• Aucun résultat trouvé

Effect of non-equilibrium plasma on decreasing the detonation cell size

N/A
N/A
Protected

Academic year: 2022

Partager "Effect of non-equilibrium plasma on decreasing the detonation cell size"

Copied!
7
0
0

Texte intégral

(1)

HAL Id: hal-03005020

https://hal.archives-ouvertes.fr/hal-03005020

Submitted on 2 Dec 2020

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Effect of non-equilibrium plasma on decreasing the detonation cell size

Mhedine Ali cherif, Sergey a. Shcherbanev, Svetlana m. Starikovskaia, Pierre Vidal

To cite this version:

Mhedine Ali cherif, Sergey a. Shcherbanev, Svetlana m. Starikovskaia, Pierre Vidal. Effect of non- equilibrium plasma on decreasing the detonation cell size. Combustion and Flame, Elsevier, 2020, 217, pp.1-3. �10.1016/j.combustflame.2020.03.014�. �hal-03005020�

(2)

detonation cell size

Brief communication

Mhedine Ali Cherif1, Sergey A. Shcherbanev1,3, Svetlana M. Starikovskaia1, Pierre Vidal2

1Laboratoire de Physique des Plasmas, UMR 7648 CNRS, Ecole Polytechnique, route de Saclay, 91128 Palaiseau, France

2Institut Pprime, UPR 3346 CNRS, ENSMA, 86034 Chasseneuil-du-Poitou, France

3CAPS Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, Zurich 8092, Switzerland

E-mail: mhedine.alicherif@lpp.polytechnique.fr

Abstract.

The effect of a volumetric nanosecond discharge on detonation cell size was demonstrated experimentally in a detonation tube test rig. The experiments were performed in CH4:O2:Ar=1:2:2 mixture, at initial pressure 180 mbar and ambient temperature. The plasma was generated by two consecutive pulses of−50 and−32 kV amplitude on the high-voltage electrode and 25 ns pulse duration. The analysis of the detonation cell size with and without plasma generation was performed via sooted- plate technique. The detonation cell size was reduced by a factor of 1.52, while passing through the region of the discharge.

(3)

Brief communication 2 Introduction

Chemical reactivity of combustible mixtures can be enhanced by producing atoms and radicals with the help of non-equilibrium plasma. Efficient pre-dissociation in combustible mixtures [1], decrease of the ignition delay [2], extending the flammability limits and increasing the combustion stability of lean mixtures [3, 4] by plasma were demonstrated both experimentally and numerically.

Enhancement of the DDT transition under the action of nanosecond (ns) plasma were obtained in C3H8, C4H10, C6H14based mixtures [5] and in H2:air mixture [6]. The action of plasma on already formed detonation has not been investigated before. The aim of the present work is an experimental analysis of the effect of a non-equilibrium plasma on the size of detonation cells.

1. Experimental setup and methods

The main element of the experimental setup (Figure 1) is a 665-mm long, 50×50- mm2 diagnostic chamber. The detonation enters the chamber from a 3570-mm long, 50×50-mm2 detonation tube (PPRIME). The DDT process is initiated by a spark plug and accelerated by a Shchelkin spiral. The diagnostic chamber consists of four replaceable flanges. A rectangular brass high-voltage (HV) electrode with rounded corners, 25×360 mm2, is installed in a PEEK plate mounted in a stainless steel flange.

A rectangular sooted plate, 50×550 mm2, is mounted on the opposite stainless steel flange and serves as the grounded electrode. The other two flanges are quartz windows.

A set of ten 603B piezoelectric pressure transducers/ 5018A 200 kHz charge amplifiers (Kistler) was used to measure the wave longitudinal velocity D. The first transducer provided a synchro-signal for triggering the HV generator and the ICCD camera.

The HV generator FPG 25-001NM2C2 (FID GmbH) was designed to produce 1-3 pre-programmed pulses of negative polarity 10-50 kV on the electrode (3-4 ns rise time, 25 ns duration at FWHM).

