CEC-500-2012-043 ovooooo

7/29/2019 CEC-500-2012-043 ovooooo

1/112

Publ ic Interest Energy Research (PIER) ProgramFINAL PROJECT REPORT

ADVANCEDLASERIGNITIONSYSTEMINTEGRATEDARICESYSTEMFORDISTRIBUTEDGENERATIONINCALIFORNIA

MAY 2012

CEC 500 2012 043

Preparedfor: CaliforniaEnergyCommissionPreparedby: ArgonneNationalLaboratory

7/29/2019 CEC-500-2012-043 ovooooo

2/112

Prepared by:

Primary Author(s):Sreenath GuptaRaj Sekar

Argonne National LaboratoryArgonne, IL, 60439

Contract Number: 500-02-022

Prepared for :

California Energy Commission

Avtar Bining, Ph.D.Project Manager

Mike GravelyOffice ManagerEnergy Systems Research Office

Laurie ten HopeDeputy DirectorRESEARCH AND DEVELOPMENT DIVISION

Robert P. OglesbyExecutive Director

DISCLAIMER

This report was prepared as the result of work sponsored by the California Energy Commission. It

does not necessarily represent the views of the Energy Commission, its employees or the State ofCalifornia. The Energy Commission, the State of California, its employees, contractors andsubcontractors make no warrant, express or implied, and assume no legal liability for the informationin this report; nor does any party represent that the uses of this information will not infringe uponprivately owned rights. This report has not been approved or disapproved by the California EnergyCommission nor has the California Energy Commission passed upon the accuracy or adequacy ofthe information in this report.

7/29/2019 CEC-500-2012-043 ovooooo

3/112

i

Acknowledgments

TheauthorsthanktheCaliforniaEnergyCommissionforthefunding,supportandguidance

forthisproject.TheauthorswouldalsoliketothankMr.RonFiskum,TechnologyManager

oftheAdvancedReciprocatingEngineSystemsProgramattheUnitedStatesDepartmentof

Energyforcofundingthisproject.Wealsorecordourappreciationfortheinteractionwith

AdvancedLaserIgnitionSystemConsortiumpartners.

Pleasecitethisreportasfollows:

Gupta,Sreenath,andRajSekar(ArgonneNationalLaboratory).2008.AdvancedLaserIgnitionSystemIntegratedARICESystemforDistributedGenerationinCalifornia.CaliforniaEnergy

Commission,PIEREnvironmentallyPreferredAdvancedGenerationProgram.CEC500

2012043.

7/29/2019 CEC-500-2012-043 ovooooo

4/112

ii

7/29/2019 CEC-500-2012-043 ovooooo

5/112

iii

Preface

TheCaliforniaEnergyCommissionsPublicInterestEnergyResearch(PIER)Program

supportspublicinterestenergyresearchanddevelopmentthatwillhelpimprovethe

qualityoflifeinCaliforniabybringingenvironmentallysafe,affordable,andreliableenergy

servicesandproductstothemarketplace.

ThePIERProgramconductspublicinterestresearch,development,anddemonstration

(RD&D)projectstobenefitCalifornia.

ThePIERProgramstrivestoconductthemostpromisingpublicinterestenergyresearchby

partneringwithRD&Dentities,includingindividuals,businesses,utilities,andpublicor

privateresearchinstitutions.

PIERfundingeffortsarefocusedonthefollowingRD&Dprogramareas:

BuildingsEndUseEnergyEfficiency

EnergyInnovationsSmallGrants

EnergyRelatedEnvironmentalResearch

EnergySystemsIntegration

EnvironmentallyPreferredAdvancedGeneration

Industrial/Agricultural/WaterEndUseEnergyEfficiency

RenewableEnergyTechnologies

Transportation

AdvancedLaserIgnitionIntegratedARICESystemforDistributedGenerationinCaliforniaisthe

finalreportfortheAdvancedLaserIgnitionIntegratedAdvancedReciprocatingInternal

CombustionEngine(ARICE)SystemforDistributedGenerationinCaliforniaproject

Contractnumber50002022conductedbyArgonneNationalLaboratory.Theinformation

fromthisprojectcontributestoPIERsEnvironmentallyPreferredAdvancedGeneration

Program.

FormoreinformationaboutthePIERProgram,pleasevisittheEnergyCommissions

websiteatwww.energy.ca.gov/research/orcontacttheEnergyCommissionat9166544878.

7/29/2019 CEC-500-2012-043 ovooooo

6/112

iv

7/29/2019 CEC-500-2012-043 ovooooo

7/112

v

Table of Contents

Preface:................................................................................................................................................ iii

Abstract............................................................................................................................................. xiii

ExecutiveSummary............................................................................................................................ 1

1.0 Introduction............................................................................................................................. 5

1.0 Introduction............................................................................................................................. 5

1.1. Background................................................................................................................ 5

1.2. FundamentalsofIgnition......................................................................................... 8

1.3. WhyLaserIgnition?.................................................................................................. 9

1.4. ALISConsortium..................................................................................................... 10

1.5. GoalsandObjectives............................................................................................... 11

2.0 (Task2.2)NaturalGasAirIgnitionExperimentalStudy............................................... 13

2.1. RationaleforTask2.2.............................................................................................. 13

2.2. ExperimentalSetup................................................................................................. 14

2.2.1. Rapidcompressionmachine.................................................................................. 14

2.2.2. Laserignitionsystem.............................................................................................. 17

2.2.3.

Conventionalignitionsystem................................................................................ 17

2.2.4. Operationalprocedure............................................................................................ 18

2.3. ResultsandDiscussion........................................................................................... 19

2.3.1. TestMatrix................................................................................................................ 19

2.3.2. IgnitionLimits.......................................................................................................... 20

2.3.5. ConclusionsforTask2.2......................................................................................... 24

3.0 (Task2.3)DesignofALISComponents............................................................................ 25

3.1. GoalsandObjectivesofTask2.3........................................................................... 25

3.2. LaserSystem............................................................................................................ 28

3.3. LaserPlugs............................................................................................................... 31

3.4. HighPowerOpticalMultiplexer.......................................................................... 34

7/29/2019 CEC-500-2012-043 ovooooo

8/112

vi

3.4.1. ElectroOpticModulator(PockelsCell)............................................................... 34

3.4.2. RotatingMirror........................................................................................................ 35

3.4.3. Flipflop.................................................................................................................... 37

3.5.

FiberOpticDelivery............................................................................................... 38

3.5.1. Solidcorefibers........................................................................................................ 39

3.5.2. HollowGlassWaveguides(HGWs)..................................................................... 41

3.5.3. Advancedaircorefibers........................................................................................ 42

3.6. ElectronicInterface.................................................................................................. 43

3.7. ResultsandConclusionsforTask2.3................................................................... 44

4.0 (Task2.4)SingleCylinderLaserIgnitionStudies............................................................ 47

4.1.

StatementofWorkforTask2.4............................................................................. 47

4.2. ExperimentalSetup................................................................................................. 48

4.2.1. SingleCylinderEngine........................................................................................... 48

4.2.2. OpenPathLaserIgnitionSetup............................................................................ 50

4.2.3. Fibercoupledlaserignitionsetup........................................................................ 52

4.3. TestMatrix................................................................................................................ 54

4.4. ResultsandDiscussionforTask2.4...................................................................... 56

4.4.1. FullLoadComparison(15barBMEP).................................................................. 58

4.4.2. PartLoadComparison(10barBMEP)................................................................. 62

4.4.3. FiberCoupledLaserIgnitionResults................................................................... 64

4.5. ConclusionsforTask2.4......................................................................................... 65

5.0 (Task2.5)IntegrateALISandRefineforPerformanceonaMultiCylinderEngine..67

5.1. EngineandNaturalGasFuelingSystemInstallation........................................ 67

5.1.1.

Multicylinderengine............................................................................................. 67

5.1.2. NaturalGasFuelingsystem................................................................................... 68

5.2. ALISIntegration...................................................................................................... 69

5.2.1. Mechanicalintegration........................................................................................... 70

5.2.2. ElectronicIntegration.............................................................................................. 72

7/29/2019 CEC-500-2012-043 ovooooo

9/112

vii

5.2.3. ALIStesting.............................................................................................................. 75

6.0 (Task2.6)PerformanceTestingofIntegratedALISARICESystem............................. 79

6.1. StatementofWorkforTask2.6............................................................................. 79

6.2.

MultiCylinderEngineTests.................................................................................. 79

7.0 (Task2.7)EconomicEvaluationforFeasibility................................................................ 81

8.0 SummaryandConclusions................................................................................................. 83

9.0 References.............................................................................................................................. 85

10.0 GLOSSARY............................................................................................................................ 87

APPENDIXA:AdvancedLaserIgnitionSystem(ALIS)Consortium

APPENDIXB:FutureHighPowerOpticalMultiplexingTechnologies

7/29/2019 CEC-500-2012-043 ovooooo

10/112

viii

List of Figures

Page

Figure1.ComparisonofMaintenanceCostsforRichBurnandLeanBurnEngines...............6

Figure2.OperationalRegionofaTypicalLeanBurnEngine.(Courtesy:SwRI)...................... 7

Figure3.IgnitionLimitsofaTypicalFuelairSystem................................................................... 8

Figure4.SchematicofaCapacitanceDischargeIgnition(CDI)System..................................... 9

Figure5.ALISDevelopmentConsortium..................................................................................... 11

Figure6.IgnitionLimitsofMethaneairMixturesEstablishedinaStaticChamber.Initial

MixtureTemperature~22C.............................................................................................. 14

Figure7.SchematicoftheRapidCompressionMachine............................................................ 16

Figure8.APictureofArgonnesRapidCompressionMachine................................................. 16

Figure9.SchematicoftheOpticalArrangementintheLaserIgnitionSystem........................ 17

Figure10.ConventionalIgnitionSystemCart.............................................................................. 18

Figure11.TypicalPressureTracesfromRCMOperation;P1=1bar,=0.7........................... 20

Figure12.MeasuredversusCalculatedPeakCombustionPressuresforVariousMethaneair

Mixtures,1.0

7/29/2019 CEC-500-2012-043 ovooooo

11/112

ix

Figure24.PhotographofaPockelsCellBasedTwoChannelMultiplexer.............................. 35

Figure25.SchematicofaRotatingMirrorMultiplexer............................................................... 36

Figure26.PhotographofArgonnesRotatingMirrorMultiplexer............................................ 36

Figure27.SchematicofaFlipFlopMultiplexer........................................................................... 37Figure28.(a)SchematicofSetuptoMeasuretheTimeResponseoftheFlipFlop(b)A

TypicalDetectorResponseCurve...................................................................................... 37

Figure29.SchematicofLaserRefocusingSchemeattheDistalEndoftheOpticalFiber......39

Figure30.FiberFaceLaserIntensityDistributionProfilesforanInjectionSchemeUsing(a)

PlanoConvexLens,(b)CombinationofAxiconandPlanoConvexLens................... 40

Figure31.TheRefractiveIndexDistributioninTwoSolidCoreFibers:(a)StepIndexFiber,

and(b)GradientIndexFiber.............................................................................................. 41

Figure32.(a)SchematicoftheCrossSectionofaHollowGlassWaveguide(HGW),and(b)APhotographShowingSparkGenerationUsingHGWintheLab.............................. 42

Figure33.(a)SchematicoftheCrossSectionofaMultiLayerHollowGlassWaveguide,and

(b)PhotographofanAirCorePhotonicBandgapFiber................................................ 43

