Nanosecond discharges: high power density for …...High pressures, low temperatures Temperature:...

Laboratoire de Physique des Plasmas

Nanosecond discharges: high power density for distributed in space ignition

Svetlana Starikovskaia

Laboratory for Plasma Physics, Ecole Polytechnique, Paris

2

Our scientific team:

Laboratory for Plasma Physics, Ecole Polytechnique, Paris: Sergey Stepanyan, Sergey Shcherbanev Moscow State University, Skobeltsyn Institute of Nuclear Physics: Nikolay Popov PC2A, Lille University of Science and Technology: Mohamed Boumehdi, Guillaume Vanhove, Pascale Desgroux Moscow Institute of Physics and Technology: Ilya Kosarev, Vladimir Khorunzhenko, Victor Soloviev

3

Outline of talk

Introduction. High pressures (7-15 bar), low T (600-1000 K). Do we need very high [O] densities for plasma assisted ignition (PAI)? Rapid compression machine (RCM): ignition by nanosecond discharge. Analysis of experimental results and perspectives Surface dielectric barrier discharge (SDBD): quasi-uniform and filamentary mode Surface dielectric barrier discharge (SDBD): what can we get from E-field measurements by emission? Conclusions

• 150 ms x 2.5 m/ms (M=8) = 375 m

• TGV Eurostar: TransManche Super Train, 393.72 m (20 cars)

A typical ignition length for uniform flow

4

F+O

1998 2001 2004 2007 2010 2013Years

OH

CH

History of plasma assisted combustion

6

Available reviews

Starikovskaia (J. Phys. D 2006) Popov (High Temp. 2007) Adamovich (PSST, 2009) Starikovskaia and Starikovskiy (In: Handbook of Combustion, 2010) Starikovskiy and Aleksandrov (Aeronautics & Astronautics 2011) Popov (43rd AIAA Plasma Dyn. Lasers Conf. 2012) Starikovskiy and Aleksandrov (Progr. Energy Comb. Sci. 2013)

7

Close of faraway from the combustion threshold: what is the difference?

I: wall recombination

II: volume recombination

III: heat dissipation

Parameters of Shock Tube PAI experiments: temperature, pressure, ignition delay time

1 2 3 4 5

1200

1400

1600

1800

2000

PAI

Autoignition

T 5, K

Number of C atoms

1 2 3 4 50

2

4

6

8 Autoignition

PAI

n 5, 10

18 c

m-3

Number of C atoms

1 2 3 4 5

100

101

102

103

10-30 mJ/cm3

PAI

Autoignition

Igni

tion

dela

y tim

e, µs

Number of C atoms

NeQ MIPT Lab, Moscow, 1998-2008

9

Active species produced by plasmas and their role in kinetics

- Rotationally excited molecules (RT-relaxation)

- Vibrationally excited molecules (VT-relaxation+ acceleration of chain branching/prolongation)

- Electronic states (dissociation, chemistry, ∆T)

- Atoms and radicals (chemistry, ∆T)

- Charged particles (chemistry, heating)

“reaction path”: AB+C = A + BC

Ea

k=Aexp(-E /R )a T

Q

(ABC)*

pote

ntia

l ene

rgy

Pressure: 10-15 bar

10

High pressures, low temperatures

Temperature: 600-1000 K

11

Induction time as a function of “atomic oxygen density” (difference:

discharge & cool flame)

1E-3 0.01 0.1 1 10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4 Butane stoichiometric mixture diluted by 76 % of Ar

