High-pressure non-equilibrium plasmas form the basis of many practical technologies including plasma television displays and other lighting sources, semiconductor manufacturing processes, and processes for hazardous waste mitigation. In the last three to five years, new potential applications have been proposed for non-equilibrium plasmas in the area of combustion, including strategies for reduction in pollutant emissions, improved-efficiency fuel synthesis, and high-speed ignition and flame holding. While an array of non-equilibrium plasma combustion-related phenomena have been observed, the ability to predict the effectiveness of potential new processes and systems has lagged due to a distinct lack of fundamental kinetic data in this field.
This research is an integrated experimental / modeling study of hydrocarbon oxidation mechanisms in plasmas under conditions of extreme thermal non-equilibrium. Large, highly non-equilibrium pools of important hydrocarbon combustion intermediates and electronically excited air species will be created in a short pulsed fuel-air plasma, created using specialized discharge technology available at Ohio State University. The time evolution of critical species will be measured experimentally using advanced laser-based optical diagnostic methods and then compared to theoretical predictions in order to validate and improve fundamental plasma kinetic models.
The major benefit to society will be to advance a truly different ignition methodology that improves combustion engine technology. Furthermore, the combination of experiment and analysis provides excellent opportunities for teaching, learning, and training. As a result of this grant, one team member will incorporate a module on plasma aerodynamics, including plasma combustion, into his undergraduate fluids curriculum.
This project focuses on an integrated experimental/modeling study of hydrocarbon oxidation mechanisms under conditions of extreme thermal non-equilibrium. Large, and highly non-equilibrium, initial pools of important hydrocarbon combustion intermediate and electronically excited air species are created in a short pulsed fuel-air plasmas, created using ~10-20 nsec duration – high (~20 kV) voltage pulsers, capable of operation at repetition rates as high as 40-50 kHz. The time evolution of critical species and temperature are experimentally determined using advanced laser-based optical diagnostic methods, and compared to theoretical predictions in order to validate and improve fundamental plasma kinetic models. The ultimate goal is to provide predictive capability for the efficiency of non-equilibrium plasma devices as tools for improving a variety of combustion-based devices and processes such as: high speed (including supersonic) propulsion systems, air pollutant mitigation processes, and combustion efficiency of non-traditional fuels. This three year program focused, principially, on the following laser diagnostic-based studies: i., Coherent Anti-Stokes Ramans Spectroscopy (CARS) thermometry studies of plasma assisted oxidation, heat release, and ignition of ethylene/air and hydrogen/air mixtures; ii., The development of a new, first principles, computer code for hydrogen/air plasma assisted oxidation and ignition; iii., single and two photon Laser Induced Fluorescence (LIF) studies of the temporal evolution of atomic oxygen and the hydroxyl (OH) radical in nanosecond pulsed hydrogen/air plasmas; iv., Development of a new first principles two-dimensional model for electron impact energy deposition in nanosecond pulsed plasmas; and v., preliminary studies on the effect of metastable singlet delta oxygen on ignition delay in hydrogen/oxygen/argon nanosecond pulsed plasmas. The work performed during the three year program resulted in seven journal publications, with at least one additional manuscript to be submitted in the near future, and eight refereed conference proceedings. A total of five graduate students were directly supported by the program, two of whom, Dr. Yvette Zuzeek and Dr. Inchul Choi, received their PhD degrees during the three year period of performance of the program. Three other PhD students are presently continuing their research, all of whom should graduate within the next 1-2 years.
