Plasma Assisted Combustion...AFOSR MURI November 9 –10, 2011 Fundamental Mechanisms, Predictive...
Transcript of Plasma Assisted Combustion...AFOSR MURI November 9 –10, 2011 Fundamental Mechanisms, Predictive...
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Plasma Assisted Combustion:Discharge Energy Balance, Bootstrap Effect in Plasma-Chemical Kinetics
1. Nano-Second Pulse Plasma Ignition Below Self-Ignition Threshold• LIF, PLIF, CRD Experiments
2. Energy Efficiency of Plasma Assisted Combustion• Kinetic Modeling of Discharge Energy Balance • Combustion Assisted Plasma • Modeling of Bootstrap Effect in PAC
AFOSR MURI ● November 9-10, 2011Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion
Modified Team:
AlexanderFridman
MikhailPekker
LiangWu
DanilDobrynin
AndreyStarikovskiy
NickCernansky
DavidMiller
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Energy Efficiency of Plasma Assisted Combustion (Scramjet)Kinetic Modeling of Active Species Energy Cost in Different Discharges
AFOSR MURI ● November 9 – 10, 2011Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion
7.4 ns
Streamer Discharge (300 Td)
Dielectric Barrier Discharge
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PAC Energy Efficiency, Modeling of Transitional DischargesCombustion Assisted Plasma, 1D Methane-Air Modeling
o If W ≈ 10 eV, G~10 (transitional discharges, microwave/gliding arcs, non-premixed: collective effects)
• 0.01 eV/mol (≈ 30 K)• specific enthalpy H ≈ 0.03
MJ/kg • total flow enthalpy 1.5 – 2.5
MJ/kg at M = 5 – 7• power 10 MW/m2
o If W ≈ 0.3 – 1 eV, G~100-300 (transitional discharges, partially premixed, combustion assisted plasma; Gmax, exp ~ 3000 for PO)
• 0.0003 - 0.001 eV/mol (1-3 K)• specific enthalpy H ≈ 1 – 10
kJ/kg • total flow enthalpy 1.5 – 2.5
MJ/kg at M = 5 – 7• power 0.3 – 1 MW/m2
AFOSR MURI ● November 9 – 10, 2011Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion
Gliding Arc
GAT
MW
Not only radicals/excited species/ions but easy-to-ignite intermediates (CH2O, CH3OH, etc.) play role in PAI
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Nano-Second Pulse Plasma Ignition Below Self-Ignition Threshold
Laser Induced Fluorescence
Methane 300 K
OH Planar LIF
Cavity Ring-Down Spectroscopy
• Three different diagnostic methods
• Homogeneous [OH] distribution along
the discharge channel
• Long life time of OH at low
temperature below ignition threshold
Methane 500 K @2 μs delay
AFOSR MURI ● November 9 – 10, 2011Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion
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Time resolved PLIF and CRDS diagnostics of OH radicals in the afterglow of plasma discharge in hydrocarbon mixtures
•Methane / Air mixture•Equivalence ratio: Lean (φ=0.1)•Temperature regimes:
Room temperature, 300 KElevated temperature, 500 K
•Premixed and preheated flowFlow rate ~20 cm/s
Liang Wu, J. Lane, N. Cernansky, D. Miller, A. Fridman, A. Starikovskiy, 7th US National Combustion Meeting, Atlanta, March 20-23, 2011
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PLIF diagnostics has shown quite homogeneous
distribution of OH formation along the discharge channel
CRDS has provided the absolute [OH] which can be further
used for kinetic model development
Liang Wu, J. Lane, N. Cernansky, D. Miller, A. Fridman, A. Starikovskiy, 7th US National Combustion Meeting, Atlanta, March 20-23, 2011
Time resolved PLIF and CRDS diagnostics of OH radicals in the afterglow of plasma discharge in hydrocarbon mixtures
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What causes the oxidation chemistry in afterglow?
T = 300 K 1D CH4-Air Mixture Kinetic Modeling (Konnov & GRI Mechs) with Analysis of Contribution of:1. Plasma generated radicals (O, OH ~10-4 – 10-3)
• Disappear within ~1-10 ms
2. Positive and negative ion catalysis (lifetime ~10 ms, low contribution, Langevin model)• HO2 + H2(M+) → OH + H2O + M+
• O2- + H2 → OH- +OH
• OH- + H(HO2) → H2O (+O2) + e• e + O2(+M) → O2
-
3. Plasma generated NO (~10-3 – 10-2, low contribution)• NO + HO2 → NO2 + OH• H + NO2 → NO + OH
4. Plasma generated excited species (unknown kinetics, alpha model)• HO2(group) + (N2
*) → OH + O + N2
• CH3O2 + (N2*) → CH2O + OH + N2
5. “Bootstrap” effect• Indirect effect of plasma (change of
macroparameters: T, stable components)• Plasma chemistry/reforming add’l heating• Plasma chemistry/reforming change of mixture
T = 500 K
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Plasma assisted combustion mechanisms
Plasma catalysis
Chain reactions sustained by ions and excited species
Bootstrap effect
• Indirect effect of plasma (change of macroparameters:
temperature and stable components) to shorten ignition delay
• Plasma chemistry/reforming additional heating due
to chain oxidation by primary plasma species
• Plasma chemistry/reforming change of mixture due
to chain oxidation by primary plasma species (formation of
small amount of easy-to-ignite stable species)
Munchausen effect
Thermal effectNon-Thermal Radical effect
Radical chains terminate below autoignition limit
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Bootstrap Effect in Plasma-Assisted Ignition (Atmospheric Pressure Methane-Air Mixture at Temperatures Below Auto-Ignition Limit)
Heating due to radicals: 12K
Kinetic Modeling (Konnov’s Mechanism); T0 = 960 K, direct discharge heating: 40 K, 10-3 [O]
Disappearance of radicals
Accumulation of easy-to-ignite stable species
Ignition delay
Bootstrap effect: plasma induced change of primary ignition macroparameters (T, Comp.)