T0=800 KP0=8.6 bar

OH fr

actio

n

Time, ms

Ignition

Cool flame initiation

1E-3 0.01 0.1 1 108.68.89.09.29.49.69.8

10.010.210.410.6

0 % 0.05 % 0.1 % 0.2 % 0.3 % 0.4 % 0.5 % 0.6 % 0.7 % 0.8 % 0.9 % 1 %

1 %0.9 %

0.8 %0.7 %

0.6 %0.5 %

0.4 %

0.2 %

0.3 %

0 %

0.1 %

T0=800 KP0=8.6 bar

Butane stoichiometric mixture diluted by 76 % of Ar

Pres

sure

, bar

Time, ms

0.05 %Cool flame initiation

Artificial action: O2 -> O + O

(C4H10:O2, ER=1):Ar, P=8.6 bar, T=800 K

D. HEALY, H.J. CURRAN, J.M. SIMMIE et al, Combustion and Flame 155(3): 441-448 (2008).

12

Remark: why discharge is NOT a cool flame

1E-3 0.01 0.1 1 10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

0.5% of O

0.05% of O

Butane stoichiometric mixture diluted by 76 % of Ar

T0=800 KP0=8.6 bar

OH fr

actio

n

Time, ms

Ignition

Cool flame

Relaxation of W leads to ∆T and initiates chemistry

Equilibrium: chemistry leads to ∆T

Ignition delay at additions of O-atoms: weak dependence at [O]>0.5%

13

0.0 0.2 0.4 0.6 0.8 1.0

0

10

20

30

40

50 Tc=800 KPTDC=8.6 bar

Butane stoichiometric mixture diluted by 76 % of Ar

Indu

ctio

n de

lay

time,

ms

Percent of initially dissociated O2

0.0 0.2 0.4 0.6 0.8 1.01

10

Tc=800 KPTDC=8.6 bar

Butane stoichiometric mixture diluted by 76 % of Ar

Indu

ctio

n de

lay

time,

ms

Percent of initially dissociated O2

14

Energy cost for active species in C2H6:O2 mixture: too much dissociation?

0 200 400 600 800 1000

10H

CH3

O(3P)

O2(a1∆g)

Ener

gy c

ost,

eV /

part

icle

E/N, Td

10-30 ns

PSST, 21(2012) 045012

Energy W=50 mJ; volume V=5 mm3: [O] is about 1019 cm-3

15

ICCD image (camera gate is 0.5 ns) of discharge in 1 atm air: “combined” SDBD

16

All the experiments are performed in SINGLE-SHOT regime

±(25-50) kV pulses, 15-25 ns duration, 0.5-3 ns rise time 17

Electrode system and applied pulses

18

Machine at PC2A laboratory, Lille University

19

Combustion chamber for RCM with discharge

Temperature and pressure

High-voltage pulse

RCM core temperature: TC=640-980 K

Pulse duration: 25 ns, front rise time: 0.5 ns

Pulse amplitude on the electrode: ± (24-54) kV

Pressure at Top Dead Center: PTDC=7.5-16 atm

20

Initial parameters of the experiments

3) C4H10/O2/Ar, φ=1, 76 % of Ar

4) C4H10/O2/N2, φ=1, 76 % of N2

1) CH4/O2/Ar, φ=1, 0.5, 0.3, 76 % of Ar

2) C4H10/O2/Ar/N2, φ=1, 38 % of N2, 38 % of Ar

21

Mixtures used in the high pressure (RCM) experiments

Methane is not the easiest fuel to burn

22

0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85100

101

102

103

104

105

CH4-C5H12, PAI, 0.2-0.7 atm

C2H6-C5H12, auto, 0.2-0.7 atm

CH4, auto, 0.4-0.7 atm

CH4, auto, 2 atm

Igni

tion

dela

y tim

e, µ

s

1000/T, K-1

Auto Exp, C2H6 Auto Calc, C2H6 PAI Exp, C2H6 PAI Calc, C2H6, , , C3H8, , , C4H10, , , C5H12

Comb. & Flame, 2008, 2009

Aldehydes and chain branching: RO2 → R’ + R’’CHO R’’CHO + O2 →R’’CO + HO2

aldehyde

D. Healy, N.S. DONATO, C.J. AUL et al, Combustion and Flame 157: 1526-1539 (2010).

Negative temperature coefficient

23

(P,T) - field of RCM ignition experiments

24

n=2 natm

n=4.3 natm

600 650 700 750 800 850 900 950 10006

8

10

12

14

16

Region of calculations

(CH4:O2, φ=0.5) + 75% Ar

(CH4:O2, φ=0.3) + 75% Ar

(C4H10:O2, φ=1) + 38% Ar + 38% N2 (C4H10:O2, φ=1) + 76% N2 (C4H10:O2, φ=1) + 76% Ar

(CH4:O2, φ=1) + 76% Ar

No autoignition

Pres

sure

Pd,

atm

Temperature Tc, K

Induction time decreases significantly 25

0 50 100 150 2000

10

20

30

40

Plasma assisted ignition, U=-24 kVPTDC=14.7 atmTC=972 K

discharge initiation

(blue step)

Pres

sure

, atm

Time, ms0 50 100 150 200

0

10

20

30

40PTDC=14.7 atmTC=972 K

Pres

sure

, atm

Time, ms

Autoignition

Auto- and plasma assisted ignition. CH4:O2:Ar, ER=1, 71% of Ar

26

Confirmed statistically (30 experiments)

