UNDERSTANDING the ignition of air fuel mixtures is

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1 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 1, JANUARY On the Effect of Nonequilibrium Plasma on the Minimum Ignition Energy Part 1: Discharge Model Albina A. Tropina, Mruthunjaya Uddi, and Yiguang Ju Abstract The mathematical model of a repetitive nanosecond pulse discharge at atmospheric-pressure conditions has been presented. The influence of initial gas temperature, chemical kinetics, and vibrational nonequilibrium on the ignition of methane air and ethylene air mixtures has been analyzed. Index Terms Chemical kinetics, repetitive nanosecond pulse discharge, vibrational nonequilibrium, vibrational temperature. I. INTRODUCTION UNDERSTANDING the ignition of air fuel mixtures is one of the important challenges for fundamental combustion research as well as for combustion applications. Many studies have examined the most popular spark-induced ignition commonly used in the automotive industry, but there are many applications where other ignition sources have benefits. Most of these techniques are based on the so-called nonequilibrium plasma creation. Such a nonequilibrium plasma allows us to optimize combustion by controlling the average electron energy for electron-impact species excitation and dissociation that, in turn, can enhance combustion stability, increase efficiency, and reduce undesirable emissions. Most modern applications of plasma-based ignition have focused on aerospace [1] [6]. Recent works have demonstrated the capability of air fuel mixture ignition and combustion control by nonequilibrium discharges in supersonic flows by means of flame front stabilization with a significant increase in flame velocity compared with arc and spark discharges [7], [8]. A nonequilibrium discharge plasma can be created in different ways, the most popular of which are corona discharge, microwave, pulsed nanosecond discharge, and dielectric barrier discharge. As it has been shown by several recent experimental studies, the repetitive nanosecond pulse discharge can be considered as a reliable ignition source under different operation conditions and should be viewed as one of the leading technologies for plasma-assisted combustion [9], [10]. However, there are still many unknowns in nonequilibriumplasma-assisted combustion connected with such fundamental Manuscript received September 9, 2010; revised October 10, 2010; accepted October 11, Date of publication November 15, 2010; date of current version January 7, This work was supported in part by a Fulbright grant from the U.S. Department of State and in part by the MURI Plasma-Assisted Combustion Program from AFOSR. A. A. Tropina is with the Department of Mechanics and Hydraulics, Kharkov National Automobile and Highway University, Kharkiv, Ukraine ( albina.tropina@fulbrightmail.org). M. Uddi and Y. Ju are with the Combustion and Energy Laboratory, Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ USA ( muddi@princeton.edu; yju@princeton.edu). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /TPS aspects of the combustion theory, such as minimum ignition energy (MIE), which is an important parameter to characterize ignition efficiency, fire safety, as well as plasma-assisted combustion efficiency. Conventionally, MIE is determined by the minimal amount of energy required to heat gas from its initial state to the adiabatic flame temperature with a size of flame thickness [11]. Even with the numerous studies, the data on MIE are only available in the limited range of initial temperature, pressure, and mixture equivalence ratio. For the case of repetitive nanosecond discharge ignition in [10], the authors present the results of the MIE measurements as a function of pressure for propane air mixtures. Compared with the case of spark ignition, the values of MIE are higher. In this case, no direct comparison between thermal and nonequilibrium plasma ignition and MIE evaluation can be done as the plasma volume created by the discharge is bigger, and it will be desirable if MIE can be determined numerically. It will allow us to answer the question how the energy stored in the vibrational degrees of freedom during repetitive nanosecond discharge ignition affects the initial phase of flame propagation and MIE. The numerical simulation of the effect of a nonequilibrium plasma on MIE can be divided into two parts, such as the calculations of a nonequilibrium plasma composition after the discharge action and the MIE evaluation based on nonequilibrium-plasma-assisted combustion simulation. This paper presents the results of the first part of the problem solution concerning repetitive nanosecond pulse discharge modeling at atmospheric-pressure