PLASMA ASSISTED COMBUSTION OF PARAFFIN MIXTURE O.A. Nedybaliuk1, V.Ya. Chernyak1, E.V. Martysh1, T.E. Lisitchenko1, O.Yu. Vergun2, S.G. Orlovska3 1
Faculty of Radio-Physics, Kiev National Taras Shevchenko University, Kiev, Ukraine; 2
Faculty of Physics, Kiev National Taras Shevchenko University, Kiev, Ukraine; 3
Dept. of Thermal Physics, Odessa National University, Odessa, Ukraine E-mail:
[email protected]
In this work the results of solid paraffin combustion with the aid of the plasma of transverse and rotational gliding arc studies are represented. The question of the additional activation of paraffin based solid fuels is examined. The mixture of n-paraffin and stearin in the solid state as the model of the solid paraffin based fuel is used. The plasma assisted combustion of this model is experimentally investigated. The voltage-current characteristics of discharge at the different regimes are measured. The population temperatures of excited rotational levels are determined. The flame temperature during the combustion of solid paraffin containing mixture is calculated. PACS: 50., 52., 52.50.Dg
INTRODUCTION The idea of using nonequilibrium low temperature plasma for ignition or combustion stabilization seems to be promising today [1]. A number of papers devoted to results review on different gas discharges, used for plasma-assisted ignition and combustion, namely: streamers, dielectric barrier discharges, radiofrequency discharges, pulsed nanosecond discharges (sparks, dielectric barrier discharges, volume nanosecond discharges) and different mechanisms for them, such as ion chemistry and chemistry of excited species, are proposed and investigated [2, 3, 4]. However, the focus was only gas-phase fuel mixtures, and studies to stabilize the solid fuels combustion are practically absent. In recent years the idea of using paraffin to create new fuel was realized [5]. It is well-known that paraffin is saturated carbons which contain only carbon and hydrogen and have the general formula CnH2n+2. The paraffin can be found in the liquid and solid state depending on the number of –CH2– groups [6]. In spite of the presence of merit significant paraffin based fuel, the question about its advantage in the comparison with the traditional petrol fuels is debatable. One of this discussion reasons connected with chemical sluggishness of paraffin [7, 8]. The need for an additional activation of the combustion appears in
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connection with this fact. Plasma stimulation is the most effective means for this purpose. Depending on the field of application, the paraffin based fuels can exist in a liquid and solid state. Such experiments for solid paraffin and its mixtures were not carried out in contrast to liquid paraffin.
1. EXPERIMENTAL SETUP The mixture of n-paraffin and stearin in the solid state as the model of the solid paraffin based fuel is used [9]. The fuel composition is 80 % n-paraffin mixture with the number – CH2– groups from С18Н38 to С35Н72 and 20 % stearin (C17H35COOH). The schematic view of the plasma-dynamic system (PDS) for combustion activation of the paraffin containing solid mixture with transversal and rotating gliding arc is represented in Fig. 1. The PDS consists of the main steel chamber (1) into which through the dielectrics (3) are introduced two copper electrodes (2). The voltage was supplied between the electrodes (2) with the help of the DC power source powered up to 7 kV. The airflow will be given perpendicular to electrodes, forming the torch plasma (4). Compressor formed airflow, which was measured by rotameter. The torch of plasma is surrounded by wire grid (5) in the form of the cylinder with a diameter of 1 cm.
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Fig. 1. The schematic view of the plasma-dynamic system (PDS) for combustion activation of the paraffin containing solid mixture with transversal (a) and rotating gliding arc (b) ISSN 1562-6016. ВАНТ. 2013. №1(83)
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The grid is attached to the steel cylindrical capsule (6). The space between the grid (5) and the steel capsule (6) filled with the investigated substance (7) whose weight was 3·10-3 kg. The flame (8) on the outlet of steel capsule (6) after discharge burning was formed. Optical studies of flame were conducted with the aid of the optical system (see Fig. 1,a,b). Its composition is illuminating system (9), light-emitting diode (10), the spectrometer S-150-2-3648 USB (11) which measures of the spectra in the range of wavelengths from 200 to 1100 nm and computers (12). Combustion chamber (13) was connected to the steel capsule (6). The airflow (15) will be given tangentially to surface of cylindrical combustion chamber (13) through orifice (14). The steel capsule (6) was immersed into combustion chamber on the length l = 20 mm.