58 59 60

20

22

24

26

C4H10/O2/Ar/N2, φ = 1, 38 % of Ar, 38 % of N2

Pres

sure

, atm

Time, ms

Atoignition with knocking

58 59 60

20

22

24

26

C4H10/O2/Ar/N2, φ = 1, 38 % of Ar, 38 % of N2

Pres

sure

, atm

Time, ms

PAI, U=-50 kV

Possible knocking suppression (CH4:O2:N2:Ar, T=730 K)

27

Intermediate modification of pressure profile occurs in experiments with cool flames

0 50 100 150 2000

5

10

15

20

25

Pres

sure

, atm

Time, ms

discharge initiation

(blue step)

PAI, U=-37 kV

20 ms

0 50 100 150 2000

5

10

15

20

25

Pres

sure

, atm

Time, ms

30 ms

Autoignition

0 50 100 150 2000

5

10

15

20

25PAI, U=-35 kV

Pres

sure

, atm

Time, ms

discharge initiation

(blue step)

Cool flame regime modification under the discharge action

28

25 30 35 400

5

10

15

20

P

Pres

sure

, atm

Time, ms

P/2

τ

Discharge initiation

Definition of the ignition delay time

29

Ignition delay time vs voltage/deposited energy. CH4:O2:Ar, ER=0.3 and 0.5, 76% of Ar

0 10 20 30 40 500

50

100

150

200

250

300

350

CH4/O2/Ar, φ = 0.3, 76 % of Ar PTDC=15.5 atmTc=962 K

Indu

ctio

n tim

e, m

s

Voltage on HV electrode, kV0 10 20 30 40 50

0

50

100

150

200

250

300

350

CH4/O2/Ar, φ = 0.5, 76 % of ArPTDC=15.1 atm

Tc=943 K

Indu

ctio

n tim

e, m

s

Voltage on HV electrode, kV

ER=0.3 ER=0.5

30

Ignition delay time vs deposited energy. CH4:O2:Ar, ER=0.3, 76% of Ar

0 5 10 15 20 25 3020

40

60

80

100

120

140

160

180Ig

nitio

n de

lay

time,

ms

Deposited energy, mJ

PTDC=15.1 atm Tc=943 K

31

MIE: minimal ignition energy, CH4:O2:Ar

2 4 6 8 10 12 14 16

0.1

1

10

MIE, 1 bar, 300 K PAI-total, 15 bar, 960 K PAI/channel (qu), 15 bar, 960 K PAI/channel (fil), 15 bar, 960 K

MIE

, mJ

% of CH4 in the mixture

MIE: 1 bar/300 K ns PAI: 15 bar/960 K

<ms

32

820 840 860 880 9000,0

0,5

1,0

40

50

60

70

C4H10/O2/Ar, φ = 1De

lay

time,

ms

Core gas temperatureTc, K

Autoignition PAI, U=-55 kV

Suppression of NTC phenomena by nanosecond discharge (10-20 mJ)

33

NTC region calculation: P=8.6 bar, T=800 K

0 10 20 30 40 50 60

9

10

11

12

13

14 P0=8.6 bar, T0=840 K P0=8.6 bar, T0=800 K

Pres

sure

, bar

Time, ms

cool flame

ignition

600 700 800 900 10000

100

200

300

400 P=8.6 bar P=7.6 bar

Indu

ctio

n de

lay

time,

ms

Temperature, K

Buthane stoichiometric mixture diluted by 76 % of Ar

T=843 K, P=(8.6-7.7) bar, τ=68 msT=844 K, P=(8.6-7.7) bar, τ=68 msT=822 K, P=(8.7-7.8) bar, τ=65 ms

Experimental results:

Experiments are in this region

NTC

65 and 68 ms

34

Calculated (smooth) change of ignition delay time

1E-3 0.01 0.1 1 10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

0.5% of O

0.05% of O

Butane stoichiometric mixture diluted by 76 % of Ar

T0=800 KP0=8.6 bar

OH fr

actio

n

Time, ms

Ignition

Cool flame

35

High speed flame propagation imaging. LaVision Phantom v9 camera

CH4/O2/Ar, Φ = 1, 76% Ar, TC = 911 K, PTDC = 15.4 bar

36

Induction time as a function of deposited energy (Popov’s mechanism)

0.02 0.04 0.06 0.08

0.01

0.1

1

10

275 K4%

207 K3%173 K

2.5%

138 K2%104 K

1.5%

83 K1.2%

70 K1%

Indu

ctio

n tim

e, m

s

Deposited energy, eV/mol

Methane/oxygen mixture diluted by 76 % of ArPgas=960 KPgas=15 bar

Heating and production of O-atoms are taken into account

343 K5%

14 mm

37

Preliminary modeling: coupling of afterglow-combustion kinetics?

