1. University of Southern California - School of Engineering Corona discharge ignition of premixed flames & applications to pulse detonation engines (& NO x reduction) Jian-Bang Liu, Paul D. Ronney, Martin Gundersen University of Southern California Los Angeles, CA 90089-1453 USA

2. University of Southern California - School of Engineering Pulse detonation engine concept Nearly constant-volume cycle vs. constant pressure - higher ideal thermodynamic efficiencyNearly constant-volume cycle vs. constant pressure - higher 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(  high thermal efficiency) and repetition rate (  thrust)Need rapid ignition and transition to detonation(  high thermal efficiency) and repetition rate (  thrust) Conventional ignition sources inadequateConventional ignition sources inadequate

3. University of Southern California - School of Engineering Deflagation and detonation structure

4. University of Southern California - School of Engineering Unsuccessful vs. successful ignition

5. University of Southern California - School of Engineering Our approach - corona discharge CoronaCorona Initial phase of spark discharge - highly conductive (arc) channel not yet formedInitial phase of spark discharge - highly conductive (arc) channel 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 greater than arc or laser sourcesUSC-built discharge generator wall-plug efficiency (>50%) far greater 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)

6. University of Southern California - School of Engineering Corona vs. arc discharge Corona phase (0 - 100 ns) Arc phase (> 500 ns)

7. University of Southern California - School of Engineering Physical 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, electron attachment/detachment...Ion production, UV photons, molecular excited states, 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 participatePlasma chemistry - ions, electrons & neutrals participate Spatially inhomogeneousSpatially inhomogeneous Flow effects due to ion motionFlow effects due to ion motion

8. University of Southern California - School of Engineering Corona vs. arc discharges for ignition

9. University of Southern California - School of Engineering USC corona discharge generator "Inductive adder" circuit "Inductive adder" circuit Pulse shaping to minimize duration, maximize peak power Pulse shaping to minimize duration, maximize peak power Parallel placement of multiple MOSFETs (thyratron replacement) all referenced to ground potential Parallel placement of multiple MOSFETs (thyratron replacement) all referenced to ground potential > 40kV, 40kV, < 100 ns pulse

10. University of Southern California - School of Engineering Characteristics of corona discharge I max = 24 A V max = 26 kV 100 ns/div P max = 625 kW Discharge terminates during corona phase, before arc phase beginsDischarge terminates during corona phase, before arc phase begins Very low noise & light emission compared to arc with same energy depositionVery low noise & light emission compared to arc with same energy deposition

11. University of Southern California - School of Engineering Experimental apparatus for corona ignition

12. University of Southern California - School of Engineering Images of corona discharge & flame Radial view of discharge Axial view of discharge & flame (6.5% CH 4 -air, 33 ms between images)

13. University of Southern California - School of Engineering Characteristics of corona discharges “Optimal” energy above which ignition properties are nearly constant

14. University of Southern California - School of Engineering Ignition delay & rise time comparisons Both ignition delay time (0 - 10% of peak P) & rise time (10% - 90% of peak P) ≈ 3x smaller with corona ignition (constant-volume combustion chamber, “optimal” energy)

15. University of Southern California - School of Engineering Pressure effects Results similar or even better at reduced pressure - useful for high-altitude ignition

16. University of Southern California - School of Engineering Other application - NO removal Diesel engine exhaustDiesel engine exhaust Needle/plane corona discharge (20 kV, 30 nsec pulse)Needle/plane corona discharge (20 kV, 30 nsec pulse) Lower left: before pulseLower left: before pulse Lower right: 10 ms after pulseLower right: 10 ms after pulse Upper: difference, showing single- pulse destruction of NO (≈ 40%)Upper: difference, showing single- pulse destruction of NO (≈ 40%)

17. University of Southern California - School of Engineering NO–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 destroyedCorresponds to 0.2 % of fuel energy input per 100 ppm NO destroyed

18. University of Southern California - School of EngineeringConclusions 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?

19. University of Southern California - School of Engineering Future 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 promising)Integration into PDE test facility (initial results at U. S. Naval Postgraduate School very promising)