Recommendation of Sharath Nagaraja for the Bernard Lewis Fellowship

Transcription

1 School of Aerospace Engineering Atlanta, Georgia U.S.A. PHONE FAX May 6, 2014 The Combustion Institute Recommendation of Sharath Nagaraja for the Bernard Lewis Fellowship Dear Sir or Madam: I write this letter to enthusiastically support and recommend Sharath Nagaraja for the Bernard Lewis Fellowship offered by the Combustion Institute to outstanding young researchers in the field of combustion. First, I would like to confirm that Mr. Nagaraja is the lead author of the following two high quality papers accepted for the 35th International Combustion Symposium in the area of plasma assisted combustion, 1. Nanosecond Plasma Enhanced H 2 /O 2 /N 2 premixed flat flames (PROCI-D ) 2. Effect of Non-equilibrium Plasma on two-stage ignition of nheptane (PROCI-D ) By way of introduction, I am the William R. T. Oakes Professor and Chair of the School of Aerospace Engineering at the Georgia Institute of Technology (Georgia Tech). I have been a member of the Combustion Institute for more than 30 years. Mr. Nagaraja is pursuing his Ph.D. degree at Georgia Tech under my supervision. His thesis research deals with plasma assisted combustion, funded by an AFOSR MURI (Multi University Research Initiative). He has been investigating the potential of using non-equilibrium plasma discharges generated by high-voltage, nanosecond pulses for enhancing ignition and improving flame-holding in premixed and non-premixed combustion systems. Mr. Nagaraja is consistently productive, independent and displays an aptitude for significant work. He has successfully developed a comprehensive, multi-scale theoretical/numerical framework to study the effects of non-equilibrium, nanosecond plasma discharges on the ignition and combustion of hydrogen and hydrocarbon fuels. The model can resolve electric field transients in sub-nanosecond timescales, as well as calculate the radical concentrations and temperature rise over millisecond timescales in a spatially accurate manner. The model incorporates detailed plasma combustion chemistry mechanisms including electron impact ionization, excitation and dissociation processes apart from the traditional chainbranching and oxidation reactions. This work represents one of the first attempts in comprehensive modeling of pulsed nanosecond discharges for combustion applications. After establishing the novel numerical framework, Mr. Nagaraja conducted several original studies in understanding plasma effects on ignition, premixed flame dynamics and supersonic combustion listed below, a. Mr. Nagaraja s first project was on understanding the ignition of H 2 -air mixtures subjected to pulsed nanosecond discharges in a plane-to-plane geometry. He successfully validated the model with O and OH densities, temperature and ignition delay measurements from the plasma flow reactor experiments conducted by our collaborators at the Ohio State University. Simulation results revealed A Unit of the University System of Georgia An Equal Education and Employment Opportunity Institution