OH OCHOCH
OH CHCHOH
22 3
2 34
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Bootstrap coefficient:
Effective increase of temperature
exceeds direct plasma heating
heat
compRheat
heat
0eff
compRheat0eff
ΔT
ΔTΔTΔT
ΔT
TTK
ΔTΔTΔTTT
For the example above: K=3
DTheat – Direct heat 40KDTR – Heat due to radicals 12KDTcomp – Effective heating due to
change of composition (CH2O) 68K
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Bootstrap Effect in Methane-Air Mixture:change of composition (plasma reforming, CH2O) contributes more than radical heating
Direct heating:[CH4]=0.0944, [O2]= 0.189 [N2]=0.7130 [O]=0.001T0=960K, P0=1atm. G-factor for O = 6.0===========================DTheat =40K
[O]=0.001Tin=DTheat+T0=40+960=1000[K]
Temperaturebefore discharge
Direct Heating
Bootstrap effect
Heatingdue to
Radicals
Effective Heatingdue
to change of composition
960K DTheat=40 K
DTR=12 K DTcomp=68K
3ΔT
ΔTΔTΔTK
heat
compRheat
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Bootstrap Effect in Methane-Air Mixture:effect of initial temperature, 5·10-4 [O]
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Bootstrap Effect in Methane-Oxygen Mixture
Direct heating (estimation):[CH4]= 0.0944, [O2] = 0.9051 [O] = 0.0005T0=979K, P0=1atm.G-factor for O = 8.0
DTheat=15.6K [O]=0.0005T0=DTheat+Tin=15.6+984.6=1000[K]
Temperaturebefore discharge
Direct Heating
Bootstrap effect
Heatingdue to
Radicals
Effective Heating due to change of composition
984.6K DTheat=15.6 K
DTR=21 K DTcomp=83.3 K
D
OH OCHOCH
OH OCHOCH
OH CHCHOH
2
1
2 3
22 3
2 34
[O2(1D)]=0.002
OH OCHOCH
OH CHCHOH
22 3
2 34
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Bootstrap Effect in Ethylene-Air Mixturequazi-stable intermediates CH2O, HO2
22
342
HOCOOHCO
OHCOOHCO
HCOCHOHC
3242
223
CHOCHOHHC
OHOCHOCH
Production of radicals and HO2
Chain reactions
0
0.0002
0.0004
0.0006
0.0008
0.001
0 0.00001 0.00002 0.00003 0.00004 0.00005
Time(s)
O
OH
HO2
CO
CH3
CH2O
850
852
854
856
858
860
862
864
0 0.00001 0.00002 0.00003 0.00004 0.00005
T[K
]
Time(s)
Direct heating (estimation):[C2H4]= 0.066, [O2] = 0.198 [N2]=0.735[O] = 0.001 P0=70tor.
DTheat=42.4 K [O]=0.001T0=DTheat+Tin=42.4+807.6=850 [K]
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Bootstrap Effect in Ethylene-Air Mixture
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
1000
1200
1400
1600
1800
2000
2200
2400
2600
Time(s)
T
[K]
T=850 O=0.0001
T=850
T=865
T=865 CH2+Radicals
T=865 H2O
K=3.2Teffect=943K
Temperaturebefore discharge
Direct Heating
Bootstrap effect
Heatingdue to
Radicals
Effective Heating due to change of composition
807.6 K DTheat=42. 4K
DTR=15. 4K DTcomp=77.6K
T[K] [O] [CH3]+[OH] [CH2O] [HO2] Delay time (s)
850 0 0 0 0 6.75
850 0.001 0 0 0 0.675
865 0 0 0 0 4.61
865 0 0.0003+0.000016 0.000537 0 1.052
865 0 0 0 0.000232 0.756
Direct heating (estimation):[C2H4]= 0.066, [O2] = 0.198 [N2]=0.735[O] = 0.001 P0=70tor.
DTheat=42.4 K [O]=0.001T0=DTheat+Tin=42.4+807.6=850 [K]
quazi-stable intermediates CH2O, HO2
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Plasma assisted combustion mechanisms
Plasma catalysis
Chain reactions sustained by ions and excited species
Bootstrap effect
• Indirect effect of plasma (change of macroparameters:
temperature and stable components) to shorten ignition delay
• Plasma chemistry/reforming additional heating due
to chain oxidation by primary plasma species
• Plasma chemistry/reforming change of mixture due
to chain oxidation by primary plasma species (formation of
small amount of easy-to-ignite stable species)
Munchausen effect
Thermal effectNon-Thermal Radical effect
Radical chains terminate below autoignition limit
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Plasma Fuel Reforming vs Plasma Assisted Ignition
CH4
[L/min]
Air
[L/min]
[O/C] W
[watt]
From Discharge
[eV/molec]
From Reaction
[eV/molec]
Total
[eV/molec]
Add Air
[L/min]
Total
[eV/Molec]
5.39 20.09 1.55 480 0.26 0.074 0.34 (DT≈876K) 31.42 0.15 (DT≈390K)
Ignition temperature
about 700K
H2 CO CO2 N2 CH4 C2H4 C2H2 O2
12.15 5.97 0.50 60.74 12.043 0.21 0.79 9.59
Reforming Mixture
CH4 + Air Reforming Mixture +Air
T=1025K(delay ⋍ 0.1s) T= 850 K(delay 0.1s)
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AFOSR MURI ● November 9 – 10, 2011Fundamental Mechanisms, Predictive Modeling, and Novel Aerospace Applications of Plasma Assisted Combustion
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