheelbootstrapconfigurationrequiresmorecomponents,butthereisacompressor
turbineassemblythatallowstheuseofaturbochargertopackagethosecomponents. An
electricfanisneededtoprovideairflowovertheintercooleratlowvehiclespeeds. Thisallows
forsimplerpackaginginasmallenginebaythanductingairfromaremotelylocatedfan. The
twowheelconfigurationprovidesthelowestturbinedischargetemperatureofallthesetups.
Thisisimportantinanautomotiveapplicationbecausethepressureratiosavailablearelimited
duetoengineconstraints. Alowerpressureratiowillreducethetemperaturedropacrossthe
turbine,assumingeverythingelseremainsconstant. Thetwowheelbootstrapconfigurationis
usedforthisprojectbecauseitmeetsthegoalsthathavebeenset. Thisconfiguration,inthe
contextoftheenginemountedsystemtobetestedinthisproject,canbeseenbelow.
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T
p
o
p
c
al
T
g
e
p
heonengine
ressurizedin
intakemani
ressure. Boo
mpressoro
llowsforafr
heturbineb
ting"becau
nergy.Thec
reventingex
Fig
ACMconfig
aketubing
t
foldpressur
stcontrolist
tletpressur
ctionofthe
passvalveis
eanyfractio
mpressorbl
essiveboost
re2.3Onen
rationopera
the
intake
orboost,a
ypicallyperf
andcloses
exhaustgast
commonlyr
noftheexh
edconfigur
.
9
inetwowhee
tesbybleedi
anifold.Th
ommonna
rmedbyusi
ropensafla
obypassthe
ferredtoas
ustthatisall
tionusesthi
lbootstrapsc
ngairfromt
bleed
air
c
ereferringt
ngapneuma
ppervalvelo
turbine,limi
awastegate
lowedtobyp
swastedene
ematic.
heengine'sf
nfiguration
ointakeman
ticactuatort
catednextt
tingturbine
. Itisreferre
asstheturbi
rgytopower
rcedinducti
llowsfor
co
ifoldgauge
hatsenses
theturbine.
owerandb
dtoas"wast
eiswasted
theACMwh
on
trol
This
ost.
e
ile
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10
Whiletheonengine,twowheelbootstrapconfigurationistheprimarygoalofthisproject,the
turbinecompressormatchmustfirstbevalidated. Thisisperformedonastandalonetest
standwithcompressedairsuppliedtotheACMbytheshopaircompressorsystem. This
configurationcanbeseeninFigure3.1.
2.5COPDefined
TraditionallyCOPisdefinedastheratioofcoolingloadcomparedtothepowerrequiredtodrive
thesystem. Thisisapracticaldefinitionformostairconditioningsystemswherethe
compressor,dynamicorfixeddisplacement,isdrivenfromamotororengine. Thepower,with
anassociated
cost,
going
to
the
air
conditioning
system
is
easier
to
determine
than
that
of
the
turbochargerbasedsystemdescribedinthisprojectsincethereisaphysicalconnection
betweenthemotorandcompressor.
,(Eqn.2.1)ThisisnotasclearwhenconsideringanACMpoweredbytheenginesturbocharger;notallof
thepowerdeliveredtotheACMhasacostassociatedwithit. Aportionofthepowerthatwent
todrivetheprimarycompressorwasfromheatenergythatwouldhavebeenwastedthrough
theexhaustanywaysorlostthroughwastegating.
AnewmethodfordeterminingpowerconsumptionspecificallybytheACMisproposed.This
canbedonebyfindingthechangeinfuelflowratewithandwithouttheACMoperatingand
usingbrake
specific
fuel
consumption
(bsfc)
to
calculate
power
used
by
the
ACM.
This
representstheeffectivepowertodrivetheACM,inotherwords,onlypowerthathasan
associatedincreaseinfuelcost. ThisappliestoACMoperationoutsideofnormalwastegate
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11
operationtolimitboost. ACMoperationtolimitboostlevelsinsteadofusingthewastegate
hasminimalimpactonenginefuelconsumption,lendingtoasignificantlyincreasedCOP.
(Eqn.
2.2)
, (Eqn.2.3)COPeffectiveisnottheonlyconcerninACMdesign;thecoolingcapacityisthedrivingrequirement
inthedesignprocess. Inoptimizingthesystem,whilemeetingcoolingcapacityrequirements,
COPismaximizedforagivensetofambientandACMinletconditions. TheeffectiveCOPand
coolingcapacitytogetherarereferredtoasACMperformance.
2.6PreviousworkperformedatQueensUniversity,Belfast
Totheauthor'sknowledge,therehasonlybeenoneotherrecentgrouptoperformaircycle
researchforautomotiveapplications. Theideaofusingaircycleairconditioningforthistypeof
applicationiswellfoundedbytheory,butpracticallimitationsinimplementingthesystemcan
considerablydecrease
the
performance
of
an
ACM.
This
can
be
observed
in
the
previous
work
describedbelow.
AresearchgroupatQueensUniversity,Belfast,hasdesignedandimplementedasupercharger
basedACMforrefrigeratedtrailersinroadtransportapplications[2,3]. Thegroupimplemented
atwowheelbootstrapcyclesimilartotheoneinthisproject. Theprimarycompressorisgear
drivenfrom
the
crankshaft,
and
it
feeds
compressed
air
to
the
typical
bootstrap
ACM.
Instead
ofbleedingairfromtheengineintakemanifoldasdoneinthisproject,thesuperchargeris
dedicatedtosupplyingairtotheACM. ThisconfigurationsomewhatdecouplesengineandACM
operation,makingiteasiertocontrolandquantifyACMperformance. Ithasasevere
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12
shortcominginthatitwillalwaysbeaparasiticpowerlossfromtheenginecrankshaft,rather
thanfreepowerfromaturbochargerbasedsystemthatisdemonstratedinthissystem. The
theoreticalCOPoftheirACMwas0.294,correspondingtotheCOPtraditionaldefinedabove,while
anoptimizedmodelshowedapossibilityof0.62. Theirperformancegoalwasnotachieveddue
toexcessivelylowefficiencyofthegearboxtodrivethesupercharger,heatexchanger
performance,andexcessivelylargeturbochargerbearinglosses. Overall,thefuelconsumption
oftheenginewasapproximatelythreetimesgreaterwiththeACMoperating,andnoactual
COPfigureswereprovidedfromthistesting. Whiletheirtestingdidnotshowpromisingresults,
thelowerthanexpectedperformancelikelycamefromlimitationsincomponentsselected
ratherthantheaircycleconceptitself.