Figure34.SchematicDiagramoftheElectronicInterface........................................................... 44

Figure35.SchematicoftheControlSchemeoftheBSCRESingleCylinderEngineUsing

SwRIsRPECS...................................................................................................................... 49

Figure36.PhotographShowingtheInstalledLaserPlugintheCombustionChamber........51

Figure37.SetupfortheOpenPathLaserIgnitionTestsonaLargeBore,SingleCylinder

BombardierBSCRE04Engine............................................................................................ 51

Figure38.LayoutoftheFiberCoupledLaserIgnitionSystem.................................................. 52

Figure39.FiberCoupledLaserIgnitionSystemasMountedontheBombardierBSCRE04

Engine..................................................................................................................................... 53

Figure40.ArbitraryCylinderPressureandHeatReleaseComparisontoClarify

NomenclatureofCombustionParameters....................................................................... 57

Figure41.COVofIMEPversusEquivalenceRatio(EQR)ataBMEPof15bar...................... 58

Figure42.CombustionStabilitywithConventionalSparkIgnitionataBMEPof15bar......59

Figure43.CombustionStabilitywithLaserIgnitionataBMEPof15bar................................ 59

Figure44.BSNOXBrakeThermalEfficiencyTradeoffataBMEPof15bar............................. 61

Figure45.CylinderPressureComparison..................................................................................... 61

7/29/2019 CEC-500-2012-043 ovooooo

12/112

x

Figure46.CylinderPressureandHeatReleaseComparison..................................................... 62

Figure47.COVofIMEPversusEquivalenceRatioataBMEPof10bar.................................. 63

Figure48.BSNOXBrakeThermalEfficiencyTradeoffataBMEPof10bar............................ 63

Figure49.AComparisonofBurnDurationsforDifferentModesofIgnition......................... 64Figure50.APhotographoftheCumminsQSK19GEngineinoneoftheEngineTestCellsat

ArgonneNationalLaboratory............................................................................................ 68

Figure51.ASchematicoftheIntegratedALIS............................................................................. 70

Figure52.AschematicoftheIntegratedALISShownInstalledonOneCylinderofaMulti

CylinderEngine.................................................................................................................... 71

Figure53.PictureoftheALISAssemblyMountedonArgonnesQSK19GEngine(Top

View).LaserHeadontheRightisnotShown................................................................. 72

Figure54.(a)SchematicRepresentationoftheuseofElectronicInterfaceina6cylinderEngine,(b)SchematicRepresentationoftheuseofElectronicInterfaceforLabScale

Testing.................................................................................................................................... 73

Figure55.FunctionalRepresentationoftheElectronicInterface............................................... 74

Figure56.TimingDiagramfor1800rpmOperation,redPulsesTriggerLaserPowerSupply

#1WhileBluePulsesTriggerLaserPowerSupply#2................................................... 74

Figure57.Pictureofthe6ChannelALISAssemblyontheTestrig(TopView).AlsoShown

aretheLaser,BNC565PulserandtheElectronicInterface.LaserPlugsarenot

Visible..................................................................................................................................... 75

Figure58.PictureofMisfireDetectionSystem............................................................................. 76

Figure59.DataFromoneoftheLongTermDurabilityTests.................................................... 77

FigureB1.(a)PhotographofaGalvanometerBasedSystem.Courtesy:Cambridge

Technology,Inc.(b)UseofGalvanometerforLaserScanning[28]................................ 1

FigureB2.PhotographofaPiezoBasedLaserScanner.Courtesy:PhysiqueInstrumente......2

FigureB3.(a)PhotographofaMEMSBasedMirrorArray,and(b)TexasInstruments

DigitalMirrorDevice............................................................................................................. 2

7/29/2019 CEC-500-2012-043 ovooooo

13/112

xi

List of Tables

Page

Table1.Performancetargetsforadvancedreciprocatinginternalcombustionengines..........5

Table2.PerformanceRequirementsofanAdvancedIgnitionSystem(Courtesy:Caterpillar,

CumminsandWaukesha).................................................................................................. 28

Table3.PerformanceSpecificationsofSomeCommerciallyAvailablePulsedDPSSL..........31

Table4.HollowGlassWaveguidesTestedforHighPowerLaserTransmission.................... 41

Table5.SpecificationsofSwRIsBSCREEngine.......................................................................... 50

Table6.TestMatrixforSingleCylinderLaserIgnitionStudies................................................. 55

7/29/2019 CEC-500-2012-043 ovooooo

14/112

xii

7/29/2019 CEC-500-2012-043 ovooooo

15/112

xiii

Abstract

TheprimarygoalofthisprojectwastodevelopandtestanAdvancedLaserIgnitionSystem

(ALIS)forimprovingefficiencyandreducingengineoutemissionsofoxidesofnitrogen

(NOx)fromnaturalgasfueledreciprocatingenginescommonlyusedfordistributed

generationinCalifornia.Thespecificobjectiveoftheprojectwastodesign,developanddemonstrateanintegratedALISonamulticylindernaturalgasfueledreciprocatingengine

meetingorexceedingCaliforniasDistributedGenerationEmissionsStandards.

Leanoperationhasbeenthepreferredmodeofoperationfornaturalgasfueled

reciprocatingenginesasitallowslowNOxemissionsandhighoverallefficiency.Laser

ignitionappearspromisingasitachievesignitionathighpressuresandunderlean

conditionsrelativelyeasily.Lasersarebecominglessexpensiveandmorecompactthan

beforeandareattractivemeansofignitionforengines.

Initially,thebasicdesignrequirementsforlaserignitionundertypicalincylinderconditions

(temperaturenear500degreesCelsius,pressureunder77bar)wereestablished.Throughfundamentalignitionstudiesperformedinarapidcompressionmachine,thecharacteristics

oflaserignitionandconventionalsparkignitiononmethaneairmixtureswerecompared.

Therapidcompressionmachinestudiesdemonstratedsignificantdifferencesbetweenthe

combustionprocessesassociatedwithlaserignitionandconventionalsparkignition.

Subsequenttestsonalargeboresinglecylinderengineshowedthatlaserignitioncould

potentiallyreduceNOxemissionsupto70percent.Alternately,foragivenNOxemissions

level,laserignitioncanenhanceenginefuelconversionefficiencyby3percentagepoints.

VariouscomponentsrequiredforALISweredeveloped.Afreespacelasertransmission

designapproachwasusedduetononavailabilityofsuitablefiberoptics.Thesuccessfully

developedcomponentswereintegratedandoptimizedforusewithamulticylinderengine.TheintegratedALISwastestedforanextendedperiodoftimeinthelaboratorytoprove

systemreliability.AbriefenginetestwithALISwasattemptedinatestcellatCummins

EngineCompanyandthesystemintegrationissueswereidentified.Futureworkisexpected

tosuccessfullydemonstratetheperformanceandemissionsbenefitsofAdvancedLaser

IgnitionSystemoperationinamulticylindernaturalgasfueledreciprocatingengine

suitablefordistributedgenerationapplicationsinCalifornia.

Keywords: Emissions,Engine,Ignition,Laser,Spark

7/29/2019 CEC-500-2012-043 ovooooo

16/112

xiv

7/29/2019 CEC-500-2012-043 ovooooo

17/112

1

Executive Summary

Introduction

Withelectricgridinfrastructurecapabilitieslaggingbehindtheeverincreasingpower

demandsinCalifornia,DistributedPowerGenerationhascomeintovogue.Mostofsuchinstallationsarenaturalgasfueledinternalcombustionengineswitheitherrichburn

(equivalenceratio,~1.0)orleanburn(

7/29/2019 CEC-500-2012-043 ovooooo

18/112

2

Approach

Theprojectcommencedwithanexhaustivesurveyoftheignitionliterature.Followingthis

literaturereview,fundamentalignitiontestswereperformedonaRapidCompression

Machinetocompareconventionalsparkignitionandlaserignition.

AninitialsurveyofpossibleAdvancedLaserIgnitionSystemschemeswasperformedand

twopromisingconfigurationswereidentified:(i)thelaserpercylinderconcept,and(ii)the

multiplexedlaserconcept,whereintheoutputofasinglelaserisdistributedovervarious

cylinders.Thelatterconceptwaschosenasitpromisedlowcostandsimplicityofthermal

management.However,thisconceptrequiredthedevelopmentofthreemaincomponents,

namely,laserplugs,multiplexersandfiberopticbeamdelivery.Forbreakdowntooccurin

gases,therequiredlaserfluencyatthefocalpointisoftheorderof1012WattsperSquare

Centimeter(W/cm2).Toachievesuchpeakfluencies,highpowerlaserpulseswithpeak

powerofseveralmegawatts(MW)arerequired.Therefore,themaincomponentsofthe

AdvancedLaserIgnitionSystemmustbedesignedtowithstandsuchhighpowerlevels.

Guidancewasderivedinthedevelopmentofthesecomponentsthrough(i)datafromfundamentalignitionstudiesconductedontheRapidCompressionMachine,and(ii)

requirementsoftheadvancedignitionsystemasspecifiedbyenginemanufacturers.Specific

detailsofthehighpowercomponentsconsideredinthepresentprojectaredescribedbelow:

LaserPlugs:Atwolensdesignthatsuccessfullymeetsthephysicalandfunctional

requirementsofalaserplugwasdeveloped.Adaptationofthisdesignforvariousengine

geometriesispossible.

Multiplexers:Threeschemesthatdistributetheoutputofasinglelaseramongvarious

cylinderswerepursued:(i)anelectroopticswitch,(ii)arotatingmirrorscheme,and(iii)a

flipflopswitch.Thefirsttwoschemesfellshortoftherequirementseitherduetohighcostortheinabilitytoprovideignitiontimingvariationsinindividualcylinders.Theflipflop

scheme,however,provedeffectiveinallrespects.

FiberOpticBeamDelivery:Throughtestsandanalysesitwasdeterminedthatthefiber

opticdeliveryrequirementsare(i)lowdivergenceatdistalend,(ii)highpowerlaser

transmission,and(iii)preservationofmodequality.Initialtestsperformedusingsolidcore

fibersshowedthattheyarelimitedbythematerialdamagethreshold.Subsequenttests

performedusingHollowGlassWaveguidesshowedthattheyarelimitedbymodeshifts

introducedbybendingoftheopticalfibers.Whilephotonicbandgapfibersappear

promising,theyarenotreadilyavailablefortestsandtheirdevelopmentisexpectedtobe

expensive.

ElectronicInterface:AnelectronicinterfaceisrequiredfortheAdvancedLaserIgnition

SystemtocommunicatewiththeElectronicControlUnitofanengineforignitiontiming

coordination.InconsultationwithArgonnesindustrialpartner,Altronic,Inc.,thetiming

modulesfromexistingignitionsystemsweremodifiedforthepresentpurpose.

7/29/2019 CEC-500-2012-043 ovooooo

19/112

3

Inparallel,thebenefitsoflaserignitionweredemonstratedinasinglecylinderresearch

engine.Forthispurpose,a9.5inchbore,11literdisplacementBombardiersinglecylinder

engineatSouthwestResearchInstitutewasused.Testswereperformedcomparing

conventionalcapacitancedischargesparkignition,freespacelaserignition,andfiber

coupledlaserignition.