2. RESULTS AND THEIR DISCUSSION The voltage-current characteristics of discharge with presence and absence of the investigated substance under investigation are represented in Fig. 2. For this case the airflow composed of G = 55 cm3/s. As can be seen from Fig. 2 the form of the voltage-current characteristic in the range of currents from 200 to 400 mA with presence and absence of investigated substance are various. For the first case the curve is characterized by the larger slope of the drop than at the second case. It can be connected with the presence of stearin.
Fig. 2. The voltage-current characteristics of discharge with presence and absence of the investigated substance in the air flow G=55 cm3/s When the combustion was stimulated by plasma the flame was present. The flame jet disappeared during the disconnection of discharge. But the airflow supply in this case remained constant. The relationship of the complete combustion energy of the investigated mixture to the energy that spent on the plasma generation for this regime is near 100/1. The plasma torch emission spectrum contains bands of monoxide nitrogen NO, hydroxyl ОН (A-X) and also the copper lines Cu (324.75; 327.39 nm). Hydroxyl molecules origination connected, of course, with water vapor presence in airflow. It is well-known that these molecules essentially supported various mixtures combustion. The flame emission spectrum is continuous and its intensity grows at the wavelength increasing. It also has imposition of the Na duplicate lines (588.99; 589.59 nm), the K resonance lines (766.49; 769.89 nm) and the band of hydroxyl ОН (A-X). The flame emission spectrum can be considered as similar to the blackbody
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radiation spectrum. Hydroxyl origination connected, of course, with water vapor presence in airflow. It is wellknown that these molecules essentially assisted to various mixtures combustion. The calculations of the emission spectrum of the band of ОН (A-X) hydroxyl with the aid of the program SPECAІR [10] were carried. The results of calculation were compared with the experimental spectrum for determining of the population temperature of excited rotational levels Tr*. For the comparison was used the part of the hydroxyl band ОН (A-X) in the range of wavelengths from 310 to 320 nm, which depends of the population temperature of excited rotational levels Tr*. The rotational temperature Tr* = 2700 ± 500 K ОН (AX) in the case without investigated substance under investigation. The rotational temperature in the plasma torch is Tr* = 2300 ± 500 К. For comparison, the emission spectrum of flame which appears with the other combustion conditions of the model fuel was investigated. We will call this flame the abbreviated form FUOC (Flame Under Other Condition). In this case, the ignition was achieved with the aid of the burner device and combustion of investigated substance took place into atmospheric air. The region of the greatest temperature FUOC flame was used for investigating of the emission spectrum. The comparison of experimental results with by the calculated radiation spectrums of blackbody was conducted on the basis of the continuous nature of the PAC (plasma assisted combustion) emission spectra and FUOC spectrum (Fig. 3). Calculations were performed with the aid of the Planck formula. The calculated grid with the step of 100 K in the range temperatures from 1200 to 3000 K, the emission spectrums of FUOC and flame of plasma assisted combustion. The data of Fig. 3 attest to the fact that the emission spectrum of the FUOC is closed to calculated spectrum at the temperature Т=2100 К. In addition, the emission spectrum of PAC-flame coincides with calculated by formula (1) for the temperature Т = 2500 К. The PAC-flame temperature ТPAC = 2500 ± 100 К for 400 K exceeds the temperature of the FUOC ТFUOC = 2100 ± 100 К. It should be noted that rotational temperature at the plasma assisted combustion Tr* = 2300 ± 500 К close to the temperature
Fig. 3. The emission spectrums of FUOC, the emission spectrums of PAC-flame (G = 55 сm3/s, I = 300 mA, U = 0.6 kV) and the calculated radiation spectrum of blackbody ISSN 1562-6016. ВАНТ. 2013. №1(83)
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Fig. 4. Axial distribution of temperature in flame: (a) – without combustion chamber; (b) – outlet of combustion chamber of the PAC-flame ТPAC = 2500 ± 100 К. The population temperature of rotational excited levels of the ОН (А-Х) hydroxyl in the flame (Tr* = 2300 ± 500 K) is less than in the torch plasma (Tr* = 2700 ± 500 K). Axial distributions of temperature in flame with and without combustion chamber are shown in Fig. 4.