1 10 100

1016

1017

1018

0.05 eV/mol

CH2O

H2OOH

CH3

H

O(1D)

O(3P)

Dens

ity, c

m-3

Time, ns

38

- 24 kV discharge; O2: Ar; T=300 K; P=3.2 bar

0.5 ns 2 ns 13 ns

21 ns 27 ns 35 ns

-10 0 10 20 30 40

-25

-20

-15

-10

-5

0

Volta

ge, k

V

Time, ns

U = + 24 kV on the electrode

2 ns ICCD gate

39

+ 24 kV discharge; O2: Ar; T=300 K; P=3.2 bar

0.5 ns 2 ns 4 ns

12 ns 17 ns 40 ns

U = + 24 kV on the electrode

-10 0 10 20 30 40

0

5

10

15

20

25

Volta

ge, k

V

Time, ns

2 ns ICCD gate

Quasi-uniform (“diffusive”) and filamentous modes

40

ICCD imaging: air, gate=2 ns. Emission of the 2+ system of molecular nitrogen

41

0 30 60 90 120 150 180 210 240-30

-20

-10

0

10

20

305 atm, -55 kV

Volta

ge in

cab

le, k

V

Time, ns0 30 60 90 120 150 180 210 240

-30

-20

-10

0

10

20

303 atm, -35 kV

Volta

ge in

cab

le, k

V

Time, ns

Oscillograms corresponding to different high pressure discharge modes

42

Uniform-filamentary transition: 337 nm spectra

335.0 335.5 336.0 336.5 337.0

0.01

0.1

1

Inte

nsity

, a.u

.

Wavelength, nm

region 0-2 mm from HV electrode region 3-5 mm from HV electrode theoretical fit, T=360 K

P=1 atm, U=-24 kVt=5 ns

335.0 335.5 336.0 336.5 337.00.01

0.1

1

t=40 nsIn

tens

ity, a

.u.

Wavelength, nm

Filamentous Theoretical fit, T=420

Transition between quasi-uniform and filamentous modes, synthetic air

1 2 3 4 5 638

40

42

44

46

48

50

52Vo

ltage

am

plitu

de o

n HV

ele

ctro

de, k

V

Pressure, bar

Negative polarity pulses

P= 3 bar, U=-47 kV on the HV electrode

Diffusive beginning (first 6 ns)

Transition to filaments

Filamentous

Transition between quasi-uniform and filamentous modes, synthetic air

45

Uniform-filamentary transition, P=3 atm in synthetic air: deposited energy

20 25 30 35 40 45 50 55

0

20

40

1 atm, synthetic air

Depo

site

d en

ergy

, mJ

Voltage, kV

3 atm, synthetic air

transition filamentousquasi-uniform

46

Uniform-filamentary transition, P=3 atm, air: currents and emission

0 5 10 15 20 25 30 35 40

-60

-40

-20

0

20

40

60

80

1.6 A/ch

1.8 A/ch

Curr

ent,

A

Time, ns

Mode: quasi-uniform transtion filamentous

0.1 A/ch

0 5 10 15 20 25 30 350.0

0.2

0.4

0.6

0.8

1.0

1.2

Inte

nsity

, a.u

.

Time, ns

Mode: quasi-uniform transition filamentous

Transition point

Electrical current 337 nm emission

47

Electric field in SDBD: emission measurements, 391/337 ratio

][1

][1

) ]([) ]([

)(

0

)(

0

2

2

2

2

Mk

Mk

CNBN

kk

CNq

C

BNq

B

C

B

Σ+

Σ+×=

+

+

τ

τ

''''''

0

..* ][

vvvv

l u m

Ah vIN τ

= KII

kk

C

B

C

B ×= Measured

εεεεεσ dfm

ke

e x c )(.2) .(∫=

=

NEf

kk

C

B

Calculated

(**)

48

Emission measurements, 391/337 ratio: experimental calibration

P Paris, M Aints, F Valk, T Plank, A Haljaste, K V Kozlov and H-EWagner J. Phys. D: Appl. Phys. 38 (2005) 3894–3899

R391/337=0.07 E/N = 600 Td

- assumption about the plasma uniformity: not true 49

0 1 2 3 4 50

1

2

3

4

Dry air, edge of HV electrode, P=4 atm, U=+24 kV

Inte

nsity

, a.u

.

