In-cylinder Ion Sensing Opportunities

Designing Electronic Powertrain Controls SymposiumMay 4-6, 2004, Austin, TexasIn-cylinderIon SensingOpportunitiesYiqun Huang, Senior Research EngineerPowertrain ControlsEngine, Emissions and Vehicle Research DivisionSouthwest Research Institute ®

Why Do We Need Ion Sensing ?• For SI engine, to increase performance and lower fuel consumption,n,operating close to MBT timing is desirable– But it is limited by knocking– Accurate knock detection over all engine operating conditionsis required• To meet stringent emissions standard, misfire detection is requiredredfor all engine speeds for OBD-II• Deficiencies of current methods– Accelerometer sensor for knock detection loses accuracy athigh engine speed due to vibration noise and could not detectearly knocking– Traditional speed variation method for misfire detectionbecomes difficult for multiple cylinder engines (V6, V8) and athigh engine speed• Other sensors to accomplish these tasks have cost and technicallimitations• All these problems can be solved by in-cylinder ion sensing

What Is Ion Sensing?• Ion Sensing-Measuring ionization currentgenerated from combustion through sparkplug electrodes• Extra measurement provided from the existingignition system, - no added in-cylinderinstrumentation• Electronics added to existing hardware• Directly reflects in-cylinder combustionprocess• Provides accurate misfire and knock detection• Potentials for advanced engine controlapplication

Background of Ion Sensing• Being studied for automotive byresearchers before 1980 for A/F ratio,cylinder pressure estimation• Installed in-cylinder or outside cylinderclose to the exhaust port• Used on SAAB Direct-IgnitionTM systemsince 1987 and later on SAAB Trionicsystem (by Mecel)• Originally for cylinder synchronizationand pre-ignition detection• Knock and misfire detection wereintroduced in 1992 on SAAB (by Mecel)• In-cylinder detection is used - eachcylinder

Mechanism of In-cylinder Ion Sensing• Ions produced by chemical and thermalionization:CH + O → CHO + + e -CHO + +H 2 O → H 3 O + + COM+ E ion ←→ M + + e -• Measuring circuitry integrated with the ignitionelectronics system• Controlling of spark event is unaffected• No mechanical modification of engine needed

Mechanism of In-cylinder Ion SensingFrom EuropeanAutomotive Des(Delphi AutomotSystem)• Ion current sensing is based on applying a low-voltageDC bias to the spark plug electrodes• The spark current used to create this bias voltage isaccumulated by a capacitor inside the ignition coil,eliminating the need for any additional voltage source

Mechanism of In-cylinder Ion SensingFrom EuropeanAutomotive Des(Delphi AutomotSystem)• The measured current after the spark event reflects thecombustion process• Other related parameters are extracted through signalprocessing

Mechanism of In-cylinder Ion SensingFrom EuropeanAutomotive Des(Delphi AutomotSystem)• Knock causes high frequency modulation of ion currentsignal• The modulated signal is obtained by passing through aband pass filter

Example Hardware ofIn-cylinder Ion SensingMitsubishi ElectricIonization DetectionModuleSAAB Trionic SystemSAAB Ion Detection and Ignition coilDelphi IonizationDetection System

Example Hardware ofIn-cylinder Ion SensingInfineon Technologies AG:Smart IGBT block with possiblefunctionsSmart IGBT on Chip-on-ChipFrom SAE 2004-01-0518

Current EffortsEarly knock detection- traditional accelerometer type knocksensor could not detect early,inaudible knockCombustion condition detection - leanlimit control- cold start application

Knock DetectionIon & cylinderpressure signalsKnock sensorKnock signalfrom ion sensing& pressuresensorSAE 2003-0101-3149• Heavy, audible knocking• Knock sensor, ionsensing and pressuresensor pick up theknocking signal• Light knocking, inaudible• Knock sensor at the noiselevel and misses knock• Ion sensing and pressuresensor pick up theknocking signal

