Flame initiation by nanosecond plasma discharges: Putting some new spark into ignition Paul D. Ronney University of Southern California, USA National Central University Jhong-Li, Taiwan, October 3, 2005 Research supported by U.S. AFOSR, ONR & DOE Research supported by U.S. AFOSR, ONR & DOE Travel supported by the Combustion Institute Travel supported by the Combustion Institute Faculty collaborator: Martin Gundersen (USC-EE) Research Associates: Nathan Theiss, Jian- Bang Liu Graduate students: Jason Levin, Fei Wang, Jun Zhao, Tsutomu Shimizu Undergraduate students: Brad Tallon,
Transcript
Flame initiation by nanosecond plasma discharges:
Putting some new spark into ignition
Paul D. RonneyUniversity of Southern California, USA
National Central UniversityJhong-Li, Taiwan, October 3, 2005
Research supported by U.S. AFOSR, ONR & DOEResearch supported by U.S. AFOSR, ONR & DOETravel supported by the Combustion InstituteTravel supported by the Combustion InstituteFaculty collaborator: Martin Gundersen (USC-EE)Research Associates: Nathan Theiss, Jian-Bang LiuGraduate students: Jason Levin, Fei Wang,
Jun Zhao, Tsutomu Shimizu Undergraduate students: Brad Tallon, Matthew Beck
Jennifer Colgrove, Merritt Johnson, Gary Norris
University of Southern CaliforniaUniversity of Southern California
Established 125 years ago Established 125 years ago this week!this week! ……jointly by a Catholic, a Protestant and a Jew - USC has jointly by a Catholic, a Protestant and a Jew - USC has
always been a multi-ethnic, multi-cultural, coeducational always been a multi-ethnic, multi-cultural, coeducational universityuniversity
Today: 32,000 students, 3000 facultyToday: 32,000 students, 3000 faculty 2 main campuses: University Park and Health Sciences2 main campuses: University Park and Health Sciences USC Trojans football team ranked #1 in USA last 2 yearsUSC Trojans football team ranked #1 in USA last 2 years
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Naming gift by Andrew & Erma ViterbiNaming gift by Andrew & Erma Viterbi Andrew Viterbi: co-founder of Qualcomm, co-inventor of CDMAAndrew Viterbi: co-founder of Qualcomm, co-inventor of CDMA 1900 undergraduates, 3300 graduate students, 165 faculty, 30 1900 undergraduates, 3300 graduate students, 165 faculty, 30
degree optionsdegree options $135 million external research funding$135 million external research funding Distance Education Network (DEN): 900 students in 28 M.S. Distance Education Network (DEN): 900 students in 28 M.S.
degree programs; degree programs; 1171 MS degrees awarded in 200571 MS degrees awarded in 2005 More info: More info: http://viterbi.usc.eduhttp://viterbi.usc.edu
Paul RonneyPaul Ronney B.S. Mechanical Engineering, UC BerkeleyB.S. Mechanical Engineering, UC Berkeley M.S. Aeronautics, CaltechM.S. Aeronautics, Caltech Ph.D. in Aeronautics & Astronautics, MITPh.D. in Aeronautics & Astronautics, MIT Postdocs: NASA Glenn, Cleveland; US Naval Research Lab, Postdocs: NASA Glenn, Cleveland; US Naval Research Lab,
Washington DCWashington DC Assistant Professor, Princeton UniversityAssistant Professor, Princeton University Associate/Full Professor, USCAssociate/Full Professor, USC Research interestsResearch interests
Microscale combustion and power generation Microscale combustion and power generation (10/4, INER; 10/5 NCKU)(10/4, INER; 10/5 NCKU)
Microgravity combustion and fluid mechanics Microgravity combustion and fluid mechanics (10/4, NCU)(10/4, NCU) Turbulent combustion Turbulent combustion (10/7, NTHU)(10/7, NTHU) Internal combustion enginesInternal combustion engines Ignition, flammability, extinction limits of flames Ignition, flammability, extinction limits of flames (10/3, NCU)(10/3, NCU) Flame spread over solid fuel bedsFlame spread over solid fuel beds Biophysics and biofilms Biophysics and biofilms (10/6, NCKU)(10/6, NCKU)
Multi-point ignition of flames has potential to increase Multi-point ignition of flames has potential to increase burning rates in many types of combustion engines, e.g.burning rates in many types of combustion engines, e.g. Pulse Detonation EnginesPulse Detonation Engines Reciprocating Internal Combustion EnginesReciprocating Internal Combustion Engines
»(Simplest approach) Leaner mixtures (lower NOx)(Simplest approach) Leaner mixtures (lower NOx)»(More difficult) Redesign intake port and combustion chamber for (More difficult) Redesign intake port and combustion chamber for
lower turbulence since the same burn rate is possible with lower lower turbulence since the same burn rate is possible with lower turbulence (reduced heat loss to walls, higher efficiency)turbulence (reduced heat loss to walls, higher efficiency)
High altitude restart of gas turbinesHigh altitude restart of gas turbines Lasers, multi-point sparks challengingLasers, multi-point sparks challenging
Lasers: energy efficiency, windows, fiber opticsLasers: energy efficiency, windows, fiber optics Multi-point sparks: multiple intrusive electrodesMulti-point sparks: multiple intrusive electrodes
How to obtain multi-point, energy efficient ignition?How to obtain multi-point, energy efficient ignition?