TheturbochargerbasedACMdiffersfromthesuperchargerbasedunitbecausethereisenergy
availablethatwouldhavebeenwastedduringtheturbinebypassprocess,wastegating,without
thepresenceoftheACM. Insteadofwastingthisenergy,itcanbeutilizedforpoweringthe
ACMwithoutanyadditionalcosttotheengine. Thisisessentiallyfreecooling,orinfiniteCOP.
Sincetheuseofaturbochargerastheairsourceallowsincreasedupperlimitsofperformance
thanthesuperchargerbasedsystem,thereisanimprovedlikelihoodofsuccess.
2.7TheoreticalACMPerformance
Aircycleanalysiscanbeperformedassumingdryormoistair. Theanalysisforthisproject
assumesdryair,exceptforusingthedryairrated(DAR)analysisforcoolingcapacity. DAR
temperatureis
the
equivalent
temperature
ifthe
entrained
water
or
ice
in
the
air
exiting
the
turbineisadiabaticallyevaporated[4]. Dryair isassumedbecause,formostofthesystem,the
differenceinenthalpychangeacrosscomponentsisminimalbetweenthetwomethods. This,
however,isnottruefortheturbinebecausetheairtemperaturefallsbelowthatoftheambient
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13
conditionsandmoisturecandropoutasaliquid,orpossiblyice. Thiscanhaveasignificant
impactintheenthalpychangeacrosstheturbine,affectingturbinepoweranddischarge
temperature. Dryairisassumedforsimplicityindesigningthefirstprototype. Detailed
derivationsofthedryair,perfectgasequationscanbefoundinAppendixB.
TheturbinecompressormatchingprocessforanACMisdifferentthanthatofamatch
performedforanengineapplication. Thisisprimarilyduetothedifferenceinturbineinlet
conditions. Correctedparameters,suchasflowandspeed,fortheturbinearedependentupon
temperature. TheturbineinlettemperatureissignificantlylowerforanACMthantypical
exhaustgas
temperatures
of
either
diesel
or
gasoline
engines.
This
presents
achallenge
becausecommercialturbochargersaredesignedforengineapplications,anditrequiresanew
compressortobematchedtotheturbinetomaximizeperformanceintheACMapplication. The
compressorturbinematchingprocesscanbefoundinAppendixC. Thedifferencesinthetypical
onengineapplicationandtheACMapplicationbecomeapparentwhenviewingaTsdiagram
withboththeBraytonandReverseBraytoncycles. TheBraytonCycleismodelingtheengineas
aheatinputtotheturbochargersystem. Figure2.4showstherelativetemperatureandentropy
changesthrougheachcycle.
Theprocessstartsatthecompressorinletandthevolumedecreasesasthepressureincreases.
TheBraytonAirStandardCycleismodeledwiththeengineasacontinuousthermodynamic
machineandwithamassfractionbypassingtheturbinetopreventoverpressurizingtheintake.
Theintake
air
is
then
drawn
into
the
engine
where
it
goes
through
the
combustion
process
wheretheburnedfueladdsheattotheflowbeforeitisdischargedintotheexhaustmanifold.
Theexhaustflowincreasevolumeanddecreasesinpressureasitexpandsthroughtheturbine.
Alineconnectingtheturbineoutletandthecompressoroutletrepresentstheairpossiblybeing
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r
e
t
d
T
e
a
s
cycledatso
nergythanc
ecompress
ifferentappr
heelproves
aximizingtu
Figur
hereare
afe
nergybalanc
renoleaksin
me. Withth
epointand
mparedtot
randturbin
oachtothec
obeabette
rbineefficien
2.4Comparis
things
kno
e,andopera
thesystem,
eassumptio
closesthec
eBraytonC
,lowercom
ompressort
matchforr
cy,whilestill
onoftheRev
nabout
the
ingspeedso
themassflo
thatthebe
14
cle. TheRev
cle. Thisre
pressorpres
rbinematch
ducingexce
keepingco
rseBraytonA
system,
as
fthecompre
ratethrou
aringlosses
erseBrayton
ultsinchang
ureratios,a
ingprocess.
ssivecorrect
pressoreffi
irCoolingCycl
ithmany
sys
ssorandtur
hthecompr
renegligible
Cycleinvolv
esincorrect
drequiresa
Arelativelyl
dturbinesp
iencyinmin
eandtheBra
tems,such
a
inewheels.
essorandtur
,whichisthe
esmuchless
dcondition
somewhat
rgercompr
eedsfor
.
tonCycle.
smass
balan
Assumingth
binewillbet
caseinmos
for
ssor
e,
re
he
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15
engineapplicationswheretheuncertaintyofmanyotherparametersoutweighthis,thepower
outputoftheturbinewillbematchedbythecompressorpowerrequirementinsteadystate
operation. Consideringthecompressorandturbinewheelsaredirectlymountedonthesame
shaft,theshaftspeedswillbeequal. Evenwithasmanyknownparametersasthereare,itisan
iterativeprocesstofindamass,power,andspeedbalancebecauseofthegraphicalnatureof
thecompressorandturbineperformancemaps.
ItisimportanttoinvestigatetheeffectsofvariouscomponentperformancesonoverallACM
performance. AparametricstudyofACMcomponentefficiencieswasconductedandthe
resultsare
in
Figure
2.5
2.6
and
Table
2.2.
With
the
results
from
the
parametric
study,
attention
canbegiventothemostcriticalcomponentsfirst. Theanalysispresentednextshowsthatheat
exchangereffectiveness(E_htxr2,Figure2.52.6)andturbineefficiency(Eta_t2,Figure2.52.6)
aremoreimportanttooverallsystemperformancethancompressorefficiency. Thedatainthe
followingfiguresarecalculatedassumingaprimarycompressorefficiencyof70%andambient
conditionssimilartothosefoundatthetestinglocation. Thecompressorefficiencychosenis
representativeofattainableperformanceoverawiderangeinairflowinmodernautomotive
turbochargersystems[6]. Thecodeusedtogeneratethefollowingplotscanbefoundin
AppendixK.
Table2.1Ambientconditionsfortheoreticalperformancemodel.
AmbientCondition
Temperature[Deg.F] 70Pressure[psia] 14.69
RelativeHumidity[] 0.50
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16
Figure2.5ParametricstudyofACMperformanceforacompressorwith60%efficiencyandvaryinglevels
ofturbineefficiencyandheatexchangereffectiveness.
Figure2.6ParametricstudyofACMperformanceforacompressorwith80%efficiencyandvaryinglevels
ofturbineefficiencyandheatexchangereffectiveness.