Theenginewasoperatedat10barand15barBrakeMeanEffectivePressure(BMEP)at900

revolutionsperminute(rpm).Sweepsoffuelairequivalenceratio(from0.5to0.65)and

ignitiontiming(from25degreesBeforeTopDeadCenter,to8degreesAfterTopDead

Center)wereperformedwhileadjustingtheairboosttokeepthemeanpowerconstant.

Results

Reviewofpreviouslypublishedignitionliteratureshowedsignificantspreadindata

concerningthecombustionbehaviorofnaturalgasairmixtureswithlaserignition.

Subsequently,intheRapidCompressionMachinestudies,methaneairmixturesunder

typicalincylinderconditions(temperature~500degreesCelsius,pressure

7/29/2019 CEC-500-2012-043 ovooooo

20/112

4

Inviewoftheaforementionedbenefitsoflaserignition,effortsweredirectedatdeveloping

anintegratedAdvancedLaserIgnitionSystem.Previouslydevelopedcomponentswere

integratedintoasinglesystemwhilerelyingonafreespacelaserbeamdelivery.Tests

conductedinalaboratoryenvironmentshowedtheintegratedsystemtohavetherequired

timeresponseandperformance.

Conclusions

Inconclusion,theprojecttitledAdvancedLaserIgnitionIntegratedARICESystemfor

DistributedGenerationinCaliforniaproducedimportantresultsofpracticalsignificance

towardthedevelopmentofanadvancedlaserignitionsystemforreciprocatingengines.

FundamentalRapidCompressionMachinestudiesclearlyshowedthepotentialbenefitsof

laserignitioncomparedtoconventionalsparkignition:(i)Laserignitionextendedthelean

operatinglimitofmethaneairmixturestotheleanflammabilitylimit(ll=0.5),and(ii)Combustionrateswereacceleratedwithlaserignition.

SinglecylinderengineexperimentsperformedwithlaserignitionrealizedthepotentialbenefitsevidencedintheRapidCompressionMachinestudies.Comparedtoconventional

sparkignition,laserignitionextendedtheleanmisfirelimitbyabout10percentatBMEPsof

10and15bar,increasedoverallburnrates,andimprovedcombustionstabilityatalltest

points.Mostimportantly,laserignitionshowedareductionofbrakespecificNOx(BSNOx)

emissionsby~70percentatconstantengineefficiencyoralternately,anincreaseinbrake

thermalefficienciesofupto3percentagepoints,whilemaintainingBSNOxemissions

constant.

Thisprojectwasasuccessattheresearchlevel,whereforthefirsttimeamulticylinder

enginedesignoflaserignitionsystemwasshowntoworkeffectivelyinthelaboratory.Itis

recommendedthataseparatematerialsresearchprojectbeundertakentodevelopfiber

opticlaserenergydeliverysystemsuitableforengineconditions.Thefinalstep,toestablish

thetechnicalviabilityoftheAdvancedLaserIgnitionSystemconcept,isperformingaseries

ofmulticylinderengineteststodocumenttheefficiencyandemissionsbenefitsofthelaser

ignitionsystem.

7/29/2019 CEC-500-2012-043 ovooooo

21/112

5

1.0 Introduction

1.1. Background

ReciprocatingInternalCombustionEnginearecommonlyusedforDistributedGeneration

(DG)andCombinedHeatandPower(CHP)applications.AsshowninTable1,accordingtotheCaliforniaEnergyCommissionsAdvancedReciprocatingInternalCombustionEngine

(ARICE)program,theperformanceandemissiontargetssetforstationaryreciprocating

enginesbyyear2010arebrakethermalefficiencygreaterthan44%andbrakespecific

nitrogenoxideemissionslessthan0.01gramsperbrakehorsepowerhour(g/bhphr).

Table 1. Performance Targets for Advanced Reciprocating Internal Combustion Engines

Parameter 2007 2008 2009 2010Efficiency

Brake Thermal Efficiency 35% 38% 40% 44%Fuel-to-Electric Efficiency*** 32% 34% 38% 42%

Overall Efficiency (CHP) 85% 85% 85% 85%Emissions shaft power (g/bhp-hr)

Oxides of Nitrogen (NOx)

7/29/2019 CEC-500-2012-043 ovooooo

22/112

6

Primarily,therearethreetechnicalapproachestomeetCaliforniasDGemissionsand

performancetargetsspecifiedinTable1:Richburn(equivalenceration[]greaterthan1.0)operationwithexhaustgasrecirculation(EGR)anduseofthreewaycatalyst,Low

temperaturecombustionstrategiessuchasHomogenousChargeCompressionIgnition

(HCCI),andLeanburnoperation(~0.60.7).

Richburnengineoperation(~1.0),usuallyentailstheuseofanexhaustgasoxygensensoralongwithanadvancedenginecontroller.Thecontrolleroscillatesthecombustion

equivalenceratiobetween0.95and1.05therebyenablingtheoxidationandreduction

processesinthethreewaycatalyst.EGRhelpskeepthecombustiontemperatureslowand

theoverallefficiencyhigh.However,suchastrategyintroducescorrosivecombustion

byproductsandothercontaminantsbackintotheenginewhichcompromiseshardwarelife

andlubricantquality.Suchastrategycouldprovetobeverycompetitivewithefficienciesas

highas38%andverylowemissions.However,asshowninFigure1,effortsbyGeneral

ElectricJenbacherspreadover1.3millionrunninghourson17differentengineshave

shownthatenginemaintenancecostsincreaseby42%.

Figure 1. Comparison of Maintenance Costs for Rich-Burn and Lean-Burn Engines.

HCCIandothersimilarstrategiesrelyonextremelyleanfuelairmixtures(

7/29/2019 CEC-500-2012-043 ovooooo

23/112

7

timingcontroland(iii)startabilityarereportedtobeaproblem.Inlightofsuchissues,the

leanburntechnologyappearsverypromising.

Leanburnoperation(~0.60.7),hasremainedtheprimarychoiceofthegasengineindustry.Inthisstrategy,air,farinexcessofthatrequiredforcompletecombustionofthe

fuel,isinductedintothecylinderduringeachcombustioncycle.Tooffsettheenergydensity,intakeairboostisemployedwiththeuseofaturbocharger.Theresultinglow

combustiontemperaturesandhighincylinderpressuresensureverylowNOxemissions

(~0.5gramsperkilowatthour[g/kWh]or0.37g/bhphr)whilesimultaneouslyachieving

highfuelconversionefficiencies(~38%).Usuallyanaftertreatmentsystemisnotusedwith

leanburnengines.

Figure2showsthetypicaloperationofaleanburnengine.Theseenginesareoperatedat

theintersectionofknock(autoignition)limitandmisfire(leanignition)limit,soastoattain

maximumefficiencyandsimultaneouslylowNOxemissions.Boostlimitandpreturbine

limitareimposedbytheturbochargerconstruction.Also,asthesparktimingisadvanced,

combustionstartsearlyinthecompressionstrokeandtheknocklimitisencountered.Ontheotherhand,assparktimingisretarded,thegasdensityatthetimeofignitiontendstobe

higherresultinginmisfire.Byextendingthemisfirelimitthroughjudiciouschoiceofan

ignitionsystem,substantialbenefitsinefficiencyandemissionscanbeachieved.

0

10

20

30

40

50

60

6.5 7 7.5 8 8.5 9 9.5 10

Dry Exhaust Gas Oxygen Mole Fraction (%)

SparkTiming(deg

BTDC)

KnockLimi

t

KnockLim

it

MisfireLim

itMisfi

reLimit

BoostL

imit

BoostL

imit

Pre-TurbinePre-Turbine

LimitLimit

DesiredCa

libration

DesiredCa

libration

MaxMax

BTEBTE

The shape of this windowThe shape of this window

is combustion chamber &is combustion chamber &

ignition system dependentignition system dependent

Figure 2. Operational Region of a Typical Lean-Burn Engine. (Courtesy: SwRI)

Figure2,recastincombustionterminology,isshowninFigure3.Thisrepresentsthe

ignitionlimitsofatypicalfuelairsystemfor0.51.0.Forrichmixtures,selfignitionoccursaboveacertainpressuretherebydefiningtheselfignitionlimit.Alsoforagiven

modeofignition,aleanlimitexists(ll)formixturesleanerthanwhich(

7/29/2019 CEC-500-2012-043 ovooooo

24/112

8

cannotbeachieved.Formethaneairmixturesllis5.01%.ForachievingmaximumcombustionefficiencyandlowNOxemissions,leanburnenginesareoperatedatthe

intersectionofleanignitionlimitandtheselfignitionlimit.Betterperformancecanbe

achievedbyextendingtheleanignitionlimitbychoosinganadvancedignitionsystem.

Equivalence Ratio,

0.40.50.60.70.80.91.0

Pressure(au.)

1

2

3

4

NonFlamableRegion

Self-ignitionlimit

LeanIgnitionLimit

IgnitableMixture

Lean-burn engine Operation

Figure 3. Ignition Limits of a Typical Fuel-Air System.

1.2. Fundamentals of Ignition

Inatypicalsparkplug,successfulsparkingisachievedwhenthepotentialdropacrossthe

sparkgapexceedsthedielectricbreakdownthresholdoftypicalgases.Thesparking

potentialacrosstheelectrodesisgivenbyPaschenslaw:

( )dpfVb ,= (1)

where,pisthepressureofthegasanddisthesparkgap.Thebreakdownvoltage,Vb,

exhibitsalineardependenceontheproductpd.Theelectrodeshapeandmaterialarealso

foundtohavesignificantinfluenceonthesparkignitionprocess[1].Oncegasbreakdown

occursandaplasmakernelisestablished,energytransferoccursmainlythroughdiffusion

onthesurfacetothesurroundinggas.Whethersuchadiffusionprocessresultsina

successfulcombustionflamefrontdependsuponthekernelenergyexceedingMinimum

IgnitionEnergy(MIE),thekernelsizeexceedingacertainsize,turbulenceandgasspeed[2].

Inpractice,factorsinfluencingsuccessfulsparkcreationfaroutweighthoseinfluencingits

transformationintoaflamefront,anditisnormallyassumedthatonceasparkiscreatedthe

mixtureissuccessfullyburned.

7/29/2019 CEC-500-2012-043 ovooooo

25/112

9

1.3. Why Laser Ignition?

Inpresentturbochargedoftheleanburnnaturalgasengines,CapacitanceDischarge

Ignition(CDI)systemsareusedasschematicallyshowninFigure4.Thoughthesesystems

areratedat100150millijoules(mJ)perstrike,afterthermallossestypically4060mJis

transmittedtothesparkkernelatratesofvoltageriseof500Voltspermillisecond(V/s).In

CDIsystems,energystoredinahighvoltagecapacitor(at~175VoltsDirectCurrent(VDC)

isdischargedthroughahighvoltagecoilresultinginvoltagesinexcessof28kilovoltsdirect

current(kVDC)acrossthesparkpluggaps.

HVCoil

SparkPlugs

DCSource

ElectronicDistributor

CapacitorCircuit

Figure 4. Schematic of a Capacitance Discharge Ignition (CDI) System.