Not to be confused with “plasma torch”Not to be confused with “plasma torch” Initial phase of spark discharge (< 100 Initial phase of spark discharge (< 100
ns) - highly conductive (arc) channel ns) - highly conductive (arc) channel not yet formednot yet formed
CharacteristicsCharacteristics Multiple streamers of electronsMultiple streamers of electrons High energy (10s of eV) electrons compared High energy (10s of eV) electrons compared
to sparks (~1 eV)to sparks (~1 eV) Electrons not at thermal equilibrium with Electrons not at thermal equilibrium with
ions/neutralsions/neutrals Ions stationary - no hydrodynamicsIons stationary - no hydrodynamics Low anode & cathode drops, little radiation Low anode & cathode drops, little radiation
& shock formation - more efficient use of & shock formation - more efficient use of energy deposited into gasenergy deposited into gas
Images of corona discharge & flameImages of corona discharge & flame
Axial (left) and radial (right) views of discharge Axial (left) and radial (right) views of discharge with rod electrodewith rod electrode
Axial view of discharge & flame Axial view of discharge & flame (6.5% CH(6.5% CH44-air, 33 ms between images)-air, 33 ms between images)
Characteristics of corona dischargesCharacteristics of corona discharges
For short durations (1’s to 100’s of ns depending on For short durations (1’s to 100’s of ns depending on pressure, geometry, gas, etc.) DC breakdown threshold of pressure, geometry, gas, etc.) DC breakdown threshold of gas can be exceeded without breakdown gas can be exceeded without breakdown if high voltage if high voltage pulse can be created and stopped quickly enoughpulse can be created and stopped quickly enough
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TransientSteady
Time (ns)
Characteristics of corona dischargesCharacteristics of corona discharges
If arc forms, current increases some but voltage drops more, If arc forms, current increases some but voltage drops more, thus higher consumption of capacitor energy with little thus higher consumption of capacitor energy with little increase in energy deposited in gas (still have corona, but increase in energy deposited in gas (still have corona, but followed by (relatively ineffective) arc)followed by (relatively ineffective) arc)
Corona only Corona + arc
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-50 0 50 100 150 200 250 300
Time (ns)
Energy
Voltage
Current
Startof arc
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Time (ns)
EnergyVoltage
Current
Corona discharges are energy-efficientCorona discharges are energy-efficient
Discharge efficiency Discharge efficiency dd ≈ 10x higher for corona than ≈ 10x higher for corona than
conventional sparksconventional sparks
€
d =Energy deposited in gas
Electrical discharge energy=
ΔP ⋅Volumeγ −1
IVdt∫
0.01
0.1
1
10 100 1000
Energy (mJ)
Corona, Threaded rod electrodeCylindrical combustion chamber
Spark, plain wire electrodes, gap = 1 mmCylindrical combustion chamber
Spark, Car spark plugIC engine like chamber
Corona, ring electrodeIC engine like chamber
Corona, 1 pin, Cylindrical combustion chamber
ObjectivesObjectives
Compare combustion duration and ignition energy Compare combustion duration and ignition energy requirements of spark-ignited and corona-ignited flames in requirements of spark-ignited and corona-ignited flames in constant-volume vesselconstant-volume vessel
Determine effect of corona electrode geometry and ignition Determine effect of corona electrode geometry and ignition energy on combustion durationenergy on combustion duration
Determine if reduced combustion duration observed for Determine if reduced combustion duration observed for corona ignition in quiescent, constant-volume experiments corona ignition in quiescent, constant-volume experiments also applies to turbulent flamesalso applies to turbulent flames
Integrate pulsed corona discharge ignition system into Integrate pulsed corona discharge ignition system into premixed-charge IC enginespremixed-charge IC engines
