Plasma Combustion of Ethanol/Air Mixture in The Transverse Arc

1V. Yukhymenko, 1V. Chernyak, 2V. Naumov, 1Iu. Veremii, 1V. Zrazhevskij
1Faculty of Radiophysics, Dept. of Physical Electronics, Taras Shevchenko Kyiv National University, Prospect
Acad. Glushkova 6, 03127 Kyiv, Ukraine; e-mail: yvitaliy@ukr.net;
2Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences Prospect Nauki 45, Kiev
03028, Ukraine; e-mail: naumov@ifpht.kiev.ua.
Abstract. The influence of preliminary plasma reforming of fuel on plasma combustion efficiency was investigated. The
ethanol was chosen as researched fuel. The electrical discharge in the gas channel with a liquid wall was used for
preliminary ethanol reforming. The burning was supported by transverse arc discharge in a flow of mix air + reformed
ethanol. Emission spectroscopy of plasma was applied to control of burning process. The population distribution
temperatures of excited states of plasma components was determined on relative intensity of spectral lines and molecular
bands.
Keywords: plasma reforming, plasma combustion, discharge, emission spectra, temperature.
PACS: 50.; 52.; 52.50.Dg.
INTRODUCTION
Today the generation of non-equilibrium air plasma is very actual for combustion technologies. The transversal
electric arc placed into the blowing gas is considered as one of the efficient non-equilibrium plasma generators. An
intensive transverse ventilation of the arc leads to increasing of plasma non-izothermality. Such discharge can be
used for ignition and for assisted combustion of different substances. Plasma activation allows solving such
problems of homogeneous igniting of combustible mixes as: reduction of ignition delay time, flame holding and
flame stability improvement, flame blow-off prevention, and extension of fuel flammability limits [1], controlling of
energy release processes in a plasma streams, and plasma modification of burning products [2].
EXPERIMENTAL SET-UP
The burning of air and ethanol mix was investigated in work. The burning of a mix was initiated and supported
by plasma of the transverse arc discharge at atmospheric pressure. For improvement of burning efficiency the
hydrogen received by plasma reforming of ethanol was added in mix. The experimental set-up is shown on Fig. 1.
The scheme of air and ethanol mix reception is shown on Fig. 1а. The flow of air was supplied in test-tube with
ethanol. The speed of airflow was adjusted by the rotameter. The mix of air + ethanol was obtained on the outlet of
test-tube. To change the proportion between mixed components the heating of the ethanol was carried out. The
discharge was ignited in the obtained mix between two copper electrodes (Fig. 1b) from a source of a constant
voltage. A diameter of electrodes 6 mm. A nominal gap between the electrodes from which we started usually was
1,1 mm.
For increase of burning efficiency of a mix the hydrogen was added to the mix. The hydrogen was obtained by
plasma reforming of ethanol. The reactor for such reforming is represented on Fig. 1а. It consists of a quartz tube
from above tightly closed by a cover. Both the system of gas inlet, outlet, and electrodes system, between which is
igniting the glow discharge in the gas channel with a liquid wall, were built in the cover. The tube from below was
closed by flange, which was one of the electrodes of secondary discharge. The plasma of glow discharge was
another electrode of the secondary discharge. Both the discharges glow and secondary were ignited from sources of
a constant voltage. The discharges were burned in volume of ethanol. The volume of ethanol was hold constant with
the help of informed vessels system. As a result of such treatment on the outlet of reactor the mix air + C2H5OH +
H2 + CxHy +… was obtained. For removal from mix of ethanol vapour it was directed to a condenser. After that a
mix air + H2 + CxHy +…added to the basic flow air + ethanol, in which transverse arc discharge was ignited.
For optical diagnostics, the emission UV-VIS-NIR spectroscopy was applied. Plasma radiation was measured by
portable rapid PC-operated CCD-based multi-channel optical spectra analyser (MOSA), which has a wide
wavelength survey (200-1100 nm) with spectral resolution (~0.2 nm). The spectra were measured along to axis (Z)
of the discharge by goniometric table, on which the lens and optical receiver were fixed.
RESULTS AND DISCUSSIONS
The typical emission spectrum of transverse arc plasma shown on Fig. 2. It is rich of spectroscopic information.
We recognised here nitride oxide NO γ-system (A2Σ+-X2Π: (0-0) 226.9 nm, (0-1) 236.3 nm, (0-2) 247.1 nm, etc);
hydroxyl OH UV system (A2Σ-X2Π: (0-0) 306.4-308.9 nm); nitrogen N2
+ 1- system (B2Σ+
u-X2Σg
+: (1-0) 358.2, (1-1)
388.4, (0-0) 391.4 nm, etc); N2 2+ system (C3Πu-B3Πg: (0-0) 337.1, (0-1) 357.7, (0-2) 380.5, (1-0) 316.0 nm, etc).
Among atomic lines, we recognized HI Balmer α line 656.3 nm, OI lines (777.3, 844.6, 926.0 nm), and NI lines
(746.8, 818.8, 868.3 nm). There are a lot of Cu lines due to evaporation of copper electrodes, but intensities of the
most strong CuI lines 324.7 and 327.4 nm were overlap with N2
+ 1(-) bands, therefore we used CuI lines 465.1, 510.5,
FIGURE 1. Experimental set-up.
H2 + CxHy +… was obtained. For removal from mix of ethanol vapour it was directed to a condenser. After that a
mix air + H2 + CxHy +…added to the basic flow air + ethanol, in which transverse arc discharge was ignited.
For optical diagnostics, the emission UV-VIS-NIR spectroscopy was applied. Plasma radiation was measured by
portable rapid PC-operated CCD-based multi-channel optical spectra analyser (MOSA), which has a wide
wavelength survey (200-1100 nm) with spectral resolution (~0.2 nm). The spectra were measured along to axis (Z)
of the discharge by goniometric table, on which the lens and optical receiver were fixed.
RESULTS AND DISCUSSIONS
The typical emission spectrum of transverse arc plasma shown on Fig. 2. It is rich of spectroscopic information.
We recognised here nitride oxide NO γ-system (A2Σ+-X2Π: (0-0) 226.9 nm, (0-1) 236.3 nm, (0-2) 247.1 nm, etc);
hydroxyl OH UV system (A2Σ-X2Π: (0-0) 306.4-308.9 nm); nitrogen N2
+ 1- system (B2Σ+
u-X2Σg
+: (1-0) 358.2, (1-1)
388.4, (0-0) 391.4 nm, etc); N2 2+ system (C3Πu-B3Πg: (0-0) 337.1, (0-1) 357.7, (0-2) 380.5, (1-0) 316.0 nm, etc).
Among atomic lines, we recognized HI Balmer α line 656.3 nm, OI lines (777.3, 844.6, 926.0 nm), and NI lines
(746.8, 818.8, 868.3 nm). There are a lot of Cu lines due to evaporation of copper electrodes, but intensities of the
most strong CuI lines 324.7 and 327.4 nm were overlap with N2
+ 1(-) bands, therefore we used CuI lines 465.1, 510.5,