Withapushtowardsleanengineoperation,withaconcomitantrequirementtomaintain

enginespecificpower,theintakeairpressureisincreased.Leanoperationalongwithhigh

intakeairpressureresultsinveryhighchargedensitiesatthetimeofignition.Suchhighgas

densitiesnecessitatesparkgapvoltagesinexcessof40kilovolts(kV)thatcannotbe

achievedusingcurrentCDIsystems.Thisoftenleadstoincreasedmisfiringwithsubsequent

lossoffuelefficiencyandincreasedunburnedhydrocarbon(UHC)emissions.HigherUHC

emissionsareessentiallyvolatileorganiccompounds(VOC),whicharecurrentlyregulated

inCalifornia.Toaddresstheseproblems,variousresearchorganizationshavebeenexploringalternatewaystoachieveignition[36].Amongthesealternatemethods,laser

ignitionprovesattractiveasitoffersthefollowingperformancebenefits:

Successfulignitionofmixturesathighpressuresensuresreducedoccurrenceof

misfire,andconsequentlyimprovedfuelefficiencyandlowerUHCemissions,

Potentiallylowermaintenanceastherequirementtomaintainareasonablesparkgap

iseliminated,

7/29/2019 CEC-500-2012-043 ovooooo

26/112

10

Extensionofleanoperatinglimits,therebyenablinglowerNOxemissions,

Shorterignitiondelaysandenhancedcombustionrates,whichallowretarded

timingstherebyreducingNOxemissions,and

Locationofignitionkernelawayfromthewalls,therebyenhancingoverallefficiency

duetoreducedheatlosstothecylinderhead.Withsuchpotentialbenefits,anattempttouselaserignitionforreciprocatingengineswas

madebyDaleandSmyasearlyas1974[7].However,thesizeandcostoflasersystemsat

thattimeweretoolargetoreducelaserignitiontopractice.Overthelasttwodecades,on

accountofthedevelopmentsinelectroopticsystems,thereisarenewedinterestinlaser

ignitionforreciprocatingengines.Thepresenteffortaimedto(i)determinethebenefitsthat

accruewiththeuseoflaserignition,and(ii)developandintegratesystemstoreducelaser

ignitiontopracticeoncommercialmulticylinderengines.Thiswascarriedoutintechnical

tasks,Tasks2.12.6,asdescribedbelow.

AspartofTask2.2,fundamentalignitionstudieswereperformedinaRapidCompression

Machine(RCM)tocomparethecharacteristicsoflaserignitionandconventionalsparkignitiononmethaneairmixtures.TheRCMstudiesdemonstratedsignificantdifferences

betweenthecombustionprocessesassociatedwithlaserignitionandconventionalspark

ignition.InTask2.4,thepracticalimplicationsofthealteredcombustionbehaviorwithlaser

ignitionweredeterminedthroughexperimentsonasinglecylinderresearchengine.Ina

paralleltask(Task2.3),variouscomponentsrequiredforanAdvancedLaserIgnition

System(ALIS)weredeveloped.InTask2.5,thesuccessfulcomponentsdevelopedinTask

2.3wereintegratedintoasinglesystemandoptimizedforusewithamulticylinderengine.

Task2.6,fieldtestingforperformance,isstillanongoingeffort.AbrieftestingonaQSK

19G6cylinderengineatCumminsTechnicalCenterwascarriedout.Theprogressmadein

individualtasksisgivenhenceforth.Thisisconcludedwithasummaryoftheoverallproject.

1.4. ALIS Consortium

AttheinitiativeoftheUnitedStatesDepartmentofEnergy(U.S.DOE)Advanced

ReciprocatingEngineSystems(ARES)programmanager,Mr.RonaldFiskum,andthe

EnergyCommissionsARICEprogrammanager,Dr.AvtarBining,anALISconsortiumwas

formed.AsshowninFigure5,thisconsortiumcomprisedArgonneNationalLaboratory

(ANL),ColoradoStateUniversity(CSU),NationalEnergyTechnologyLaboratory(NETL)

andSouthwestResearchInstitute(SwRI)astechnicalpartners.Oversightfortheprogram

wasprovidedbyindustrialpartnersCaterpillar,Cummins,WaukeshaandAltronicInc.

aswellasthefundingagenciesU.S.DOEDistributedEnergyProgramandCalifornia

EnergyCommissionsARICEProgram.Researchideasandprogresswerediscussedand

sharedthroughregulartechnicalmeetings.Additionally,therewasenoughinteraction

amongparticipantsthroughsidebarmeetingsheldatvariousconferencesites.Asummary

ofconsortiumactivitiesandalistofpublicationsareprovidedinAppendixA.

7/29/2019 CEC-500-2012-043 ovooooo

27/112

11

Figure 5. ALIS Development Consortium

1.5. Goals and Objectives

Laserignitioncanovercometheignitionproblemsinleanburnnaturalgasenginesand

furtherhasthepotentialtoimproveengineefficiencyandloweremissions.Theoverall

benefitsduetolaserignitioncanbesummarizedas:

1. Improvedoverallefficiency,

2. Reducedfuelconsumption,3. LowerNOxandunburnedhydrocarbon(UHC)emissions,

4. Enhancedpowerdensity,and

5. Reducedoverallmaintenancerequirements.

Theseperformanceimprovementstranslatetoimprovingtheenergycost/valueofCalifornias

electricity.Simultaneously,byloweringNOxandUHCemissions,theenvironmentalandpublic

healthcosts/riskofCaliforniaselectricityarereduced.

TheoverallgoalsoftheproposedALISsystemare:

1.

MeetorexceedthecurrentandfutureCaliforniaemissionsrequirementsandhaveotherdesirableenvironmentalattributes.

2. Improvefueltoelectricityconversionefficiency.

3. Lowercapitalcosts,installationcosts,operationandmaintenancecost,andlifecycle

costs.

4. Enhancereliability,maintainability,durabilityandusability.

5. Possessmultifuelusecapabilities,suchaswithsewergas,landfillgasetc.

7/29/2019 CEC-500-2012-043 ovooooo

28/112

12

Ingeneral,theproposedALISsystemisexpectedtoleadtotheadoptionanduseof

improvedARICEtechnologieswithinCalifornia.

Technical and economic/cost performance objectives

TheoveralltechnicalgoalofthisprojectwastodevelopaCommercial/ProductionReady

ALISintegratedARICEfordistributedgeneration(DG)inCaliforniabymeetingorexceedingYear2007PerformanceTargetsofARICE(cf.Table1.).

Thespecifictechnicalobjectivesoftheprojectwere:

1. Completionofexperimentalstudiestodeterminecomponentdesignspecifications.

2. Developmentofviablecomponentsforhighpowerlasertransmissionandtheir

integrationintoanALIS.

3. SuccessfulintegrationanddevelopmentofALISthatachievesthetechnical

requirementsspecifiedbytheindustry.

4. PerformanceevaluationofanintegratedALISARICEsystemonamulticylinderengine.

5. DemonstrationoftheintegratedALISARICEsysteminmeetingorexceeding2007

ARICEperformancetargets.

7/29/2019 CEC-500-2012-043 ovooooo

29/112

13

2.0 (Task 2.2) Natural Gas-Air Ignition Experimental Study

2.1. Rationale for Task 2.2

Withtherenewedinterestinlaserignition,therehavebeenquiteafewpaststudies

evaluatinglaserbasedignitioninstaticchambers[8,9].AsshowninFigure6,suchstudieshaveshownthatlasersenableignitionofmixturesatpressureshigherthanthosethatcanbe

ignitedbyconventionalcoilbasedCapacitanceDischargeIgnition(CDI)systems.However,

nosignificantextensionofleanignitionlimitwasfoundwithlaserignition.Thelean

ignitionlimitsforbothmodesofignitionappearedtocoincideat equalto0.67.

Similarly,throughtestsperformedonRicardoProteussinglecylinderengineequivalent

ration,McMillianetal.[10]reportextensionofleanignitiontoequivalentto0.51with

Kopeceketal.[11]reportingthesametoequivalentto0.42(useablerangeequivalentto

0.46).Withmostoftheleanburnenginesoperatedclosetotheintersectionofleanignition

limitandselfignitionlimit,suchaspreadindatawarrantsasystematicstudyunderin

cylinderlikeconditions.Toattainthisgoal,oneneedstoperformignitiontestsinaRapidCompressionMachine(RCM)thatsimulatestypicalnaturalgasengineconditions.Asmost

oftheleanburnenginesareoperatedclosetotheintersectionofignitionlimitandknock

limit,theselfignitionlimitneedstobedeterminedaswell.Also,mappingoftheminimum

laserenergiesrequiredforsuccessfulignitionunderdifferentmixtureconditionswould

assistinthedevelopmentofALIS.

7/29/2019 CEC-500-2012-043 ovooooo

30/112

14

Figure 6. Ignition Limits of Methane-Air Mixtures Established in a Static Chamber(Initial Mixture Temperature ~ 22 C).

2.2. Experimental Setup

2.2.1. Rapid Compress ion Machine

Asmostofthecurrentstationarypowergenerationenginesareoperatedatspeedslessthan

1800rpm,therapidcompressionmachine(RCM)wasdesignedwithcompressiontimeless

than17milliseconds.Overallthesystemwasdesignedtowithstandconditionsattheendof

combustionof362barand3,000Kelvin(K).Also,withthecompressionratio(CR)oftypical

gasenginesbeing12.5,theRCMwasdesignedforaCR=12.

7/29/2019 CEC-500-2012-043 ovooooo

31/112

15

ThedesignconceptthatwasusedbyArgonneisanimprovementovertheonedeveloped

byMassachusettsInstituteofTechnology(MIT)[12].AschematicoftheRCMisshownin

Figure7.ApictureofthesystemisshowninFigure8.ThisRCMconsistsoftwopistons

which,whenreleased,traveltowardseachotherwithextremelysmallresultantvibration.

EachsideoftheRCMconsistsofthreeseparatechamberseachcarryingapiston.Allthe

threepistonsaremountedontothesamecentralTitaniumshaftthatforcestheirmovementinunison.Theoutermostchamberisapneumaticchambercarryinga6inchdiameter

aluminumpiston.Theinnermostisacompressionchamberwhereina2.5inchdiameter

aluminumpistoncompressestheexperimentalgasesintothecentralignitionchamber.In

themiddleisahydraulicchamberthatcontainshydraulicoilpressurizedto165bar.Special

designfeatureswithinthehydraulicchamberallowedholdingthepistonintheretracted

positioneventhoughpressurizedairat20.7barwaspresentinthepneumaticchamber.The

samedesignfeaturesallowedreleaseofthepistonsynchronizedwithanexternalsparking

event.Similaradditionalfeaturesinthehydraulicchamberallowedholdingthepistonin

thecompressedpositiontherebyavoidingthepistonbounceatthecommencementof

combustion.VariousportsonthecompressionchambersallowedfillingtheRCMwithdrycompressedairand99.99%puremethane.Fineorificesinthegaslinesalongwithahigh

resolutionpressuretransducerallowedestablishingmixturesoftherequiredpressuresand

equivalenceratiosaccurately.Aportonthecombustionchamberallowedignitionwitha

conventionalsparkplug(18mmthread,Jstyle)poweredbytheAltronicPM1(CDI)

ignitionsystem.Asecondportalloweddirectingandfocusingalaser(focallength13mm)

toachieveignition.AthirdportcarryingaKistler4073A500pressuretransducerallowed

recordingthepressuretraces.Afourthportcarriedanexhaustvalve.Atotalof22

pneumaticallydrivensolenoidvalvesinterfacedtoacomputerallowedremoteoperationof

theRCM.AcomputerprogramwritteninNationalInstruments(NI)LabviewdrivingNI

FieldPointsystemallowedautomationoftheprocesses.

7/29/2019 CEC-500-2012-043 ovooooo

32/112

16

Figure 7. Schematic of the Rapid Compression Machine.

Figure 8. A Picture of Argonnes Rapid Compression Machine.