Compare performance of corona-ignited and spark-ignited Compare performance of corona-ignited and spark-ignited enginesengines EfficiencyEfficiency EmissionsEmissions
Oscilloscope Trigger Pulse
Generator
HV DCPowerSupply
Transformer
Pressure Transducer
AirFuel
Vacuum
Central Electrode
Cylindrical Combustion Chamber
Experimental apparatus (constant volume)Experimental apparatus (constant volume) Pulsed corona discharges generated using thyratron or Pulsed corona discharges generated using thyratron or
“pseudospark” gas switch + Blumlein transmission line“pseudospark” gas switch + Blumlein transmission line 2.5” (63.5 mm) diameter chamber, 6” (152 mm) long2.5” (63.5 mm) diameter chamber, 6” (152 mm) long Rod electrode (shown below) or single-needleRod electrode (shown below) or single-needle Energy release (stoich. CHEnergy release (stoich. CH44-air, 1 atm) ≈ 1650 J energy release ≈-air, 1 atm) ≈ 1650 J energy release ≈
Discharge energy input for ignition is trivial fraction of heat release!Discharge energy input for ignition is trivial fraction of heat release!
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-0.02 0 0.02 0.04 0.06 0.08 0.1Time (s)
Rise Time
10% of total pressure rise
90% of total pressure rise
DefinitionsDefinitions
Delay time: 0 - 10% of peak pressureDelay time: 0 - 10% of peak pressure Rise time: 10% - 90% of peak pressureRise time: 10% - 90% of peak pressure
Rod electrode Single pin electrode
1 ring with multi-pins(only 4 pins case is shown)
Multi-rings with 2 pins/ring(Only 4 rings case is shown)
Insulation is indicated with shaded patern
Electrode configurationsElectrode configurations
Pulsed corona discharges in IC engine-like geometryPulsed corona discharges in IC engine-like geometry
Top viewTop view Side viewSide view
QuickTime™ and aCinepak decompressor
are needed to see this picture.
QuickTime™ and aCinepak decompressor
are needed to see this picture.
0.1
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0.6 0.7 0.8 0.9 1 1.1 1.2 1.3Equivalence ratio
CH4/Air
1 pin electrode 1 atm
Pulsed corona
Spark (Lewis and von Elbe)
Minimum ignition energy vs. mixtureMinimum ignition energy vs. mixture
1 pin corona discharge vs. spark - ≈ same geometry1 pin corona discharge vs. spark - ≈ same geometry MIE significantly higher (≈ 100x) for corona - more distributed MIE significantly higher (≈ 100x) for corona - more distributed
energy deposition in streamers?energy deposition in streamers? Minimum spark kernel diameter ≈ 0.2 mm for stoich. CH4-air Minimum spark kernel diameter ≈ 0.2 mm for stoich. CH4-air
Pressure effects on MIEPressure effects on MIE
MIE for pulsed corona does NOT follow EMIE for pulsed corona does NOT follow Eminmin ~ P ~ P-2-2 as spark as spark ignition does; more like Pignition does; more like P-1-1 at low P, P at low P, P00 at higher P at higher P
Smaller chamber diameter enables ignition at higher P - Smaller chamber diameter enables ignition at higher P - higher voltage gradienthigher voltage gradient
Effect of geometry on delay timeEffect of geometry on delay time
Effect of geometry on delay timeEffect of geometry on delay time
Delay time of spark larger (≈ 1.5 - 2x) than 1-pin corona (≈ Delay time of spark larger (≈ 1.5 - 2x) than 1-pin corona (≈ same geometry)same geometry)
Consistent with computations by Dixon-Lewis, Sloane that Consistent with computations by Dixon-Lewis, Sloane that suggest point radical sources improve ignition delay ≈ 2x suggest point radical sources improve ignition delay ≈ 2x compared to thermal sourcescompared to thermal sources
More streamer locations (more pins, rod) yield lower delay More streamer locations (more pins, rod) yield lower delay time (≈ 3.5x lower for rod than spark)time (≈ 3.5x lower for rod than spark)
Suggests benefit of corona is both chemical (1.5 - 2x) and Suggests benefit of corona is both chemical (1.5 - 2x) and geometrical (≈ 2x)geometrical (≈ 2x)
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0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05