conditions. It should be noted that there are a lot of studies which focus on the combustion kinetics of nonequilibrium plasma ignition assisted by a nanosecond discharge summarized in [13]. For the case of repetitive nanosecond pulse discharge in more recent studies [14], [15] at low-pressure conditions, the authors presented the results of time-dependent measurements of oxygen atom and NO density in air, air/methane, and air/ethylene mixtures. At atmospheric-pressure conditions, only limited data of species measurements are available. The results of the measurements of N 2 (C 3 Π u ) and N 2 (B 3 Π) metastable content for the nanosecond repetitively pulsed discharge in nitrogen and air preheated at 1000 K are presented in [16]. For methane air mixture, no direct measurements of species concentrations are available, but as the test data, the results of the vibrational temperature measurements in air and methane air plasma presented in [17] can be used. The main objective of this paper is to analyze the effects of vibrational nonequilibrium, temperature, and fuel variation on ignition process assisted by a repetitive nanosecond pulse discharge at atmospheric-pressure conditions /$ IEEE

2 616 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 1, JANUARY 2011 II. PROBLEM FORMULATION It is known that, at atmospheric-pressure conditions, a repetitive nanosecond pulse discharge can operate in diffuse or filamentary form. Usually, air fuel plasma chemistry incorporates a large number of neutral, charged, and excited species and can be described in quasi-one-dimensional (1-D) approximation [18]. As it was shown in [19], the densities of species after the stage following the formation of a plasma channel bridging a gap are distributed practically uniformly along a streamer channel, which can be one of the arguments of such an approach. In this paper, a nonequilibrium plasma is treated in 1-D approximation based on the NON-EQU_PLASMA code presented in [46], combined with the CHEMKIN GAS-PHASE KINETICS package [47], taking into account that the results obtained can be underestimated due to the higher electric field values in filaments. The discharge model includes quasi-1-d flow equation, translational and vibrational temperature equations, and number density and species concentration equations. The kinetic model includes the reactions between neutral and excited species, ions, and electrons and the reactions caused by an electron impact. The rate constants of methane air and ethylene air plasmas were taken from [20] and [21]. To model fuel air plasma, the model incorporates a set of equations for the number density of neutral species (53 neutrals for the GRI 3.0 mechanism [22], 87 neutrals for the C 2 mechanism of hydrocarbon combustion [23], positive ions (N + 4, N+ 2, NO+, O +, N +, O + 4, NON+ 2, NOO+ 2, O 2N + 2, N+ 3, N 2O +, O + 2, NO+ 2, NONO + ), negative ions (O 2, O, NO, O 3, NO 3, NO 2, O 4, N 2 O ), electrons, and excited species O 2 (a 1 Δ), O 2 (b 1 ), O 2 (c 1 ), O( 1 D), O( 3 P), N 2 (B 3 Π), N 2 (C 3 Π), N( 2 D), N( 2 P), N( 4 S), N 2 (a 1 ), and vibrationally excited nitrogen molecules in the ground electronic state N 2 (x 1,ν). All the plasma reactions incorporated in the model are listed in Table I (Appendix A). All the rate constants of electron-impact reactions such as ionization, dissociation, and electronic and vibrational excitation were calculated, using the Boltzmann equation solver BOLSIG+ [24], based on the standard electron-impact crosssectional package added by the cross-sectional data for the hydrocarbons from [25]. The processes, connected with vibrational kinetics, focus on nitrogen which has a large vibrational frequency and, in the absence of other collision partners, have a very slow conversion of translational to vibrational energy. As it was shown in [38], nitrogen is the only species whose vibrational kinetics has the potential of affecting flame characteristics (flame translational temperature) significantly. All other species are treated as being in vibrational equilibrium. The vibrationally excited nitrogen molecules in the ground electronic state N 2 (x 1,ν) were treated as single species, i.e., specific vibrational kinetics is not considered, and the microscopic kinetic processes by the levels (V V exchange) have been neglected. The rate of production of N 2 (x 1,ν) was based on the sum of the cross-sectional data for the first eight vibrational levels [26]. The influence of vibrational temperature on reaction rate, with the participation of neutral molecules, was neglected, but the possibility of vibrational excitation influence on dissociation, detachment, and excitation reactions was taken into account by multiplying the reaction rate by a factor k V = 