Time, ns

337.1 nm

391.4 nm

0 1 2 3 4 50

200

400

600

800

1000 Dry air, edge of HV electrode, P=4 atm, U=+24 kV

E/N,

Td

Time, ns

Intensity of 391.4 and 337.1 nm emission; Electric field in air at 4 atm and +24 kV

Electric field is higher in case of positive polarity pulses

High values of the E-field right after peak 50

0 1 2 3 4 50

200

400

600

800

1000

1200 Dry air, edge of HV electrode, P=1 atm, U=+24 kV

E/N,

Td

Time, ns0 1 2 3 4 5

0

200

400

600

800

1000

1200 Dry air, edge of HV electrode, P=1 atm, U=-24 kV

E/N,

Td

Time, ns

Comparison of “E-field” in positive and negative polarity pulses

- higher values of the electric field for positive polarity

- higher P → lower Emax 51

Discharge: T=300 K; P=5 atm

RCM: T=900 K; P=15 atm

W=10-30 mJ 1 2 3 4 5

300

400

500

600

700

800

900

1000

Max

imal

E/N

, Td

Pressure, atm

Positive polarity Negative polarity

Dry air, edge of HV electrode, ±24 kV

Comparison of “E-field” in positive and negative polarity pulses vs pressure

V R Soloviev and V M Krivtsov, J. Phys. D: Appl. Phys. 42 (2009)

measured ch gapI I I= +

The same order of Ich and Igap is possible 52

Principal explanation of observed results

53

Results of numerical modeling (Soloviev)

0 0.2 0.4 0.6 0.8 1 1.2 1.40

0.1

0.2

y,

E/N =f(x,y,t) I(N2(C))=f(x,y,t)

I(N2+(B))=f(x,y,t)

I(N2(C)) I(N2

+(B))=f(x,y,t) integrated over Y

Ratio of integrals

54

Electric field in the discharge: analysis of numerical modelling

0.00 0.05 0.10 0.15 0.20 0.25

0.00

0.02

0.04

0.06

0.08

U=+24 kV: <200 TdRatio

of I

nteg

rals

391

/337

ove

r Y

Y,mm

391/337; 0.002 mm, -24kV 391/337; 1 mm, -24kV 391/337; 2 mm, -24kV 391/337; 3.35 mm, -24kV 391/337; 0.002 mm, +24kV 391/337; 0.004 mm, +24kV 391/337; 3 mm, +24kV 391/337; 5 mm, +24kV 391/337; 7 mm, +24kV 391/337; 8 mm, +24kV 391/337; 8.1 mm, +24kV

U=-24 kV: 400-430 Td

55

Electric field in the discharge: analysis of numerical modelling

1 2 3 4 5 6 7 8 90.00

0.05

0.10

0.15

0.20

0.25

0.30

Ratio

of i

nteg

rals

of e

miss

ion

391.

4/33

7.1

alon

g O

Y

X, mm

-24 kV, t=2.15 ns +24 kV, t=4.85 ns +24 kV, t=0.75 ns

Calculations

56

Electric field in the discharge: analysis of numerical modelling

100 100010-4

10-3

10-2

10-1

100

+24 kV, calculations

-24 kV, calculations

-24 kV, measurements

Ratio

of i

nteg

rals

, A, a

nd b

ase

curv

e, R

(391

/337

)

E/N, Td

+24 kV, measurements

57

Conclusions

Low T, high P: The ignition delay time decreases significantly under the action of nanosecond SDBD, from tens and hundreds milliseconds to units of milliseconds at deposited energy within a range 10-30 mJ. It is possible to describe qualitatively the results taking into account O-atoms production and ∆T. Starting from some O-density, ignition delay time remains close to a fixed value determined by gas mixture composition. NTC region and cool flame kinetics are significantly influenced by addition of radicals. Detailed discharge-combustion mechanism for heavy hydrocarbons is a challenge. Uniform discharge is a challenge. Discharge study is necessary for each range of conditions. Multipoint ignition is efficient.

58

Acknowledgements

-EOARD AFOSR

- Russian Foundation for Basic Research

-ANR, French National Agency for Research, Project PLASMAFLAME (2011-2015)

- PUF Collaborative Grant (Ecole Polytechnique-Princeton University)

- French Academy of Science (CNRS) / Russian Academy of Science (RAS) collaborative grant No 23994 2010-2012) and PICS-RFBR grant (5745-11.02.91063-a/5745)

59

Thank you for your attention… …You are invited

4th Aerospace Thematic Workshop “Fundamentals of aerodynamic-flow and combustion control by plasmas” CNRS Conference Centre Paul Langevin, Aussois, France 7-12 April, 2013; the next is in 2015 Questions: Restrictions for March 2013? Program?