corona, 1 pin, 75 mJ
spark, 75 mJ
corona, 3.9 mm dia. rod, 710 mJ
corona, 2 ring x 2 pin, 170 mJ
corona, 4 ring x 2 pin, 170 mJ
Rise Time (ms)
Equivalence ratio
CH
4
/Air
P = 1 atm
Effect of geometry on rise timeEffect of geometry on rise time
Effect of geometry on rise timeEffect of geometry on rise time
Rise time of spark larger ≈ same as 1-pin corona (≈ same Rise time of spark larger ≈ same as 1-pin corona (≈ same flame propagation geometry)flame propagation geometry)
More streamer locations (more pins, rod) yield lower rise More streamer locations (more pins, rod) yield lower rise time (≈ 3 - 4x lower for rod than spark), but multi-pin almost time (≈ 3 - 4x lower for rod than spark), but multi-pin almost as good with less energyas good with less energy
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corona, 1 pin, 75 mJspark at center, 75 mJcorona rod, 710 mJcorona, 2 ring x 2 pin, 170 mJcorona, 4 ring x 2 pin, 170 mJ
Peak P/P
o
Equivalence ratio
CH4/Air
1 atm
Peak pressuresPeak pressures
Peak pressuresPeak pressures
Peak pressures significantly higher for multi-point corona Peak pressures significantly higher for multi-point corona that one-pin corona or sparkthat one-pin corona or spark
Improvement (for rod) nearly independent of mixtureImprovement (for rod) nearly independent of mixture Probably due to change in flame propagation geometry, not Probably due to change in flame propagation geometry, not
heat lossesheat losses Radial propagation (corona) vs. axial propagation (arc)Radial propagation (corona) vs. axial propagation (arc) Corona: more combustion occurs at higher pressure (smaller Corona: more combustion occurs at higher pressure (smaller
quenching distance)quenching distance) Corona: lower fraction of unburned fuelCorona: lower fraction of unburned fuel Consistent with preliminary measurements of residual fuelConsistent with preliminary measurements of residual fuel
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corona, 1 ring x 2 pin
corona, 2 ring x 2 pin
corona, 4 ring x 2 pin
corona, 3.9 mm dia. rod
Spark
Delay Time (ms)
Discharge energy (mJ)
CH
4
/Air
φ = 1.0
= 1 P atm
Energy & geometry effects on delay timeEnergy & geometry effects on delay time
What is optimal electrode configuration to minimize What is optimal electrode configuration to minimize delay/rise time for a given energy?delay/rise time for a given energy?
Delay time: 2-ring, 4-ring & plain rod similar (all are much Delay time: 2-ring, 4-ring & plain rod similar (all are much better than spark)better than spark)
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corona, 1 ring x 2 pin
corona, 2 ring x 2 pin
corona, 4 ring x 2 pin
corona, 3.9 mm dia. rod
Spark
Rise Time (ms)
Discharge energy (mJ)
CH
4
/Air
φ = 1.0
= 1 P atm
Energy & geometry effects on rise timeEnergy & geometry effects on rise time
Rise time: 2-ring or 4-ring bestRise time: 2-ring or 4-ring best Note “step” behavior for multi-point ignition at low energies Note “step” behavior for multi-point ignition at low energies
- not all sites ignite- not all sites ignite Delay time doesn’t show “step” behaviorDelay time doesn’t show “step” behavior
Rise time: 4-ring stands outRise time: 4-ring stands out
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corona, 1 ring x 2 pin
corona, 2 ring x 2 pin
corona, 4 ring x 2 pin
spark
corona, 3.9 mm dia rod
Rise Time (ms)
Discharge Energy (mJ)
CH
4
/Air
φ = 0.7
= 1 P atm
Rod diameter effectsRod diameter effects
Plain rod: optimal diameter Plain rod: optimal diameter exists (≈ 0.15”), dexists (≈ 0.15”), drodrod/d/dcylcyl ≈ 0.06 ≈ 0.06 Large d: low field Large d: low field
concentration, few streamers?concentration, few streamers? Small d: Too many streamers, Small d: Too many streamers,
too much energy deposition?too much energy deposition?0
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File:030820
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ/pulse)
CH4/Air
Equivalence ratio: 1.0
P=1 atm.