CONCLUSIONS In the regime of stable burning the emission spectrum of flame is continuous and corresponds to the radiation spectrum of blackbody. The population temperature of rotational excited levels of hydroxyl OH (A-X) (Tr* = 2300 ± 500 K) is close to the temperature of the PAC-flame (TPAC = 2500 ± 100 K). The population temperature of rotational excited levels of the ОН (А-Х) hydroxyl in the flame (Tr* = 2300 ± 500 K) is less than in the plasma torch (Tr* = 2700 ± 500 K). ACKNOWLEDGEMENTS This work was partially supported by the State fund for fundamental researches (Grant F41.1/014), Ministry of Education and Science of Ukraine, National Academy of Sciences of Ukraine.
REFERENCES 1. S. Starikovskaia, A. Starikovskii. Physics and chemistry of nanosecond pulsed discharges // Pap. 7th ICRP and 63rd GEC. 2010, UF1-001. 2. K. Becker, U. Kogelschatz, K. Schoenbach, R. Barker. Non equilibrium air plasmas at atmospheric pressure // IOP Publisching Ltd. 2005, p. 682. 3. S. Starikovskaia. Plasma assisted ignition and combustion // Journal of Physics D: Applied Physics. 2006, v. 39, R265-R299. 4. A. Fridman. Plasma Chemistry. Cambridge: «University Press». 2008, p. 963. 5. M. Dornheim, Aviation week and space technology. 2003, v. 3, p. 52. 6. R. Morrison, R. Boyd. Organic Chemistry // Prentice Hall, New Jersey 6th ed. 1992, p. 1360. 7. Y. Sohn, S. Baek, T. Kashiwagi. Transient Modeling of Thermal Degradation in Non-Charring Solids // Combustion Science and Technology. 1999, v. 145, p. 83. 8. W. Leithe // Anal. Chem. 1951, v. 23, № 3, p. 493. 9. G. Knothe, J. Gerpen // Biotechnology Journal. 2007, v. 2, № 12, p. 1571. 10. C.O. Laux. http://www.specair-radiation.net
Article received 20.10.12 ПЛАЗМЕННОЕ СТИМУЛИРОВАНИЕ ГОРЕНИЯ СМЕСИ ПАРАФИНОВ
О.А. Недыбалюк, В.Я. Черняк, Е.В. Мартыш, Т.Е. Лиситченко, Е.Ю. Вэргун, С.Г. Орловская Представлены результаты исследования горения твердых парафинов с помощью плазмы поперечной и вращательной скользящих дуг. Рассматривается вопрос о дополнительной активации горения твердого топлива на основе парафина. Смеси n-парафинов и стеарина в твердом состоянии использовались в качестве модельного твердого топлива. Экспериментально исследована плазменная активация горения этого модельного топлива. Измерены вольт-амперные характеристики разряда при различных режимах работы. Определены температуры заселения возбужденных вращательных уровней. Вычислена температура пламени при сжигании смесей твердых парафинов. ПЛАЗМОВЕ СТИМУЛЮВАННЯ ГОРІННЯ СУМІШІ ПАРАФІНІВ О.А. Недибалюк, В.Я. Черняк, Є.В. Мартиш, Т.Є. Лиситченко, О.Ю. Вергун, С.Г. Орловська Представлено результати дослідження горіння твердих парафінів за допомогою плазми поперечної та обертальної ковзаючих дуг. Розглядається питання про додаткову активацію горіння твердого палива на основі парафіну. Суміші n-парафінів і стеарину в твердому стані використано в якості модельного твердого палива. Експериментально досліджено плазмове стимулювання горіння цього модельного палива. Виміряно вольт-амперні характеристики розряду за різних режимів роботи. Визначено температури заселення збуджених обертальних рівнів. Обчислено температуру полум'я під час спалювання сумішей твердих парафінів. ISSN 1562-6016. ВАНТ. 2013. №1(83)
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