60

PAI/PAC task formulation: assumptions

- Initial mixture parameters are the following: (F+O+D) mixture of known composition; - Initial gas pressure is P; - Initial gas temperature is T

- Plasma is nonequilibrium (Te>>Tg, shorter than needed to arc transition) and can be modeled by E/N(t), [70-200 Td], and ne(t)

- The PAI/PAC problem can be considered in 0D;

61

Plasma action (tens-hundreds of ns)

Drawbacks: For fuels, no self-consistent data set is available for higher hydrocarbons

Advantages: for majority of oxidizers and diluters, the discharge action is well-known: the sets of cross-sections measured by using electron beams technology (60th-70th) are self-consistent and verified on the basis of the experimentally measured swarm parameters (ionization coefficient, drift velocity, electron mobility)

{E/N(t), ne(t)} EEDF(t) M+, M*, A*, M(v)

62

Afterglow (hundreds of ns - ms)

Drawbacks: the main classes of reactions are well-known, but a lack of data is observed when trying to describe the details of minor species behavior in chemically active mixtures

Advantages: ”plasma” and “combustion” kinetics are separated in time; “plasma” kinetics with participation of electronically and vibrationally excited species is well known at room temperatures for N2, O2, Ar…

{ne, M+, M*, A*, M(v), E/N->0 } kinetics, T

63

Ignition: µs – ms, f(P, T, composition)

Drawbacks: There is no ready mechanism for the low-temperature ignition: it must be built as an intersection of available “pure” oxidation mechanism, “common” combustion mechanism and “plasma” action.

Advantages: main classes of plasma-gas interaction are well-known, there is no risk to miss a whole class of chemical transformation; although special attention and detailed literature analysis is needed to know the limits of used kinetic schemes.

{M*, A*, M(v), T} “combustion” kinetics

64

Peculiarities and universal (C1-C3) and extended (low T) mechanisms

GRI C3 -- GRI C30

500

1000

1500

2000Number of reactions

Number of species

CH4/C2H6/C3H8 oxidation at high P and high, intermediate and low T (2008)

289 species 1580 reactions

D. HEALY, H.J. CURRAN, J.M. SIMMIE et al, Combustion and Flame 155(3): 441-448 (2008).

65

ICCD imaging: air, gate=0.5 ns, P=1 atm, U=-22 kV (time in ns)

I N Kosarev, V.I. Khorunzhenko, E. I. Mintoussov, P.N. Sagulenko, N.A. Popov, S.M. Starikovskaia, Plasma Sources Sci. Technol. 21 (2012) 045012 (15pp)

Ignition by spark discharge: 1 atm of C2H6:O2=2:7, Tin=300 K

Single pulse spark discharge ignition of C2H6:O2=2:7 at 1 bar and ambient temperature.

Plasma Sources Sci. Technol. 21 (2012) 045012 (15pp)

67

Ignition by surface DBD at 1 atm, C2H6:O2

Plasma Sources Sci. Technol. 21 (2012) 045012 (15pp)

68

Preliminary numerical modelling: CH4:O2:Ar. P=20 bar; T=950 K

Autoignition Ignition initiated by 0.05% of O 45 ms 9 ms

69

Preliminary numerical modelling: n-C4H10:O2:Ar. P=8 bar; T=700 K

Autoignition

Ignition initiated by 0.05% of O 43 ms 6 ms

Cool flame: 37 ms Cool flame: 2 ms

70

Comparison of experiments and numerical modeling: all (CH4-C5H12) mixtures

0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85100

101

102

103

104

105

CH4-C5H12, PAI, 0.2-0.7 atm

C2H6-C5H12, auto, 0.2-0.7 atm

CH4, auto, 0.4-0.7 atm

CH4, auto, 2 atm

Igni

tion

dela

y tim

e, µ

s

1000/T, K-1

Auto Exp, C2H6 Auto Calc, C2H6 PAI Exp, C2H6 PAI Calc, C2H6, , , C3H8, , , C4H10, , , C5H12

I N Kosarev, N L Aleksandrov, S V Kindysheva, S M Starikovskaia, A Yu Starikovskii, Combustion and Flame, 156 (2009) 221-233