Rod-cylinder electrode
Rod diameter: 0.09"
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File:030813
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ/pulse)
CH4/Air
Equivalence ratio: 1.0
P=1 atm.
Rod-cylinder electrode
Rod diameter: 0.155"
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File:030818
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ/pulse)
CH4/Air
Equivalence ratio: 1.0
P=1 atm.
Rod-cylinder electrode
Rod diameter: 0.375"
Effect of number of pins on 1 ringEffect of number of pins on 1 ring
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File:030416
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ)
CH4/Air
Equivalence ratio: 0.7
P=1 atm.
1 ring x 1 pin electrode
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File:030509
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ)
CH4/Air
Equivalence ratio: 0.7
P=1 atm.
1 ring x 2 pin electrode
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File:030515a
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ)
CH4/Air
Equivalence ratio: 0.7
P=1 atm.
1 ring x 4 pin electrode
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File:030516
Delay Time (ms)
Rise Time (ms)
Delay or Rise Time (ms)
Energy (mJ)
CH4/Air
Equivalence ratio: 0.7
P=1 atm.
1 ring x 8 pin electrode
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Minimum ignition energy
Maximum energy without arcing
Average delay time
Average rise time
Energy (mJ) or time (ms)
Number of pins
CH
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φ = 0.7
= 1 P atm
Effect of number of pins on 1 ringEffect of number of pins on 1 ring
MIE lower (!!) with more pins, optimal 4MIE lower (!!) with more pins, optimal 4 More pins: Slightly beneficial effect on delay time, slightly More pins: Slightly beneficial effect on delay time, slightly
adverse effect (!) on rise timeadverse effect (!) on rise time More is not necessarily better!More is not necessarily better!
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Discharge energy (mJ)
CH4/Air
φ = 1.01 atm
Threaded electrode
- Thyratron switched generator
- Pseudo spark generator
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Energy (mJ/pulse)
CH4/Air
φ = 1.01 atm
Threaded electrode
- Thyratron switched generator
- Pseudo spark generator
Thyratron vs. pseudospark generatorThyratron vs. pseudospark generator
Little effect of discharge generator type (pseudospark: ≈ 1/2 Little effect of discharge generator type (pseudospark: ≈ 1/2 discharge duration compared to thyratron)discharge duration compared to thyratron)
combustion chamber, rod electrodecombustion chamber, rod electrode Turbulence intensity ≈ 1 m/s, u’/STurbulence intensity ≈ 1 m/s, u’/SLL ≈ 3 (stoichiometric) ≈ 3 (stoichiometric) Benefit of corona ignition ≈ same in turbulent flames - shorter rise Benefit of corona ignition ≈ same in turbulent flames - shorter rise
& delay times, higher peak P& delay times, higher peak P Note quiescent corona faster than turbulent spark! (Faster burn Note quiescent corona faster than turbulent spark! (Faster burn
with less heat loss)with less heat loss)
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Pressure (V)
Time (s)
CH4/Air
φ = 0.71 atm
, Quiescent spark
, Turbulent spark
, Turbulent corona
, Quiescent corona
Turbulence effectsTurbulence effects
Similar results for lean mixture but benefit of turbulence Similar results for lean mixture but benefit of turbulence more dramatic - higher u’/Smore dramatic - higher u’/SLL (≈ 8) (≈ 8)
Engine experimentsEngine experiments2000 Ford Ranger I-4 engine with dual-plug head to test 2000 Ford Ranger I-4 engine with dual-plug head to test
corona & spark corona & spark at same time, same operating conditionsat same time, same operating conditionsNational Instruments / Labview data acquisition & controlNational Instruments / Labview data acquisition & controlHoriba emissions bench, samples extracted from corona - Horiba emissions bench, samples extracted from corona -
Macor machinable ceramic used for insulatorMacor machinable ceramic used for insulator Coaxial shielded cable used to reduce EMICoaxial shielded cable used to reduce EMI Simple single-point electrode tip, replaceableSimple single-point electrode tip, replaceable ““Point to plane” geometry first step - by no means optimalPoint to plane” geometry first step - by no means optimal
On-engine corona ignition systemOn-engine corona ignition system
Corona electrode and spark plug with pressure transducer Corona electrode and spark plug with pressure transducer in #1 cylinderin #1 cylinder
Wired for quick change between spark and corona ignition Wired for quick change between spark and corona ignition under identical operating conditionsunder identical operating conditions
