University of Southern California - School of Engineering Corona discharge ignition of premixed flames & applications to pulse detonation engines (& NO

University of Southern California - School of Engineering

Corona discharge ignition of Corona discharge ignition of premixed flames & applications premixed flames & applications

to pulse detonation engines to pulse detonation engines (& NO(& NOxx reduction) reduction)

Jian-Bang Liu, Paul D. Ronney, Jian-Bang Liu, Paul D. Ronney, Martin GundersenMartin Gundersen

University of Southern CaliforniaUniversity of Southern CaliforniaLos Angeles, CA 90089-1453 USALos Angeles, CA 90089-1453 USA


Pulse detonation engine conceptPulse detonation engine concept

Fill TubeDetonateMixture

Exhaust

Refill Tube, Repeat

Fuel

Air(or otheroxidizer)

• Nearly constant-volume cycle vs. constant pressure - Nearly constant-volume cycle vs. constant pressure - higher ideal thermodynamic efficiencyhigher ideal thermodynamic efficiency

• No mechanical compressor neededNo mechanical compressor needed• Can operate from zero to hypersonic Mach numbersCan operate from zero to hypersonic Mach numbers• Need rapid ignition and transition to detonation(Need rapid ignition and transition to detonation( high high

thermal efficiency) and repetition rate (thermal efficiency) and repetition rate ( thrust) thrust)• Conventional ignition sources inadequateConventional ignition sources inadequate


Deflagation and detonation structureDeflagation and detonation structure

DISTANCE

DEFLAGRATION

TemperatureDensity

Pressure

Direction of

propagation

(velocity SL

)

δ

DISTANCE

DETONATION

Temperature

Pressure

Direction of

propagation

Shock

front

cb

τ

( Velocity Mcj

co

)


Unsuccessful vs. successful ignitionUnsuccessful vs. successful ignition


Our approach - corona dischargeOur approach - corona discharge

• CoronaCorona• Initial phase of spark discharge - highly conductive (arc) Initial phase of spark discharge - highly conductive (arc)

channel not yet formedchannel not yet formed• High field strengthHigh field strength• Multiple streamers of high energy (10s of eV) electronsMultiple streamers of high energy (10s of eV) electrons• More efficient use of energy deposited into gasMore efficient use of energy deposited into gas• USC-built discharge generator wall-plug efficiency (>50%) far USC-built discharge generator wall-plug efficiency (>50%) far

greater than arc or laser sourcesgreater than arc or laser sources• Conventional arcConventional arc

• Single unnecessarily large, high current conductive pathSingle unnecessarily large, high current conductive path• Low field strength (like short circuit)Low field strength (like short circuit)• Large anode & cathode voltage dropsLarge anode & cathode voltage drops• Low energy electrons (1s of eV)Low energy electrons (1s of eV)


Corona vs. arc dischargeCorona vs. arc discharge

Arc channel

High voltage pulse

Corona StreamersPlasma Zone

Corona dies out in pulsed mode

Coaxial ground electrode - no dielectric barrier needed

High voltage pulse

Corona phaseCorona phase(0 - 100 ns)(0 - 100 ns)

Arc phaseArc phase(> 500 ns)(> 500 ns)


Physical mechanism of electric dischargesPhysical mechanism of electric discharges

• Electron Avalanche/ Streamer Formation (0-100 ns)Electron Avalanche/ Streamer Formation (0-100 ns)• Ion production, UV photons, molecular excited states, Ion production, UV photons, molecular excited states,

electron attachment/detachment . . .electron attachment/detachment . . .• Production of chemically active speciesProduction of chemically active species• Ions stationary - no hydrodynamicsIons stationary - no hydrodynamics

• Charge Neutral Chemistry (500 ns - )Charge Neutral Chemistry (500 ns - )• Plasma chemistry - ions, electrons & neutrals participate Plasma chemistry - ions, electrons & neutrals participate • Spatially inhomogeneousSpatially inhomogeneous• Flow effects due to ion motionFlow effects due to ion motion


Corona vs. arc discharges for ignitionCorona vs. arc discharges for ignition


USC corona discharge generatorUSC corona discharge generator

• "Inductive adder" circuit"Inductive adder" circuit• Pulse shaping to minimize Pulse shaping to minimize

duration, maximize peak powerduration, maximize peak power• Parallel placement of multiple Parallel placement of multiple

MOSFETs (thyratron replacement) MOSFETs (thyratron replacement) all referenced to ground potentialall referenced to ground potential

• > 40kV, < 100 ns pulse> 40kV, < 100 ns pulse


Characteristics of corona dischargeCharacteristics of corona discharge

Imax = 24 A

Vmax = 26 kV100 ns/div

Pmax = 625 kW

• Discharge terminates during corona phase, before arc phase Discharge terminates during corona phase, before arc phase beginsbegins