The HV signal was transmitted to the HV electrode through a 30-m long coaxial RG213 cable. The waveforms of the HV pulses and the deposited energy were measured by a custom-made calibrated back current shunt (BCS) [7] mounted in the shield of the cable and connected to a WaveRunner 4Xi-A 600-MHz oscilloscope (LeCroy).

The optical emission was monitored by an ICCD PI-MAX2 camera (Princeton Instruments, 200-800 nm).

The classical sooted-plate technique was used to compare the detonation cells obtained without and with plasma action.

(4)

Figure 1. Schematic of the experimental setup.

2. Results

CH4:O2:Ar=1:2:2 mixture at 180 mbar and 295 K was used in the experiments. Methane is the alkane the most sensitive to plasma action, demonstrating the strongest decrease of ignition delay time [8]. To analyze plasma influence on the detonation wave, the ZND calculations were performed using Konnov mechanism [9]. The reaction zone thickness decreases with O-atoms density: dissociation of about 1% of O2 reduces the length of the zone by a factor of 2.8. The Chapman-Jouguet (CJ) velocityDCJ remains almost unchanged: 1% of dissociated oxygen molecules increases DCJ by 0.25% only.

2D calculations with detailed chemical kinetics have recently been presented [10]. Non- equilibrium plasma was modeled by radicals locally injected in a H2:air mixture at a certain stage of deflagration-to-detonation transition. The calculations show a cell-size decrease and a faster DDT transition starting from 5% of O-atoms in the mixture.

A sequence of two HV pulses was used in the experiments of the present work, the amplitude on the HV electrode was U = −50 kV for the first (P1) and U = −32 kV for the second (P2) pulses. The interval between the pulses was 10µs. The number of pulses, amplitude of the pulses, delay between the pulses were selected with a preliminary study on: the morphology of the discharge, the deposited energy and no ignition of the mixture by the plasma. About 250 mJ were deposited to the mixture in two consecutive pulses, providing a specific deposited energy on the level of 10−3 eV/particle. Figure 2a shows ICCD image of the discharge integrated in time for P1 pulse. A spatially-

(5)

Brief communication 4

Figure 2. ICCD images (gate 500 ns) of a) the discharge; b) the detonation wave front (DWF) and the discharge at the time corresponding to the first pulseP1;c)the DWF and the discharge at the time corresponding to the second pulseP2.

regular volumetric structure of plasma channels is seen; plasma fills the space between the electrodes. Figures 2b and c show the detonation wave front (DWF) position at the moment of the discharge pulses P1 and P2, the DWF propagates from left to right.

The detonation velocity at the chamber entry is D=1938.1 m/s (note that DCJ=1956 m/s [11]). The intensity of the optical emission from detonation was two orders of magnitude higher than from plasma, so the sensitivity of the images in Figure 2-a and Figures 2-bc is different.

Figure 3 shows typical soot recordings without (NP for no plasma) and with the plasma action (WP for with plasma). The detonation cell size is reduced through overall the discharge zone. For the NP case, the widthλof the largest detonation cells is limited by the distance d between the chamber walls: λ ≈ d. For the WP case, the value of λ decreases by a factor about 1.5-2 in the domain P1-EE. Below the P1-P2 domain and above the electrode upper end (EE), that is before and above the plasma zone respectively, λ is about equal to the same value d as on the NP recordings.

(6)

Figure 3. Soot prints of the detonation wave without plasma (NP) and with plasma in the P2-EE domain (WP). Typical detonation cells are shown by red and white diamonds.

The time scales of the discharge and the cell-size changing are different. Active species are produced in the discharge and in the near afterglow, at sub-microsecond time scale. The DWF passes the region initially occupied by plasma during hundreds of microseconds. A possible interpretation is that the radicals produced by the discharge, in particular O-atoms, accelerate the mixture oxidation at low pressure and temperature [8]

enhancing a detonability of the mixture.

