Two types of nanosecond spark discharges in atmospheric air

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Two types of nanosecond spark discharges in atmospheric air

Nicolas Minesi, Sergey Stepanyan, Erwan Pannier, Pierre Mariotto, Gabi Stancu, Christophe O Laux

To cite this version:

Nicolas Minesi, Sergey Stepanyan, Erwan Pannier, Pierre Mariotto, Gabi Stancu, et al.. Two types of nanosecond spark discharges in atmospheric air. 70th Gaseous Electronics Conference, Nov 2017, Pittsburg, United States. �hal-01866390�

400 500 600 700 0

10 20 30

N 2 (B - A)

Intens ity (a .u. )

 (nm)

4 ns 12 ns 22 ns

N 2 (C - B)

Measurements

400 500 600 700

0 5 10 15 20 25 30

400 420 440 460 480 500

1 2 3 4

O + N +

N + N

2

(C)

 (nm)

Intens ity (a .u. )

Time :

4 ns 12 ns 22 ns

Measurements

 (nm)

Int . (a .u.)

Two types of nanosecond spark discharges in atmospheric air

[1] E Sher, J Ben-Ya’Ish, and T Krachvchik, 1992, Combustion and flame, 89 186

[2] A Lo, A. Cessou, C Lacour, B Lecordier, P Boubert, D A Xu, C O Laux and P Vervisch, 2017, PSST, 26 045012 [3] D L Rusterholtz, D A Lacoste, G D Stancu, D Z Pai, C O Laux, 2013, J. Phys. D: Appl. Phys., 46 464010

[4] D Z Pai, D A Lacoste, C O Laux, 2010, PSST, 19 065015

[5] H L Olsen, R B Edmonson, E L Gayhart, 1952, J. Appl. Phys., 23 1157

[6] S Stepanyan, J Hayashi, A Salmon, G D Stancu, C O Laux, 2017, PSST, 26 04LT01

References Conclusions

Two regimes of spark discharges have been evidenced: contracted and non- contracted sparks. A correlation between spark contraction, emission of N ⁺ /O ⁺ and toroidal expansion [5,6] has been found. In future work, we aim to determine which parameters trigger this transition.

Repetitive nanosecond sparks have potential applications in combustion:

• Ignition & stabilization of lean/diluted flames

• Control of thermo-acoustic instabilities

• Reduction of pollutant emission (soot, NO _x )

Fully ionized sparks in air were predicted [1] and recently observed [2] in nanosecond discharges. This is in contrast with the partially ionized sparks of [3, 4].

Motivation Experimental setup

Nanosecond sparks are investigated in air (300 K, 1 atm) by (i) OH planar LIF and (ii) Optical Emission Spectroscopy

Laboratoire EM2C, CNRS, CentraleSupélec, Université Paris-Saclay, France

N. Minesi, S. Stepanyan, E. Pannier, P. Mariotto, G.D. Stancu, С.O. Laux

-0,4 -0,2 0,0 0,2 0,4 0,0

0,5 1,0

No rm aliz ed In ten sity ( a.u .)

Radius, mm

Time:

4 ns 12 ns 22 ns

Imaging of ns discharge

After transition (t > 7ns), we observe:

➢ Contraction of conductive channel radius

➢ Stark broadening

➢ [N ⁺ ]/[O ⁺ ] = 4. 1 (± 1.0)

→ LTE @ 38,600K gives 3.8

OH PLIF (ambient air)

E = 1.5 mJ

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

450 460 470 480 490 500 510 520 530 -0,1

0,0 0,1

O

⁺

(29 eV)

Inte ns ity (a .u.)

Measurement - t = 22 ns SPECAIR - N

⁺

SPECAIR - N

⁺

and O

⁺

N

⁺

(23 eV)

N

⁺

(30 eV) N

⁺

(21 eV)

Fits of t = 22 ns

 (nm)

Residual

Non-contracted spark (E/N = 200 Td)

(P = 1 bar, 6-mm gap, single pulse of 10 ns)

OH PLIF in pin-to-pin geometry

E = 3.5 mJ

Imaging of ns discharge

➢ Emission: N ₂ first and second positive system

➢ Cylindrical expansion of the active medium

➢ n _{e, max} = 2 x 10 ¹⁵ cm ^-3 [3]

➢ T _max = 2500 K [3]

Transition to contracted spark (E/N = 440 Td)

(P = 1 bar, 1-mm gap, single pulse of 10 ns ⁾

4 ns 12 ns

Scale: 0-100 Scale: 0-5

4 ns 22 ns

1 mm 6 mm

OH simulations

E = 0.8 mJ

6 mm

1 mm

➢ Emission: N ⁺ , O ⁺ , free-free & free-bound continuum

➢ Toroidal expansion

➢ n _{e-, max} = 1.2 (± 0.2) x 10 ¹⁹ cm ^-3

➢ T _e = T _N+ = T _O+ = 39,000 (± 4000) K

5 mm 3 mm

[Castela, Stepanyan, Fiorina, Coussement, Gicquel, Darabiha, Laux , 2017, Proc. Comb. Inst. 36 4095]

-1,2 -0,8 -0,4 0,0 0,4 0,8 1,2

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

No rm aliz ed in ten sity ( a.u .)

Radius, mm

4 ns 12 ns

Scale: 0-100 Scale: 0-100

20 μs 50 μs 150 μs

20 μs 50 μs 150 μs