2 that nanosecond voltage pulses create a pool of radicals over a large volume which ignite the fuel-air mixture simultaneously at different locations, with heat transport playing a minor role. It was confirmed, for a broad range of operating conditions, that the ignition delay can be reduced by an order of magnitude using nanosecond plasma discharges as compared to ignition achieved through volumetric heating. b. Next, he focused on studying the effect of nonequilibrium plasma on the low temperature ignition of nc 7 H 16 -air mixtures through self-consistent simulations in a plane-to-plane geometry at 160 torr (0.2 atm). He discovered that the plasma generated radicals initiated and significantly accelerated the H abstraction reaction from fuel molecules and triggered a self-accelerating feedback loop via lowtemperature kinetic pathways. Application of only a few discharge pulses was sufficient to reduce the initiation time of the first-stage temperature rise by a factor of 10. The plasma effect on the low temperature chemistry was independent of the equivalence ratio, but became more pronounced at lower initial temperatures ( K). c. Mr. Nagaraja conducted multi-scale, pulsed discharge simulations with detailed plasma combustion kinetics to develop insight into the complex plasma - flame interactions. The study was performed with and without a burst of 200 nanosecond discharge pulses to quantify the effect of nonequilibrium plasma on a pre-existing lean premixed H 2 /O 2 /N 2 flame. The predictions were validated with OH and temperature measurements in companion experiments with good agreement. Results showed a significant increase in O and H densities due to plasma chemistry, with peak values increasing by a factor of 6 and a factor of 4, respectively. It was demonstrated that Joule heating alone cannot move the temperature and species profiles as far upstream (i.e. closer to the burner surface) as the pulsed plasma source of the same total power. d. At present, Mr. Nagaraja is performing high-fidelity Large Eddy Simulations (LES) of plasma assisted ignition of H 2 jets injected into supersonic O 2 cross-flow. This comprehensive numerical study will help us understand the nanosecond plasma effects on ignition and flame-holding in realistic turbulent flow environments encountered in high-speed propulsion systems. He has successfully incorporated a reduced order plasma model into our in-house parallel, compressible flow solver. In order to resolve the fine-scale turbulent flow structures, the simulation is run parallel on 846 processors using 40 million grid points. Mr. Nagaraja s technical writing skills have particularly impressed me. As an undergraduate researcher at IIT Madras, he published two journal articles on combustion instabilities. During his PhD studies at Georgia Tech, he has successfully written four journal papers, two of which will be presented at the 35 th International Combustion Symposium and are under consideration for publication in the Proceedings of the Combustion institute. In addition, he has presented at several AIAA conferences in the past four years. A complete list of his publications is attached to the application. In summary, Mr. Nagaraja is an outstanding young researcher, who has worked on important projects advancing our understanding of combustion and modeling. New modeling strategies he has developed can be used to solve practical engineering issues in emerging energy and propulsion technologies. I wholeheartedly support Mr. Nagaraja for the Bernard Lewis Fellowship offered by the combustion institute. Sincerely, Vigor Yang A Unit of the University System of Georgia An Equal Education and Employment Opportunity Institution

3 APPLICATION FOR THE BERNARD LEWIS FELLOWSHIP NOMINATION PACKAGE Name: ID: Mailing Address: Affiliation: Current Position: Sharath Nagaraja 3446 North Druid Hills Road Apt F, Decatur, GA School of Aerospace Engineering, Georgia Institute of Technology Graduate Research Assistant

4 SHARATH NAGARAJA 3446 North Druid Hills Road, Decatur, GA SUMMARY 5 years research experience in computational fluid dynamics (CFD), turbulence modeling, and multicomponent reacting flows. Extensive experience in scientific software development, parallel computing, and experimental validation. Excellent technical writing and oral communication skills demonstrated by several peer reviewed journal publications and conference presentations. EDUCATION Ph.D. Aerospace Engineering Expected: Aug 2014 Georgia Institute of Technology Atlanta, GA Advisor: Prof. Vigor Yang Thesis Topic: Multi-Scale Modeling of Nanosecond Plasma Assisted Combustion B.Tech and M.Tech (Dual Degree) Aerospace Engineering August 2008 Indian Institute of Technology Madras Chennai, India Advisor: Prof. R. I. Sujith Thesis Topic: Non-normal stability analysis of Combustion Systems RESEARCH EXPERIENCE Graduate Research Assistant Jan 2009 to present School of Aerospace Engineering, Georgia Institute of Technology Applied research on a new nanosecond plasma technology for next generation supersonic propulsion systems. Independently developed a high fidelity, multi-scale modeling framework to simulate the interaction between reacting flows and non-equilibrium plasma discharges. Model is able to accurately resolve the physical & chemical processes over a wide range of timescales (10-12 s s). Performed first ever Large Eddy Simulation (LES) of plasma assisted ignition of H 2 jet injected into supersonic O 2 cross-flow. Project Officer June 2008 to Dec 2008 Department of Aerospace Engineering, Indian Institute of Technology Madras Mentored 3 undergraduate researchers on linear stability theory, combustion instabilities and numerical methods. Research Assistant Aug 2006 to May 2008 Department of Aerospace Engineering, Indian Institute of Technology Madras Developed a reduced order modeling framework to study the non-normal and nonlinear nature of combustion-acoustic interactions. Published two peer reviewed journal papers as an undergraduate researcher which have been cited in the combustion community. Project Intern May 2007 to Aug 2007 Department of Aerospace Engineering, Indian Institute of Science, Bangalore Conceptualized and fabricated a novel ducted vertical take-off vehicle (VTOL).