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17
Thisanalysisindicatesthatminimumacceptableintercoolereffectivenessisapproximately0.70
beforerapidlydecreasingoverallACMperformance. Whilecompressorandturbineefficiencies
remainconstant,thecurvesforACMCOPdecreasebylargeramountsasheatexchanger
effectivenessdecreases.
Usingrepresentativevaluesfromthepreviousanalysis,attainableperformancewithautomotive
turbochargercomponents,forintercoolereffectiveness,turbineefficiency,andcompressor
efficiency,thefollowingtablewasconstructed:
Table2.2Tabulateddatafromparametricstudyofperformanceanalysisforarelativehumidityof50%.
PressureRatio
[]
Intercooler
Effectiveness[]
Turbine
Efficiency[]
Compressor
Efficiency[]COPDAR[]
1.5 0.80 0.80 0.600.80 1.051.25
0.600.80 0.80 0.821.25
0.60 0.80 0.600.80 0.861.07
0.600.80 0.80 0.611.07
Itcanbeobservedthattheturbineperformanceismorecriticaltotheoverallcycle
performance. Thisistobeexpectedbecausethemoreefficienttheturbineis,themoreheat
willberemovedfromtheairexpandingthroughtheturbine,andthemorepowerwillbe
extractedtodrivehigherpressureratiosacrossthecompressor. Thehigherpressureand
temperatureenteringtheheatexchangerallowsmoreheattoberemovedbeforeenteringthe
turbine. Obviously,thereisalimittothiscycleandasteadystateoperatingpointbecauseof
thedecreasingenergycontentintheairflowtotheturbineasmoreheatisremovedbythe
intercooler.
ItshouldbenotedthattheACMinthistestingisoperatedatthelowerpressureratiorangedue
toboostlimitationsonthetestengineandtypicalboostpressuresforgasolineengines. The
theoreticalanalysisisextendedtotheupperlimitsofpressureratiosthatcanbeachievedby
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18
singlestagecompression. Thisisrepresentativeofwhatcanbeseeninoperatingintake
pressuresindieselengines.
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T
d
d
p
3
T
b
ai
c
c
hapter3
herearetwo
esignedtov
esiredperfor
erformance.
.1Shop-a
hefirstseto
etweencom
irsourceand
mpressora
mpressorh
Experim
testingconfi
rifythecom
mancecanb
rTestCo
testsconsist
onentspow
thelocation
dlargeairst
stosupplyt
entalAp
gurationsne
ressorturbi
eachieved.
figuratio
Figure3.1
softheACM
redby
shop
ofthesens
oragetanks.
hetankswit
19
aratus,
dedtocom
nematchfor
hesecondt
n
hopairtestin
turbocharg
air.Figure
3
rs. Thetest
Arelativelyl
125psig,an
rocedur
letetesting
theACMits
stisdesigne
gconfiguratio
r,intercoole
.1shows
the
facilityhasa
argeshopai
theACMai
s,andC
orthisproje
lfandtode
dtodemons
n
r,andrequir
connectiont
75hprecipr
supplyisne
rsupplyisre
nditions
ct. Thefirsti
onstrateth
rateonengi
dducting
othe
compr
cating
ededbecaus
ulateddow
s
tthe
ne
ssed
the
toa
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21
Figure3.2PhysicalACMteststandusingshopair.
TypeTthermocoupleswereusedbecausetheyworkwellwiththelowertemperaturerange
thattheACMwillbeoperatingin. Inadditiontothis,thestandardlimitoferrorfortypeT
thermocouplesis1oC,comparedto2.2oCfortypeK. Eachthermocouplewascalibratedwithin
thestandardlimitoferror. Allsensorswerecheckedperiodicallybetweensetsofexperiments
toensurequalitydata. ThecalibrationdataareinAppendixE.
ThistestingconfigurationgathereddataforabaselineusinganunmodifiedGT12turbine41mm
compressorwheelassemblyfortheACMandaGT12turbine44mmcompressorwheel
assemblyforimprovedefficiency. Thelargercompressorreducedcorrectedturbinespeedsto
improveperformance.The41mmcompressorwheelplacedcorrectedturbinespeedoperating
pointoffthehighendoftheturbineperformancemap. Thecompressorprovidedsimilar
efficiencycontourstothesmallercompressorwheel,sotherewasn'tasignificantdecreasein
performanceonthatend. ThedifferencesintheunmodifiedGT1241andmodifiedGT1244
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22
compressorturbinematchesareduetothedifferencesinthecomponentinletoperating
conditionsfortheintendedapplications,asdiscussedinSection2.7.
Theinstallationofthenewcompressorrequiredmanufacturingashaftadapterduetoalarger
boresizeinthelargercompressorwheel. ThespecificationsfromGarrettTurbochargers
indicatedthatboreinsideto outsidediameterrunoutandperpendicularitytotheendfaces
needtobewithin0.0001inch. Ashaftadapterwasproducedthatmettheacceptablevibration
limitsatpeakoperatingspeeds. Thiswasverifiedbeforecontinuingwithtestingbyslowly
increasingtheturbochargerspeed,whiledirectlymeasuringshaftspeedandbearinghousing
vibrationlevels.
TheprocedureforperformingthetestsonboththeunmodifiedGT1241andmodifiedGT1244
assembliesincluded:blowingoutliquidwaterfromtheshopairlinesandtanks,gatheringlocal
ambientconditions,andmanuallyregulatingtheACMinletpressuretoachievedesired
operatingpointsandsteadystateconditionsbeforecollectingeachdataset. Steadystate
operatingconditionscanbedetectedandverifiedseveralways,suchasmonitoringshaftspeed,
temperatures,andpressures.