Photo Credit: Argonne National Laboratory

7/29/2019 CEC-500-2012-043 ovooooo

33/112

17

2.2.2. Laser Ignition System

ThelaserignitionsystemisschematicallyshowninFigure9.Thebeamoutputofa

frequencydoubledNeodymium:YttriumAluminumGarnet(Nd:YAG)laser(Spectra

PhysicsGCR170)wasroutedthroughacombinationofhalfwaveplateandpolarizerto

varythelaserpower.Abeamsplitterandapowermeterallowedmonitoringofthelaserpower.Afastshutterwith3millisecondtimeresponseallowedincidenceofasinglepulse

fromthelaserpulsetrain.AllofthetimingwascontrolledbytheNIFieldPointsystem.

To RCM FastShutter

Iris

Laser powerHead & Meter

532 nm

GCR170Nd:YAGLaser

BeamDump

1064 nm

Protective Enclosure 2

BeamDump

1/2 wavplateGlan Taylor

PolarizerT70/R30 Mirror

Protective Enclosure 1

Figure 9. Schematic of the Optical Arrangement in the Laser Ignition System.

2.2.3. Conventional Ignition System

ACDIsystem,modifiedforthepresenttests,wassuppliedbyAltronic,Inc.Thissystem,

whenactivatedremotelybya5volt(V)pulsesuppliesignitionenergytothesparkplug

placedonthewallofthecombustionchamber.Thearrangementwassuchthatthespark

wassupplied30msfollowingtheendofpistonstroke.Suchadelaywasnecessarytoallow

thelockingmechanismtoengagecompletelybeforetheinitiationofcombustion.Figure10

showsapictureofthisignitionsystem.

7/29/2019 CEC-500-2012-043 ovooooo

34/112

18

Figure 10. Conventional Ignition System Cart.


2.2.4. Operational Procedure

Inatypicalexperiment,theRCMpistonswereretractedandheldintheretractedposition.

Subsequently,agasmixtureoftherequiredequivalenceratioandinitialpressure,P1,was

establishedinthecompressionchambers.Afterallowing5minutesforthegasestomix,the

pneumaticchamberswerepressurizedwithcompressedairat20.7barsuppliedbya150

Literairtank.Thepistonswerereleasedbyactivatingtheappropriatevalvesequencing.A

photodetectorsensingthepistonpositionprovidedthenecessarysignalforsequencingthe

laserpulseortheconventionalignitionspark.Toallowforlockingofthepistonsinthe

compressedpositionandtherebyavoidapistonbouncebackatthecommencementof

combustion,ignitionwasinitiated30msfollowingtheendofcompressionstroke.Also,one

secondfollowingtheendofcompressionstroke,theexhaustvalvewasopened.

Subsequently,thepistonswereretractedandthecompressionandcombustionchambers

werepurgedtoprepareforthenextexperimentalrun.Atypicaltestrunrequired20to30

minutesforexecution.

Oscillosco e

Sparkplugs

Ignition

coils

Electronic

control

24VDCpower

7/29/2019 CEC-500-2012-043 ovooooo

35/112

19

2.3. Results and Discussion

2.3.1. Test Matrix

Withtheabovesetup,testswereperformedwhilevaryingtheinitialpressureofthe

mixture,P1,andtheequivalenceratio,.ThemixturesestablishedintheRCMwerelimited

to1.0>>0.4,3.0>P1>1.0barandinitialtemperature,T1=298K.AtypicalpressuretraceobtainedduringonesuchtestrunisshowninFigure11.AsshowninFigure11,whenthe

pistonsarereleased,thegaseousmixtureisisentropicallycompressedtoP2.Astheignition

(sparking)eventissequenced20to30msfollowingendofcompression,thereisasmall

pressuredropresultingfromheattransfertothecombustionchamberwalls,(P2P2).

Followinganignitiondelayaftertheincidenceofspark,thepressurerisessteeplytoP3due

tocombustion.Subsequentpressuredropisprimarilyduetocondensationofwatervapor

andheattransfertowallsofthechamber.

Fromthermodynamics,onehastherelations

( )

CRPP 12 = (2)

and

( )( )112= CRTT (3)

where,CRisthecompressionratioandistheratioofspecificheatatconstantpressure(Cp)tospecificheatatconstantvolume(Cv),whichequals1.4forair.

AregressionanalysisperformedonthemeasuredvaluesofP2assumingas1.4showedthatthecompressionratioforthepresentRCMis10.0asopposedto12.0thatitwas

originallydesignedfor.Withthisadjustedcompressionratio,calculationswereperformed

assumingadiabaticcombustionbyusingNationalAeronauticsandSpaceAdministration(NASA)ChemicalEquilibriumforApplications(CEA2)program.Fromsuchcalculations,as

showninFigure12,itwasobservedthatthemeasuredP3valueswereonanaverage83%of

thecalculatedP3values,withleanermixturesexhibitinglowervalues.Also,itoughttobe

notedthatinthepresenttests,forallmixtureconditions,thetemperatureatthetimeof

ignition,T2wasabout765K(perEquation3).

7/29/2019 CEC-500-2012-043 ovooooo

36/112

20

Time (ms)

-50 0 50 100 150 200 250 300

Pressure(Bar)

0

10

20

30

40

50

60

70

trial 1trial 2

trial 3P2

P1

P3

Ignition

IsentropicCompression

Pr. risedue to

combustion

Pr. drop due to watercondensation and heat transfer

Pr. dropdue toheat transferP2'

Figure 11. Typical Pressure Traces from RCM Operation; P1 = 1 bar, = 0.7

P3 Calculated (Bar)

0 50 100 150 200 250 300

P3

Measur

ed(Bar)

0

50

100

150

200

250

300

Figure 12. Measured Versus Calculated Peak Combustion Pressures for

Various Methane-Air Mixtures, 1.0 < P1

7/29/2019 CEC-500-2012-043 ovooooo

37/112

21

betweenthemaximumpulseenergyofabout75mJandminimumpulseenergyof5mJ.

Witheachtestthewindowwithinwhichthethresholdenergywaspresentwashalveduntil

thefinalthresholdvaluewasdeterminedwithinanaccuracyof2.25mJ/pulse.

Theignitionboundariesdeterminedthroughsuchtestsexpressedasafunctionofpressure

atthetimeofignition,P2,areshowninFigure13.ItisprominentlynoticedthatselfignitiondominatesformixtureswithP2greaterthan63bar.Also,itisnoticedthattheleanignition

limitwhileusingtheCDIsystemisat0.6.Ontheotherhand,byusinglaserignitionthis

couldbeextendedallthewaytotheflammabilitylimitofofabout0.5.Suchextensionsare

ofsignificanceasthecurrentleanburnenginesareoperatedattheintersectionofself

ignitionlimitsandleanignitionlimits.

Followingsuchobservations,wearenotsureoftheclaimsmadebyresearchersatGE

Jenbacherwhoreportextensionofleanignitiontoof0.417byusingalaser.

Figure 13. Ignition Boundaries Determined by Using an RCM.

2.3.3. Minimum Required Energy Scans

Fortheignitionboundariesestablishedabove,MinimumRequiredEnergy(MRE)valuesfor

successfullaserignitionweredeterminedforvariousmixtureconditions.Values

determinedforalensfocallength,fof13millimetersandlaserbeamqualityofM25areshowninFigure14.Itisobservedthatexceptforof1.0,MREvaluesdecreasedwith

increaseinpressurefinallyresultinginselfignition.ThevaluesalongacrosssectionofP2of

7/29/2019 CEC-500-2012-043 ovooooo

38/112

22

37.7barareshowninFigure15.Foravariationoftheequivalenceratio,itisnoticedthata

minimaexistsatof0.85forthesemethaneairmixtures.Alsoitisnoticedthatthereisa

sharpriseintheMREvaluesformixturesleanerthanof0.7.Suchatrendwasalsonoticed

atotherpressures.

P2

(Bar abs.)

20 30 40 50 60 70

M

RE(mJ/pulse)

0

20

40

60

80

100

= 1.0 = 0.7 = 0.65 = 0.6 = 0.55 = 0.5

Figure 14. Minimum Required Laser Energies (MRE) for a Lens Focal Length f = 13 mm and

Laser Beam Quality of M2 5.

0.50.60.70.80.91.0

MRE(mJ/pulse)

20

30

40

50

60

70

Figure 15. Minimum Required Laser Energies for P2 37.7 bar.

7/29/2019 CEC-500-2012-043 ovooooo

39/112

23

2.3.4. Ignition Delays and Rates of Pressure Rise

Leannaturalgasairmixturesarecharacterizedbyslowflamevelocitiesandlongerignition

delaysthatareofconcernforleanburnengineoperation.Previousstudiesin1cylinder

engines[10,13]haveshownthatlaserignitionresultsinsmallerignitiondelaysandfaster

combustion.AsshowninFigure16,similartestsperformedintheRCMshowedthatignitiondelayincreasedwithleanoperationforbothCDIignitionaswellaslaserignition.

However,thebenefitsintermsofsmallerignitiondelayswereonlypronouncedunderlean

conditionsandatof1.0.

SimilarcomparisonoftherateofpressureriseisshowninFigure17.Againitwasfound

thatfastercombustionratesoccurforleanoperationandforof1.0bytheuseoflaser

ignition.Thereversaloftrendsfor0.75

7/29/2019 CEC-500-2012-043 ovooooo

40/112

24

2.3.5. Conclusions for Task 2.2

ThroughignitiontestsconductedinaRapidCompressionMachinethatsimulatedin

cylinderconditionsofaleanburnnaturalgasengine,itwasobservedthatlaserignition

extendstheleanoperatinglimitofmethaneairmixturestotheflammabilitylimit(of0.5)

whereasconventionalCDIignitiononanaverageislimitedtomixturesricherthanof0.6.

MinimumRequiredEnergiesforsuccessfullaserignitionexhibitedasharpincrease

followedbyaplateauregionformethaneairmixturesleanerthanof0.7.Suchatrend

showsthatalaserignitionsystemdevelopedtooperateatof0.65willsuccessfullyoperate

underallotherpossibleoperatingconditions.

Toreapthetruebenefitsoflaserignition,therequiredhardwarecomponentsfortheALIS

needtobedeveloped.ThiswaspursuednextinTask2.3.

7/29/2019 CEC-500-2012-043 ovooooo

41/112

25

3.0 (Task 2.3) Design of ALIS Components

Fromaninitialsurveyofpossibleconfigurationsforalaserbasedignitionsystem,two

promisingconceptswereidentified:(i)Thelaserpercylinderconcept,and(ii)The

multiplexedlaserconcept.

InthelaserpercylinderconceptschematicallyshowninFigure18,aminiaturelaserisbuilt

directlyoverthecylinderhead.Thecostofsuchaconfigurationislikelytobeveryhigh,as

asinglelaserisrequiredforeachcylinder.Also,thermalmanagementinthelasersystem

becomesanissueasthecylinderheadtemperaturescouldbeashighas130oCelsius(C).

However,thisconfigurationdoesnotrequiretheuseofahighpowerdeliverysystem(e.g.,

afiber).AspartoftheALISconsortium,NationalEnergyTechnologyLaboratory(NETL)

haspursuedthedevelopmentofalaserpercylinderignitionsystem,detailsofwhichare

providedinReference[14].