10 Cz/θ2 as in [39], where C =28.3, z = exp( hw 0 /k B T υ ), hw 0 is the energy of the first vibrational level of nitrogen molecules, and θ = E/N in V cm 2. The vibrational distribution for N 2 was assumed to be an equilibrium one with the temperature T V. The vibrational temperatures for other molecules and all the rotational temperatures were assumed to be equal to the gas temperature T. The equation for the vibrational energy of excited nitrogen molecules ε V was taken in the form of dε V dt = α V Q E ε V ε 0 (T ) τ VT (1) where ε 0 (T ) is the equilibrium vibrational energy, α V is the part of an electromagnetic field energy transferred into the vibrational degrees of freedom, and Q E is the electromagnetic field energy. For the vibrational translational relaxation time τ VT,the expression proposed in [40] was used, which includes the correction, depending on the oxygen atom concentrations [ ( 1 = N exp 141 ) τ VT T 1/3 ] + α o N exp( 128 T 1/2 ) (2) where N is the number density of mixture and α o is the mole fraction of atomic oxygen. One of the questions is whether methane molecules affect the vibrational relaxation of nitrogen molecules. We were oriented on the results presented in [48], where the acoustic attenuation measurements in the mixture of nitrogen, methane, and water vapor at atmospheric-pressure conditions and T = 300 K for the different frequencies of electromagnetic field had been presented. As acoustic attenuation results from the molecular relaxation processes (generally), these results can be considered as the evaluation of the methane content effect on the relaxation process of nitrogen. It was shown in [48] that the dependence of acoustic attenuation on methane concentrations is weak, except for very high frequencies of Hz. Therefore, the influence of methane content on the vibrational relaxation of nitrogen molecules was neglected. The influence of vibrational nonequilibrium on mixture heat capacity was accounted by the specific heat correction in the form of C p = C p N N 2 ρ dε V dt where ε V is the vibrational energy of nitrogen molecule, T V is the vibrational temperature, and N N2 is the molar fraction of nitrogen molecules. The part of an electromagnetic field energy transferred into the vibrational degrees of freedom was taken as a function of a reduced electric field by interpolation of the data presented in [41] for air plasma based on the solution of Boltzmann kinetic equation for plasma electrons. It was assumed that, for air fuel mixture, we have the same energy division corrected on the percentage of air in the mixture. (3)

3 TROPINA et al.: ON THE EFFECT OF NONEQUILIBRIUM PLASMA ON THE MIE It was also assumed that vibrational excitation occurred mainly because the electronically excited species relax to the vibrationally excited nitrogen. For the electric field calculations, the following iteration procedure was proposed. On the first stage, the mean electric field value Ẽ during the pulse was estimated from the measured discharge voltage characteristics [16], [17]. The pulse form is presented in a trapezoidal form, with the maximum electric field value taken as Ẽ =(U U c)/d, where d is an interelectrode distance, and the cathode voltage drop is equal to U c =0.2 kv [19]. The discharge current density was evaluated from Ohm s law, with electron drift velocity taken from the EEDF calculations combined with the external resistance influenced by Kirchhoff s law. On the second stage, the electric field distribution was calculated based on the 1-D approach with the calculated rate constants of electron-impact reactions as an input parameter. The system of equations on this stage includes the set of equations for the kinetics of charge species, including the drift fluxes and the electron temperature equation. The mean electric field value Ẽ based on the field value in the center of a gap was corrected, taking into account discharge nonuniformity and sheath layer formation. Diffusion processes were neglected because the characteristic diffusion time ( 10 4 s) is much longer than the pulse duration. All the presented numerical results correspond to the cases of dry air, methane air, and ethylene air mixtures. The effects connected with cluster hydrocarbon ions and the ionic composition change depending on the water content in a mixture are not taken into account. This question, as well as EEDF form in humid air, is discussed in detail in [42]. Fig. 1. N 2 (C 3 Π) dependence on time. (1) No quenching reaction by nitrogen. (2) With quenching reaction by O 2. (3) With temperature dependence of quenching reactions by nitrogen and oxygen (T 0 = 1000 K). Fig. 2. Negative-ion dependence on time for air plasma, pulse of 10-ns duration, 7-kV amplitude, and T 0 = 1000 