Thecomponentthatcontributedmosttothelengthoftimerequiredtoreachsteadystatewas
theintercooler. Ithasarelativelylargemassandtooksometimetoreachasteady
temperature. Itisveryimportanttowaitforsteadystateconditionsbeforecollectingdata
becausefictitiouslyhighperformancenumberscanbeobserved. Thisisbecauseofthethermal
capacitanceofthealuminumcomprisingtheintercoolercoreandendcaps;itprovidesasecond
meansofheatremovalfromtheairflowuntiltheintercoolerissaturatedwithheat. Oncethe
intercooleris"heatsoaked",theonlymeansofdissipatingheatistothecoldairflowstream,
insteadoftransferringheatfromthehotairstreamtothethermalcapacitanceofthealuminum
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a
d
el
T
a
u
e
S
n
3
ndtothecol
uringthetra
liminatingthi
heshopairs
dequatecom
seableACM
ficiency. Th
ction4.2. T
iththe
com
extstepison
.2On-eng
airflowstr
sientperiod
seffect.
andtesting
pressorturbi
peratingran
resultsoft
heuncertain
ressorturbi
enginetesti
ineTesti
Fig
am. Initialt
. Alldatawa
emonstrate
inematch,w
gebyincrea
eshopairte
ycalculation
ematch
ver
ng.
gConfigu
ure3.3Onen
23
stingshowe
scollecteda
thattheba
hilethemodi
ingtheeffici
ststandexp
sforthese
ifiedand
the
ration
inetestingco
dlargeappa
steadystat
elineGT124
ifiedGT1244
encyoverth
rimentsare
easurement
performanc
nfigurationsc
entintercoo
conditionsf
turbocharg
turbocharge
trangeclos
discussedin
canbefoun
of
the
ACM
ematic
lereffectiven
orthisproje
rprovideda
providedal
rtothepea
ection4.1a
dinAppendi
optimized,t
ess
t,
n
arger
d
xA.
e
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24
TheonengineconfigurationusesthesameACMteststandconfigurationwiththeexceptionof
thecompressorinletbeingfedcompressedairfromtheintakemanifoldofthedieselengine.
Thiswasachievedusingaypipeaftertheprimary,orengine,intercooler. Theflowcontrol
valveislocatedbeforetheACMcompressorinletandiscapableofturningtheflowtotheACM
onoroffandthrottlingflow. TheconnectionfromtheenginetotheACMisillustratedinFigure
3.3.
TheengineusedinthisexperimentisasixliterPerkinsdieselengine. Itisafourstroke,inline
sixcylinderengine. Thischoiceofengineplatformisrelevanttosportscarandracing
applicationsbecause
the
engine
displacement
is
similar,
even
though
the
speed
range
is
lower.
Thisisnotnecessarilyaproblembecausetheengineturbocharger'sturbineissizedforthe
engineinconsideration,andintheworstcase,itwillprovidealowerlimitforloadandspeed
thattheACMcanbeeffectivelyoperated. Since,inracingapplications,theengineistypicallyat
higherloadandspeed,thisisnotaconcern.
Theengineisfullyinstrumentedandisconnectedtoadynamometer. Theengine
dynamometersetupispartofanengine'sclass,andthesensorsarecalibrated. Acalibrationlog
ismaintained,butevenso,thesensorswereverifiedtomatchtheirpreviouscalibrations.
ThePerkinsdieselenginewasfirsttestedwiththestockturbochargertosetabaselinefor
comparisonofthenewcompressorfortheprimary,orengine,turbocharger. Thesecond
turbochargerissizedtoefficientlyaccommodatetheadditionalairflowrequiredforthe
operationoftheengineandACM. Thenewturbochargerhasalargercompressorandavariable
nozzleturbine.
TheexperimentsperformedtoassesstheeffectsofACMoperationonengineperformance
wereconductedbyrunningtheengineatanoperatingpointallowingmaximumboostlevelsto
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25
bereachedbeforeopeningthedivertervalvetotheACM. ThisdemonstratestheeffectofACM
systemairflowrequirementsonboostlevelavailabletotheengineandchangeinfuel
consumption,thetwoprimaryfactorsconsideredinaracingapplication.
3.3ACMTurbine-CompressorMatching
ThematchingprocessfortheACMrotatingassemblyfollowsthemethodpresentedinAppendix
C,buttherearesomenewconsiderationsregardingtheACMapplication. Theturbineand
compressorsthatarepairedonproductionturbochargersarewellmatchedforgasolineor
dieselengineapplications,wherethereishotexhaustgasdrivingtheturbine. Thistemperature
differencein
the
engine
and
ACM
applications
causes
alarge
change
in
corrected
turbine
speed
andcorrectedmassflowrate,twoparametersusedtomapturbineperformance. Sincethe
ACMturbineinletconditionswillalwaysbecoolerthantheoriginalengineapplication,alarger
compressorwillbeneededtoreducecorrectedturbinespeeds. Thecompressormatching
techniqueisessentiallyunchanged,sincethecompressorconditionsaresimilarinboth
applications.
3.4PrimaryCompressorResizingforACMoperation
Resizingtheprimaryengineturbochargercompressorwasrequiredtoaccommodatethe
additionalairflowrequiredduringACMoperationbutstillhasasufficientsurgemarginforsafe
engineoperation. Themethodemployedinsizinganewcompressorforthisprojectsplitthe
operatingpointssymmetricallyaroundtheimaginarylinethatpassesthroughthecenterofthe
efficiencycontours
up
the
map.
This
is
graphically
demonstrated
below.
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S
e
t
c
a
c
n
p
c
igure3.4Pri
littingthe
o
ficiencyifth
ecase. Ho
cleisunkno
asnot50%d
ailablecom
nstantwhet
earestefficie
rocess,butd
rvesforthis
aryengineco
peratingpoin
eACMwaso
ever,sincet
nanda50
uetoavailab
ressorsize
herornotth
ncycontour.
etailed,appli
projectares
mpressormat
tsaround
th
peratedthe
isprojectd
dutycyclei
lecommerci
aschosen.
eACMisope
Thereisopp
cationspecif
howninthe
26
chingprocess
fullload.
epeak
efficie
ameamoun
esnotinvol
assumed.
alcompresso
heprimary
ratingbypla
ortunityfor
icdataisreq
igurebelow.
ithanengin
ncyline
pro
oftimeasit
easpecific
hesplitont
rassemblies.
ompressore
cingtheope
ptimizingth
uired.Theco
operatingpo
idesthe
best
wasoff. Thi
pplication,t
eactualco
. Therefore,
fficiencyrem
atingpointo
ecompresso
mpressorop
intof1600rp
average
sisnotlikely
eactualdut
pressormat
henearest
ainsnearly
neachside
rselection
eratingboos
and
tobe
h
fthe
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T
c
Figure3.5Pri
hecompress
ithouttheA
mpressoro
maryenginec
rselected
f
Moperating
erspeed,wh
ompressorma
curve
rthe
Perkin
. Thismatch
ileoptimizin
27
tchwiththeP
withtheACM
dieselengin
providesas
efficiencya
erkinsdieselb
operating.
eallows
for
f
ufficientsurg
muchaspo
oostcurvean
ullengine
op
emarginand
ssibleforthis
thetargetb
erationwith
lowriskof
project.