Alternately,asshowninFigure19,theoutputofasinglelasercanbedistributedamongthevariouscylindersofamulticylinderengine.ThiswasprimarilypursuedbyArgonne

NationalLaboratory.Thisconfigurationbenefitsfromthecostsavingsthatresultfromthe

useofasinglelaseraslasersarethemostexpensivecomponentsofALIS.Also,thelaser

systemisisolatedfromtheheatandvibrationoftheengine.However,thissystemrequires

thedevelopmentofassociatedhighpowercomponentsincludinglaserplugs,optical

multiplexerandfiberdeliverysystem.

OutsidetheconsortiumGEJenbacher,andAVLarepursuingbothlaserpercylinderand

multiplexedlaserapproachesoracombinationapproachofthetwo[11].

3.1. Goals and Objectives of Task 2.3

ThegoalofTask2.3wastodevelopvarioushardwarerequiredforALIS,accordingtothe

specificationsdeterminedthroughtestsinearliertask,Task2.2.Thisentailsselectionof

somecandidatetechnologiesandtestingthemforperformance.Thesuccessfulcandidates

weresortedfurthertomeettheprojectobjectives.

7/29/2019 CEC-500-2012-043 ovooooo

42/112

26

Figure 18. Schematic of the Laser-Per-Cylinder Concept.

Laserplugs

Laser Multiplexer

fiber optic delivery

ElectronicInterface

EngineECU

Natural Gas Multi-cylinder Engine

Figure 19. Schematic of the Multiplexed Laser Concept.

7/29/2019 CEC-500-2012-043 ovooooo

43/112

27

Thespecificobjectivesofthistaskaredescribedbelow:

1. Designanddeveloplaserplugswiththefollowingspecifications.

i. Havethesamethreadsizeasaconventionalsparkplug,i.e.,M18x1.5,

ii. Providepressuresealingto3,000poundspersquareinch(psi).

iii. Withstandtemperaturesashighas2,400C.

iv. Minimizefirstandsecondsurfacereflections.

v. Minimizeoveralllaserenergyrequirements.

vi. Providesufficientreliabilitywhiletransmittinglaserenergiesofabout60mJ

perpulse.

vii. Beselfcleaningofanydeposits.

viii. Facilitatecouplingtofiberoptictransmission.

2. Developfiberopticsystemsthatareabletotransmittherequiredlaserenergiesfor

ALISoperation.Intheprocess,evaluatetheperformanceofthefollowingtechnologies,amongothers,fortransmissivity,flexibility,andeaseofconnectivity.

i. Conventionalsilicacoreof1to2millimeter(s)diameterfiberswith

appropriatecladding.

ii. Fiberswithtaperedends.

iii. Hollowfibersystems.

3. Developanopticalmultiplexercapableofdistributingthelaseroutputamong

variouscylindersofanaturalgasengine,whileminimizingtransmissionlossesand

facilitatingtherequiredignitiontimingadvanceorretard.Thiscanbeperformedby

evaluatingthefollowingcandidatetechnologiesamongothers.

i. Fiberoptictelecommunicationmultiplexer.

ii. Rotatinggratingtypeindexingsystem.

4. Developorselectalasersystemthatcan

i. Providetherequiredlaserenergies.

ii. Operatewithminimalmaintenance.

iii. Haveasmallfootprint.

iv. Providetheaforementionedfeaturesatalowcost.

5. DevelopanelectronicinterfaceincollaborationwithAltronic,Inc.,whichintegrates

thefunctionsoflaserhead,ElectronicControlUnit(ECU),andindexerintoone

singleunit.Thiselectronicinterfaceshouldenhanceeaseofinstallation,improve

durability,satisfythesafetyrequirementsofnaturalgasengines,haveasmall

footprint,belightweight,andfacilitatemanufacturinginlargequantities.

InadditiontothedatagatheredintheearlierTask2.2,guidanceindesignwasalsoderived

fromperformancerequirementsoftheignitionsystemasspecifiedbyengine

manufacturers,asgiveninTable2.

7/29/2019 CEC-500-2012-043 ovooooo

44/112

28

Table 2. Performance Requirements of an Advanced Ignition System (Courtesy: Caterpillar,Cummins and Waukesha )

1 Cost (current dollars) Value Units

- First Cost (add $1/kWe for CSA requirement) 4.00 $ / kWe- Life Cycle Cost (including system replacement at major) 0.25 $ / MWe-h

2 Performance

-Maximum ignition pressure (peak cylinder pressure) 220 bar

-Minimum air/fuel ratio 0.9 -

-Maximum air/fuel ratio (with swirl) 2.5 -

-Minimum methane number (hydrogen capable) 0 -

- Maximum methane number (landfill capable) 140 -

- Ignition timing repeatability (non-mechanical) 0.08 CA

- Ignition timing accuracy (non-mechanical) 0.08 CA

- COV (ARES steady state, 0.5 g/bhp-hr NOx, 25 bar BMEP)

7/29/2019 CEC-500-2012-043 ovooooo

45/112

29

havewavelengthsof1064nanometers(nm),532nmor266nm.Thefocalspotdiameterofa

collimatedlaserbeamfocusedbyalensisgivenby[15]

==D

f

M

Ww oo

4 (4)

where,

wo=focalspotdiameterforidealGaussianmodelaser(microns),

Wo=focalspotdiameterforatypicalmultimodelaser(microns),

M=isthemodequality,

=laserwavelength(microns),

f=lensfocallength(cm),and

D=laserbeamdiameter(cm).

AsevidentfromEquation4,smallerwavelengthsresultinsmallerfocalspotdiameters.Asa

result,theuseofsmallerwavelengthsisdesirabletoachievealaserfluxdensityofabout

1012Wattspersquarecentimeter(W/cm2),whichisrequiredforsparking.Withtheharmonic

generationprocessbeingatbest50%efficient,theoreticallyspeaking,afactoroftwo

advantageisachievedbygoingtoahigherharmonic.However,acompromiseisnecessary

asthesystemcomplexityincreases.Forthepresentpurpose,awavelengthof532nmwas

chosen.

Fromafunctionalstandpoint,itwasidentifiedthatthelaserneedstohavethefollowing

operationalcharacteristics:

Wavelength=532or1064nm,

pulsewidth

7/29/2019 CEC-500-2012-043 ovooooo

46/112

30

mitigatedinthecaseofdisklasersandfiberslasersduetothelargesurfaceareatovolume

ratioofthelasingmedia.Onaccountoftherapidadvancementsinfiberlasertechnology,it

isexpectedthatdisklaserswouldbecomeobsoleteinthenearfuture[16].However,asof

2005,bothfiberlasersanddisklaserswerecostprohibitiveforthecurrentapplication.

Figure 20. A Commercially-Available Diode Pumped Solid State Laser (DPSSL)Model: Centurion, Manufacturer: Big Sky Laser, Inc., 100 Hz, 45mJ/pulse.


DiodePumpedSolidStateLasers(DPSSL),ontheotherhand,areideallysuitedforthe

presentpurpose.Withthecostoflaserdiodescontinuallydecreasingandtheirpower

continuallyincreasing,DPSSLareanticipatedtomakemanynewapplicationspossible.

Mostattractivetothecurrentapplicationisthefactthattheonlycomponentthatrequires

maintenance,thelaserdiode,hasalifetimegreaterthan109shots,whichforatypicalARICE

enginecantranslateto2.5years.AnexampleofacommerciallyavailableDPSSLisshownin

Figure20.TheperformancedataofDPSSLfromthreedifferentmanufacturersistabulated

inTable3below.TheMK88lasersystemfromKigre,hasthesmallestfootprintandhas

alreadybeenshowntoachievesparkinginthelabusinga13millimeter(mm)focallength

lens.However,therepetitionrateofthislasermakesitsuitableonlyforthelaserper

cylinderapplicationshowninFigure18.Ontheotherhand,thesystemsfromBigSkylaser

andJMARaresuitableforthepresentapplication.

Table3providesasnapshotoftheDPSSLtechnologyavailableasof2005.Thistechnologyis

makingrapidprogresswithaveryfavorablecostandperformancetrajectoryamenableto

thelaserignitionapplication.Basedontheseconsiderations,itwasdecidedtopostponethe

selectionofaspecificlaserforthepresentapplication.Consequently,allofthe

demonstrationsinthepresentprojectareperformedusingcompactNd:YAGlasersthatare

alreadyavailableatArgonneNationalLaboratory.Exceptforlongevityofthepumpsource,

theperformanceoftheselaserswillmimicthatofDPSSLinallotherrespects

7/29/2019 CEC-500-2012-043 ovooooo

47/112

31

Table 3. Performance Specifications of Some Commercially-Available Pulsed DPSSL

Specification

Manufacturer

Kigre Big Sky Laser JMARModel number MK-88 Centurion Britelight-24

Wavelength ( m) 1.54 1.064 1.064

Energy/pulse (mJ/pulse) 3-5 45 80

Pulse width (ns) 7 7 7

Repetition rate (Hz) 0 20 100 300

Beam quality (M2) 1.1 * 109 >1010

Beam diameter (mm) 0.8 3 8

Laser head size (W x D x L) 0.85 2 3 5 3 9 18 30 12

Laser Power Supply size 10 5 3.5 * 19 rack 38 high

* Informationnotavailable

3.3. Laser Plugs

Laserplugsareelementsthatintroduceanopticalwindowsothatlaserradiationcanbe

focusedtocreateasparkinsidethecylinder.Additionalrequirementsfortheirperformance

aregivenbelow:Footprintsimilartothatofstandard18mmsparkplug[17],Pressure

rating~300bar,Temperaturerating~3,000Konelementsexposedtocombustion,and

shouldbeselfcleaningofcarbonandoildeposits.

Afteracoupleofiterations,atwolensdesignwasfoundtobeappropriateforALIS.As

showninFigure21,theoutputofafiberopticcableiscollimatedusingaplanoconvexlens.

Thecollimatedoutputisrefocusedinsidethecylinderusingasapphirelensof13mmback

focallength.Suchanarrangementallowedrefocusingtoaspotsizeof240micrometers

(m).RaytracingiterationsperformedusingZEMAXsoftwareshowedthattheuseof

multielementlensesdoesnotreducethefinalspotsizeanyfurther.

7/29/2019 CEC-500-2012-043 ovooooo

48/112

32

Figure 21. Ray Propagation Scheme Inside a Laser Plug.

InthearrangementshowninFigure21,thethicknessoftheplanoconvexsapphirelenswas

chosentowithstandpressuresupto300bar.Withsuchathicklens,itisveryimportantthat

thecurvedsideofthelensbepointedtowardsthelasersoastoavoidinternalreflections

thatwillleadtointernalcrackingofthelens.Suchalenswasalsofoundtowithstand

typicalincylindercombustiontemperatures.

ThephysicalarrangementoftheaforementionedlensconfigurationisshowninFigure22.

Asnoticedinthisarrangement,thelaserplugconsistedofatoppartandabottompart

separatedbyanaluminumspacer.Thebottompartcarriedthenecessaryexternalthreadsto

fastentheentirelaserplugassemblyintothecylinderhead.Acoppercrushgasketinthe

bottompartprovidedthenecessarysealingtopreventleakageofcombustiongasesbeyond

thesapphirelens.Thetoppartcarriedalenstube,whichinturn,housedthecollimating

planoconvexlens.Afiberopticconnector(SMAtype)separatedfromthecollimatinglens

allowedcouplingoftheincominglaserradiation.