5 SOFTWARE SKILLS Programming: FORTRAN, C, MPI, OpenMP Commercial Software: ANSYS Fluent, CHEMKIN, MATLAB COURSES Computational Fluid Dynamics Kinetics & Thermodynamics of Gases Numerical Methods in Engineering Gas Dynamics Partial Differential Equations for Scientists Combustion REFEREED JOURNAL PUBLICATIONS 1. Nagaraja, S., Sun, W., and Yang, V. Effect of Non-equilibrium plasma on two-stage Ignition of n- Heptane" accepted for presentation at the 35 th Combustion Symposium. 2. Nagaraja, S., Li, T., Sutton, J., Adamovich, I., and Yang, V. Nanosecond Plasma Enhanced H 2/O 2/N 2 premixed flat flames" accepted for presentation at the 35 th Combustion Symposium. 3. Nagaraja, S. and Yang, V. A Frozen Electric Field Approach to Simulate Pulsed Nanosecond Discharges and Ignition of H 2-air mixtures" submitted to Journal of Physics: D. 4. Nagaraja, S., Yang, V., Yin, Z. and Adamovich, I.V. Ignition of Hydrogen-Air Mixtures using Pulsed Nanosecond Dielectric Barrier Plasma Discharges in Plane-to-Plane Geometry" Combustion and Flame, Nagaraja, S., Yang, V., and Adamovich, I.V. Multi-Scale Modeling of Nanosecond Dielectric Barrier Plasma Discharges in Plane-to-Plane Geometry" Journal of Physics: D, Nagaraja, S., Kedia, K., and Sujith, R.I. Characterizing Energy Growth during Combustion Instabilities: Eigenvalues or Singular values?" Proceedings of the Combustion Institute, Kedia, K., Nagaraja, S., and Sujith, R.I. Impact of Linear Coupling on Thermo-acoustic Instabilities" Combustion Science and Technology, SERVICE and AWARDS Georgia Tech Graduate Research Assistantship, 2009-present Top 10 hottest articles on Science Direct (Energy and Combustion Sciences), 2009 EXTRA CURRICULAR ACTIVITIES Volunteer for AID (Association for India s Development) Atlanta Chapter. Organized dance concerts for fund-raising. Keen interest in literature and fine arts. Won awards in poetry and essay writing competitions in high school and during undergraduate years.

6 LIST OF PUBLICATIONS Peer-Reviewed Journal Publications 1. Nagaraja, S., Sun, W., and Yang, V. Effect of Non-equilibrium plasma on two-stage Ignition of n- Heptane" accepted for 35 th Combustion Symposium, 2014 (PROCI-D ). 2. Nagaraja, S., Li, T., Sutton, J., Adamovich, I., and Yang, V. Nanosecond Plasma Enhanced H 2/O 2/N 2 premixed flat flames" accepted for 35 th Combustion Symposium, 2014 (PROCI-D ). 3. Nagaraja, S. and Yang, V. A Frozen Electric Field Approach to Simulate Pulsed Nanosecond Discharges and Ignition of H 2-air mixtures" submitted to the Journal of Physics: D. 4. Nagaraja, S., Yang, V., Yin, Z. and Adamovich, I.V. Ignition of Hydrogen-Air Mixtures using Pulsed Nanosecond Dielectric Barrier Plasma Discharges in Plane-to-Plane Geometry" Combustion and Flame, Vol. 161, No. 4, April 2014, Nagaraja, S., Yang, V., and Adamovich, I.V. Multi-Scale Modeling of Nanosecond Dielectric Barrier Plasma Discharges in Plane-to-Plane Geometry" Journal of Physics: D, Vol. 46, No. 15, , Nagaraja, S., Kedia, K., and Sujith, R.I. Characterizing Energy Growth during Combustion Instabilities: Eigenvalues or Singular values?" Proceedings of the Combustion Institute, Vol. 32, No. 2, 2009, Kedia, K., Nagaraja, S., and Sujith, R.I. Impact of Linear Coupling on Thermo-acoustic Instabilities" Combustion Science and Technology, Vol. 180, No. 9, Conference Presentations 1. S. Nagaraja and V. Yang, Energy Coupling in Nanosecond Dielectric Barrier Discharges in a plane-toplane geometry 51 th AIAA Aerospace Sciences Meeting, Grapevine, Texas, 2013 (AIAA ) 2. S. Nagaraja and V. Yang, Chemical and Transport effects of Nanosecond Plasma Discharges on H 2-air and C 2H 4-air mixtures 50 th AIAA Aerospace Sciences Meeting, Nashville, Tennessee, 2012 (AIAA ) 3. S. Nagaraja and V. Yang, Nanosecond Plasma Enhanced Counterflow Diffusion Flames 42 nd AIAA Lasers and Plasmadynamics Conference, Honululu, Hawaii, 2011 (AIAA )

