22F03
Transient phenomena in a premixed burner flame superimposed with adielectric barrier discharge
誘電体バリア放電重畳予混合バーナー火炎における過渡現象
Kazunori Zaima1, Haruaki Akashi2, Akihiro Kono1 and Koichi Sasaki3
財満和典1, 明石治朗2，河野明廣1，佐々木浩一3
1

Department of Electrical Engineering and Computer Science, Nagoya University,Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan1
名古屋大学大学院工学研究科電子情報システム専攻，〒464-8603 名古屋市千種区不老町
2
Department of Applied Physics, National Defense Academy of Japan, 1-10-20 Hashirimizu, Yokosuka 239-8686,Japan2
防衛大学校応用物理学科，〒239-8686 神奈川県横須賀市走水一丁目10-20
3Division of Quantum Science and Engineering, Hokkaido University,Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan3
北海道大学大学院工学研究院量子理工学部門，〒060-8628 札幌市北区北13条西8丁目
We are investigating control methods of combustion chemical reactions by superimposing nonequilibrium
plasmas. In this work, we activated combustion chemical reactions by superposing a dielectric barrierdischarge (DBD) onto a premixed burner flame with methane/oxygen/argon mixture. We observed
transient phenomena in the flame using a CCD camera with a gated image intensifier when we excited
DBD by pulsed high voltage.

1. Introduction
Development of new combustion technologies
is necessary to reduce the consumption of fossil
fuels and to avoid the global warming due to theemission of CO2. Normal combustion is sustainedby chemical reactions under thermodynamicequilibrium.
Innovations
incombustion
technologies are considered to be difficult under
the limitation of thermodynamic equilibrium. On
the other hand, the activation of combustion
chemical reactions would be possible with thehelp of plasma which could produce radicals suchas oxidants and resolved fuels by electron impact
processes. We are investigating mechanisms andcontrol of combustion chemical reactions bysuperimposing a dielectric barrier discharge(DBD) onto a premixed burner flame. We haveobtained experimental results which suggest
enhanced burning velocity. The enhanced burning
velocity may be attributed to new pathways ofcombustion reactions with the help ofhigh-energy electrons in DBD.
In this work, we examined transientphenomena in the premixed burner flame bycapturing the optical emission image using aCCD camera with a gated image intensifier.
2. Experimental setup
We superimposed coaxial-type DBD onto apremixed burner flame with methane/oxygen/argon
mixture. Figure 1 shows a schematic illustration of
the experimental apparatus. A burner waselectrically grounded, and the nozzle was attached
on a dielectric base plate. The burner nozzle played
a role of the ground electrode. A slender flame wascovered with a quartz tube. An aluminum electrode
was attached on the outside of the quartz tube, andit was connected to a high-voltage, low-frequency
power supply, resulting in DBD inside the quartz
tube. The power supply consisted of a function
generator (HP 8116A) and a high-voltage amplifier(Trek Japan 10/10B). In the following experiments,
the flow rates of methane, oxygen, and argon were0.38, 1.0 and 5.6 slm, respectively, corresponding
to an equivalence ratio of 0.76. The discharge
power evaluated from a V-Q Lissajous curve,
which was approximately 3W, was 2% of theDG
Interference
filterICCD
CameraAMPFG

Premixed GasFig. 1 Experimental apparatus.

chemical power yielded by combustion reactions.
3. Experimental results and discussion
In the first experiment, the pulse frequency and thevoltage were set at 1 kHz and ±8 kV, respectively,
and the distance between the electrodes was set at
80 mm. We synchronized the trigger to the gate of
the ICCD camera with the pulsed voltage, and theorigin of the time axis in the following results is therise time of the pulsed voltage. The gate width was
25 µs. We attached interference filters in front of
the ICCD camera to separate the optical emissionsof OH and Ar from other emissions. The results
shown in Fig. 2 were observed at delay times
between 475 and 600 µs. From these pictures, weconfirmed that the bright emission of Ar wassynchronized with that of OH and the bright area ofthe Ar emission was the same as that of the OHemission. The optical emission image of Ar at 550µs suggests that the pathway of the discharge
current is the flame region, since the opticalemission of represents the location of high-energy
electrons. Hence the enhancement of the opticalemission intensity of OH is considered to be mainly
caused by electron impact excitation.
In the second experiment, the pulse frequency andthe voltage were set at 2 kHz and +8 kV,
respectively, and the distance between theelectrodes was set at 15 mm. Figure 3 shows theoptical emission image of OH at various delaytimes. According to these pictures, discharges
occurred at delay times of 25-50 and 275-300 µs.
On the other hand, it was observed that the lengthof the flame was shortened at any delay times. The
shortened flame length indicates the enhancementof the burning velocity in the flame. Hence, it issuggested that the lifetimes of chemically active
species, which are produced by electron impact
processes, are much longer than the period of thepulsed voltage as well as the discharge duration,and the enhanced combustion state is sustained fora long time by DBD with a short duration. Inaddition, the experimental results indicate that thesuperposition of DBD onto the bottom part of theflame changes the entire shape of the flame, which
also suggests the long lifetimes of chemically active
species.

ArOH

Delay time 475
[µs]

500

525

550

575

600

Fig. 2 The comparison of the emission
from Ar and OH radicals

Delaytime W/O DBD 0[µs]255075

100

125

150

175

200

225

250

275

300

325

350

375

400

425

450

475

Fig. 3 The change in the flame shapeand the emission intensity from OH
radicals