K. III. NUMERICAL RESULTS To verify the model presented, the numerical simulation of the discharge was carried out for the case of a high-voltage pulse of 10-ns duration, 6-kV amplitude, an interelectrode gap of 4 mm, and a flow rate 0.5 m s 1, which corresponds to the conditions of the experimental measurements of the N 2 (C 3 Π u ) density at atmospheric pressure in air preheated at 1000 K [16]. The pulse form was presented in a trapezoidal form with a rise/fall time of 5 ns and a flat top of 10 ns. The temperature dependence of the quenching reactions of N 2 (C 3 Π u ) by nitrogen and oxygen was measured in [45] for a low-temperature range until 300 K. As we know, there are no data published at high temperatures for this rate coefficient. In calculations, we applied the same dependences as that in [45] up to 1000 K 2000 K. The profiles of N 2 (C 3 Π u ) density as a function of time after one pulse are shown in Fig. 1 for three sets of reactions: 1) without N 2 (C 3 Π u ) quenching reaction by nitrogen; 2) with the reaction of N 2 (C 3 Π u ) quenching by molecular oxygen without temperature dependence; and 3) with the reaction of N 2 (C 3 Π u ) quenching by molecular oxygen and nitrogen with the temperature dependence as in [45]. All the presented data in Fig. 1 were normalized on the maximum concentration of N 2 (C 3 Π u ) max = It is seen that the model predicts molecular oxygen as the main quencher of N 2 (C 3 Π u ), and the influence of nitrogen is weaker. Taking into account some uncertainty of the model presented, the correlations between the experiments and the model are pretty good. It should be noted that the calculations have shown the negligible influence of most of the negative ions, except ion O as the main formed negative ion (Fig. 2). We have also carried out numerical simulation for the case of a high-voltage pulse of 70-ns duration, 19-kV amplitude, an interelectrode gap of 3 mm, and a flow velocity of 3 m/s at the nozzle exit, which corresponds to the conditions of the experiments [18]. The authors measured the distribution of rotational and vibrational temperatures in air and air methane plasma at T = 300 K. A series of calculations was performed for the stoichiometric (Φ = 1) and lean (Φ = 0.5, 0.65) methane air and ethylene air mixtures. The calculated dependences of the vibrational and translational temperatures on time for methane air plasma with equivalence ratio Φ=0.65 are shown in Fig. 3. It is seen that the proposed model quite well coincides with the experimental data for the lean methane air mixture, except after the ignition region where the processes of species diffusion, neglected in the model, become essential. At the same time, the model fails in the prediction of vibrational- and translational-temperature evolution in time for air plasma (Fig. 4). The model could predict quantitatively and qualitatively the translational temperature behavior (except the region marked I) but gives too high vibrational temperature values compared with the experimental data. The main reason for that, in our opinion, is the V V exchange processes which are not accounted for in the model. The indirect sign of that

4 618 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 1, JANUARY 2011 Fig. 3. Distribution of translational and vibrational temperatures for methane air mixture as a function of time (Φ = 0.65). The experimental data are from [17] (T 0 = 300 K). Fig. 6. O atom distribution for the different equivalence ratios (methane air mixture), T 0 = 300 K, and p =1atm. Fig. 4. Distribution of translational and vibrational temperatures for air plasma as a function of time. The experimental data are from [17]. Fig. 5. Positive-ion dependence on time for methane air plasma (Φ = 0.65), a pulse of 70-ns duration, and 19-kV amplitude. is the absence of the minimum on both curves detected in the experiments, which can be caused by V V cooling. It was obtained that the main positive ions formed by the discharge for the lean methane air mixture are NO + and O + 2 ions (Fig. 5), and the major negative ion in such conditions is ion O. The heat generated in the reactions with negative ions slightly influences the distribution of a gas temperature if the initial concentrations of all charged particles are equal to zero, i.e., n e = n i =0(i =1,m). However, this input can be significant due to three-body reactions R96 if the electron initial concentration is high. The calculated O atom evolution in time for the methane air mixture ignited by a nanosecond pulse discharge of 70-ns duration at 19-kV amplitude is shown in Fig. 6 for four cases such as the following: 1) Φ=0.65, the full model; 2) Φ=0.65,thesame Fig. 7. Concentrations of the components (methane air mixture; 1 3, 7 Φ =0.65; 4 