Throughtestsperformedbyincorporatingthislaserplugina4kilowatts(kW)naturalgas

engine,itwasobservedthatthelaserfluxdensityontheexitfaceofthesapphirelenswas

critical.Atlowlaserfluxdensitiesdistinctcarbondepositswerevisibleonthelens.Abovea

certainthreshold,thelaserradiationablatedsuchdepositsandthelenswasfoundtobeselfcleaning.Cautionneedstobeexercisedtokeepthelaserfluxdensitieswellbelowthe

materialdamagethresholdof5gigawattspersquarecentimeter(GW/cm2).Similarlaser

ignitiontestswereperformedbyGEJenbacherandtheydemonstratedsatisfactory

performanceofthelensarrangementforover5000hoursofoperation[9].

7/29/2019 CEC-500-2012-043 ovooooo

49/112

33

Figure 22. Schematic of a Two-Lens Laser Plug.

7/29/2019 CEC-500-2012-043 ovooooo

50/112

34

3.4. High-Power Optical Multiplexer

Theopticalmultiplexerperformsafunctionsimilartotheconventionalignitionsystem:It

distributestheoutputofapulsedlaseramongvariouslaserplugsinstalledindifferent

enginecylinders.Thefunctionalrequirementsofsuchahighpoweropticalmultiplexerare

listedbelow:

Ignitiontimingvariationof048crankangle(CA)beforetopdeadcenter(BTDC).

Lasertriggerpulsegeneration.

Individualcylinderignitiontimingvariationof6CA.

Additionally,thesystemneedstobeoflowcostandmustconformtothedurabilitytargets

oftheoverallsystemof80,000hours.

Asurveywasperformedtoevaluatepotentialtechnologiesthatconformtothe

aforementionedrequirementsandthefollowingthreewereidentified:(i)Electrooptic

switches,(ii)Rotatingmirrorsystems,and(iii)Flipflopsystems.Theresultsfromtheperformanceevaluationofprototypesofthesesystemsarediscussedbelow.Itoughttobe

notedthatthesystemdesignsconsideredbelowconformtoa6cylinder,1800rpm,4stroke

engine.Thesecanbeextendedtoengineswithmorenumberofcylinders,ifnecessary.

3.4.1. Electro-Optic Modulator (Pockels Cell)

APockelscellactsasanelectroopticswitchbecauseitrotatesthepolarizationofthelaser

lightby90degreeswhenactivated.AsshowninFigure23,apolarizingbeamsplittercan

directthebeamonewayortheotherbasedonthepolarizationstateofthelaserbeam

incidentonitfromthePockelscell.AlineararrayofsuchPockelscellbeamsplitter

combinationscanbeusedforthepresentmultiplexingpurpose.Forevaluation,atwochannelsystemwasfabricatedatANLanditdemonstratedtherequiredperformance(see

Figure24).

Figure 23. Schematic of a Pockels Cell-Based Multiplexer [18].

7/29/2019 CEC-500-2012-043 ovooooo

51/112

35

Figure 24. Photograph of a Pockels Cell-Based Two-Channel Multiplexer.


Thisschemefacilitatesmanipulationofthelaserbeamwithouthavinganymechanical

movementofthecomponents.However,thenumberofrequiredopticalsurfacesincreases

withthenumberofenginecylindersandeventuallybecomestoounwieldy.Additionally

voltagesashighas5kVarerequiredforactivatingthePockelscell.Underthepresent

marketconditions,itwasestimatedthatthecostassociatedwiththisschemeamountsto

about$2,000percylinder,whichisconsideredtobetoohigh.

3.4.2. Rotating Mirror

Thisschemeisbasedonthetraditionalmechanicaldistributorsystemofthe1980s.As

showninFigure25,amirror,placedat45degreestotheincominglaserbeam,isrotated

synchronouslywiththecamshaft.Asaresult,thebeamisrotatedat90degreesaboutan

axiscoincidentwiththeincominglaserbeam.Laserfiringattheappropriatecrankangleis

facilitatedbyatimingdiskfittedontheshaft.Adifferentialgearsystemallowsignition

timingvariationbyintroducingaphaseshiftbetweenthemirrorandthecamshaft.Allof

thecomponentsrequiredforthissystemaresimple,costeffective,andoffertherequired

durability.Therefore,aprototypesystemwasdesignedandassembled.Aphotographofthe

systemisshowninFigure26.Testsperformedinthelabusingasmallelectricalmotorfordrivingthesystemshowedthatithastherequiredperformance.Throughsuchtrialsitalso

becameevidentthatsignificantperformanceadvantagescanbegainedbyusingamirror

inclinedatangles

7/29/2019 CEC-500-2012-043 ovooooo

52/112

36

gasengines.Therotatingmirrorsystemdoesnotallowthisflexibility.Therefore,

developmentoftheflipflopmultiplexingschemewaspursued.

Figure 25. Schematic of a Rotating Mirror Multiplexer.

Figure 26. Photograph of Argonnes Rotating Mirror Multiplexer.


7/29/2019 CEC-500-2012-043 ovooooo

53/112

37

3.4.3. Flip-flop

Aflipflopmultiplexerconsistsofalineararrayofmirrors.Anindividualmirror,when

activated,movesintothepathofthelaserbeamanddeflectsitintotherespectivefiber

injectionport.Thissystem,schematicallyshowninFigure27,facilitatestimingvariationof

individualcylinders.Totesttheperformanceoftheflipflopsystem,arotaryactuator(Model6EM)wasobtainedfromtheLedexDivisionofSaiaBurgess,anautomotiveparts

supplier.Thisactuator,whenactivated,rotatesitsshaftby22.5andmovesthemirrorinto

oroutofthepathofthebeam.Ina4stroke,1800rpm,6cylinderenginethetargetresponse

timeforsuchasystemis11ms.Thetimeresponseofaonechannelsystemwasmeasured

usingthearrangementshowninFigure28(a).AsnoticedinFigure28(b),thesystemshows

verylittlebounceandinaddition,exhibitsatimeresponseoflessthan7ms.Subsequently,

effortswereundertakentodevelopasixchannelsystemforusewitha6cylinderengine.

Asmentionedpreviously,withadvancesinactuatorsandmicroelectromechanicalsystems

(MEMS)technologymanyothermultiplexingschemes,otherthanthosediscussedabove,

arepossible.SomeofthesearediscussedinAppendixB.Thefinalchoiceislikelytobedictatedbydurabilityandthecostofthesesystems.

Figure 27. Schematic of a Flip-Flop Multiplexer.

Time (ms)

0 5 10 15 20

N

ormalizedDetectorResponse

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

(a) (b)

Figure 28. (a): Schematic of Setup to Measure the Time Response of the Flip-Flop(b): A Typical Detector Response Curve.

Fiber couplingassembly

Mirror

Laser beam

Lens

Diode

LaserDeactivated

Activated

5 mm high Laser Sheet

7/29/2019 CEC-500-2012-043 ovooooo

54/112

38

3.5. Fiber-Optic Delivery

AspartofthecurrentALISscheme,itwasenvisionedthatthepulsedoutputofalaserwill

betransmittedviaopticalfiberstolaserplugsinstalledinindividualcylinders.The

functionalrequirementsspecifiedbyenginemanufacturersfortheopticalfiberstobeused

inamulticylinderenginearegivenbelow:

Length>3m.

Atleastone90obendwitharadiusofcurvature130C.

Additionally,toachievesparkingatthedistalendofthefiber,alaserfluxdensityof1012

W/cm2isnecessarywhenrefocused.

ForagivenfiberandatwolenssystemshowninFigure29,theLagrangeinvariantyields

se NAsNAa = (5)

Asaresult,thelaserfluxdensityatthefocalspot=2s

llaser (6)

where,

a = corediameterofthefiber(microns)

s = focalspotsize(microns)

NAe = numericalapertureatthefiberexithalfconeangleatfiberexit

NAs

= numericalapertureatthefocalspot

Ilaser = intensityoflaser(Watts).

CombiningEquations5and6,thefollowingequationisobtained:

Laserfluxdensityatthefocalspot

2

2

e

slaser

NA

NA

a

l (7)

InEquation7,thefirsttermisdeterminedbythefibercorematerialdamagethreshold.In

thesecondterm,NAsisdeterminedbythespaceavailableforthelaserplug.Forfibersof

shortlengths(~3m)thenumericalapertureatinjectionendisapproximatelyequaltothat

atthefiberexit,i.e.,NAiNAe;inotherwords,theexitconeangleisdeterminedbytheinjectionschemeused.Hencethelaserfluxdensitycanbemaximizedbymakingajudicious

choiceofboththeopticalfiberandtheinjectionscheme.

However,inderivingEquation7ithasbeenassumedthatthefiberismodepreserving.For

thepresentcasewheretransmissionofhighlaserpowerisrequired,theuseofmultimode

fibersisrequired.Asisusuallythecase,withtheintroductionofhigherordermodesthe

energyisnotequallydistributedandisskewedtowardsthehigherordermodes.These

7/29/2019 CEC-500-2012-043 ovooooo

55/112

39

aspectsofactualphysicalbehaviorarenotcapturedbyEquation7.Nevertheless,this

equationprovidesanacceptablebasisthatassistsinthechoiceoftheopticalfiberandthe

injectionscheme.

Withtheinsightprovidedintheaforementionedarguments,differenttypesoffiberswere

obtainedandtestedforsparkinginthelaboratory.Theresultsofsucheffortsarediscussedbelow.

aNAe NAs

R

s

Figure 29. Schematic of Laser Refocusing Scheme at the Distal End of the Optical Fiber.

3.5.1. Solid Core Fibers

Largelydrivenbyadvancesinthetelecomindustry,therehavebeenrapiddevelopmentsin

solidcorefibertechnologyoverthepasttwodecades.Currently,stepindex(seeFigure

31(a))solidcorefiberswith1mmcorediameterandadamagethresholdof5GW/cm2are

readilyavailable.Initialeffortstoinjectsuchfiberslimitedthemaximumlaserenergy

transmissionto8mJperpulse.Theprimarymodeoffailureinsuchfiberswasmaterialdamageattheentranceendofthefiber.Analysisshowedthatsignificantgainsintermsof

transmittedlaserenergycouldbeobtainedbyensuringthatthelaserbeamcrosssection

profileisincidentonthefaceofthefiberasuniformlyaspossible.Forinstance,asshownin

Figure30(a),thebeamcrosssectionincidentonthefiberfacewiththeuseofasimpleplano

convexlenshadaPeaktoAverage(P/A)ratioof15.6.However,aprofilethatdistributed

theenergymoreevenlyonthefiberfacewasachievedusinganappropriateaxiconlens

combination(seeFigure30(b)).TheP/Aratioinsuchacasewas3.9andtransmittedlaser

energywasashighas30mJ/pulse.

Nevertheless,suchadvancedinjectionschemesintroducehigherordermodesandthe

qualityofthebeamexitingthefiberdegrades.Despitethebesteffortstocountertheseeffects,thetradeoffbetweenthemaximumtransmittablelaserenergyandthegenerationof

higherordermodesproveddifficulttoovercomeandsparkingcouldnotbeachieved.In

thisrespect,thegradientindexfibershowninFigure31(b)appearedpromisingasithad

bettercapabilitytopreservebeamquality.Initialtrialsinthelabshowedthatthesefibers

sufferfromlowmaterialdamagethreshold.Ultimately,itwasdecidedtodirectthepresent

efforttowardstrategieswithhollowcorefibers.