Knock Detection at High SpeedIon signalKnock sensorKnock signalfrom ion sensing• Audible knocking at high speed• Knock sensor loses thecapability to detect knock due tohigh noise from vibration• Ion sensing picks up theknocking signalSAE 2003-0101-3149• No knocking at high speed• Knock sensor at the noiselevel and may indicateknock• Ion sensing shows noknocking

Further Improvement Needed forQuantitative ApplicationHardware Development:– High speed sampling for cycleresolved ion signal– ECU throughput improvement forcycle resolved data processing– Current coil design tends to low-pass filter ion signal• Coil redesign required

Further Improvement Needed forQuantitative Application - (Cont.)Ion signals are also affected by:– Engine operating conditions– Fuel additives– Spark plug conditionMust quantify these effects byadditional fundamental research

Fundamental Research• Understandingmechanism andaffecting factors• DesignimprovementKnife EdgeMirror 2Lens 3CameraLens 2Lens 1SwRI Combustion Bombs andHigh Speed Combustion ImagingMirror 1

Fundamental Research - (Cont.)1.4Ignition Command, Ionization, volts1.210.80.60.40.25.55 ms6.57 ms28.60 msignition commandion signal, voltscylinder pressure15001000500Cylinder pressure, kPa000 20 40 60 80 100Time, ms- Ion signal timing relations

Characteristics of Ion Signal0.40.350.3Location of the peak ionizationsignal from spark commandSignal reflectingthe sparkPeak of the ionization signalThe characteristicsof ion signal:–Peak–Peak location–AreaIon Signal, volts0.250.20.150.10.050Ignition dwellInitial Ionizationassociated withthe flame front1.0950 10 20 30 40TIME (ms)φ =Area covered by the ionization signalIonization under controlledenvironment

Location & Magnitude of Ionization Peaks andIntegration of Ionization - Combustion Bomb ResultIntegration of Ionization, volt. ms400350300250200150100500Integration - Test 1Integration - Test 2Integration - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5phiLocation of the Peak Ionization from spark, ms4540353025201510Location of Peak Ionization (ms) - Test 1Location of Peak Ionization (ms) - Test 2Location of Peak Ionization (ms) - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5phiPeak Magnitude, volts0.450.400.350.300.250.200.150.100.050.00Peak Ionization - Test 1Peak Ionization - Test 2Peak Ionization - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5phi• The timing of the peak ion signal isminimum at slightly rich• The area covered by ion signal peaksat slightly rich, but decays faster onthe lean side• Peak magnitude of ion signal showssimilar trends as area covered by theion signal

Neural Network Prediction- Combustion Bomb ResultsLocation of the Peak Ionization from spark, ms4540353025201510Location of Peak Ionization (ms) - Test 1Location of Peak Ionization (ms) - Test 2Location of Peak Ionization (ms) - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.24001.3 1.4 1.5phiIntegration of Ionization, volt. ms35030025020015010050Integration - Test 1Integration - Test 2Integration - Test 3Equivalence Ratio1.81.61.41.210.8PredictedMeasured00.450.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.50.40 phi0.350.6Peak Magnitude, volts0.300.250.200.150.100.050.00Peak Ionization - Test 1Peak Ionization - Test 2Peak Ionization - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5phi0.40 20 40 60 80 100 120 140 160Test Points•The predicted results show lessaccuracy at Φ = ~1.0 to 1.1.

