23P009-O
Electron behaviors in methane and air pre-mixture gas flame under microwave
electric field
マイクロ波照射による空気メタン予混合ガス火炎中の電子の挙動
Haruaki Akashi1, Tomokazu Yoshinaga1, Koichi Sasaki2
明石 治朗1, 吉永 智一1，佐々木 浩一2
1

Dept. Appl. Phys., National Defense Academy, 1-10-20 Hashirimizu Yokosuka, 239-8686, Japan
防衛大学校 応用物理学科 〒239-8686 横須賀市走水1-10-20
22Div. Quant. Sci. and Eng., Hokkaido University, N13-W8 Kita Warad, Sapporo, 060-8628 , Japan
北海道大学大学院 量子理工学部門 〒060-8628 札幌市北区北13条西8丁目

Recently, plasma-assisted combustion has been focused on for achieving more efficient combustion
way of fossil fuels and so on. Shinohara et al has reported that the flame length of methane and air
premixed burner shortened by irradiating microwave power without increase of gas temperature.
This suggests that electrons heated by microwave electric field assist the combustion. To clarify thismechanism, electron Monte Carlo simulations and simple rate equations in methane and air
mixture gas have been done. And it is found that the simulated emission from Second Positive Band
System agrees with the experimental result.

electric field decreases, high energy electrons decreasesignificantly. It is found that the electric field at more

10-1

10-2

10-310-410-510-6)-3/2

2. Modeling
To simulate inside the flame under microwave
electric field, zero dimensional model was used.
The simulated area is inside the flame as shown in
Figure 1(unburned gas area).
To determine the electron energy distributionfunction (eedf) and transport parameters, electronMonte Carlo simulation has been done in zero
dimension. The simulated conditions are applied
electric field ~300V/cm with frequency of 2.45GHz
and the total gas pressure of 1atm. The gas
temperature is assumed to be 2000K. The gas is
mixture of nitrogen, oxygen and methane and themixture ratio is 8:2:1. Figure 2 shows the eedfs
obtained from e-MCS. As shown in the Figure, as theFigure 1. Configuration of present model.

eedf (eV

1. Introduction
Recently, plasma-assisted combustion[1] hasbeen focused on due to achieve more efficient
way of fossil fuels combustion, reducing
pollutants and so on. Shinohara et al[2] hasreported that the flame length of methane and air
premixed burner shortened by irradiating
microwave power without increase of gas
temperature. This result suggests the electron
heating by microwave power affect on burning
velocity in combustion system. To clarify thisphenomena, electron behavior under microwave
power should be examined. For the first step, in
this paper, electron Monte Carlo simulation inmethane and air mixture gas has been done.

E=100V/cm
E=200V/cm
E=250V/cm
E=300V/cm
E=350V/cm

05101520

electron energy (eV)Figure 2. Electron energy distributionfunctions in methane and air.

25-326Electric field: 300V/cm, Freq.2.45GHz
Excitation frequency for C3Pu: 1.1x107(1/s)
Electron density 1.0(cm-3)
Einstein’s A coefficient: 2.45x107(1/s)

electron density x10 (cm )than 300V/cm is suitable for this model. To solve inside
the flame using simple rate equations, the parameters andreactions written below were used.

Reactions considered
N2+eÆ N2*(C) + e
N2*(C)
Æ N2*(B) + hνN2+e
Æ N2*(A) + e**
N2 (A) + N2 (A) Æ N2*(C) + N2N2*(C) + N2
Æ N2*(a’) + N2*
Æ N2+O +ON2 (C) + O2
O2+ N2*(A) Æ O2+ N2 + e
O2+ N2*(B) Æ O2+ N2 + e

10012Time (ms)3Figure 3. Temporal evolution of Electron density .

At this condition, effective ionization freq. isalmost zero. And gas flow is assumed and the value
is 5 l/min.
The electron density was solved using eq. (1)dnen= C− edtτ(1)

C is assumed to be electron density which isdiffused from the flame and τ is assumed aselectron loss coefficient by gas flow.
3. Results and discussions
Figures 3 and 4 show temporal evolution ofelectron density and Intensity from 2nd positive
band system in nitrogen gas. In Figure 3, electron
density quickly increases as microwave electricfield is applied. And the electron density reaches
about 2x106cm-3. After the electric field is off, theelectron density gradually decreases. As shown inFigure4, The intensity from 2nd positive bandsystem in nitrogen gas agrees with the experimentalresults. It is found that the time constant τON isrelated to gas flow parameter. It is not shown in thepaper, but the intensity is not so sensitive by thetime constant τON. And the initial electron density
sensitivity is also examined. And it is found that thevalue of the initial electron density supposes to below.
Acknowledgments
This work was supported by Grant-in-Aid for
Scientific Research (B) 22340170

Figure 4. Intensity from 2nd positive band system .
References[1]V.Bychkov et al. IEEE Trans. Plasma Sci.,37,122280-2285 (2009)[2] K. Shinohara et al, J. Phys. D:Appl. Phys., 42,182008 (1-7) (2009)