7 ACCOMPLISHMENTS Independently developed a multi-scale framework for modeling and simulation of nanosecond plasma assisted combustion. The one of a kind model can self-consistently simulate multiple nanosecond, high voltage pulses in fuel-air mixtures with detailed chemistry datasets consisting of radicals, charged, excited and neutral species with hundreds of reactions. The model is capable of resolving electric field transients and electron impact dynamics in sub-nanosecond timescales, as well as calculating the accumulation of radicals, temperature rise, chain branching, and ignition over millisecond timescales. Equations for species, electric field and electron energy are solved. In addition, conservation equations for mass, momentum and energy are considered to simulate flow dynamics. The electron transport and reaction rate coefficients are calculated as functions of electron energy in advance by solving the electron Boltzmann equation over a range of electron energies. During the simulation, the coefficients are read from a lookup table and interpolated every time-step. Performed original and pioneering numerical studies of plasma assisted ignition, plasma-flame interactions, and plasma assisted supersonic combustion using the independently developed multi-scale modeling framework The effect of nanosecond discharges on ignition of H 2-air mixtures was simulated and the results validated with experimental data. The second project focused on understanding the effect of nonequilibrium plasma on the ignition of a heavy fuel (nheptane) which exhibits rich low temperature chemistry. It was discovered that plasma generated radicals create a self-accelerating chemistry loop through which the fuel decomposition and the first stage heat release is accelerated by a factor of 10. The impact of nanosecond discharges on a premixed laminar flame was the focus of the third study. It was shown that electron impact reactions reduce the thickness of the pre-heat zone and the flame position shifts upstream with plasma. The fourth project is on Large Eddy Simulations of nanosecond plasma ignition of H 2 jet injected into supersonic O 2 crossflow. This work will help in substantially improving the understanding of plasma assisted ignition in realistic turbulent flow environments encountered in high-speed propulsion systems. Successfully published, as the lead author, four peer-reviewed journal articles on plasma assisted combustion The four articles which have been published or accepted are provided in the list of publications. Two of the accepted articles will be presented at the 35 th international combustion symposium. In addition to the above four articles, one paper is under review with the Journal of Physics: D. Initiated and successfully led collaborative projects with researchers from Ohio State University (OSU) on plasma assisted ignition and plasma-flame interactions Successfully validated the model predictions with plasma species, temperature and ignition delay measurements performed in the OSU plasma flow reactor experiments. Computational results confirmed the simultaneous, large volume ignition using nanosecond discharges observed in ICCD emission images. Performed multi-scale simulations of nanosecond plasma enhanced H 2/O 2/N 2 premixed laminar flames, and validated the predictions with OH and temperature measurements conducted at OSU. The numerical calculations allowed in depth study of plasma kinetics and its impact on the species and temperature distribution across the flame.