Corona discharge ignition of premixed flames

Corona discharge ignition of premixed flames www.phwiki.com

Corona discharge ignition of premixed flames

Ronning, Bill, Music Director has reference to this Academic Journal, PHwiki organized this Journal Corona discharge ignition of premixed flames Jian-Bang Liu, Paul Ronney, Martin Gundersen University of Southern Cali as long as nia Los Angeles, CA 90089-1453 USA Flame ignition by pulsed corona discharges Characteristics Initial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet as long as med Multiple streamers of electrons High energy (10s of eV) electrons - couple efficiently with cross-section as long as ionization, electron attachment, dissociation More efficient use of energy deposited into gas Enabling technology: USC-built discharge generators having high wall-plug efficiency (>50%) – far greater than arc or laser sources Pulse detonation engine concept Advantages over conventional propulsion systems Nearly constant-volume cycle vs. constant pressure – higher ideal thermodynamic efficiency No mechanical compressor needed Can operate from zero to hypersonic Mach numbers Courtesy Fred Schauer

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Pulse detonation engines – initiation Need rapid ignition in addition to transition to detonation ( high thermal efficiency) in addition to repetition rate ( thrust) Conventional spark ignition sources may initiate detonations, but need obstacles – heat & stagnation pressure losses Multiple high-energy discharges may be too energy-intensive Need energy-efficient, minimally intrusive means to initiate detonations Courtesy Fred Schauer Transient plasma (corona) discharge Not to be confused with “plasma torch” Initial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet as long as med High field strength Multiple streamers of electrons Corona vs. arc discharge Corona phase (0 - 100 ns) Arc phase (> 500 ns)

Transient plasma (corona) discharge Not to be confused with “plasma torch” Initial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet as long as med High field strength Multiple streamers of electrons High energy (10s of eV) electrons - couple efficiently with cross-section as long as ionization, electron attachment, dissociation Corona vs. arc discharges as long as ignition Transient plasma (corona) discharge Not to be confused with “plasma torch” Initial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet as long as med High field strength Multiple streamers of electrons High energy (10s of eV) electrons - couple efficiently with cross-section as long as ionization, electron attachment, dissociation Electrons not at thermal equilibrium with ions/neutrals Ions are good chain branching agents Ions are energy-efficient chain-branching agents Rates Reaction Pre-exponential Activation energy H + O2 OH + O 3.1 x 10-10 s/cm3mol 16.81 kcal/mol H + O2- OH- + O 1.2 x 10-9 0 Rate ratio at 1000K: 1/18,000 Energy cost of O2- higher than H, but not 18,000x higher! Reaction Energy CH4 CH3 + H 4.6 eV vs. O2 + e- O2+ + e- + e- 12.1 eV N2 + O2 + e- N2 + O2- Transient plasma (corona) discharge Not to be confused with “plasma torch” Initial phase of spark discharge (< 100 ns) - highly conductive (arc) channel not yet as long as med High field strength Multiple streamers of electrons High energy (10s of eV) electrons - couple efficiently with cross-section as long as ionization, electron attachment, dissociation Ions are good chain branching agents Electrons not at thermal equilibrium with ions/neutrals Ions stationary - no hydrodynamics Low anode & cathode drops, little radiation & shock as long as mation - more efficient use of energy deposited into gas USC-built discharge generators have high wall-plug efficiency (>50%) – far greater than arc or laser sources Comparison with conventional arc Single unnecessarily large, high current conductive path Low field strength (like short circuit) Large anode & cathode voltage drops – large losses Low energy electrons (1s of eV) Flow effects due to ion motion – gasdynamic losses Less efficient coupling of energy into gas