ost
and
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28
Chapter4:Results,Conclusions,andFutureWork
4.1ResultsandDiscussionfromUnmodifiedGT1241ShopAirTest
Stand
TheunmodifiedGT1241turbochargerwasusedasaperformancebaselineforcomparisonof
modificationstotheturbocharger,anditperformedbetterthanexpected. TheACM
performanceisshowninFigures4.1and4.2. Anaccuratepredictionofperformancewashard
toobtainduetolimitedcompressorandturbineperformancedatafromthemanufacturer. This
isbecausetheACMoperatingconditions,specificallyturbineinlettemperatureandpressure,
causedanincreaseincorrectedturbinespeed,comparedtoanonengineapplication. TheACM
operatingconditionsputthetargetcorrectedturbinespeedoutsideoftheknownturbine
performancemap. However,theincreasedcorrectedturbinespeeddidnotcauseasharp
turbineefficiencydrop,whichwaslikelytooccurduetoexcessivespeedfromtherelatively
smallcompressor. Thelimitingfactorinthisconfigurationwastheintercooler,whichcanbe
seeninFigure4.3. Therelativelylowintercoolereffectivenesslimitedheatremovalfromtheair
enteringtheturbine. Thisisdetrimentaltoperformanceasanincreaseinturbineinlet
temperaturewillgenerallycauseanincreaseinturbineoutlettemperature,decreasingthe
coolingcapacityoftheACM. ThedatapointsinFigures4.14.3werecollectedsimultaneously,
sothemassflowratecanberelatedtotheACMpressureratio,DARCOP,andDARcooling
capacity. Forexample,thethirdpointfromtherightinFigure4.1correspondstothethirdpoint
fromthe
right
in
Figure
4.2
4.3.
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Figure4.1DryairratedCOPfortheunmodifiedGT1241turbocharger. DatapointsinFigures4.14.3have
aonetoonecorrespondence.
Figure4.2DryairratedACMcoolingcapacity. DatapointsFigures4.14.3haveaonetoone
correspondence.
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30
Thecoolingcapacityrequiredinaperformanceautomotiveapplicationisapproximatelyoneton
ofcooling.ThiswasdeterminedfromreviewingR134acompressorperformancemapsfrom
Sanden[AppendixH]. ThisisdiscussedingreaterdetailinSection4.4.
Figure4.3IntercoolereffectivenessvariationwithmassflowrateintheGT1241ACMwiththeelectricfan.
Datapoints
Figures
4.1
4.3
have
aone
to
one
correspondence.
TheACMintercoolereffectivenesswaslimitedbecauseofpoorelectricfanperformance. The
heatexchangerperformancewasshowntohaveasignificantimpactonoverallACM
performanceinSection2.7,sothiswasremediedinlatertestsbymanuallyregulating
compressedairtopassoverthecoldsideoftheheatexchanger. However,tocontinuewith
testingonschedule,thenextcompressorwasinstalledbeforetheheatexchangerperformance
wasimproved. TheDARCOPhasapeakbecauseasthepressureratioacrosstheACMstartsat
unityandincreases,boththeACMcompressorandturbinewillpassthroughtheirpeak
efficiencies. TheDARcoolingcapacitywillincreaseuntilboththecompressorandturbinehave
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passedtheirpeakefficienciesandbegintodeclineinperformanceasthepressureratioacross
theACMisfurtherincreased.
ThepeakdryairratedCOP,withthe70%primarycompressorefficiencyassumption,isonpar
withaCOPofthetheoreticaloptimizationoftheACMfromQueen'sUniversity,Belfast[3],a
COPof0.62. However,themaximumcoolingcapacitydoesnotoccuratthemaximumCOP;the
dryairratedCOPfallstoapproximately0.48atthatpoint.
4.2ResultsandDiscussionfromModifiedGT1244ShopAirTestStand
TheinitialtestingoftheGT1244turbochargerusedthesameintercoolerfanassemblyasthe
previoustesttohaveadirectcomparisonofasinglecomponentchangeinthesystem. The
changeinthecompressorwheelandhousingdidnotchangethepeakdryairratedCOPofthe
ACM,butitdidgreatlyexpandtheusefuloperatingrangeoftheACMandincreasethesystem
coolingcapacity,pushingitclosertoonetonofcabincooling. ThiscanbeseeninFigures4.4
4.5. Theperformanceimprovementsfromthecompressorwheelandhousingchangefromthe
unmodifiedGT1241configurationareshownbelow. Theintercoolereffectivenessis
approximatelythesameasintheunmodifiedGT1241testing,Figure4.6. Theintercoolerisstilla
limitingfactor.However,withitsperformanceapproximatelythesameasintheGT1241ACM
testing,theresultsstillshowarelativeimprovementofthe44mmcompressorwheeloverthe
previous41mmcompressorwheel. Thedatapointswerecollectedsimultaneouslyduringthis
testing,andeachpointcorrespondstothesamedatapointnumberintheotherplotsinFigure
4.44.6.
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Figure4.4DryairratedCOPforthemodifiedGT1244turbocharger. DatapointsFigures4.44.5havea
onetoonecorrespondence.
Figure4.5DryairratedACMcoolingcapacity. DatapointsFigures4.44.5haveaonetoone
correspondence.
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Figure4.6IntercoolereffectivenessvariationwithACMmassflowrateusingtheelectricfan. Datapoints
Figures4.44.5haveaonetoonecorrespondence.
Next,theintercoolercoldsideairflowproblemwasfixed. Thiswasachievedbyrouting
manuallyregulatedcompressedairoverthecoldside. Theairflowoverthecoldsideofthe
intercoolerwaskeptwithinreasonablelevelsthatcouldbeobtainedwithatypicalconfiguration
seeninautomotiveapplications. Thiswasdeterminedtobeapproximately350CFM,andthis
agreeswithvolumetricflowratesobservedinR134acondensers[9]. Basedonintercoolercold
flowentrancearea,thisresultsinanaverageairvelocityofapproximately8.5ft/senteringthe
faceoftheintercoolercore. Thisiseveneasiertoachievewhenthevehiclewouldbemoving.
The
results
from
the
improved
intercooler
configuration
can
be
seen
below.
The
intercooler
performanceincreaseimprovedbothACMCOPandDARcoolingcapacity,Figure4.74.8.The
increaseinintercoolereffectivenesscanbeseeninFigure4.9. Thedatapointswerecollected
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simultaneouslyduringthistesting,andeachpointcorrespondstothesamedatapointnumber
intheotherplotsinFigure4.74.9.
