development of an air-cycle environmental control system for auto

8/2/2019 Development of an Air-cycle Environmental Control System for Auto

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i

DEVELOPMENTOFANAIRCYCLEENVIRONMENTALCONTROLSYSTEMFORAUTOMOTIVE

APPLICATIONS

Athesis

Presentedto

thefacultyofCaliforniaPolytechnicStateUniversity

SanLuis

Obispo

InPartialFulfillmentof

theRequirementsfortheDegreeof

MasterofScienceinMechanicalEngineering

by

ChristopherJ.Forster

December2009


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ii

2009

ChristopherJ.Forster

ALLRIGHTSRESERVED


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iii

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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vii

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




Figure4.6IntercoolereffectivenessvariationwithACMmassflowrateusingtheelectricfan.

DatapointsFigures4.44.5haveaonetoonecorrespondence.................................................. 33

Figure4.7DryairratedCOPforthemodifiedGT1244turbocharger. Datapoints




Figure

4.9

Intercooler

effectiveness

variation

with

ACM

mass

flow

rate.

Data

points


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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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

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m


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4

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

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7

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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8

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.


22/231

T

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llowsforafr

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ACMconfig

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mpressorbl

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intake

orboost,a

ypicallyperf

andcloses

exhaustgast

commonlyr

noftheexh

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.

9

inetwowhee

tesbybleedi

anifold.Th

ommonna

rmedbyusi

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obypassthe

ferredtoas

ustthatisall

tionusesthi

lbootstrapsc

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bleed

air

c

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ngapneuma

ppervalvelo

turbine,limi

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lowedtobyp

swastedene

ematic.

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nfiguration

ointakeman

ticactuatort

catednextt

tingturbine

. Itisreferre

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owerandb

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This

ost.

e

ile


23/231

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


26/231

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


27/231

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


28/231

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


31/231

18

singlestagecompression. Thisisrepresentativeofwhatcanbeseeninoperatingintake

pressuresindieselengines.


32/231

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


33/231


34/231

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


35/231

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


36/231

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


37/231

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


38/231

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.


39/231

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


40/231

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


41/231

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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29

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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31

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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32

Figure4.4DryairratedCOPforthemodifiedGT1244turbocharger. DatapointsFigures4.44.5havea

onetoonecorrespondence.


correspondence.


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33

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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34

simultaneouslyduringthistesting,andeachpointcorrespondstothesamedatapointnumber

intheotherplotsinFigure4.74.9.

Figure4.7DryairratedCOPforthemodifiedGT1244turbocharger. DatapointsFigures4.74.9havea



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35


correspondence.

Figure4.9IntercoolereffectivenessvariationwithACMmassflowrate. DatapointsFigures4.74.9havea



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36

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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39

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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40

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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41

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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42

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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43

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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44

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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45

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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46

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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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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(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

development of an air-cycle environmental control system for auto

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