Experimental apparatus as long as corona ignition (constant volume) Experimental apparatus as long as corona ignition USC corona discharge generator “Inductive adder” circuit Pulse shaping to minimize duration, maximize peak power Parallel placement of multiple MOSFETs (thyratron replacement) all referenced to ground potential > 40kV, < 100 ns pulse Images of corona discharge & flame Axial (left) in addition to radial (right) views of discharge Axial view of discharge & flame (6.5% CH4-air, 33 ms between images) Characteristics of corona discharge Arc leads to much higher energy consumption with little increase in energy deposited in gas Corona has very low noise & light emission compared to arc with same energy deposition Corona only Corona + arc Characteristics of corona discharges “Optimal” energy above which ignition properties are nearly constant Ignition delay & rise time (methane-air) Both ignition delay time (0 - 10% of peak P) & rise time (10% - 90% of peak P) 3x smaller with corona ignition Rise time more significant issue Longer than delay time Unlike delay time, can’t be compensated by “spark advance” “Brush” electrode provides localized field strength enhancement with minimal increase in surface area ( drag, heat loss) Peak pressures Peak pressure higher with corona discharge Radial propagation (corona) vs. axial propagation (arc) Corona: more combustion occurs at higher pressure (smaller quenching distance) Corona: lower fraction of unburned fuel Consistent with measurements of residual pressure (need GC verification) Modified electrode “Brush” electrode provides localized field strength enhancement with minimal increase in surface area ( drag, heat loss) 5x faster rise time than arc Pressure effects Results similar at reduced pressure - useful as long as high-altitude ignition Pressure effects Results similar at higher pressure Pressure & fuel effects - propane-air Results similar with other fuels (e.g. propane) Ronning, Bill KFLT-AM Music Director www.phwiki.com

Fuel effects n-butane in addition to iso-butane exhibit similar trends but greater difference between corona in addition to arc as long as n-butane (more weaker secondary C-H bonds) PDE testing at U.S. Naval Postgraduate School 1 day facility time Ethylene-air, 1 atm, 2 inch diameter tube, no obstacles Initial results promising – 3x shorter time to reach peak pressure than with arc ignition, much higher peak pressure (17 psig vs. 1 psig) Prior work: Diesel Emission NO – Plasma Interactions Energy efficient: 10 eV/molecule or less possible Transient plasma provides dramatically improved energy efficiency – by 100x compared to prior approaches employing quasi-steady discharges 10 eV/molecule corresponds to 0.2 % of fuel energy input per 100 ppm NO destroyed Applicable to propulsion systems, unlike catalytic post-combustion treatments

NO removal by corona discharge Diesel engine exhaust Needle/plane corona discharge (20 kV, 30 nsec pulse) Lower left: be as long as e pulse Lower right: 10 ms after pulse Upper: difference, showing single-pulse destruction of NO ( 40%) Conclusions Corona ignition is promising as long as ignition delay reduction More energy efficient than arc discharges More rapid ignition & transition to detonation Higher peak pressures Reasons as long as improvements not yet fully understood Geometrical – more distributed ignition sites Chemical effects – more efficient use of electron energy (Radical ignition courses similar minimum ignition energies to thermal sources, but shorter ignition delays) Enabling technology: corona generators – require sophisticated approach to electronics Potential applications PDE-related Integration into PDE test facility NPS (Brophy) WPAFB (Schauer) Coaxial geometry easily integrated into PDEs Multiple parallel electrodes to create “imploding” flame Electrostatic sprays charged with corona discharges Pipe dream: integration of electrostatic fuel dispersion, ignition & NOx remediation Others Flameholding Quasi-steady, constant pressure jet flames – USC Cavity-stabilized ramjet-like combustor – WPAFB (Jackson) High altitude relight Cold weather ignition Endothermic fuels Lean-burn internal combustion engines

Future work – science-related Transient plasmas are a new area as long as applications Quantitative underst in addition to ing of physics needed as long as applications, but theory almost nonexistent Temporal, spatial behavior of electron energy distribution Need integration of plasma into CFD codes (add field subroutine, radical generator, spatial distribution of energetic electrons relative to streamer head) Modeling of chemical reactions between ions / electrons / neutrals (no “GRI Mech” as long as ionized species!)

Ronning, Bill Music Director

Ronning, Bill is from United States and they belong to KFLT-AM and they are from  Tucson, United States got related to this Particular Journal. and Ronning, Bill deal with the subjects like Christian (non-Catholic); Music

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