Figure4.7DryairratedCOPforthemodifiedGT1244turbocharger. DatapointsFigures4.74.9havea
onetoonecorrespondence.
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Figure4.8DryairratedACMcoolingcapacity. DatapointsFigures4.74.9haveaonetoone
correspondence.
Figure4.9IntercoolereffectivenessvariationwithACMmassflowrate. DatapointsFigures4.74.9havea
onetoonecorrespondence.
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TheACMintercoolerprovedtobeacriticalcomponentinoverallACMperformance. The
improvedintercoolereffectivenessapproximatelydoubledthedryairratedCOPandcooling
capacity.
Thetheoreticalperformanceanalysiswasshowntobeagoodapproximationoftheactual
performanceoftheACM. Theflowpredictionfromthecompressorturbinematchandthe
turbinepressureratioflowprofileandactualflowconditionsareoverplottedonthe
compressorperformancemapforthe44mmcompressorwheel. Atlowerpressureratios,all
measurementsandcorrespondingpredictedvaluesagreewithin7%differenceorbetter. At
higherpressure
ratios
across
the
ACM
the
dry
air
rated
COP
and
DAR
cooling
capacity
calculationsbothmatchedactualperformancewithinapproximately13%,butthemassflow
ratedeviatesmore. Themassflowratedeviatesupto12%differencefromthemeasuredmass
flowrate. Atthispoint,thepressureratioacrosstheACMisapproximately1.84. Theresultsof
thecompressoroperatingpointscomparisoncanbeseeninFigure4.10. TheDARcooling
capacityandDARCOPcomparisonsagreewellandareshowninTable4.2.
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Si
p
b
c
li
si
a
Figure4.10L
ncetheoper
erformance
alancepoint
mpletelocu
iteddata,t
mulationma
ndEngineeri
atchingpro
cusoftheore
ationofthe
atacollecte
couldbeob
sofoperatin
hepartofth
tcheswell
wi
gEquationS
essdescribe
icalandactua
CMplacedt
bytheturb
ained. Ifmo
gpointscoul
locusofop
ththe
experi
olver(EES),
inAppendi
37
loperatingpo
heoperation
chargerma
recompone
beobtaine
ratingpoint
mentaldata.
setheequa
C. Acompa
intsoverplott
oftheACM
ufacturer,li
tperforman
withtheco
thatwasob
The
compu
ionsderived
risonofthet
edonGT1244
attheouterl
itedspeed,
cedatawas
mputersimu
tainedfrom
ersimulatio
inAppendix
heoreticalan
compressor
imitsof
power,and
vailable,a
lation. Even
hecompute
s,in
both
M
Bandthe
dactual
ap.
ass
ore
with
atlab
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38
operationusingtheconditionsspecifiedinTable4.1resultsintheperformancepresentedin
Table4.2.
Table4.1OperatingConditionsforsinglepointcomparisonoftheoreticalandactualperformance.
AmbientandOperatingConditions Value Units Uncertainty[+/]
AmbientTemperature 531 [Deg.R] 1.7
AmbientPressure 14.69 [psia] 0.02
AmbientRelativeHumidity 0.4 [] 0.08
ACMCompressorInletTemperature 526 [Deg.R] 1.7
ACMCompressorInletPressure 26.95 [psia] 0.02
ACMCompressorEfficiency 0.72 [] 0.02
ACMCompressorOutletPressure 37.08 [psia] 0.02
ACMIntercoolerEffectiveness 0.83 [] 0.04
ACMIntercooler
Pressure
Drop
0.3
[psi]
0.03
ACMMassFlowRate 13.73 [lbm/min] 0.6
ACMTurbineInletTemperature 536 [Deg.R] 1.7
ACMTurbineEfficiency 0.56 [] 0.02
Table4.2Resultsofsinglepointcomparisonoftheoreticalandactualperformance.
PerformanceParameter
Theoretical
Operation
Actual
Operation Uncertainty[+/]
COP,DryAirRated[] 0.61 0.64 0.04
CoolingCapacity,DryAirRated[ton] 1.7 1.5 0.06
4.3ResultsandDiscussionfromGT1244On-EngineTesting
TheonenginetestingwaslimitedbecauseofabearingfailureintheACMturbocharger.
However,oneoperatingpointwastestedbeforethefailureoccurred. Thetestingthatwas
completedbeforefailurewasstillasuccesswithgoodperformance. TheCOPbasedonchange
inbsfcandfuelflowratesindicatedaCOPof0.56,withacorresponding0.72tonsofcooling
capacity. ThetheoreticaloptimizationoftheACMfromQueen'sUniversity,BelfasthadaCOPof
0.62,whileactualperformancebeingmuchless[2,3]. Theiractualperformancenumberwas
notstated,otherthanbeinglessthanexpected. TheCOPfortheonenginetestingforthis
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projectisassumingtheACMisrunningatatimetheengine'sturbochargerwouldnothavebeen
wastegating,otherwisetheCOPisessentiallyinfinitebecausethepotentialpowerwouldhave
beenwastedintheturbinebypassfreeexpansionprocess.
ThetestingconductedwiththeACMbeingpoweredbythePerkinsdiesel'sturbochargerhad
reducedperformancefromtheshopairteststand. TheDARcoolingcapacitydecreasedfrom
approximately0.90to0.72tons,andtheDARCOPdecreasedfromapproximately0.73to0.56
forcorrespondingoperatingpointsoftheshopairtestingoftheGT1244andtheonengine
testing. ThisisduetomuchhigherACMinlettemperaturescomingfromtheintakemanifoldof
theengine.
The
on
engine
testing
conditions
represent
real
world
operation
more
accurately
thantheshopairteststand.
4.4ComparisonofACMtoR134aSystemsThetargetcoolingcapacityfortheACMwasdeterminedbyobservingtheaveragecooling
capacitybasedontheSandenperformancechartsoftheSD5H09R134asystemcompressors
[AppendixH]. ThisperformancechartindicatesthecoolingcapacityofatypicalR134asystem
usingtheSandencompressor. Thecoolingcapacitywillvarywithsuctionsuperheatand
operatingpressures. TheaveragerangewasselectedfromtheSandencharttorepresentthe
targetcoolingcapacity. Thisisapproximatelyonetonofcoolingcapacity(12000BTU/hr). The
SandenperformancechartwasusedbecauseSandenisaworldwidemanufacturerof
automotiveairconditioningcompressors,usedinalltypesofvehicles[10]andwouldcreatea
goodapproximation
of
the
cooling
requirements
for
ahigh
performance
vehicle.