7/29/2019 CEC-500-2012-043 ovooooo

56/112

40

With Axicon

(P/A) = 3.9

Max. Transmitted 27 mJ/p

Axicon

Simple Plano-convex lens

(P/A) = 15.6


With Axicon

(P/A) = 3.9


With Axicon

(P/A) = 3.9


Axicon


(P/A) = 15.6


AxiconAxicon


(P/A) = 15.6



(P/A) = 15.6


(a) (b)

Figure 30. Fiber Face Laser Intensity Distribution Profiles for an Injection Scheme Using(a): Plano-Convex Lens, (b): Combination of Axicon and Plano-Convex Lens.

7/29/2019 CEC-500-2012-043 ovooooo

57/112

41

n

n

(a) (b)

Figure 31. The Refractive Index Distribution in Two Solid Core Fibers: (a) Step-Index Fiber, and(b) Gradient-Index Fiber.

3.5.2. Hollow Glass Waveguides (HGWs)HollowGlassWaveguides(HGW)havethestructureillustratedinFigure32(a).Theyare

essentiallyglasscapillarytubescoatedontheinsidewithsilverandareflectivityenhancing

dielectric.ThemodeoftransmissionthroughHGWsisfirstsurfacereflectionwhiletotal

internalreflectionisthemodeoftransmissioninsolidcorefibers.Asaresultofthe

transmissioninairthedamagethresholdofthesefibersis40timeslarger,i.e.,200GW/cm2.Also,HGWstendtopreservethemodequalityandexitthebeamatalowcone

angle,bothcharacteristicsrenderingthemideallysuitedforsparkgeneration.However,

thesefiberstendtohavehighertransmissionlossescomparedtosolidcorefibers.

Additionally,theyexhibitcertainuniquecharacteristics:

Transmissionlosses(corediameter)3.

Bendinglosses(bendradius)1.

Initialevaluationsinthelabshowedthatthe700mcoreHGWswereideallysuitedastheyofferedthebestcompromisebetweenflexibilityandtransmission.Subsequently,700mcoreHGWswereobtainedfromthreedifferentsourcesandtestedinthelaboratory.Their

characteristicsareasgivenbelowinTable4.

Table 4. Hollow Glass Waveguides Tested for High-Power Laser Transmission

Source CoatingOptimized for

Wavelength

Polymicro Technologies Proprietary 3.2 m

Rutgers University Ag/CdS 0.532 m

Tohoku University Ag/ COP 0.532 m

7/29/2019 CEC-500-2012-043 ovooooo

58/112

42

QuartzAir core

Silver Dielectric

(a) (b)

Figure 32. (a) Schematic of the Cross-Section of a Hollow Glass Waveguide (HGW), and (b) APhotograph Showing Spark Generation Using HGW in the Lab.


SparkingwasachievedinthelaboratorywithallthreefibersshowninTable4.Inallthree

cases,theinjectionwasperformedwithlensesoffocallengthgreaterthan250mminto

fiberstypically12meterslong.However,thefibersfromTohokuUniversity[19]offeredthe

lowesttransmissionlosses(seeFigure32(b)).Subsequently,afibercoupledlasersystem

wasdevelopedusingthesefibersandtheoperationofasinglecylinderenginewas

demonstrated[18,20].However,thedownsidewiththesefiberswasthattheywerevery

bendsensitive;forbends>45,sparkingwasseverelyaffected[18,21].Consequently

advancedfibersthatarerelativelybendinsensitivearedesirable,whileretainingthe

favorablecharacteristicsoftheHGWfibersfromTohokuUniversity.

3.5.3. Advanced Air-Core Fibers

Forfutureonenginelaserignitionapplications,twokindsofadvancedfibertechnologies

appearpromising:(i)multilayerhollowglasswaveguides,and(ii)hollowcorephotonic

bandgapfibers.TheseareschematicallyshowninFigures33(a)and33(b).Bothrelyon

multiplereflectionstoconfinelighttothecentralaircore,andmostimportantlybothfibers

arebendinsensitive.Manufacturingprocessesofbothkindsoffibersareveryinvolvedand

thosethatarecommerciallyavailablewithcorediameters

7/29/2019 CEC-500-2012-043 ovooooo

59/112

43

Several layers ofDielectric coatings

Air core

(a) (b)

Figure 33. (a) Schematic of the Cross-Section of a Multi-Layer Hollow Glass Waveguide, and(b) Photograph of an Air-Core Photonic Bandgap Fiber

3.6. Electronic Interface

Innaturalgasfueledstationaryengines,theElectronicControlUnit(ECU)performstwo

primaryfunctions:(i)providingignitionwithfeedbackfromatimingdisk,and(ii)speed

controlwithfeedbackfromagovernor.Inmostofthegasfueledengines,thesefunctions

areperformedbytwoseparateunits.Earlierinthereport,asshowninFigure19,itwas

envisionedthatanelectronicinterfacewouldberequiredfortheALIStocommunicatewith

theignitioncontrolpartofECUforignitiontimingcoordination.InconsultationwithArgonnesindustrialpartner,Altronic,Inc.,anelectronicinterfacewasdevelopedthat

utilizescommerciallyavailableconventionalignitionsystems.

Onesuchsystemtodriveaflipflopmultiplexerandalaserisschematicallyshownin

Figure34.Thepositionofatimingdiskmountedonthecrankshaftissensedbyamagnetic

pickup.ThesignalfromthemagneticpickupisprocessedbytheECU/Conventional

ignitionsystemtoprovidea165VDCpulsethatisusuallyfedtotheprimarysideofthe

ignitioncoil.Inthepresentelectronicinterfacesuchasignalisusedtogeneratea24VDC

pulseusingaresistorstepdowncircuit(representedasaboxinFigure34).The24VDCsignal,inturn,isusedtodriveacorrespondingrotaryactuator.Theendofstrokeofthe

rotaryactuatorissensedbyanopticalsensorandatriggersignalisprovidedtothelaser

afterroutingitthroughanORgate.Insuchasystem,theindividualcylinderignitiontiming

variationisprovidedbytheECU/conventionalignitionsystem.Onesuchsystemwas

successfullysimulatedandtestedatArgonneusingAltronic,Inc.sCD200system.

Howeverthebasicdesignofthesystemisnotspecifictoaparticularmodelor

manufacturer.

7/29/2019 CEC-500-2012-043 ovooooo

60/112

44

RotaryActuator

opticalsensor

1 2 3 4 5 6

ECU/Conv.

Ign Sys

Laser

ORGate

165 VDC7 ns pulse

primary

24 VDC8 s wide pulse

5 VDC TTL

Mag.Pickup

TimingDisk

Electronic Interface

Mirror

Figure 34. Schematic Diagram of the Electronic Interface

3.7. Results and Conclusions for Task 2.3

FromaninitialsurveyofseveralpossibleALISschemes,twopromisingconfigurationswere

identified:(i)thelaserpercylinderconcept,and(ii)themultiplexedlaserconcept,wherein

theoutputofasinglelaserisdistributedovervariouscylinders.Thelatterconceptwas

chosenasitpromisedlowcostandsimplicityofthermalmanagement.However,this

conceptrequiredthedevelopmentofthreehighpowercomponents,namely,laserplugs,

multiplexersandfiberopticbeamdelivery.Guidancewasderivedinthedevelopmentof

suchcomponentsthrough(i)datafromfundamentalstudiesconductedinanearliertask(Task2.2),and(ii)requirementsoftheadvancedignitionsystemasspecifiedbyengine

manufacturers.Specificdetailsofthehighpowercomponentsconsideredinthepresenttask

aredescribedbelow:

LaserPlugs:Atwolensdesignthatsuccessfullymeetsthephysicalandfunctional

requirementsofalaserplugwaseasilyachieved.Adaptationofthisdesignforvarious

enginegeometriescanbeeasilyachieved.

Multiplexers:Threeschemesthatdistributetheoutputofasinglelaseramongvarious

cylinderswerepursued:(i)anelectroopticswitch,(ii)arotatingmirrorscheme,and(iii)a

flipflopswitch.Thefirsttwoschemesfellshortoftherequirementseitherduetohighcost

ortheinabilitytoprovideignitiontimingvariationsinindividualcylinders.Theflipflop

scheme,however,provedeffectiveinallrespects.

HighPowerFiberOpticBeamDelivery:Throughtestsandanalysesitwasdeterminedthat

thefiberopticdeliveryrequirementsare(i)lowdivergenceatdistalend,(ii)highpower

lasertransmission,and(iii)preservationofmodequality.Initialtestsperformedusingsolid

corefibersshowedthattheyarelimitedbythematerialdamagethreshold.Subsequenttests

7/29/2019 CEC-500-2012-043 ovooooo

61/112

45

performedusingHollowGlassWaveguidesshowedthattheyarelimitedbymodeshifts

introducedbybendingoftheopticalfibers.Whilephotonicbandgapfibersappear

promising,theyarenotreadilyavailablefortestsandtheirdevelopmentisexpectedtobe

expensive.

ElectronicInterface:AnelectronicinterfaceisrequiredfortheALIStocommunicatewiththeECUofanengineforignitiontimingcoordination.InconsultationwithArgonnes

industrialpartner,Altronic,Inc.,thetimingmodulesfromexistingignitionsystemswere

adaptedforthepresentpurposeeasily.

7/29/2019 CEC-500-2012-043 ovooooo

62/112

46

7/29/2019 CEC-500-2012-043 ovooooo

63/112

47

4.0 (Task 2.4) Single-Cylinder Laser Ignition Studies

EarliertestsperformedinanRCM,inTask2.2,showedthatlaserignitionextendsthelean

ignitionlimitallthewaytotheleanflammabilitylimit(=0.5)fornaturalgasairmixtures.

Additionally,itwasfoundthatforleanoperationlaserignitionacceleratestherateof

combustion.Theobjectiveofthepresenttask(Task2.4)istodeterminetheimpactofsuch

alteredcombustionbehavioronthetradeoffbetweenbrakethermalefficiencyandNOx

emissionsinanaturalgasfueledengine.

4.1. Statement of Work for Task 2.4

Thegoalofthistaskwastoperformlaserignitiontestsonsinglecylindernaturalgas

enginesoftwosizeclassessoastoevaluatetheeffectsofignitiontiming,equivalenceratio

andintakeairpressureonemissionsandperformance.Thefollowingactionswereplanned

tobeperformedinthistask:

Prepareatestplanforoptimizingignitiontiming,efficiencyandNOxemissions

whileavoidingknockinordertodeterminetheperformancebenefitsbytheuseof

laserignition.Also,advantagesbytheuseofmultipointignitioningasengines

needstobedetermined.SuchtestsaretobeperformedbyNETLonaRicardo

Proteusengine.

PerformthetestsontheRicardoProteusenginepertheapprovedtestplan.

Prepareasimilartestplanforimplementationonalargeboreenginetodetermine

theperformancebenefitsbytheuseoflaserignition.Suchtestsaretobeperformed

bySwRIonaCAT3401engine.

PerformthetestsonCAT3401pertheapprovedtestplan.

Inatypicalreciprocatingenginechemicalenergyduringcombustionisconvertedto

mechanicalworkonthepiston.Thenetshaftpowerisaresultofsuchworkperformedon

thepistonslessthemechanicallosses.Whilethemechanicallossesoriginateatvarious

pointsofaworkingengine,themostsignificantofthem(upto50%)

Date post:	03-Apr-2018
Category:	Documents
Upload:	seva0
View:	214 times
Download:	0 times

CEC-500-2012-043 ovooooo

Documents