• Very low noise & light emission compared to arc with same energy Very low noise & light emission compared to arc with same energy depositiondeposition


Experimental apparatus for corona ignitionExperimental apparatus for corona ignition

Pulse generator

Oscilloscope

TriggerDC power

supply

High voltage

DC power

supply

To thyratron

InputOutput spark plug

circuit

Current signal

Air

Fuel

Vacuum pump

Gas outlet

+

-

Probe

Pressure

Transducer

Spark plug

Pressure

gauge

Transformer


Images of corona discharge & flameImages of corona discharge & flame

Radial view of dischargeRadial view of discharge

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

““Optimal” energy above which ignition Optimal” energy above which ignition properties are nearly constantproperties are nearly constant

0

200

400

600

800

1000

0 5 10 15 20 25

Energy (mJ)

Supply voltage (kV)

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

Rise time (ms)

Pulse energy (mJ/pulse)

CH

4

/Air

1 atm total pressure

Equivalence ratio: 0.83

Corona discharge


Ignition delay & rise time comparisonsIgnition delay & rise time comparisons

Both ignition delay time (0 - 10% of peak P) & rise time (10% - 90% of Both ignition delay time (0 - 10% of peak P) & rise time (10% - 90% of peak P) ≈ 3x smaller with corona ignitionpeak P) ≈ 3x smaller with corona ignition

(constant-volume combustion chamber, “optimal” energy)(constant-volume combustion chamber, “optimal” energy)

10

100

1000

0.5 0.6 0.7 0.8 0.9 1 1.1

arc at centerarc at tiparc at end platecorona

Equivalence ratio

10

100

0.6 0.7 0.8 0.9 1 1.1

arc at centerarc at tip of electrodearc at end platecorona

Equivalence ratio


Pressure effectsPressure effects

Results similar or even better at reduced pressure - Results similar or even better at reduced pressure - useful for high-altitude ignitionuseful for high-altitude ignition

5

10

15

20

2 4 6 8 10 12 14 16

Delay time (ms)Rise time (ms)

Initial pressure (psi)

Equivalence ratio = 1.0Corona ignition


Other application - NO removalOther application - NO removal

• Diesel engine Diesel engine exhaustexhaust

• Needle/plane corona Needle/plane corona discharge (20 kV, 30 discharge (20 kV, 30 nsec pulse)nsec pulse)

• Lower left: before Lower left: before pulsepulse

• Lower right: 10 ms Lower right: 10 ms after pulseafter pulse

• Upper: difference, Upper: difference, showing single-showing single-pulse destruction of pulse destruction of NO (≈ 40%)NO (≈ 40%)

m m m m

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8

0

2

4

6

8

1 0

1 2

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8

0

2

4

6

8

1 0

1 2

0

2 0

4 0

6 0

8 0

1 0 0

0 1 0 2 0 3 0 4 0 5 0

m m

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8

0

2

4

6

8

1 0

1 2

G a s F l o w

2 2 6 n m l a s e r

s h e e t

.


NO–Plasma InteractionsNO–Plasma Interactions

• Energy efficient: ≈ 10eV/molecule or less possibleEnergy efficient: ≈ 10eV/molecule or less possible• Corresponds to 0.2 % of fuel energy input per 100 ppm NO Corresponds to 0.2 % of fuel energy input per 100 ppm NO

destroyed destroyed


ConclusionsConclusions• Corona ignition is a promising approach to ignition in Pulse Detonation EnginesCorona ignition is a promising approach to ignition in Pulse Detonation Engines

• More energy efficient than arc dischargesMore energy efficient than arc discharges• More rapid ignition & transition to detonationMore rapid ignition & transition to detonation• Coaxial geometry convenient for corona discharges, easily integrated into PDEsCoaxial geometry convenient for corona discharges, easily integrated into PDEs

• Reasons for improvements not well understoodReasons for improvements not well understood• Geometrical - more ignition sites?Geometrical - more ignition sites?• Chemical effects - more efficient use of electron energy?Chemical effects - more efficient use of electron energy?


Future work - opportunitiesFuture work - opportunities• Application to lean-burn internal combustion enginesApplication to lean-burn internal combustion engines• Electrostatic sprays charged with corona dischargesElectrostatic sprays charged with corona discharges• Modelling of chemical reactions between ions/electrons/neutralsModelling of chemical reactions between ions/electrons/neutrals• Integration into PDE test facility (initial results at U. S. Naval Postgraduate School very Integration into PDE test facility (initial results at U. S. Naval Postgraduate School very

promising)promising)

-10

-5

0

5

10

15

20

0.005 0.01 0.015 0.02 0.025

5 in10.5 in16 in21.5 in32.5 in

Pressure (lb/in

2

, gauge)

Time (seconds)

Documents

University of Southern California - School of Engineering Corona discharge ignition of premixed flames & applications to pulse detonation engines (& NO