While
the
GT1244ACMfellalittlebitshortofthecoolingcapacitygoal,theR134asystemsareprecharge
pressureandenginespeedsensitive. Theiractualcapacityvariessomewhatandareseldom
usedatfulldutycycleatalltimes(i.e.cabinfanspeedandtemperatureshutoffswitch).
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ThesystemweightforatypicalR134asystemvariesbetween6075lbf1. TheACMsystem
weightandestimatedbracketweightstotalsat40lbf. Thisisapproximatelya40%weight
reduction. Thephysicalsizeandnumberofcomponentsofthesystemissmallerthancompared
toR134aorFreonsystems[1].
Table4.3ACMcomponentweightbreakdown.
Component Weight[lbf]
TurbochargerAssy. 10
IntercoolerCore 10
ICend
caps
4
electricfan 5.6
ducting 2.5
Clamps 1
siliconeconnectors 2
Brackets(forvehicle) 5
Total 40
Anotheraspect
of
the
ACM
that
differs
from
typical
R134a
air
conditioning
systems
is
that
the
ACMdoesnotalwaysinduceaparasiticlossontheenginecrankshaft,asopposedtoabelt
drivenR134acompressor. ThiscanbeseenonaPvdiagramforafourstrokeengine.
12008emailtoVintageAir;unreferenced
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Figure4.11Pvdiagramforfourstrokegasolineengine.
ThelowerlooponthePvdiagramisanindicatorofthepumpinglossesontheengine. The
pumpinglossesaretheareaundertheexhaustlineminustheareaundertheintakelinein
Figure4.11orFigure1.1. ItshouldbenotedthatinFigure1.1,theexhaustpressureisgreater
thantheintakepressure. Apositivelowerlooplossistypicalofnaturallyaspiratedengines. In
Figure4.11thenetpumpinglossesarenegative,indicatingthataforcedinductionsystemis
creatingahigherengineintakemanifoldpressurethanexhaustbackpressure. Turningthe
R134asystem
compressor
on
will
induce
aload
on
the
engine
and
always
hurt
engine
performance. Ontheotherhand,aturbochargercanactuallycreateahigherintakepressure
thanexhaustbackpressure. Thisisduetotheturbinerecoveringwastedexhaustheat,with
someexhaustbackpressure,providingenoughworktothecompressortodeliverhigherthan
exhaustpressurestotheengine'sintakemanifold. Thishelpstominimizeenginebsfc.
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4.5Conclusion
TheshopairstandtestingsuccessfullydemonstratedthatanACMcanbedesignedaround
automotiveturbochargercomponents. Theuseofautomotiveturbochargercomponentsis
criticaltoreducingcostindevelopmentofcommercialsystemsforautomotiveuse. Anoffthe
shelfturbochargercanbeusedincertainapplicationswithoutmodificationandprovide
adequateperformance. ThetestingontheunmodifiedGT1241turbochargerindicatedapeak
DARCOPofapproximately0.38,andaDARcoolingcapacityof0.45tons. Theperformancewas
somewhatlimitedduetotheintercoolereffectivenessinitially,inthefirsttwoexperimentsof
theGT1241andGT1244,beforetheheatexchangerissuewasremedied. Itisexpectedthatif
theintercoolereffectivenesswasincreasedwiththisturbochargerconfiguration,the
performancewouldbesignificantlyincreased,asseeninthemodifiedGT1244testing.
TheGT1244wasoptimizedoverthebaselineGT1241turbocharger. TheACMturbineand
compressorwereselectedfortheACMoperatingconditions,asopposedto thetypicalon
engineapplicationtheseturbochargersarenormallyusedfor. Initially,thepeakDARCOPand
DARcoolingcapacitywasapproximatelythesameasthebaselineGT1241configuration.
However,evenwiththeintercoolerperformancebeinglimited,theoperatingrangewas
significantlyincreased(Figure4.44.5). Oncetheintercoolereffectivenesswasincreasedby
providingadequateairflowacrossthecoldsideoftheheatexchangercore,thepeakDARCOP
reached0.73withapeakDARcoolingcapacityof1.5tons(Figure4.74.9). TheDARCOPfigures
fortheshopairtestingweredeterminedbyassumingaprimarycompressorefficiencyof70%.
Thisprimarycompressorefficiencyistypicalofmodernturbochargersinapplication. For
reference,thecompressorusedfortheonenginetestinginthisprojecthasanisentropic
efficiencyof70%,orgreateratthetargetboostpressureof11psig,overamassflowrangeof
approximately1632lbm/min.
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Theonenginetestinghasshownthatanaircycleairconditioningsystemcanbeeffectivefor
racingapplications,wherethereisplentyofopportunitytotakeadvantageoftimethatwould
haveotherwisebeenspentwastegating. ThetestingperformedpriortotheACMthrust
bearingfailureindicatedaDARCOPof0.56andDARcoolingcapacityof0.72tons. This
operatingpointwasnotatfullboostpressureduetothelowerengineloadandspeedoperating
pointinitiallytested,andthefullbenefitofthesetup,operationduringtypicalwastegating
conditions,couldnotbetested.
IncomparisontopreviousworkatQueen'sUniversity,Belfast,theACMinthisproject
performedwell.
The
theoretical
COP
of
the
previous
work
was
0.294
[1,2].
They
performed
a
theoreticaloptimizationofthesamesystemwithanexpectedCOPof0.62. Thetheoretical
optimizationusedcompressorandturbineefficienciesofstateoftheartcomponents.
However,theirfinalresultsfromactualtestingwerenotpresentedotherthanashortstatement
sayingthatfuelconsumptionoftheengineincreasedoverthreetimestheamountforthe
vaporcompressioncycletheyimplementedaswell. Thegroupattributedthelessthan
expectedperformancetoexcesslossesincomponentssuchastheACMbearingsandprimary
compressorontheengine.
IftheACMbearingfailurehadnotoccurred,thenextoperatingpointwouldhavebeenathigher
loadandspeedtoprovideabettercomparisontothewastegatedturbochargeroperation. The
operatingpointtestedcorrespondstoapointwherethestockturbochargerwasnotyetwaste
gating.
Thismeans
that
the
boost
pressure
can
be
increased
to
the
original
limit,
resulting
in
increasedcoolingcapacityduetoincreasedpressureratioacrosstheACM. Also,theeffectson
engineperformancecanbedecreasedbecausetheACMwillbeconsumingasmallerfractionof
theoverallengineairflow. Atlargerengineloadsandspeeds,thereissignificantexcessturbine
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powerthatwouldnormallybelimitedbywastegateoperation. Factorsthatinfluenceturbine
powerareturbinemassflowrate,exhaustgastemperature,andpressureratioacrossthe
turbine. Bothturbinemassflowrateandexhaustgastemperaturetypicallyincreasewith
engineloadandspeed. Withthisinmind,engineoperatingpointscorrespondingtowastegate
operationareexpectedtohaveincreasedDARCOPfollowingtheproposeddefinitionof
COPEffective inEqn. 2.2.