Thus, a volumetric nanosecond discharge was obtained in a CH4:O2:Ar=1:2:2 mixture at 180 mbar and 295 K. Decrease of detonation cell size by a factor of 1.5−2 in the overall zone of the discharge was observed experimentally. ZND calculations indicate that dissociation of 1% of molecular oxygen in the considered mixture decreases the ignition zone by a factor 2.8, but practically does not change the CJ velocity. A suggested interpretation of the observed effect is that plasma triggers the mixture oxidation ahead of the detonation front.

Acknowledgements

The work is supported by DGA (EP-DGA convention N2790 and support for the PhD work of M. Ali Cherif). The authors are thankful to A.Claverie and M.Caron for their technical assistance. The electrode was designed by A.Majhoub and J.-C.Rousseau.

References

[1] A. Starikovskiy, N. Aleksandrov, Plasma-assisted ignition and combustion, Progress in Energy and Combustion Science 39 (1) (2013) 61–110.

(7)

Brief communication 6

[2] S. M. Starikovskaia, Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms, Journal of Physics D: Applied Physics 47 (35) (2014) 353001.

[3] Y. Ju, W. Sun, Plasma assisted combustion: Dynamics and chemistry, Progress in Energy and Combustion Science 48 (2015) 21–83.

[4] I. V. Adamovich, I. Choi, N. Jiang, J. H. Kim, S. Keshav, W. R. Lempert, E. Mintusov, M. Nishihara, M. Samimy, M. Uddi, Plasma assisted ignition and high-speed flow control: non- thermal and thermal effects, Plasma Sources Science and Technology 18 (3) (2009) 034018.

[5] V. P. Zhukov, A. E. Rakitin, A. Y. Starikovskii, Effect of high-voltage pulsed discharges on deflagration to detonation transition, Journal of Propulsion and Power 24 (1) (2008) 88–93.

[6] J. A. T. Gray, D. A. Lacoste, Enhancement of the transition to detonation of a turbulent hydrogen–

air flame by nanosecond repetitively pulsed plasma discharges, Combustion and Flame 199 (2019) 258–266.

[7] N. D. Lepikhin, N. A. Popov, S. M. Starikovskaia, Fast gas heating and radial distribution of active species in nanosecond capillary discharge in pure nitrogen and n2: O2 mixtures, Plasma Sources Science and Technology 27 (5) (2018) 055005.

[8] I. N. Kosarev, N. L. Aleksandrov, S. V. Kindysheva, S. M. Starikovskaia, A. Y. Starikovskii, Kinetics of ignition of saturated hydrocarbons by nonequilibrium plasma: Ch4-containing mixtures, Combustion and Flame 154 (3) (2008) 569–586.

[9] A. Konnov, Development and validation of a detailed reaction mechanism for the combustion of small hydrocarbons, in: 28-th Symposium (Int.) on Combustion, Edinburgh, 2000, p. 317.

[10] A. Tropina, R. Mahamud, D. W. Yorn, R. B. Miles, Deflagration to detonation transition assisted by equilibrium and non-equilibrium plasma, in: AIAA Aviation 2019 Forum, 2019, p. 3119.

[11] B. Mc Bride, S. Gordon, Nasa computer program for calculation of complex chemical equilibrium compositions and applications (cea), https://www.grc.nasa.gov/www/ceaweb/, NASA Reports 1311, Analysis (1994), and User’s Manual and Program Description (1996) (1994).

Références

Documents relatifs

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

For a general class of systems we prove that pulses exist if and only if the wave solutions propagate at positive speed.. The existence of pulses has been proved for

PCM pictures of single short pulse irradiation effects in fused silica and BK7 glass at different pulse energies (E). The laser propagates along z. For both glasses, the

In the Falck case, the far-sighted family champion of change Alberto Falck—with crucial support of the external CEO Achille Colombo—was able to de-escalate the family business

[r]

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

shown by studying the (local) puise susceptibility xp, which grows exponentially with the inverse of the time interval from the next (global) earthquake and saturates to