The estimation of rotational (Tr
*) and vibrational (Tv
*) temperatures of radicals NO, OH was carried out by
comparison of the experimentally measured spectrum of plasma radiation with the theoretically calculated spectrum.
The calculation of radiation spectrum of radicals NO, OH was carried out with use of the program “LIFBASE” [4].
The results of comparison are represented on Fig. 5. The best coincidence of a calculated spectrum with
experimental is achieved Tv
* = Tr
* = 0,4 eV.
CONCLUSIONS
1. The experimental results show that transverse arc plasma could be efficiently applied for assisting combustion
of impoverished hydrocarbon-air mixes.
2. The adding of the fuel mix into discharge leads to the changes of discharge geometry, the discharge is
extended in that case.
3. The temperatures of electron population of electrodes material atoms (Сu) exceeds in 2 times temperature of
blowing gas atoms (О).
4. The temperatures rotational and vibrational in tail of a torch are equal and are close to temperature of electron
population of blowing gas atoms.
REFERENCES
1. N. Chintala, R. Meyer, A. Hicks, B. Bystricky, J.W. Rich, W.R. Lempert, I.V. Adamovich, Proc. 42nd AIAA Aerospace
Sciences Meeting and Exhibit, Reno, NV, 2004, pp. 1-18.
2. D.I. Slovetsky, Proc. 3rd Internat. Symp. on Theoretical and Applied Plasma Chemistry (ISTAPC-2002), Plyos, Russia, 2002,
V.1, pp. 55-58.
3. R.W.B. Pears and A. G. Gaydon, The identification of molecular spectra. Chapman and Hall: N.Y., 1976.
4. J. Luque and D.R. Crosley, “LIFBASE: Database and Spectral Simulation Program ”, SRI International Report MP 99-009
(1999).
FIGURE 5. The comparison of the experimentally measured spectrum of plasma radiation with the
theoretically calculated spectrum

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