Speed Effect on Ion SignalIonization Signal, volt0.250.20.150.10.050-0.05Ignition CommandPeak magnitude increases withthe increase of RPMSignal Used600 rpm800 rpm1000 rpm1200 rpm0 2 4 6 8 10 12 14Time, msAt stoichiometric, no load•Peak - increases withspeed•Peak location - close tospark with speedincrease•Area - increases withspeed increaseSpeed Effect

Load Effect on Ion SignalIonization Signal, volt0.250.20.150.10.05200 Nm20 Nm100 Nm•Peak - increases withload•Peak location - close tospark with loadincrease0-0.050 2 4 6 8Time, msLoad Effect

Equivalence Ratio Effects atHigher Load and Different Speed0.251000 rpm0.252600 rpm•Peak magnitudeof ion signal -max at Φ = ~1.1Ion signal, volt0.20.150.10.051.2981.1671.0590.9870.878Ion Signal, volt0.20.150.10.051.2711.121.030.9380.885•Peak location -closest to sparkat max ΦIon Signal, volt0.250.1500 0.001 0.002 0.003 0.004 0.005time, s0.20.11400 rpm0.8850.8790.9241.0981.185Ion Signal, volt00 0.001 0.002 0.003 0.004time, s3000 rpm0.250.20.150.11.261.1571.0250.8880.8550.050.0500 0.001 0.002 0.003 0.004 0.005time, s00 0.001 0.002 0.003 0.004time, s

Ion Signal in Time Domainand Crank Angle Domain0.250.25Ionization, volts0.200.150.103000 rpm, phi 1.0252600 rpm, phi 1.0302200 rpm, phi 1.0151400 rpm, phi 1.0981000 rpm, phi 1.059Ionization, volts0.200.150.103000 rpm, phi 1.0252600 rpm, phi 1.0302200 rpm, phi 1.0151400 rpm, phi 1.0981000 rpm, phi 1.0590.050.050.000 2 4 6Time, ms0.000 25 50 75Crank Angle Degree•Processing in crank angle domain isneeded for the area covered by ionization.

Location of Peak Ionization Signal- Engine Test vs Combustion Bomb TestLocation of the Peak Ionization from spark, ms4540353025201510Location of Peak Ionization (ms) - Test 1Location of Peak Ionization (ms) - Test 2Location of Peak Ionization (ms) - Test 30.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5phiLocation of peak ionization, ms from spark2.22.01.81.61.41.21.00.80.60.40.20.00.8 0.9 1.0 1.1 1.2 1.3 1.4Equivalence ratio3000 rpm2600 rpm2200 rpm1400 rpm1000 rpm• From bomb test -Peak location is closest tothe spark at Φ = ~ 1.05,symmetric• From engine test -Peak location is closestto the spark at max Φ

Potentials for Reducing Cold StartEquivalence ratio1.61.41.210.80.6and Warm-up Enrichmentphi: cyl. #1phi: engineEquivalence ratio could be closer to 1by closed loop control0.40 5 10 15 20 25 30TIME (Sec)Equivalence ratio duringstart and warm-up• Online calibration is needed forvariations in fuel properties andspark plug condition• Idle condition can be used as anonline calibration point• ion signal character parameterscan be normalized by the valuesat the calibration condition.AtinputinputPinput===AmeaAtPmeatmea• f (∆A)bas _ online• f (∆t)bas _ onlineP• f (∆P)bas _ online

Summary• The development of ion sensing technology isstill continuing• Successfully used in production vehicles forknock detection and misfire detection– demonstrated advantages over other methods• Early knock detection and control by ion sensingis very promising• Ion sensing has demonstrated high potential foradjusting ignition timing and air/fuel ratio onindividual cylinder basis

Summary - (Cont.)• Cold start is a very important area for ion sensingto apply for– AF ratio estimation: could be a neuralnetwork model– Could be useful as feedback for closed loopAir/Fuel ratio control during the engine warmup period when the oxygen sensor iswarming up.

Summary - (Cont.)• Engine operating conditions have strong effectson ionization detection,– including the location of peak ionization,peak magnitude and area covered byionization• Calibration issue must be resolved– idle condition can be used as an on-linecalibration point for the ionizationmeasurement after the oxygen sensorwarms up.• Measurement derived from the ion signals can behelpful for optimizing engine combustion

ContactYiqun HuangPowertrain ControlsEngine, Emissions and Vehicle Research DivisionSouthwest Research Instituteyhuang@swri.orgTel:210-522522-25642564