Theengineturbochargermatchingcriteriahaspotentialtobefurtheroptimizedforspecific
applications. ThiswillminimizeeffectsofACMoperationonengineperformance. Thenominal
ACMmass
flow
rate
relative
to
the
engine
mass
flow
rate
at
typical
engine
operating
conditions
isanimportantconsiderationbecausetoolargeofanACMandtheprimarycompressorwillnot
beabletomaintaindesiredboostpressuresathighercombinedsystemmassflowrates. Theair
flowtotheACMcanbethrottled,butthiswillreducethepotentialcoolingcapacityofanACM
beingdesignedforthevehicle. WhilethrottlingtheACMmaybenecessaryissomeengine
operatingconditions,itisnotoptimalforperformanceandshouldbeavoidedasmuchas
possible.
4.6FutureWork
WhilethereisaconsiderableamountofworktostillbedoneindesigninganACMfor
production,mostofitcanbeeasilyhandledbyaturbochargermanufacturer. Theconditions
theACMturbochargercompressorisoperatinginaresimilartoasecondturboinaseries
turbochargersetup
used
on
modern
diesel
engines
to
more
efficiently
handle
increased
boost
pressures. ThemainconsiderationisthebearingsystemfortheACM. Thebearingsystem
experienceshigherthrustloadingbecauseitneedsalargercompressorwheelrelativetothe
turbinewheel. Thisisbecausethecompressorinletseeshigherthanatmosphericpressures
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whiletheturbinestillexitstoambientpressure,andwithalargercompressorwheel,thereis
increasedareafortheinletpressuretoactupon. Stabilityoftherotatingassemblyisthefirst
priority.However,thebearingsystemefficiencyisincreasinglycriticalinlowtemperature
applicationsbecausethereislesspowerbeingtransmittedbytheshaft,andthesameamount
ofbearingdragwillnowbealargerfractionofthepowertransmitted. Toincreasestabilityand
decreasebearinglosses,magneticorairbearingsmaybeconsidered[5,7].
TheACMturbochargercanoperateinasmallerrangethanatypicalonengineapplication,and
thisallowsformoreoptimizationofthecompressorandturbinedesignsforhigherpeak
efficiencyat
the
cost
of
usable
mass
flow
rate
range
[8].
Once
aparticular
application
is
well
defined,thecompressorandturbinecanbedesignedtooperateinanarrowerrangethatis
adequatefortheapplication. Thisrequiresaconsiderableamountofresearchanddevelopment
andwouldonlybepracticalforlargerproductionquantities.
Tocompletelyproveouttheconceptwithspecificpackagingrequirements,aninvehicle
demonstrationwouldbeideal. Thetypeofvehiclecouldbeanythingperformanceoriented
withamediumtolargeengine,duetotheminimizesizeofturbochargersavailableforACM
design. TheturbochargerusedfortheACMinthisprojectisthesmallestcommerciallyavailable
fromGarrettTurbochargers. Theinvehicledemonstrationwouldallowforanoperationduty
cycletoberecordedandfacilitateinoptimizingtheengineturbocharger'scompressormatching
process.
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References
1.Scofield,PaulC.(1949).AirCycleRefrigeration.RefrigeratingEngineers,57,[558563,611
612].
2.Spence,
Stephen
W.T.,
Doran,
W.
John,
&
Artt,
David
W.
(2004).
Design,
construction
and
testingofanaircyclerefrigerationsystemforroadtransport.InternationalJournalof
Refrigeration,27,503510.
3.Spence,StephenW.T.,Doran,W.John,Artt,DavidW.,&McCullough,G.(2005).Performance
analysisofafeasibleaircyclerefrigerationsystemforroadtransport.International
JournalofRefrigeration,28,381388.
4.Arora,CP.(2000).Refrigerationandairconditioning.WestPatelNagar:TataMcGrawHill
PublishingCompanyLimited.
5.Murray,
Charles
J.
(1994).Magnetic
Bearing
Improves
Air
Cycle
Cooling
Reliability.
Design
News, 49,8586.
6.TurboTech101.Retrievedfrom
http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html
7.Burgmeler,Lyman,&Poursaba,Matt(1994).CeramicHybridBearingsinAirCycleMachines.
InternationalGasTurbineandAeroengineCongressandExposition,94GT393,19.
8.DresserRand,Olean&WellsvilleOperations.(2006).RangeVersusEfficiencyADilemmafor
CompressorDesignersandUsers[Brochure].Olean,NY:JamesM.Sorokes.
9.Hosnoz,M.,&Direk,M.(2006).Performanceevaluationofanintegratedautomotiveair
conditioningandheatpumpsystem.EnergyConversion&Management,47,545559.
10.Retrievedfromwww.sanden.com
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47
AppendixAUncertaintyAnalysis
UncertaintyofadependentvariableF(x,y,z),ingeneralcanbecalculatedas:
(Eqn.
A.1)
whereuFistheuncertaintyintheparameterofinterest,suchascompressorefficiency,andux,
uy,anduzarethemeasurementuncertainties.
TableA.1MeasurementUncertaintyBasedonCalibrationInstrumentation
Measurement MeasurementUncertainty
Pressure 0.02[psi]
Temperature 1.7[Deg.F]
VolumetricFlowRate approx.5[CFM]
A.1CompressorEfficiency
ThecompressorefficiencyuncertaintywascalculatedusingconditionsrepresentativeofACM
operatingconditions. Indoingsosomeassumptionsarerequired. Itisassumedthecompressor
andturbineefficiencyare70%andtheintercoolereffectivenessis70%.
Thecompressorefficiencycanbecalculatedas:
(Eqn.A.2)Thepartialderivatesarecalculated:
(Eqn.A.3)
(Eqn.A.4)
(Eqn.A.5)
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48
(Eqn.A.6)Equations
A.3
6can
be
used
to
find
the
total
uncertainty
in
efficiency
by,
1
1
(Eqn.A.7)
Theresultsforuncertaintyincompressorefficiencyare:
FigureA.1UncertaintyinACMcompressorefficiencyduringtypicaloperatingconditions.
Theuncertaintygrowslargeatlowcompressorpressu