≈ ≈ 500 mJ/pulse (equivalent “wall plug” energy requirement 500 mJ/pulse (equivalent “wall plug” energy requirement of ≈ 50 mJ spark)of ≈ 50 mJ spark)
Range of ignition timings for both spark & coronaRange of ignition timings for both spark & corona 3 modes tested3 modes tested
Corona onlyCorona only Single conventional plugSingle conventional plug Two conventional plugs (results very similar to single plug)Two conventional plugs (results very similar to single plug)
On-engine corona ignition systemOn-engine corona ignition system
On-engine resultsOn-engine results
Corona ignition shows increase in peak pressure under Corona ignition shows increase in peak pressure under all conditions testedall conditions tested
On-engine resultsOn-engine results
Corona ignition shows increase in IMEP under all Corona ignition shows increase in IMEP under all conditions testedconditions tested
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IMEP (spark)IMEP (corona)
COV (spark)COV (corona)
Equivalence ratio
IMEP at various air / fuel ratiosIMEP at various air / fuel ratios
Indicated mean effective pressure (IMEP) higher for corona Indicated mean effective pressure (IMEP) higher for corona than spark, especially for lean mixtures (nearly 30%)than spark, especially for lean mixtures (nearly 30%)
Coefficient of variance (COV) comparableCoefficient of variance (COV) comparable
IMEP at various loadsIMEP at various loads Corona showed an average increase in IMEP of 16% Corona showed an average increase in IMEP of 16%
over a range of engine loadsover a range of engine loads
3000 RPM, Phi = 0.7
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Torque (ft-lb)
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SparkCoronaSpark COVCorona COV
Burn rateBurn rate
Integrated heat release shows faster burning with corona Integrated heat release shows faster burning with corona leads to greater effective heat releaseleads to greater effective heat release
2900 RPM, = 0.7
Burn ratesBurn rates
Corona ignition shows Corona ignition shows substantiallysubstantially faster burn rates at faster burn rates at same conditions compared to 2-plug conventional ignitionsame conditions compared to 2-plug conventional ignition
2900 RPM, = 0.7
Emissions data - NOxEmissions data - NOx
Improved NOx performance vs. indicated efficiency tradeoff Improved NOx performance vs. indicated efficiency tradeoff compared to spark ignition by using leaner mixtures with compared to spark ignition by using leaner mixtures with sufficiently rapid burningsufficiently rapid burning
Emissions data - hydrocarbonsEmissions data - hydrocarbons
Hydrocarbons emissions similar, corona vs. sparkHydrocarbons emissions similar, corona vs. spark
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Indicated Efficiency
spark
corona
Emissions data - COEmissions data - CO
CO emissions similar, corona vs. sparkCO emissions similar, corona vs. spark
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Indicated Efficiency
spark
corona
ConclusionsConclusions
Flame ignition by transient plasma or pulsed corona Flame ignition by transient plasma or pulsed corona discharges is a promising technology for ignition delay & discharges is a promising technology for ignition delay & rise time reductionrise time reduction More energy-efficient than spark dischargesMore energy-efficient than spark discharges Shorter ignition delay and rise timesShorter ignition delay and rise times Rise time more significant issueRise time more significant issue
»Longer than delay timeLonger than delay time»Unlike delay time, can’t be compensated by “spark advance”Unlike delay time, can’t be compensated by “spark advance”
Higher peak pressuresHigher peak pressures Benefits apply to turbulent flames alsoBenefits apply to turbulent flames also
Demonstrated in engines tooDemonstrated in engines too Higher IMEP for same conditions with same or better BSNOxHigher IMEP for same conditions with same or better BSNOx Shorter burn times and faster heat releaseShorter burn times and faster heat release
Improvements due to Improvements due to Chemical effects (delay time) - radicals vs. thermal energyChemical effects (delay time) - radicals vs. thermal energy Geometrical effects - (delay & rise time) - more distributed Geometrical effects - (delay & rise time) - more distributed
engines???engines??? Transient plasma discharges for fuel electrospray Transient plasma discharges for fuel electrospray
dispersion?dispersion?
Thanks to…Thanks to…
National Central UniversityNational Central University Prof. Shenqyang ShyProf. Shenqyang Shy Combustion Institute (Bernard Lewis Lectureship)Combustion Institute (Bernard Lewis Lectureship) AFOSR, ONR, DOE (research support)AFOSR, ONR, DOE (research support)