6, 8 Φ =0.65), T 0 = 300 K, p =1 atm: 1, 4 OH; 2, 5 O; 3.6 CH; and 7, 8 HCO. kinetic model without vibrational nonequilibrium (all the discharge energy is assumed to be transferred into thermal energy); 3) Φ=0.5, the full model; and 4) Φ=1.0, the full model. On the presented curves, the first peak corresponds to oxygen atom production in the discharge zone, while the second peak is a marker of an ignition initiation. The latter coincides well with the CH, HCO maximum (Fig. 7) and with the maximum on the heat release dependence on time. The maximum on the OH radical concentration dependence on time is realized later, as it is seen from Fig. 7. It was obtained that, for this discharge, ignition occurred after one nanosecond pulse following breakdown, as it was detected in the experiments. In addition, it is also seen from Fig. 6 that the vibrational nonequilibrium can influence the ignition process by the increase of maximum O atom concentration and, as a consequence, can cause the decrease of delay time. Analysis of O atom pathways has shown that the main input into O atom production is realized through the reactions with N 2 (B 3 Π) 62%, with N 2 (C 3 Π) 18%, and N 2 (A 3 ) 9%. The comparison between two types of fuel, such as methane and ethylene, has shown that the concentration of oxygen atoms produced by the discharge decreases with the increase of C atoms in the fuel molecule (Fig. 8). IV. CONCLUSION The transient 1-D mathematical model of a nanosecond pulse discharge at atmospheric-pressure conditions has been presented. The results of the calculations were compared with

5 TROPINA et al.: ON THE EFFECT OF NONEQUILIBRIUM PLASMA ON THE MIE KINETIC MODEL Fig. 8. O atom distribution for the different fuels at Φ=0.65, 70-ns pulse, U =10kV, T 0 = 300 K, and P =1atm. the experimental data and had shown good agreement. It was obtained that N 2 (C) is mainly quenched by oxygen and that the discharge energy stored in the vibrational degrees of freedom can significantly influence the atomic oxygen production, as well as the ignition process. If we consider MIE as the amount of energy required to heat gas to the adiabatic flame temperature, the estimation of MIE can be based on the approximate analytical formula [11] H =(Aδ)ρ 0 c p (T T 0 ) where H is the MIE, A is the square of a transverse cross section of the layer (A δ 2 ), δ is the laminar flame thickness, c p is the average heat capacity, T is the adiabatic flame temperature, and T 0 is the initial mixture temperature. The possible mechanisms of the nonequilibrium plasma influence on MIE, in this case, is the increase of laminar flame velocity (it appears in the definition of δ) due to the production of active radicals by the discharge, the decrease of c p according to (3), and the increase of the square of a transverse cross section of a layer due to the energy redistribution as the part of energy goes into the vibrational degrees of freedom. The latter can be characterized by a level of nonequilibrium of the discharge defined as β =(T V T )/T. In this paper, this parameter is varied in limits, which gives the estimation of MIE (A βδ 2 ) as mj. It should be noted that, in this case, the part of energy spent on the dissociation processes causing the increase of laminar flame velocity was not taken into account. The estimated value of MIE correlates well with the calculated discharge energy of 2 mj, and this value is higher compared with the MIE values for the case of spark ignition of hydrocarbons varied in mJ limits. The obtained numerical data are the initial conditions for a nonequilibrium-plasma-assisted combustion problem. The proposed kinetic scheme after some reduction can not only be used for laminar combustion modeling but also combined with an eddy dissipation concept model for a simulation of the turbulent combustion assisted by a nonequilibrium plasma. More detailed analysis of nonequilibrium plasma influence on MIE is under study. APPENDIX A. THE KINETIC MODEL

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8 622 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 39, NO. 1, JANUARY 2011 ACKNOWLEDGMENT The authors would like to thank Dr. M. N. Shneider from Princeton University, Princeton, NJ, for his help and useful discussions. REFERENCES [1] A. B. Leonov, D. A. Yarantsev, A. P. Napartovich, and I. V. Kochetov, Plasma assisted ignition and flameholding in high-speed flow, presented at the 44th AIAA Aerospace Sciences Meeting Exhib., Reno, NV, 2006, Paper AIAA [2] A. Klimov, V. Bittiurin, I. Moralev, B. Tolkunov, A. Nikitin, A. Velichko, and I. Bilera, Non-premixed plasma-assisted combustion of hydrocarbon fuel in high-speed airflow, presented at the 44th AIAA Aerospace Sciences Meeting Exhib., Reno, NV, 2006, Paper AIAA [3] V. M. Shibkov, A. F. Aleksandrov, V. A. Chernikov, A. P. Ershov, R. S. Konstantinivskiy, and V. V. Zlobin, Combined MW-DC discharge in a high-speed propane butane air stream, presented at the 44th AIAA Aerospace Sciences Meeting Exhib., Reno, NV, 2006, Paper AIAA [4] I. I. Esakov, L. P. Grachev, K. V. Khodataev, V. A. Vinigradov, and D. M. Van Wie, Efficiency of propane air mixture combustion assisted by deeply undercritical MW discharge in cold high-speed airflow, presented at the 44th AIAA Aerospace Sciences Meeting Exhib., Reno, NV, 2006, Paper AIAA [5] N. B. Anikin, E. I. Mintoussov, S. V. Pancheshnyi, D. V. Roupassov, V. E. Sych, and A. Y. Starikovskii, Nonequilibrium plasmas and its applications for combustion and hypersonic flow control, presented at the 41th AIAA Aerospace Sciences Meeting Exhib., Reno, NV, 2003, Paper AIAA [6] S. A. Dvinin, A. P. Ershov, I. B. Timofeev, V. A. Chernikov, and V. M. Shibkov, Simulation of a DC discharge in a transverse supersonic gas flow, High Temp., vol. 42, no. 2, pp , Mar [7] W. Kim, H. Do, M. G. Mungal, and M. A. Capelli, Plasma-discharge stabilization of jet diffusion flames, IEEE Trans. Plasma Sci., vol. 34, no. 6, pp , Dec [8] I. N. Kosarev, N. L. Aleksandrov, S. V. Kindysheva, S. M. Starikovskaya, and A. Y. Starikovskii, Kinetic mechanism of plasma-assisted ignition of hydrocarbons, J.Phys.D,Appl.Phys., vol. 41, no. 3, pp , Jan [9] V. Puchkarev and M. Gundersen, Energy efficient plasma processing of gaseous emission using a short pulse discharge, Appl. Phys. Lett., vol.71, no. 23, pp , Dec [10] A. A. Tropina, L. Lenarduzzi, S. V. Marasov, and A. P. Kuzmneko, Comparative analysis of engine ignition systems, IEEE Trans. Plasma Sci., vol. 37, no. 12, pp , Dec [11] B. Lewis and G. von Elbe, Combustion, Flames and Explosion in Gases, 3rd ed. Orlando, FL: Academic, [12] S. Pancheshnyi, D. A. Lacoste, A. Bourdon, and C. O. Laux, Ignition of propane air mixture by a sequence of nanosecond pulses, presented at the 37th AIAA Plasma Dynamics Lasers Conf., San Francisco, CA, Jun. 5 8, 2006, Paper AIAA [13] S. M. Starikovskaia, Plasma assisted ignition and combustion, J. Phys. D, Appl. Phys., vol. 39, no. 16, pp. R265 R299, Aug [14] M. Uddi, N. Jiang, E. Mintousov, I. V. Adamovich, and W. R. Lempert, Atomic oxygen measurements in air and air/fuel nanosecond pulse discharges by two photon laser induced fluorescence, presented at the 46th Aerospace Sciences Meeting Exhib., Reno, NV, Jan. 8 12, 2008, Paper AIAA [15] M. Uddi, N. Jiang, I. V. Adamovich, and W. R. Lempert, Nitric oxide density measurements in air and air/fuel nanosecond pulse discharge by laser induced fluorescence, J. Phys. D, Appl. Phys., vol. 42, no. 7, pp , Mar

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Jefferson, Chemkin: A General- Purpose, Problem-Independent, Transportable, Fortran Chemical Kinetics Code Package, Sandia Nat. Lab., Albuquerque, NM, Rep. SAND , [48] Y. Dain and R. M. Lueptow, Acoustic attenuation in a three-gas mixture: Results, J. Acoust. Soc. Amer., vol.110,no.6,pp ,Dec Albina A. Tropina received the Ph.D. from Kharkov National University, Kharkov, Ukraine. in From 1990 to 1999, she was a Researcher, an Assistant Professor with Kharkov National University. She is with Kharkov National Automobile and Highway University as Senior Lecturer, Associate Professor since In , she was with Princeton University, Princeton, NJ, as a Fulbright Fellow in the Department of Mechanical and Aerospace Engineering. Her research interests are focused on the theoretical investigation of plasma-assisted combustion and combustion processes in engines and combustion in the presence of an electric field. Mruthunjaya Uddi received 5 year Integrated M.Tech from IIT Mumbai, Mumbai, India in 1999 and the Ph.D. degree from Ohio State University, Columbus in He has been a CEFRC Postdoctoral Fellow in the Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, since then, where he is currently with the Combustion and Energy Laboratory. His research interests include laser diagnostics, efficient generation of energy through plasma combustion, pollution and emission control. Yiguang Ju received the B.S. degree from Tsinghua University, Beijing, China, in 1986 and the Ph.D. degree from Tohoku University, Sendai, Japan, in He became an Assistant and Associate Professor with Tohoku University from 1995 to 2000 and a Professor with Tsinghua University in He joined Princeton University, Princeton, NJ, in 2001, where he is currently an Associate Professor with the Department of Mechanical and Aerospace Engineering and is also with the Combustion and Energy Laboratory. His research interests include energy and fuels, propulsion, flame chemistry, plasma-assisted combustion, and nanomaterial synthesis.